Comment on “Anatomy of impactites and shocked zircon grains from Dhala reveals Paleoproterozoic meteorite impact in the Archean basement rocks of Central India” by Li et al., 2018, Gondwana Research, 54, 81–101

2018 ◽  
Vol 60 ◽  
pp. 214-217
Author(s):  
J.K. Pati ◽  
W.U. Reimold ◽  
N. Hauser
Keyword(s):  
Central India ◽  
Meteorite Impact ◽  
Basement Rocks ◽  
Archean Basement

Anatomy of impactites and shocked zircon grains from Dhala reveals Paleoproterozoic meteorite impact in the Archean basement rocks of Central India

2018 ◽  
Vol 54 ◽  
pp. 81-101 ◽  
Author(s):  
Shan-Shan Li ◽  
S. Keerthy ◽  
M. Santosh ◽  
S.P. Singh ◽  
C.D. Deering ◽  
...  
Keyword(s):  
Central India ◽  
Meteorite Impact ◽  
Basement Rocks ◽  
Archean Basement

Geochemical and geochronological evidence of meteorite impact excavating Archean basement at Lonar Crater, Central India

Lithos ◽  
2021 ◽  
pp. 106479
Author(s):  
Saranya R. Chandran ◽  
S. James ◽  
M. Santosh ◽  
Cheng-Xue Yang ◽  
Cun Zhang ◽  
...  
Keyword(s):  
Central India ◽  
Meteorite Impact ◽  
Archean Basement ◽  
Geochronological Evidence ◽  
Lonar Crater

Geological environment of the Cigar Lake uranium deposit

1993 ◽  
Vol 30 (4) ◽  
pp. 653-673 ◽  
Author(s):  
P. Bruneton
Keyword(s):  
Uranium Deposit ◽  
Transitional Zone ◽  
Uranium Deposits ◽  
Athabasca Basin ◽  
Structural Framework ◽  
Basement Rocks ◽  
Metamorphic Basement ◽  
Basement Ridge ◽  
Archean Basement ◽  
East West

The Cigar Lake uranium deposit occurs within the Athabasca Basin of northern Saskatchewan, Canada. Like other major uranium deposits of the basin, it is located at the unconformity separating Helikian sandstones of the Athabasca Group from Aphebian metasediments and plutonic rocks of the Wollaston Group. The Athabasca Group was deposited in an intra-continental sedimentary basin that was filled by fluviatile terrestrial quartz sandstones and conglomerates. The group appears undeformed and its actual maximum thickness is about 1500 m. On the eastern side of the basin, the detrital units correspond to the Manitou Falls Formations where most of the uranium deposits are located. The Lower Pelitic unit of the Wollaston Group, which lies directly on the Archean basement, is considered to be the most favourable horizon for uranium mineralization. During the Hudsonian orogeny (1800–1900 Ma), the group underwent polyphase deformation and upper amphibolite facies metamorphism. The Hudsonian orogeny was followed by a long period of erosion and weathering and the development of a paleoweathering profile.On the Waterbury Lake property, the Manitou Falls Formation is 250–500 m thick and corresponds to units MFd, MFc, and MFb. The conglomeratic MFb unit hosts the Cigar Lake deposit. However, the basal conglomerate is absent at the deposit, wedging out against an east–west, 20 m high, pre-Athabasca basement ridge, on top of which is located the orebody.Two major lithostructural domains are present in the metamorphic basement of the property: (1) a southern area composed mainly of pelitic metasediments (Wollaston Domain) and (2) a northern area with large lensoid granitic domes (Mudjatik Domain). The Cigar Lake east–west pelitic basin, which contains the deposit, is located in the transitional zone between the two domains. The metamorphic basement rocks in the basin consist mainly of graphitic metapelitic gneisses and calcsilicate gneisses, which are inferred to be part of the Lower Pelitic unit. Graphite- and pyrite-rich "augen gneisses," an unusual facies within the graphitic metapelitic gneisses, occur primarily below the Cigar Lake orebody.The mineralogy and geochemistry of the graphitic metapelitic gneisses suggest that they were originally shales. The abundance of magnesium in the intercalated carbonates layers indicates an evaporitic origin.The structural framework is dominated by large northeast–southwest lineaments and wide east–west mylonitic corridors. These mylonites, which contain the augen gneisses, are considered to be the most favourable features for the concentration of uranium mineralization.Despite the presence of the orebody, large areas of the Waterbury Lake property remain totally unexplored and open for new discoveries.

Mineral exploration in the Thompson nickel belt, Manitoba, Canada, using seismic and controlled‐source EM methods

Geophysics ◽  
2000 ◽  
Vol 65 (6) ◽  
pp. 1871-1881 ◽  
Author(s):  
Don White ◽  
David Boerner ◽  
Jianjun Wu ◽  
Steve Lucas ◽  
Eberhard Berrer ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Seismic Velocity ◽  
Mineral Exploration ◽  
Laboratory Measurements ◽  
Electrically Conductive ◽  
Controlled Source ◽  
Basement Rocks ◽  
Fault Structures ◽  
Deep Sounding ◽  
Archean Basement

Seismic reflection and electromagnetic (EM) data were acquired near Thompson, Manitoba, Canada, to map the subsurface extent of the Paleoproterozoic, nickel ore‐bearing Ospwagan Group. These data are supplemented by surface and borehole geology and by laboratory measurements of density, seismic velocity, and electrical conductivity, which indicate that Ospwagan Group rocks are generally more seismically reflective and electrically conductive than the Archean basement rocks that envelop them. The combined seismic/EM interpretation suggests that the Thompson Nappe (cored by Ospwagan Group rocks) lies blind beneath the Archean basement gneisses, to the east of the subvertical Burntwood lineament, in a series of late recumbent folds and/or southeast‐dipping reverse faults. The EM data require that the shallowest of these fold/fault structures occur within the basement gneisses or perhaps less conductive Ospwagan Group rocks. The results of this study demonstrate how seismic and deep sounding EM methods might be utilized as regional exploration tools in the Thompson nickel belt.

The role of geology and climate in soil nutrient variability - potential drivers for large ungulate migrations in the Serengeti ecosystem (Northern Tanzania, East Africa)

2020 ◽  
Author(s):  
Eileen Eckmeier ◽  
Simon Kübler ◽  
Akida Meya ◽  
Stephen Mathai Rucina
Keyword(s):  
Volcanic Eruptions ◽  
East African ◽  
Near Surface ◽  
Serengeti Ecosystem ◽  
Geological Processes ◽  
Basement Rocks ◽  
Nutrient Variability ◽  
Archean Basement

<p>The East African Serengeti ecosystem hosts a great range of mammals and one of the world’s largest seasonal ungulate movements, with over 1.3 wildebeest and several hundreds of thousands of zebras and antelopes migrating through the region in a regular pattern. While climatic and biological drivers for this migration have been studied in great detail, the role of rock chemistry, weathering and resulting soil diversity as a source for nutrient provision has so far been largely neglected and needs detailed and systematic study.</p><p>Geological processes provide important controls on long-term ecosystem dynamics. Volcanic eruptions, earthquakes, and rock weathering influence soil edaphic properties, which represent the ability of soils to provide vital plant-available nutrients, which therefore control grazing patterns of herbivores, particularly during birthing and lactating seasons. Studying the geological role in providing and distributing essential nutrients is critical to understand long-term drivers and stability of animal migrations in dynamic ecosystems. We have carried out a field reconnaissance study in the Serengeti National Park, with the aim to study variations in nutrient variability in soils and vegetation in relation to the chemical composition of soil parent material, i.e. volcanic or metamorphic rocks and sediments derived from those rock units, and under consideration of climatic variations. First results show that the Serengeti ecosystem can be subdivided into three geo-edaphic subregions that correlate with seasonal wildebeest grazing habitats.</p><p>(1) The southeastern Serengeti (wet-season grazing), is characterized by soils developed on volcanic ash derived from recent eruptions of the Ol Doinjo Lengai carbonatite volcano. Here, we have identified deeper organic-rich soils with andic and vitric properties and varying amounts of carbonate concretions or near-surface calcrete horizons. High Na, K, and Ca levels of volcanic ashes suggest high levels of those elements in soils and vegetation in this region, also because the precipitation is lowest in this area.</p><p>(2) In the central Serengeti (short-term transitional grazing), soils develop on Archean basement rocks including granitic gneisses, phyllites and banded iron formations. Geochemical signatures of these rock types suggest that soils in this region have lower levels in Ca, Mg, and plant available P, compared to the SE Serengeti, which is supported by the transitional nature of this grazing habitat.</p><p>(3) Soils in the Northern Serengeti (dry-season grazing) develop on a diverse patchwork of Archean basement rocks as well as basaltic lavas and thick fluvial deposits. North of Mara river, the Insuria fault – a large normal fault of the East African Rift  - creates a wide sedimentary basin dominated by soils developed on basaltic sediments. Here, higher precipitation leads to stronger weathering and leaching of nutrient elements.</p><p>Our preliminary results suggests that geochemical variations together with continuous (syngenetic) pedogenesis through active volcanism or tectonic faulting and related fault scarp erosion created regions of high edaphic quality in the north and southeast of the Serengeti ecosystem, and that the patchy nature of soil edaphics is important to understand the underlying drivers of large scale migration of grazing animals in this region. </p>

scholarly journals Raman spectroscopy of shocked gypsum from a meteorite impact crater

2016 ◽  
Vol 16 (3) ◽  
pp. 286-292 ◽  
Author(s):  
Connor Brolly ◽  
John Parnell ◽  
Stephen Bowden
Keyword(s):  
Raman Spectroscopy ◽  
Impact Crater ◽  
Hydrothermal Systems ◽  
Microbial Colonization ◽  
Meteorite Impact ◽  
Gale Crater ◽  
Significant Statistical Difference ◽  
Basement Rocks ◽  
Hydrothermal Springs ◽  
Post Impact

AbstractImpact craters and associated hydrothermal systems are regarded as sites within which life could originate on Earth, and on Mars. The Haughton impact crater, one of the most well preserved craters on Earth, is abundant in Ca-sulphates. Selenite, a transparent form of gypsum, has been colonized by viable cyanobacteria. Basement rocks, which have been shocked, are more abundant in endolithic organisms, when compared with un-shocked basement. We infer that selenitic and shocked gypsum are more suitable for microbial colonization and have enhanced habitability. This is analogous to many Martian craters, such as Gale Crater, which has sulphate deposits in a central layered mound, thought to be formed by post-impact hydrothermal springs. In preparation for the 2020 ExoMars mission, experiments were conducted to determine whether Raman spectroscopy can distinguish between gypsum with different degrees of habitability. Ca-sulphates were analysed using Raman spectroscopy and results show no significant statistical difference between gypsum that has experienced shock by meteorite impact and gypsum, which has been dissolved and re-precipitated as an evaporitic crust. Raman spectroscopy is able to distinguish between selenite and unaltered gypsum. This shows that Raman spectroscopy can identify more habitable forms of gypsum, and demonstrates the current capabilities of Raman spectroscopy for the interpretation of gypsum habitability.

Upper-crustal, basement-involved folding in the East Range of the Sudbury Basin, Ontario, inferred from paleomagnetic data and spatial analysis of mafic dykes

2012 ◽  
Vol 49 (9) ◽  
pp. 1005-1017 ◽  
Author(s):  
M.D. Clark ◽  
U. Riller ◽  
W.A. Morris
Keyword(s):  
Spatial Analysis ◽  
Structural Characteristics ◽  
Paleomagnetic Data ◽  
The West ◽  
Plan View ◽  
Hinge Line ◽  
Sudbury Igneous Complex ◽  
Basement Rocks ◽  
Thickness Variations ◽  
Archean Basement

Tilting of crystalline basement rocks associated with folding strain at uppermost crustal levels is difficult to recognize if basement rocks are devoid of traceable marker planes. Here we use the spatial variation in strike of Paleoproterozoic mafic dyke segments complemented by compiled paleomagnetic data to identify tilting in Archean basement rocks associated with kilometre-scale folds of the eastern Sudbury Basin, Ontario. Spatial analysis of the strike of dyke segments is consistent with generation of the NE lobe and a newly identified anticline, referred to as the West Bay Anticline, in the layered Sudbury Igneous Complex (SIC). This anticline accounts better for the structural characteristics of the eastern Sudbury Basin than a previously proposed anticline with west-plunging hinge line. The West Bay Anticline is characterized by abrupt plan-view thickness variations in the lower SIC and curved faults displaying significant strike separations of SIC contacts. These structural characteristics are consistent with folding strain imparted to the SIC and adjacent Archean rocks during formation of the West Bay Anticline. Sublayer embayments and associated quartz diorite dykes likely served as zones of mechanical weaknesses, at which the higher-order folds localized. Unfolding magnitudes of the NE lobe based on primary paleomagnetic remanence directions are significantly smaller than inferred magnitudes that are based on the assumption that the basal SIC contact was initially planar. Thus, the basal SIC contact in the NE lobe likely had a trough-like geometry at the time of remanence acquisition. We advocate a scenario for the formation of the NE lobe, in which the trough geometry of the SIC is primary rather than a consequence of tilting prior to solidification of, and remanence acquisition in, the SIC. Finally, we caution the interpretation of photo lineaments in eroded basement terranes purely as a consequence of faulting.

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