Chemical Formula: Mn7(SiO4)3(OH)2 Locality: Franklin, Sussex Co., New Jersey. Name Origin: From the Greek leukos, “pale” and foinis, “red purple”, in allusion to its color
Leucophoenicite is a mineral with formula Mn7(SiO4)3(OH)2. Generally brown to red or pink in color, the mineral gets its name from the Greek words meaning “pale purple-red”. Leucophoenicite was discovered in the U.S. State of New Jersey and identified as a new mineral in 1899.
Description
Leucophoenicite is normally brown, light purple-red, raspberry-red or pink in color; in thin section it is rose-red to colorless. The name is derived from the Greek words leukos, meaning “pale”, and foinis, meaning “purple-red”, in reference to its common coloring.
Leucophoenicite typically occurs as isolated grains or it has granular massive habit. Crystals of the mineral, which occur rarely, are slender, prismatic, elongated, and striated. The mineral forms in a low pressure, hydrothermal environment or in a contact zone in the veins and skarns of a stratiform Zn-Mn ore body.
Leucophoenicite is a member of the humite group. It has been found in association with barite, barysilite, calcite, copper, franklinite, garnet, glaucochroite, hausmannite, jerrygibbsite, manganosite, pyrochroite, rhodochrosite, sonolite, spessartine, sussexite, tephroite, vesuvianite, willemite, and zincite.
History
Discovery date : 1899 Town of Origin : FRANKLIN, SUSSEX CO., NEW JERSEY Country of Origin: USA
Optical properties
Optical and misc. Properties: Transparent to translucent Refractive Index : from 1,75 to 1,78 Axial angle 2V : 74,5°
Physical Properties
Cleavage: {001} Indistinct Color: Brown, Brown, Violet red, Light red, Dark pink. Density: 3.8 Diaphaneity: Transparent to translucent Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals. Hardness: 5.5-6 – Knife Blade-Orthoclase Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Magnetism: Nonmagnetic
This map shows the distribution of the three volcanoes – the Ka’ena, Wai’anae and Ko’olau – now thought to have made up the region of O’ahu, Hawai’i. Bold dashed lines delineate possible rift zones of the three volcanoes; also shown are the major landslide deposits around O’ahu. Image credit: J. Sinton et al / University of Hawai’i’s School of Ocean and Earth Science and Technology.
As we know it today, O’ahu is the remnants of two volcanoes, Wai’anae and Ko’olau. But extending almost 100 km from the western tip of this island is a large region of shallow bathymetry called the submarine Ka’ena Ridge.
It is that region that has now been recognized to represent a precursor volcano to the island of O’ahu, and on whose flanks the Wai’anae and Ko’olau volcanoes later formed.
Prior to the recognition of Ka’ena Volcano, Wai’anae Volcano was assumed to have been exceptionally large and to have formed an unusually large distance from its next oldest neighbor – Kaua’i.
Prof John Sinton of the University of Hawai’i’s School of Ocean and Earth Science and Technology, who is the lead author of a paper published in the Geological Society of America Bulletin, explained: “both of these assumptions can now be revised: Wai’anae is not as large as previously thought and Ka’ena Volcano formed in the region between Kauai and Wai’anae.”
This image shows how Ka’ena, Wai’anae and Ko’olau overlap. Image credit: J. Sinton et al / University of Hawai’i’s School of Ocean and Earth Science and Technology.
In 2010 scientists documented enigmatic chemistry of some unusual lavas of Wai’anae.
“We previously knew that they formed by partial melting of the crust beneath Wai’anae, but we didn’t understand why they have the isotopic composition that they do. Now, we realize that the deep crust that melted under Waianae is actually part of the earlier Ka’ena Volcano,” Prof Sinton said.
The high-quality bathymetric data showed that Ka’ena Ridge had an unusual morphology.
Prof Sinton’s team then began collecting samples from Ka’ena and Wai’alu submarine Ridges.
The geochemical and age data, along with geological observations and geophysical data confirmed that Ka’ena was not part of Waianae, but rather was an earlier volcanic edifice. Wai’anae must have been built on the flanks of Ka’ena.
“What is particularly interesting is that Ka’ena appears to have had an unusually prolonged history as a submarine volcano, only breaching the ocean surface very late in its history,” Prof Sinton said.
Note : The above story is based on materials provided by GSA Release No. 14-35
The Mackenzie River (Slavey language: Deh-Cho, big river or Inuvialuktun: Kuukpak, great river) is the largest and longest river system in Canada, and is exceeded only by the Mississippi River system in North America. It flows through a vast, isolated region of forest and tundra entirely within the country’s Northwest Territories, although its many tributaries reach into four other Canadian provinces and territories. The river’s mainstem runs 1,738 kilometres (1,080 mi) in a northerly direction to the Arctic Ocean, draining a vast area nearly the size of Indonesia. It is the largest river flowing into the Arctic from North America, and with its tributaries is one of the longest rivers in the world.
Course
Rising out of the marshy western end of Great Slave Lake, the Mackenzie River flows generally west-northwest for about 300 km (190 mi), passing the hamlets of Fort Providence and Brownings Landing. At Fort Simpson it is joined by the Liard River, its largest tributary, then swings towards the Arctic, paralleling the Franklin Mountains as it receives the North Nahanni River. The Keele River enters from the left about 100 km (62 mi) above Tulita, where the Great Bear River joins the Mackenzie. Just before crossing the Arctic Circle, the river passes Norman Wells, then continues northwest to merge with the Arctic Red and Peel rivers. It finally empties into the Beaufort Sea, part of the Arctic Ocean, through the vast Mackenzie Delta.
Most of the Mackenzie River is a broad, slow-moving waterway; its elevation drops just 156 metres (512 ft) from source to mouth. It is a braided river for much of its length, characterized by numerous sandbars and side channels. The river ranges from 2 to 5 km (1.2 to 3.1 mi) wide and 8 to 9 m (26 to 30 ft) deep in most parts, and is thus easily navigable except when it freezes over in the winter. However, there are several spots where the river narrows to less than half a kilometre (0.3 mi) and flows quickly, such as at the Sans Sault Rapids at the confluence of the Mountain River and “The Ramparts”, a 40 m (130 ft) deep canyon south of Fort Good Hope.
Watershed
At 1,805,200 square kilometres (697,000 sq mi), the Mackenzie River’s watershed or drainage basin is the largest in Canada, encompassing nearly 20% of the country. From its farthest headwaters at Thutade Lake in the Omineca Mountains to its mouth, the Mackenzie stretches for 4,241 km (2,635 mi) across western Canada, making it the longest river system in the nation and the thirteenth longest in the world. The river discharges more than 325 cubic kilometres (78 cu mi) of water each year, accounting for roughly 11% of the total river flow into the Arctic Ocean. The Mackenzie’s outflow holds a major role in the local climate above the Arctic Ocean with large amounts of warmer fresh water mixing with the cold seawater.
Satellite view of the lower Mackenzie River
Many major watersheds of North America border on the drainage of the Mackenzie River. Much of the western edge of the Mackenzie basin runs along the Continental Divide. The divide separates the Mackenzie watershed from that of the Yukon River and its headstreams the Pelly and Stewart rivers, which flow to the Bering Strait; and the Fraser River and Columbia River systems, both of which run to the Pacific Ocean. Lowland divides in the north distinguish the Mackenzie basin from those of the Anderson, Horton, Coppermine and Back Rivers – all of which empty into the Arctic. Eastern watersheds bordering on that of the Mackenzie include those of the Thelon and Churchill Rivers, both of which flow into Hudson Bay. On the south, the Mackenzie watershed borders that of the North Saskatchewan River, part of the Nelson River system, which empties into Hudson Bay after draining much of south-central Canada.
Through its many tributaries, the Mackenzie River basin covers portions of five Canadian provinces and territories – British Columbia (BC), Alberta, Saskatchewan, and the Yukon and Northwest Territories. The two largest headwaters forks, the Peace and Athabasca Rivers, drain much of the central Alberta prairie and the Rocky Mountains in northern BC then combine into the Slave River at the Peace-Athabasca Delta near Lake Athabasca, which also receives runoff from northwestern Saskatchewan. The Slave is the primary feeder of Great Slave Lake (contributing about 77% of the water); other inflows include the Taltson, Lockhart and Hay Rivers, the latter of which also extends into Alberta and BC. Direct tributaries of the Mackenzie from the west such as the Liard and Peel Rivers carry runoff from the mountains of the eastern Yukon.
The eastern portion of the Mackenzie basin is dominated by vast reaches of lake-studded boreal forest and includes many of the largest lakes in North America. By both volume and surface area, Great Bear Lake is the biggest in the watershed and third largest on the continent, with a surface area of 31,153 km2 (12,028 sq mi) and a volume of 2,236 km3 (536 cu mi). Great Slave Lake is slightly smaller, with an area of 28,568 km2 (11,030 sq mi) and containing 2,088 km3 (501 cu mi) of water, although it is significantly deeper than Great Bear. The third major lake, Athabasca, is less than a third that size with an area of 7,800 km2 (3,000 sq mi). Six other lakes in the watershed cover more than 1,000 km2 (390 sq mi), including the Williston Lake reservoir, the second-largest artificial lake in North America, on the Peace River.
With an average annual flow of 9,910 m3/s (350,000 cu ft/s), the Mackenzie River has the highest discharge of any river in Canada and is the fourteenth largest in the world in this respect. About 60% of the water comes from the western half of the basin, which includes the Rocky, Selwyn, and Mackenzie mountain ranges out of which spring major tributaries such as the Peace and Liard Rivers, which contribute 23% and 27% of the total flow, respectively. In contrast the eastern half, despite being dominated by marshland and large lakes, provides only about 25% of the Mackenzie’s discharge. During peak flow in the spring, the difference in discharge between the two halves of the watershed becomes even more marked. While large amounts of snow and glacial melt dramatically drive up water levels in the Mackenzie’s western tributaries, large lakes in the eastern basin retard springtime discharges. Breakup of ice jams caused by sudden rises in temperature – a phenomenon especially pronounced on the Mackenzie – further exacerbate flood peaks. In full flood, the Peace River can carry so much water that it inundates its delta and backs upstream into Lake Athabasca, and the excess water can only flow out after the Peace has receded.
Geology
As recently as the end of the last glacial period eleven thousand years ago the majority of northern Canada was buried under the enormous continental Laurentide ice sheet. The tremendous erosive powers of the Laurentide and its predecessors, which at maximum extent completely buried the Mackenzie River valley under thousands of meters of ice and flattened the eastern portions of the Mackenzie watershed. When the ice sheet receded for the last time, it left a 1,100 km (680 mi)-long postglacial lake called Lake McConnell, of which Great Bear, Great Slave and Athabasca Lakes are remnants. Significant evidence exists that roughly 13,000 years ago, the channel of the Mackenzie was scoured by one or more massive glacial lake outburst floods unleashed from Lake Agassiz, formed by melting ice west of the present-day Great Lakes. At its peak, Agassiz had a greater volume than all present-day freshwater lakes combined. This is believed to have disrupted currents in the Arctic Ocean and led to an abrupt 1,300-year-long cold temperature shift called the Younger Dryas.
Ecology
The Mackenzie River’s watershed is considered one of the largest and most intact ecosystems in North America, especially in the north. Approximately 63% of the basin – 1,137,000 km2 (439,000 sq mi) – is covered by forest, mostly boreal, and wetlands comprise some 18% of the watershed – about 324,900 km2 (125,400 sq mi). More than 93% of the wooded areas in the watershed are virgin forest. There are fifty-three fish species in the basin, none of them endemic. Most of the aquatic species in the Mackenzie River are descendants of those of the Mississippi River and its tributaries. This anomaly is believed to have been caused by hydrologic connection of the two river systems during the Ice Ages by meltwater lakes and channels.
Fishes in the Mackenzie River proper include the northern pike, some minnows, and lake whitefish, and the river’s shores are lined with sparse vegetation like dwarf birch and willows, as well as numerous peat dogs. Further south the tundra vegetation transitions to black spruce, aspen and poplar forest. Overall, the northern watershed is not very diverse ecologically, due to its cold climate – permafrost underlies about three-quarters of the watershed, reaching up to 100 m (330 ft) deep in the delta region – and meager to moderate rainfall, amounting to about 410 millimetres (16 in) over the basin as a whole. The southern half of the basin, in contrast, includes larger reaches of temperate and alpine forests as well as fertile floodplain and riparian habitat, but is actually home to fewer fish species due to large rapids on the Slave River preventing upstream migration of aquatic species.
Migratory birds use the two major deltas in the Mackenzie River basin – the Mackenzie Delta and the inland Peace-Athabasca Delta – as important resting and breeding areas. The latter is located at the convergence of four major North American migratory routes, or flyways. As recently as the mid-twentieth century, more than 400,000 birds passed through during the spring and up to a million in autumn. Some 215 bird species in total have been catalogued in the delta, including endangered species such as the whooping crane, peregrine falcon and bald eagle. Unfortunately, the construction of W.A.C. Bennett Dam on the Peace River has reduced the seasonal variations of water levels in the delta, causing damage to its ecosystems. Populations of migratory birds in the area have steadily declined since the 1960s.
Note : The above story is based on materials provided by Wikipedia
Chemical Formula: (Na,Ca)2BeSi2(O.OH.F)7 Locality: Langesundfiord district, southern Norway. Name Origin: From the Greek leucos, “white” and phanein, ” to appear” in allusion to the white color
Leucophanite is a sorosilicate mineral with a complex composition, (Na,Ca)2BeSi2(O.OH.F)7. It may contain cerium substituting in the calcium position.
It occurs in pegmatites and alkali igneous complexes as yellow, greenish or white triclinic crystals and has been found in Norway, Quebec and Russia.
It was first described from the Langesundfiord district of southern Norway in 1840. The name is from the Greek leucos for “white” and phanein for “to appear” in allusion to the common white color.
History
Discovery date: 1840 Town of Origin: LAVEN, LANGESUNDFJORD Country of Origin : NORVEGE
Optical properties
Optical and misc. Properties: Transparent to translucent Refractive Index : from 1,56 to 1,59 Axial angle 2V : 36-50°
Physical Properties
Color: White, Greenish yellow, Yellow, Light green. Density: 2.96 Diaphaneity: Transparent to translucent Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals. Hardness: 4 – Fluorite Luminescence: Fluorescent, Short UV=pink, Long UV=pink. Luster: Vitreous (Glassy) Streak: white
Australia can no longer lay claim to the origins of the iconic New Zealand kiwi following University of Adelaide research published in the journal Science today showing the kiwi’s closest relative is not the emu as was previously thought.
Instead, the diminutive kiwi is most closely related to the extinct Madagascan elephant bird — a 2-3 metre tall, 275 kg giant. And surprisingly, the study concluded, both of these flightless birds once flew.
A new study by the University of Adelaide’s Australian Centre for Ancient DNA (ACAD), has solved a 150-year-old evolutionary mystery about the origins of the giant flightless “ratite” birds, such as the emu and ostrich, which are found across the southern continents. This group contains some of the world’s largest birds — such as the extinct giant moa of New Zealand and elephant birds of Madagascar.
The different “ratite” species were long thought to have formed as the flightless birds were isolated by the separation of the southern continents over the last 130 million years.
However, ancient DNA extracted from bones of two elephant birds held by the Museum of New Zealand, Te Papa Tongarewa, has revealed a close genetic connection with the kiwi, despite the striking differences in geography, morphology and ecology between the two.
“This result was about as unexpected as you could get,” says Mr Kieren Mitchell, PhD candidate with ACAD, who performed the work. “New Zealand and Madagascar were only ever distantly physically joined via Antarctica and Australia, so this result shows the ratites must have dispersed around the world by flight.”
The results correct previous work by ACAD Director Professor Alan Cooper conducted in the 1990s, which had shown the closest living relatives of the kiwi were the Australian emu and cassowary. “It’s great to finally set the record straight, as New Zealanders were shocked and dismayed to find that the national bird appeared to be an Australian immigrant,” says Professor Cooper. “I can only apologise it has taken so long!”
The team were able to use the elephant bird DNA to estimate when the ratite species had separated from each other.
“The evidence suggests flying ratite ancestors dispersed around the world right after the dinosaurs went extinct, before the mammals dramatically increased in size and became the dominant group,” says Professor Cooper.
“We think the ratites exploited that narrow window of opportunity to become large herbivores, but once mammals also got large, about 50 million years ago, no other bird could try that idea again unless they were on a mammal free island — like the Dodo.”
“We can now see why the evolutionary history of the ratites has been such a difficult problem,” says co-author Professor Mike Lee, of the South Australian Museum and University of Adelaide. “Many of them independently converged on very similar body plans, complicating analysis of their history.”
“We recently found fossils of small kiwi ancestors, which we suggested might have had the power of flight not too long ago,” says co-author Flinders University’s Dr Trevor Worthy. “The genetic results back up this interpretation, and confirm that kiwis were flying when they arrived in New Zealand.
“It also explains why the kiwi remained small. By the time it arrived in New Zealand, the large herbivore role was already taken by the moa, forcing the kiwi to stay small, and become insectivorous and nocturnal.”
Alan Tennyson, Curator of Vertebrates at Te Papa, New Zealand’s national museum, says: “The New Zealand kiwi is an integral part of this country’s culture and heritage. It’s fitting that Te Papa’s scientific collections have been used to resolve the mystery of its origins.”
Journal Reference:
Kieren J. Mitchell, Bastien Llamas, Julien Soubrier, Nicolas J. Rawlence, Trevor H. Worthy, Jamie Wood, Michael S. Y. Lee, Alan Cooper. Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution. Science, 2014 DOI: 10.1126/science.1251981
Note : The above story is based on materials provided by University of Adelaide.
Washington, D.C.—Breaking research news from a team of scientists led by Carnegie’s Ho-kwang “Dave” Mao reveals that the composition of the Earth’s lower mantle may be significantly different than previously thought. These results are to be published by Science.
The lower mantle comprises 55 percent of the planet by volume and extends from 670 and 2900 kilometers in depth, as defined by the so-called transition zone (top) and the core-mantle boundary (below). Pressures in the lower mantle start at 237,000 times atmospheric pressure (24 gigapascals) and reach 1.3 million times atmospheric pressure (136 gigapascals) at the core-mantle boundary.
The prevailing theory has been that the majority of the lower mantle is made up of a single ferromagnesian silicate mineral, commonly called perovskite (Mg,Fe)SiO3) defined through its chemistry and structure. It was thought that perovskite didn’t change structure over the enormous range of pressures and temperatures spanning the lower mantle.
Recent experiments that simulate the conditions of the lower mantle using laser-heated diamond anvil cells, at pressures between 938,000 and 997,000 times atmospheric pressure (95 and 101 gigapascals) and temperatures between 3,500 and 3,860 degrees Fahrenheit (2,200 and 2,400 Kelvin), now reveal that iron bearing perovskite is, in fact, unstable in the lower mantle.
The team finds that the mineral disassociates into two phases one a magnesium silicate perovskite missing iron, which is represented by the Fe portion of the chemical formula, and a new mineral, that is iron-rich and hexagonal in structure, called the H-phase. Experiments confirm that this iron-rich H-phase is more stable than iron bearing perovskite, much to everyone’s surprise. This means it is likely a prevalent and previously unknown species in the lower mantle. This may change our understanding of the deep Earth.
“We still don’t fully understand the chemistry of the H-phase,” said lead author Li Zhang, also of Carnegie. “But this finding indicates that all geodynamic models need to be reconsidered to take the H-phase into account. And there could be even more unidentified phases down there in the lower mantle as well, waiting to be identified.”
Note : The above story is based on materials provided by Carnegie Institution
Chemical Formula: K(AlSi2O6) Locality: Bearpaw Mountains., Montana, USA. Name Origin: From the Greek leukos – “white.”
Leucite is a rock-forming mineral composed of potassium and aluminium tectosilicate K(AlSi2O6). Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic.
Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhombic or monoclinic individuals, which are optically biaxial and repeatedly twinned, giving rise to twin-lamellae and to striations on the faces. When the crystals are raised to a temperature of about 500 °C they become optically isotropic and the twin-lamellae and striations disappear, although they reappear when the crystals are cooled again. This pseudo-cubic character of leucite is very similar to that of the mineral boracite.
The crystals are white or ash-grey in colour, hence the name suggested by A. G. Werner in 1701, from ‘λευκος’, ‘(matt) white’. They are transparent and glassy when fresh, albeit with a noticeably subdued ‘subvitreous’ lustre due to the low refractive index, but readily alter to become waxy/greasy and then dull and opaque; they are brittle and break with a conchoidal fracture. The Mohs hardness is 5.5, and the specific gravity 2.47. Inclusions of other minerals, arranged in concentric zones, are frequently present in the crystals. On account of the color and form of the crystals the mineral was early known as white garnet. French authors in older literature may employ René Just Haüy’s name amphigène, but ‘leucite’ is the only name for this mineral species that is recognised as official by the International Mineralogical Association.
History
Discovery date : 1791 Town of Origin : MT. VESUVE (VOLCAN), NAPLES, CAMPANIE Country of Origin : ITALIE
Optical properties
Optical and misc. Properties: Translucent to transparent Refractive Index : 1,50 Axial angle 2V : TRES PETIT
The Mekong is a trans-boundary river in Southeast Asia. It is the world’s 12th-longest river and the 7th-longest in Asia. Its estimated length is 4,350 km (2,703 mi), and it drains an area of 795,000 km2 (307,000 sq mi), discharging 457 km3 (110 cu mi) of water annually.
From the Tibetan Plateau this river runs through China’s Yunnan province, Burma (Myanmar), Laos, Thailand, Cambodia and Vietnam. In 1995, Laos, Thailand, Cambodia and Vietnam established the Mekong River Commission to assist in the management and coordinated use of the Mekong’s resources. In 1996 China and Burma (Myanmar) became “dialogue partners” of the MRC and the six countries now work together within a cooperative framework.
The extreme seasonal variations in flow and the presence of rapids and waterfalls in this river have made navigation difficult. The river is a major trading route linking China’s southwestern province of Yunnan to Laos, Burma (Myanmar) and Thailand to the south, an important trade route between western China and Southeast Asia.
Course
The Mekong rises as the Lancang (Lantsang) in the “Three Rivers Area” on the Tibetan Plateau in the Sanjiangyuan National Nature Reserve; the reserve protects the headwaters of, from north to south, the Yellow (Huang He), the Yangtze and the Mekong Rivers. It flows southeast through Yunnan Province, and then through the Three Parallel Rivers Area in the Hengduan Mountains, along with the Yangtze to its north and the Salween River (Nujiang in Chinese) to its south.
The Mekong then meets the tripoint of China, Burma (Myanmar) and Laos. From there it flows southwest and forms the border of Burma and Laos for about 100 kilometres (62 mi) until it arrives at the tripoint of Burma, Laos, and Thailand. This is also the point of confluence between the Ruak River (which follows the Thai-Burma border) and the Mekong. The area of this tripoint is sometimes termed the Golden Triangle, although the term also refers to the much larger area of those three countries that is notorious as a drug producing region.
From the Golden Triangle tripoint, the Mekong turns southeast to briefly form the border of Laos with Thailand. It then turns east into the interior of Laos, flowing first east and then south for some 400 kilometres (250 mi) before meeting the border with Thailand again. Once more, it defines the Laos-Thailand border for some 850 kilometres (530 mi) as it flows first east, passing in front of the capital of Laos, Vientiane, then turns south. A second time, the river leaves the border and flows east into Laos soon passing the city of Pakse. Thereafter, it turns and runs more or less directly south, crossing into Cambodia.
At Phnom Penh the river is joined on the right bank by the river and lake system the Tonlé Sap. When the Mekong is low, the Tonle Sap is a tributary; water flows from the lake and river into the Mekong. When the Mekong floods, the flow reverses; the floodwaters of the Mekong flow up the Tonle Sap.
Immediately after the Sap River joins the Mekong by Phnom Penh, the Bassac River branches off the right (west) bank. The Bassac River is the first and main distributary of the Mekong; thus, this is the beginning of the Mekong Delta. The two rivers, the Bassac to the west and the Mekong to the east, enter Vietnam very soon after this. In Vietnam, the Bassac is called the Hậu River (Sông Hậu or Hậu Giang); the main, eastern, branch of the Mekong is called the Tiền River or Tiền Giang. In Vietnam, distributaries of the eastern (main, Mekong) branch include the Mỹ Tho River, the Ba Lai River, the Hàm Luông River, and the Cổ Chiên River.
Drainage basin
The Mekong Basin can be divided into two parts: the ‘Upper Mekong Basin’ in Tibet and China, and the ‘Lower Mekong Basin’ from Yunnan downstream from China to the South China Sea. From the point where it rises to its mouth, the most precipitous drop in the Mekong occurs in Upper Mekong Basin, a stretch of some 2,200 km (1,400 mi). Here, it drops 4,500 metres (14,800 ft) before it enters the Lower Basin where the borders of Thailand, Laos, China and Burma (Myanmar) come together in the Golden Triangle. Downstream from the Golden Triangle, the river flows for a further 2,600 km (1,600 mi) through Laos, Thailand and Cambodia before entering the South China Sea via a complex delta system in Vietnam.
Upper Mekong Basin
The Upper Basin makes up 24% of the total area and contributes 15 to 20% of the water that flows into the Mekong River. The catchment here is steep and narrow. Soil erosion has been a major problem and approximately 50% of the sediment in the river comes from the Upper Basin.
In Yunnan province in China, the river and its tributaries are confined by narrow, deep gorges. The tributary river systems in this part of the basin are small. Only 14 have catchment areas that exceed 1,000 km2 (390 sq mi), yet the greatest amount of loss of forest cover in the entire river system per square kilometer has occurred in this region due to heavy unchecked demand for natural resources. In the south of Yunnan, in Simao and Xishuangbanna Prefectures, the river changes as the valley opens out, the floodplain becomes wider, and the river becomes wider and slower.
Lower Mekong Basin
Major tributary systems develop in the Lower Basin. These systems can be separated into two groups: tributaries that contribute to the major wet season flows, and tributaries that drain low relief regions of lower rainfall. The first group are left bank tributaries that drain the high-rainfall areas of Lao PDR. The second group are those on the right bank, mainly the Mun and Chi rivers, that drain a large part of Northeast Thailand.
Laos lies almost entirely within the Lower Mekong Basin. Its climate, landscape and land use are the major factors shaping the hydrology of the river. The mountainous landscape means that only 16% of the country is farmed under lowland terrace or upland shifting cultivation. With upland shifting agriculture (slash and burn), soils recover within 10 to 20 years but the vegetation does not. Shifting cultivation is common in the uplands of Northern Laos and is reported to account for as much as 27% of the total land under rice cultivation. As elsewhere in the basin, forest cover has been steadily reduced during the last three decades by shifting agriculture and permanent agriculture. The cumulative impacts of these activities on the river regime have not been measured. However, the hydrological impacts of land-cover changes induced by the Vietnam War were quantified in two sub-catchments of the Lower Mekong River Basin.
Loss of forest cover in the Thai areas of the Lower Basin has been the highest in all the Lower Mekong countries over the past 60 years. On the Korat Plateau, which includes the Mun and Chi tributary systems, forest cover was reduced from 42% in 1961 to 13% in 1993. Although this part of Northeast Thailand has an annual rainfall of more than 1,000 mm, a high evaporation rate means it is classified as a semi arid region. Consequently, although the Mun and Chi Basins drain 15% of the entire Mekong Basin, they only contribute 6% of the average annual flow. Sandy and saline soils are the most common soil types, which makes much of the land unsuitable for wet rice cultivation. In spite of poor fertility, however, agriculture is intensive. Glutinous rice, maize and cassava are the principal crops. Drought is by far the major hydrological hazard in this region.
As the Mekong enters Cambodia, over 95% of the flows have already joined the river. From here on downstream the terrain is flat and water levels rather than flow volumes determine the movement of water across the landscape. The seasonal cycle of changing water levels at Phnom Penh results in the unique “flow reversal” of water into and out of the Great Lake via the Tonle Sap River. Phnom Penh also marks the beginning of the delta system of the Mekong River. Here the mainstream begins to break up into an increasing number of branches.
In Cambodia, the wet rice is the main crop and is grown on the flood plains of the Tonle Sap, Mekong and Bassac (the Mekong delta distributary known as the Hậu in Vietnam) rivers. More than half of Cambodia remains covered with mixed evergreen and deciduous broadleaf forest, but forest cover has decreased from 73% in 1973 to 63% in 1993. Here, the river landscape is flat. Small changes in water level determine the direction of water movement, including the large-scale reversal of flow into and out of the Tonle Sap basin from the Mekong River.
The Mekong Delta in Viet Nam is farmed intensively and has little natural vegetation left. Forest cover is less than 10%. In the Central Highlands of Vietnam, forest cover was reduced from over 95% in the 1950s to around 50% in the mid 1990s. Agricultural expansion and population pressure are the major reasons for land use and landscape change. Both drought and flood are common hazards in the Delta, which many people believe is the most sensitive to upstream hydrological change.
Geology
The internal drainage patterns of the Mekong are unusual when compared to those of other large rivers. Most large river systems that drain the interiors of continents, such as the Amazon, Congo, and Mississippi, have relatively simple dendritic tributary networks that resemble a branching tree.
Typically, such patterns develop in basins with gentle slopes where the underlying geological structure is fairly homogenous and stable, exerting little or no control on river morphology. In marked contrast, the tributary networks of the Salween, Yangtze, and particularly the Mekong, are complex with different sub-basins often exhibiting different, and distinct, drainage patterns. These complex drainage systems have developed in a setting where the underlying geological structure is heterogeneous and active, and is the major factor controlling the course of rivers and the landscapes they carve out.
The elevation of the Tibetan Plateau during the Tertiary period was an important factor in the genesis of the south-west monsoon, which is the dominant climatic control influencing the hydrology of the Mekong Basin. Understanding the nature and timing of the elevation of Tibet (and the Central Highlands of Viet Nam) therefore helps explain the provenance of sediment reaching the delta and the Tonle Sap Great Lake today. Studies of the provenance of sediments in the Mekong Delta reveal a major switch in the source of sediments about eight million years ago (Ma). From 36 to 8 Ma the bulk (76%) of the sediments deposited in the delta came from erosion of the bedrock in the Three Rivers Area. From 8 Ma to the present, however, the contribution from the Three Rivers Area fell to 40%, while that from the Central Highlands rose from 11 to 51%. One of the most striking conclusions of provenance studies is the small contribution of sediment from the other parts of the Mekong Basin, notably the Khorat Plateau, the uplands of northern Lao PDR and northern Thailand, and the mountain ranges south of the Three Rivers Area.
The last glacial period came to an abrupt end about 19,000 years ago (ka) when sea levels rose rapidly, reaching a maximum of about 4.5 m above present levels in the early Holocene at about 8 ka. At this time the shoreline of the South China Sea almost reached Phnom Penh and cores recovered from near Angkor Borei contained sediments deposited under the influence of tides, and salt marsh and mangrove swamp deposits. Sediments deposited in the Tonle Sap Great Lake about this time (7.9–7.3 ka) also show indications of marine influence, suggesting a connection to the South China Sea. Although the hydraulic relationships between the Mekong and the Tonle Sap Great Lake systems during the Holocene are not well understood, it is clear that between 9,000 and 7,500 years ago the confluence of the Tonle Sap and the Mekong was in close proximity to the South China Sea.
The present river morphology of the Mekong Delta developed over the last 6,000 years. During this period, the delta advanced 200 km over the continental shelf of the South China Sea, covering an area of more than 62,500 km2. From 5.3 to 3.5 ka the delta advanced across a broad embayment formed between higher ground near the Cambodian border and uplands north of Ho Chi Minh City. During this phase of its development the delta was sheltered from the wave action of long-shore currents and was constructed largely through fluvial and tidal processes. At this time the delta was advancing at a rate of 17–18 m per year. After 3.5 ka, however, the delta had built out beyond the embayment and became subject to wave action and marine currents. These deflected deposition south-eastwards in the direction of the Cà Mau Peninsula, which is one of the most recent features of the delta.
For much of its length the Mekong flows through bedrock channels, i.e. channels that are confined or constrained by bedrock or old alluvium in the bed and riverbanks. Geomorphologic features normally associated with the alluvial stretches of mature rivers, such as meanders, oxbow lakes, cut-offs, and extensive floodplains are restricted to a short stretch of the mainstream around Vientiane and downstream of Kratie where the river develops alluvial channels that are free of control exerted by the underlying bedrock.
The Mekong Basin is not normally considered a seismically active area as much of the basin is underlain by the relatively stable continental block. Nonetheless, the parts of the basin in northern Laos, northern Thailand, Burma (Myanmar) and China do experience frequent earthquakes and tremors. The magnitude of these earthquakes rarely exceeds 6.5 on the Richter scale and is unlikely to cause material damage.
Note : The above story is based on materials provided by Wikipedia
PhD student Lisa Cupelli sits atop rocks in the heart of South Africa’s Vredefort impact crater, where she and Western Earth Sciences professor Desmond Moser, below, confirmed the rocks are some of the only remains of a magma sea created more than 2 billion years ago. Credit: Desmond Moser
Desmond Moser never gives up. Twenty years ago, the now Western Earth Sciences professor first visited the heart of South Africa’s Vredefort impact crater, locating what he believed to be some of the only remains of a magma sea created more than 2 billion years ago in a 300-kilometre-wide crater.
He published his finding in 1997 in the journal Geology and awaited praise from peers.
But it never came.
“It was the first paper I ever published and people keep following it up by publishing stuff knocking it. I said it looked like impact rock, while everyone else said it wasn’t. But I was still convinced I was right,” said Moser, of what he refers to as the Vredefort Gabbronorite.
In 2009, Moser, along with PhD student Lisa Cupelli, returned to the South African site to see if they could once and for all confirm his original findings.
Scientists place the asteroid that struck Vredefort among the latest ever to hit the Earth, estimating its size at 5-10-km in diameter.
Given the original location was staked out in pre-GPS 1994, the pair had only an old map and a 35mm slide to guide them.
“I told her this is the situation: If we can find more of the stuff, and we can prove it, it’s going to be good news. Or, it could be a total bust,” he said. “There are hundreds, if not thousands, of geologists going to the area all the time, but they are just walking over the stuff.”
After and hour-and-a-half, Moser and Cupelli found the site where he collected his first sample, thanks to the marking of an windmill that still stood nearby in what was now a farmer’s field.
They spent the next two-and-a-half weeks mapping and collecting samples. And the result was just what he expected.
A sample of the Vredefort Gabbronorite rock Western Earth Sciences professor Desmond Moser confirmed was impact rock created more than 2 billion years ago in South Africa. Credit: Paul Mayne / Western News
“It is definitely a rock that crystalized from the mini-sea of magma, which was created by the impact crater,” he said.
To this day, detractors still think Moser is mistaken.
“Everyone assumed over the years it (the rock) had simply been worn away. It’s not target impact that I found, but rock that is produced from the heat of the magma ocean and, once crystalized, turns into rock – new impact-created rock.”
One of the reasons Moser said other geologists kept missing the point was it didn’t look like what you expect it to look like, even to Moser.
“I did say no at first. But what people usually don’t look at is the micro-minerals,” he said. “When I brought it back to the lab, most of the rocks I got from there had all these smashed and corrupted crystals. But with this particular one they were gem-quality, beautiful little prisms, crystal clean. And then I dated them and they came out to be the age of the impact.
“Then, I knew I had something.”
Moser’s re-confirmation of his earlier work, published in this month’s Geology, will keep geologists on both sides of the fence or, in this case, both sides of the crater, debating whether or not Moser’s discovery is what he says it is.
“I think there is more to be found. We may be walking over more impact rock, but just not assuming what it is,” he said.
One thing for sure, Moser still has the scientific evidence to prove his 20-year-old point.
“I’m a big believer in the truth, and sometimes it takes that long,” he said. “But science works.”
Note : The above story is based on materials provided by University of Western Ontario
Chemical Formula: K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2 Locality: Pala, San Diego Co., California, USA. Name Origin: From the Greek lepidion – “scale” and lithos – “stone.”Lepidolite is a lilac-gray or rose-colored member of the mica group with formula K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2. It is a secondary source of lithium. It is a phyllosilicate mineral and a member of the polylithionite-trilithionite series.It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the rare alkali metals rubidium and caesium. In 1861 Robert Bunsen and Gustav Kirchhoff extracted 150 kg of lepidolite and yielded a few grams of rubidium salts for analysis, and therefore discovered the new element rubidium.
It occurs in granite pegmatites, in some high-temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.
Notable occurrences include Brazil; Ural Mountains, Russia; California, United States; Tanco Mine, Bernic Lake, Manitoba, Canada; and Madagascar.
History
Discovery date : 1792 Town of Origin : ROZNA, BYSTRICE, MORAVIE Country of Origin : TCHEQUIE
Optical properties
Optical and misc. Properties : Translucent Refractive Index : from 1,52 to 1,58 Axial angle 2V : 0-58°
Data from the Moon Mineralogy Mapper show the presence of cryptomaria (“hidden seas,” outlined in yellow). Primary material of the lunar crust is shown as blue. Areas show as yellow indicate basalt that originated below the surface.
Billions of years ago, volcanoes sent material from inside planetary bodies to the surface. Subsequent impacts have covered those original deposits. Jennifer Whitten, who receives her Ph.D. in geological sciences this year, has figured out a way to study those “hidden seas” and learn more about the early volcanic history the Moon and Mercury.
Volcanism is a planet’s way of turning itself inside out. For scientists, material blasted to the surface from volcanoes is a goldmine of information about a planet’s past.
“Volcanic deposits are important because you get a picture of how the surface has been modified, but you can also learn so much about the interior of a planet,” said Jennifer Whitten, who will receive her Ph.D. this week from the Department of Geological Sciences. “So you get a picture of the inside and the outside.”
For her dissertation, Whitten studied volcanic deposits on the Moon and Mercury that date back billions of years. She hopes that a better understanding of these ancient deposits will shed light on the formation and early evolution of those two planetary bodies.
It might also deepen our understanding of Earth in its infancy. On our home planet, ancient volcanic deposits are often ground away by the constant churning of tectonic plates. So to truly understand how volcanism shapes a young planet, Whitten says, it’s essential to look beyond the Earth.
“One of the most perplexing questions about the earliest history of the planets, including Earth, is the amount of volcanic activity that occurs then,” said Jim Head, professor of geological sciences and Whitten’s adviser. “The observational techniques Jennifer Whitten has developed have contributed greatly to our understanding of these early volcanic processes.”
Hidden volcanoes on the Moon and Mercury
On the Moon, some volcanic deposits are easy to spot. The lunar maria—the dark splotches that form the iconic “man in the Moon”—are composed largely of volcanic basalts. Termed “mare,” the Greek word for sea, because early astronomers mistook them for bodies of water, they were formed billions of years ago when molten lava flowed up from the depths and filled in deep basins formed by asteroids and other impactors.
But there are other volcanic deposits on the Moon—many of them older than the visible maria—that are hidden from view. As impacts pounded the Moon’s surface, some ancient volcanic deposits were covered with debris blasted out of impact craters. The debris, which is generally a bright whitish color, hides the dark-colored basalt from view. Those hidden maria—called “cryptomaria” after the Greek for hidden or secret seas—are what Whitten wanted to explore. Understanding where these deposits are located and what they’re made of helps to fill in missing pieces of the Moon’s volcanic history.
Whitten used a variety of techniques to look through the veneer of impact debris and definitively identify cryptomaria deposits on the Moon. One of those techniques involved looking for a very specific type of crater. When a small impactor strikes a cryptomare deposit, it digs up some of the volcanic material beneath the impact debris. The result is a crater surrounded by a dark halo of mare material.
Using these dark-halo craters as a guide, Whitten was able to identify 18 deposits of cryptomaria on the Moon. Having mapped the deposits, she was able to answer some critical questions about them.
First, she was able to use data from the Moon Mineralogy Mapper, which flew aboard India’s Chandrayaan-1 spacecraft, to identify the composition of the deposits. She found that cryptomaria had a composition similar to the visible maria—something that had been the subject of speculation before now.
“I’ve been able to show that it is actually mare basalt,” she said. “We can use the term cryptomaria and know that it means what we think it means.”
Second, Whitten was able to show that cryptomaria are concentrated on the Moon’s near side—the side facing Earth. It’s long been known that the lunar far side lacks the visible mare deposits that dominate the near side. But it wasn’t clear whether or not there may have been some cryptomaria hiding on the far side.
“Secretly I really wanted to find some major deposit on the far side so I could say, ‘Look everyone; it’s not all on the near side,'” Whitten said. “But that didn’t happen.”
The finding suggests that volcanism throughout the Moon’s history was concentrated on the near side. That appears to be in part because the crust is thinner on the nearside, allowing volcanic material to flow through more easily.
Whitten used similar techniques to look for signs of ancient volcanism on Mercury. There, she was able to show vast areas of the planet’s northern hemisphere, known as the intercrater plains, have a volcanic origin. The work added substantially to the inventory of volcanic material on the surface of Mercury.
More research ahead
Recently, Whitten accepted a position as a postdoctoral researcher at the Smithsonian Air and Space Museum in Washington, D.C. There, she’ll be involved a project that uses radar to look for more buried volcanic deposits on the Moon.
“I’m excited about learning a new technique that provides access to the few upper meters of the lunar surface, especially since my dissertation was focused on finding buried volcanic deposits,” she said. “I am optimistic about finding interesting volcanic features.”
Those features could help deepen our understanding of the solar system.
“In the big picture, understanding volcanic deposits can give a sense of the initial composition of these planets,” Whitten said. “That tells you about the materials in the cloud that formed the solar system.”
It also helps us learn about our own planet. The types of deposits Whitten looked at on the Moon and Mercury are called large igneous provinces or LIPs. LIPs have been fairly common throughout Earth’s history and have been linked to several major extinction events. So understanding how they work could be of critical importance.
“The LIPs on Earth have been eroded or are under the ocean, so it’s hard to study them,” Whitten said. “But you can get an idea of the size of these things and what affects their size because we can study them on Moon or Mercury. I think it’s really exciting that by understanding what’s happening on the Moon and Mercury, you can better understand the early history of the Earth.”
Note : The above story is based on materials provided by Brown University
Click here (PDF or JPG) to download the latest version (v 2014/02) of the International Chronostratigraphic Chart. Translations of the chart: Chinese (v2013-01: PDF or JPG), Spanish (v2013-01), Portuguese (v2013-01: PDF or JPG), Norwegian (v2013-01: PDF or JPG), Basque (v2013-01: PDF or JPG), Catalan (v2013-01: PDF or JPG), French (v2012) and Japanese (v2012).
The old versions can be download at the following links: 2008 (PDF or JPG), 2009 (PDF or JPG), 2010 (PDF or JPG), 2012 (PDF or JPG), 2013/01 (PDF or JPG).
Chemical Formula: γ-FeO(OH) Locality: Common world wide. Name Origin: From the Greek lipis – “scale” and krokis – “fibre.”
Lepidocrocite (γ-FeO(OH)), also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing substances rust underwater. Lepidocrocite is commonly found in the weathering of primary iron minerals and in iron ore deposits. It can be seen as rust scale inside old steel water pipes and water tanks.
The structure of lepidocrocite is similar to the boehmite structure found in bauxite and consists of layered iron(III) oxide octahedra bonded by hydrogen bonding via hydroxide layers. This relatively weakly bonded layering accounts for the scaley habit of the mineral.
It was first described in 1813 from the Zlaté Hory polymetallic ore deposit in Moravia, Czech Republic. The name is from the Greek lipis for scale and krokis for fibre.
History
Discovery date : 1813 Town of Origin : EISENZECHE, EISERFELD, SIEGEN Country of Origin : ALLEMAGNE
Optical properties
Optical and misc. Properties : Opaque Refractive Index : from 1,94 to 2,51 Axial angle 2V: 83°
Physical Properties
Cleavage: {010} Perfect Color: Red, Yellowish brown, Blackish brown. Density: 4 Diaphaneity: Opaque Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern. Hardness: 5 – Apatite Luminescence: Non-fluorescent. Luster: Sub Metallic Streak: dark yellow brown
Digital reconstructions of the skull of the dinosaur Erlikosaurus made from a CT scan Credit: Dr Stephan Lautenschlager
New techniques for visualizing fossils are transforming our understanding of evolutionary history according to a paper published by leading palaeontologists at the University of Bristol.
Palaeontology has traditionally proceeded slowly, with individual scientists labouring for years or even decades over the interpretation of single fossils which they have gradually recovered from entombing rock, sand grain by sand grain, using all manner of dental drills and needles.
The introduction of X-ray tomography has revolutionized the way that fossils are studied, allowing them to be virtually extracted from the rock in a fraction of the time necessary to prepare specimens by hand and without the risk of damaging the fossil.
The resulting fossil avatars not only reveal internal and external anatomical features in unprecedented and previously unrealized detail, but can also be studied in parallel by collaborating or competing teams of scientists, speeding up the pace at which evolutionary history is revealed.
These techniques have enabled palaeontologists to move beyond ‘just so stories’, explanations for why sauropod dinosaurs had such long necks, for example, by subjecting digital models of the fossils to biomechanical analysis, including using the same computer techniques that engineers use to design test bridges and aircraft.
However, the scientists from Bristol’s School of Earth Sciences highlight that the potential benefits of fossil avatars are not being realized.
Lead author Dr John Cunningham said: “At a practical level, we simply don’t have the infrastructure for storing and sharing the vast datasets that describe fossils, and the policies of world-leading museums which protect the copyright of fossils are preventing data sharing at a legal level.”
Co-author Dr Stephan Lautenschlager added: “The increasing availability of fossil avatars will allow us to bring long-extinct animals back to life, virtually, by using computer models to work out how they moved and fed. However, in many cases we are hampered by our limited understanding of the biology of the modern species to which we would ideally like to compare the fossils.”
Dr Imran Rahman, also an author of the agenda-setting study, said: “Palaeontologists are making their fossil avatars freely available as files for 3-D printing and so, soon, anyone who wants one, can have a scientifically accurate model of their favourite fossil, for research, teaching, or just for fun!”
Journal Reference:
John A. Cunningham, Imran A. Rahman, Stephan Lautenschlager, Emily J. Rayfield, Philip C.J. Donoghue. A virtual world of paleontology. Trends in Ecology & Evolution, 2014; 29 (6): 347 DOI: 10.1016/j.tree.2014.04.004
Note : The above story is based on materials provided by University of Bristol.
Subglacial lakes in Antarctica might have nutrient-rich groundwater flowing into them, say scientists investigating the origin of the water in ice streams.
Ice streams are huge, fast-flowing glaciers that meander across Antarctica. They are responsible for nearly all of the Antarctic’s contribution to sea-level rise, yet scientists have little understanding of where the water flowing through them comes from. This means that the contents of the subglacial lakes which lie underneath these streams is also a mystery.
The new research, published in Geophysical Research Letters shows for the first time where the water going in and out of these ice streams – their hydrologic budget – comes from.
‘It’s important to understand and quantify the hydrologic budget of these ice streams, as this can control the lubrication and ultimately how fast these ice streams move,’ explains Dr Poul Christoffersen of the Scott Polar Research Institute, lead researcher on the study.
‘Some of these glaciers are slowing, some are speeding up and that’s all in response to changes in the configuration of sources and sinks of water. If we’re trying to understand what they’ll be doing in future we need to understand how they have behaved in the past.’
The team studied five ice streams. They found that the water flowing into them comes mostly from the ice sheet’s deep interior. They also identified a large groundwater reservoir beneath these glacier, which the ice streams draw on to compensate when there is not enough water from the ice sheet to maintain the ice streams fast flow.
The team found that two of the streams moved much faster than three located further south.
‘For two of the ice streams there was a balance between recharge and depletion so they continually flow fast, but for the other three the system doesn’t have enough to provide replenishment, and so they end up losing water. Some are slowing down now, and one stopped altogether about 170 years ago,’ Christoffersen says.
It’s like when water from groundwater reservoirs flow into rivers in England. When an ice stream has little water flowing in from melting ice, the groundwater begins to flow into the stream instead. but unlike England it all happens beneath the ice. If this happens, and there’s lots of groundwater in the network, then the connected subglacial lakes beneath the ice streams are likely to have a a much higher nutrient content, meaning researchers are more likely to find life in them than in the subglacial lakes fed by pure glacial water.
‘Water that’s been stored for thousands of years in the pore spaces of sediments beneath the ice streams are mixing with the water in the subglacial hydrological network. These ancient waters are full of nutrients from the sediment, enough that they could provide life to a thriving microbial habitat,’ explains Christoffersen.
‘A hydrologic system that receives groundwater contributions is much more likely to have high nutrient levels compared to the fast flowing systems which are fed by pure glacial meltwater. That water is pure with very little biochemical material to provide life,’ he says.
More information: Christoffersen, P., M. Bougamont, S. P. Carter, H. A. Fricker, and S. Tulaczyk (2014), “Significant groundwater contribution to Antarctic ice streams hydrologic budget,” Geophys. Res. Lett., 41, 2003-2010, DOI: 10.1002/2014GL059250.
Note : The above story is based on materials provided by PlanetEarth Online
Chemical Formula: Zn2(AsO4)(OH)·H2O Locality: Ojuela mine near Mapimi, Durango. Name Origin: Named after the Belgian mining engineer, Legrande.
Legrandite is a rare zinc arsenate mineral, Zn2(AsO4)(OH)·H2O.
It is an uncommon secondary mineral in the oxidized zone of arsenic bearing zinc deposits and occurs rarely in granite pegmatite. Associated minerals include: adamite, paradamite, kottigite, scorodite, smithsonite, leiteite, renierite, pharmacosiderite, aurichalcite, siderite, goethite and pyrite. It has been reported from Tsumeb, Namibia; the Ojuela mine in Durango, Mexico and at Sterling Hill, New Jersey, USA.
It was first described in 1934 for an occurrence in the Flor de Peña Mine, Nuevo Leon, Mexico and named after M. Legrand, a Belgian mining engineer .
History
Discovery date : 1932 Town of Origin : MINE FLOR DE PENA, LAMPAZOS, NUOVA LEON Country of Origin : MEXIQUE
Optical properties
Optical and misc. Properties : Translucent Refractive Index: from 1,67 to 1,74 Axial angle 2V: 50°
Diagram of the Earth. Credit: Kelvinsong/Wikipeida
Breaking research news from a team of scientists led by Carnegie’s Ho-kwang “Dave” Mao reveals that the composition of the Earth’s lower mantle may be significantly different than previously thought. These results are to be published by Science.
The lower mantle comprises 55 percent of the planet by volume and extends from 670 and 2900 kilometers in depth, as defined by the so-called transition zone (top) and the core-mantle boundary (below). Pressures in the lower mantle start at 237,000 times atmospheric pressure (24 gigapascals) and reach 1.3 million times atmospheric pressure (136 gigapascals) at the core-mantle boundary.
The prevailing theory has been that the majority of the lower mantle is made up of a single ferromagnesian silicate mineral, commonly called perovskite (Mg,Fe)SiO3) defined through its chemistry and structure. It was thought that perovskite didn’t change structure over the enormous range of pressures and temperatures spanning the lower mantle.
Recent experiments that simulate the conditions of the lower mantle using laser-heated diamond anvil cells, at pressures between 938,000 and 997,000 times atmospheric pressure (95 and 101 gigapascals) and temperatures between 3,500 and 3,860 degrees Fahrenheit (2,200 and 2,400 Kelvin), now reveal that iron bearing perovskite is, in fact, unstable in the lower mantle.
The team finds that the mineral disassociates into two phases one a magnesium silicate perovskite missing iron, which is represented by the Fe portion of the chemical formula, and a new mineral, that is iron-rich and hexagonal in structure, called the H-phase. Experiments confirm that this iron-rich H-phase is more stable than iron bearing perovskite, much to everyone’s surprise. This means it is likely a prevalent and previously unknown species in the lower mantle. This may change our understanding of the deep Earth.
“We still don’t fully understand the chemistry of the H-phase,” said lead author Li Zhang, also of Carnegie. “But this finding indicates that all geodynamic models need to be reconsidered to take the H-phase into account. And there could be even more unidentified phases down there in the lower mantle as well, waiting to be identified.”
Scientists from the Magma and Volcanoes Laboratory (CNRS) and the European Synchrotron, the ESRF, have recreated the extreme conditions 600 to 2900 km below the Earth’s surface to investigate the melting of basalt in the oceanic tectonic plates. They exposed microscopic pieces of rock to these extreme pressures and temperatures while simultaneously studying their structure with the ESRF’s extremely powerful X-ray beam.
The results show that basalt produced on the ocean floor has a melting temperature lower than the peridotite which forms the Earth’s mantle. Near the core-mantle boundary, where the temperature rises rapidly, the melting basalt produces liquids rich in silica (SiO2), which react rapidly with the mantle and indicate a speedy dissolution of the basalt back into the depths of the Earth. These experiments provide a new explanation for seismic anomalies at the base of the mantle while fixing its temperature in the region of 4000 K.
The results are published in Science on the 23 May 2014.
The Earth is an active planet. The heat it contains is capable of inducing the mantle convection responsible for plate tectonics. This energy comes from the heat accumulated during the formation of our planet, the latent heat of crystallization of the inner core, and radioactive decay. The temperatures inside the Earth, however, are not well known.
Convection causes hot material to rise to the surface of the Earth and cold material to sink towards the core. Thus, when the ascending mantle begins to melt at the base of the oceanic ridges, the basalt flows along the surface to form what we call the oceanic crust. “Over the course of millennia the crust will then undergo subduction, its greater density causing it to sink into the mantle. This is why the Earth’s continents are known to be several billion years old, while the oldest oceanic crust only dates back 165 million years” said Mohamed Mezouar, scientist at the ESRF.
The temperature at the core-mantle boundary (also known as the D” region) is thought to increase by more than 1000 degrees over a few hundred kilometers, which is significant compared to the temperature gradient across the rest of the mantle. Previous authors have suggested that this temperature rise could cause the partial melting of the mantle, but this hypothesis leaves a number of geophysical observations unexplained. Firstly, the anomalies in the propagation speed of seismic waves do not match those expected for a partial melting of the mantle, and secondly, the melting mantle should lead to the production of liquid pockets in the lowermost mantle, a phenomenon which has never been observed.
The team led by Professor Denis Andrault from the Université Blaise Pascal decided instead to study the melting point of basalt at high depths, and found that it was significantly lower than that of the mantle. The melting of sub-oceanic basalt piles could therefore be responsible for the previously unexplained seismic anomalies. The researchers also showed that the melting basalt generates a liquid rich in SiO2. As the mantle itself contains large quantities of MgO, the interaction of these liquids with the mantle is expected to produce a rapid reaction leading to the formation of the solid MgSiO3 perovskite. This would explain why no liquid pockets have been detected by seismologists in the deep mantle: any streams of liquid should rapidly re-solidify.
If it is indeed the basalt and not the mantle whose melting in the D”-region is responsible for the observed seismic anomalies, then the temperature at the core-mantle boundary must be between 3800 and 4150 Kelvin, between the melting points of basalt and the Earth’s mantle. If this hypothesis is correct, this would be the most accurate determination of the temperature at the core-mantle boundary available today.
“It could solve a long time controversy about the peculiar role of the core-mantle boundary in the dynamical properties of the Earth mantle, said Professor Denis Andrault. ”We know now that the cycle of crust formation at the mid-ocean ridges and crust dissolution in the lowermost mantle may have occured since plate tectonics were active on our planet”, he added.
Chemical Formula: Pb4SO4(CO3)2(OH)2 Locality: Leadhills, Lanarkshire, Scotland. Name Origin: Named for the localiy.
Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb4SO4(CO3)2(OH)2. Leadhillite crystallises in the monoclinic system, but develops pseudo-hexagonal forms due to crystal twinning. It forms transparent to translucent variably coloured crystals with an adamantine lustre. It is quite soft with a Mohs hardness of 2.5 and a relatively high specific gravity of 6.26 to 6.55.
It was discovered in 1832 in the Susannah Mine, Leadhills in the county of Lanarkshire, Scotland. It is trimorphous with susannite and macphersonite (these three minerals have the same formula, but different structures). Leadhillite is monoclinic, susannite is trigonal and macphersonite is orthorhombic. Leadhillite was named in 1832 after the locality.
Physical Properties
Cleavage: {001} Perfect, {100} Indistinct Color: Colorless, Gray, Yellowish, White, Light blue. Density: 6.26 – 6.55, Average = 6.4 Diaphaneity: Transparent to translucent Fracture: Sectile – Curved shavings or scrapings produced by a knife blade, (e.g. graphite). Hardness: 2.5 – Finger Nail Luminescence: Fluorescent, Short UV=weak gray yellow, Long UV=weak grey yellow. Luster: Adamantine Streak: white
The Antarctic ice sheet. Credit: Stephen Hudson / Wikipedia
A newly-discovered source of oceanic bioavailable iron could have a major impact our understanding of marine food chains and global warming. A UK team has discovered that summer meltwaters from ice sheets are rich in iron, which will have important implications on phytoplankton growth. The findings are reported in the journal Nature Communications on 21st May, 2014.
It is well known that bioavailable iron boosts phytoplankton growth in many of the Earth’s oceans. In turn phytoplankton capture carbon – thus buffering the effects of global warming. The plankton also feed into the bottom of the oceanic food chain, thus providing a food source for marine animals.
The team, comprising researchers from the Universities of Bristol, Leeds, Edinburgh and the National Oceanography Centre, collected meltwater discharged from the 600 km2 Leverett Glacier in Greenland over the summer of 2012, which was subsequently tested for bioavailable iron content. The researchers found that the water exiting from beneath the melting ice sheet contained significant quantities of previously-unconsidered bioavailable iron. This means that the polar oceans receive a seasonal iron boost as the glaciers melt.
Jon Hawkings (Bristol), the lead author, said: “The Greenland and Antarctic Ice Sheets cover around 10% of global land surface. Iron exported in icebergs from these ice sheets have been recognised as a source of iron to the oceans for some time. Our finding that there is also significant iron discharged in runoff from large ice sheet catchments is new. ”
“This means that relatively high iron concentrations are released from the ice sheet all summer, providing a continuous source of iron to the coastal ocean”
Iron is one of the most important biochemical elements, due to its impact on ocean productivity. Despite being the fourth most abundant element in the Earth’s crust, it is mostly not biologically available because it is largely present as unreactive minerals in natural waters. Over the last 20 years there has been controversy over the role of iron in marine food chains and the global carbon cycle, with some groups experimenting with dumping iron into the sea in order to accelerate plankton growth – with the idea that increased plankton growth would capture man made CO2. This work indicates that ice sheets may already be carrying out this process every summer.
Based on their results the team estimates that the flux of bioavailable iron associated with glacial runoff is between 400,000 and 2,500,000 tonnes per year in Greenland and between 60,000 and 100,000 tonnes per year in Antarctica. Taking the combined average figures, this would equal the weight of around 125 Eiffel Towers, or around 3000 fully-laden Boeing 747s being added to the ocean each year.
Jon Hawkings added: “This is a substantial release of iron from the ice sheet, similar in size to that supplied to the oceans by atmospheric dust, another major iron source to the world’s oceans.
At the moment it is just too early to estimate how much additional iron will be carried down from ice sheets into the sea. Of course, the iron release from ice sheet will be localised to the Polar Regions around the ice sheets, so the importance of glacial iron there will be significantly higher. Researchers have already noted that glacial meltwater run-off is associated with large phytoplankton blooms – this may help to explain why”.
Commenting on the relevance of this study, Professor Andreas Kappler (geomicrobiologist at the University of Tübingen, Germany, who is also secretary of the European Association of Geiochemistry) said:
“This study shows that glacier meltwater can contain iron concentrations that are high enough to significantly stimulate biological productivity in oceans that otherwise are oftentimes limited in the element iron that is essential to most living organisms. Although the global importance of this flux of iron into oceans needs to be quantified and the bioavailability of the iron species found should be demonstrated experimentally in future studies, the present study provides a plausible path for nutrient supply to oceanic life.”
More information: Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans. Authors Jon R. Hawkings, Jemma L. Wadham, Martyn Tranter, Rob Raiswell, Liane G. Benning, Peter J. Statham, Andrew Tedstone, Peter Nienow, Katherine Lee & Jon Telling Nature Communications , 5:3929 , DOI: 10.1038/ncomms4929, published 21 May 2014
Note : The above story is based on materials provided by European Association of Geochemistry
