Isotope Geochronology of the Exposed Rocks in the Cyrenaica Basin, NE Libya

2021 ◽  
Author(s):  
Osama Rahil Shaltami ◽  
Fares F. Fares ◽  
Hwedi Errishi ◽  
Farag M. EL Oshebi
Keyword(s):  
Isotope Geochronology

The Cihai diabase in the Beishan region, NW China: Isotope geochronology, geochemistry and implications for Cornwall-style iron mineralization

2013 ◽  
Vol 70-71 ◽  
pp. 231-249 ◽  
Author(s):  
Tong Hou ◽  
Zhaochong Zhang ◽  
M. Santosh ◽  
John Encarnacion ◽  
Meng Wang
Keyword(s):  
Isotope Geochronology ◽  
Nw China

The Age of Gold Mineralization in the Yana–Kolyma Metallogenic Belt, Northeastern Russia: First Data of Re–Os Isotope Geochronology of Native Gold

2021 ◽  
Vol 15 (4) ◽  
pp. 293-306
Author(s):  
V. Yu. Fridovsky ◽  
N. A. Goryachev ◽  
R. Sh. Krymsky ◽  
M. V. Kudrin ◽  
B. V. Belyatsky ◽  
...  
Keyword(s):  
Native Gold ◽  
Gold Mineralization ◽  
Northeastern Russia ◽  
Isotope Geochronology ◽  
Metallogenic Belt ◽  
Os Isotope

Coastal to Abyssal Vertical Sediment Accumulation Rates Predicted via Machine-Learning: Towards Sediment Characterization on a Global Scale

2020 ◽  
Author(s):  
Giancarlo Restreppo ◽  
Warren Wood ◽  
Benjamin Phrampus
Keyword(s):  
Machine Learning ◽  
Pacific Islands ◽  
Sediment Accumulation ◽  
River Mouth ◽  
Eastern United States ◽  
Accumulation Rates ◽  
Coastal Zones ◽  
K Nearest Neighbor ◽  
Isotope Geochronology ◽  
The Pacific

<p>Observed vertical sediment accumulation rates (SARs; n = 1166) were gathered from ~55 years of peer reviewed literature.  Original methods of rate calculation include long-term isotope geochronology (<sup>14</sup>C, <sup>210</sup>Pb, and <sup>137</sup>Cs), pollen analysis, horizon markers, and box coring. These observations are used to create a database of contemporary vertical SARs. Rates were converted to cm yr<sup>-1</sup>, paired with the observation’s longitude and latitude, and placed into a machine-learning based Geospatial Predictive Seafloor Model (GPSM). GPSM finds correlations between the data and established global “predictors” (quantities known or estimable everywhere; e.g. distance from coast line, river mouths, etc.).  The result, using a k-nearest neighbor (k-NN) algorithm, is a 5-arc-minute global map of predicted vertical SARs.  The map generated provides a global reference for vertical sedimentation from coastal to abyssal depths.  Areas of highest sedimentation, ~3-8 cm yr<sup>-1</sup>, are generally river mouth proximal coastal zones and continental shelves on passive tectonic margins (e.g. the Gulf of Mexico, eastern United States, eastern continental Asia, the Pacific Islands north of Australia), with rates falling exponentially towards the deepest parts of the oceans.  Coastal zones on active tectonic margins display vertical sedimentation of ~1 cm yr<sup>-1</sup>, which is limited to near shore when compared to passive margins.  Abyssal depth rates are functionally zero at the time scale examined (~10<sup>-4</sup> cm yr<sup>-1</sup>), and increase one order of magnitude near the Mid-Atlantic ridge and at the conjunction of the Pacific, Nazca, and Cocos tectonic plates.  Predicted sedimentation patterns are then compared to established quantities of fluvial sediment discharge to the oceans, calculated by Milliman and Farnsworth in <em>River Discharge to the Coastal Ocean: A Global Synthesis</em> (2011).</p>

Constraining the process of intracontinental subduction: implications from petrology and Lu-Hf geochronology of eclogites from the Austroalpine Nappes

2020 ◽  
Author(s):  
Irena Miladinova ◽  
Nikolaus Froitzheim ◽  
Thorsten Nagel ◽  
Marian Janák ◽  
Raúl Fonseca ◽  
...  
Keyword(s):  
Eastern Alps ◽  
Ultrahigh Pressure ◽  
Garnet Growth ◽  
Published Data ◽  
Isotope Geochronology ◽  
Ultrahigh Pressure Metamorphism ◽  
Austroalpine Nappes ◽  
Short Period ◽  
Facies Metamorphism ◽  
Global Tectonics

<p>The nucleation of subduction zone remains a widely discussed topic in the global tectonics. The prevalent view is that subduction starts within an oceanic plate. However, there is strong evidence that subduction can also be initiated within a continent. To test this hypothesis, we combine petrology, isotope geochronology and thermodynamic phase equilibrium modelling on eclogites from the Austroalpine Nappes of the Eastern Alps.</p><p>The high- and ultrahigh-pressure rocks occur in a ~400 km long belt from the Texel Complex in the west to the Sieggraben Unit in the east without remnants of Mesozoic oceanic crust. Garnet growth during pressure increase was dated using Lu-Hf chronometry. The results range between c. 100 and c. 90 Ma, indicating a short period of subduction. Combined with already published data, our estimates of metamorphic conditions indicate a field gradient with increasing pressure and temperature from northwest to southeast, where the rocks experienced ultrahigh-pressure metamorphism. The oldest Cretaceous eclogites (c. 100 Ma) are found in the Saualpe-Koralpe area which comprises widespread gabbros formed during Permian to Triassic rifting. This supports the hypothesis that subduction initiation was intracontinental and localized by a Permian rift. In the Texel Complex two-phased garnets yielded a Variscan-Eoalpine mixed age indicating re-subduction of Variscan eclogite-bearing continental crust during the Eoalpine orogeny. Jurassic blueschist-facies metamorphism at Meliata in the Western Carpathians and Cretaceous eclogite-facies metamorphism in the Austroalpine are separated by a time gap of ~50 Ma and therefore do not represent a transition from oceanic to continental subduction but rather separate events.</p>

U-Pb Isotope Geochronology and Granitic Gneisses Nanoparticles from the Xiaomei Shear Zone: Implication for Caledonian Tectonic in the Hainan Island, China

2020 ◽  
Vol 12 (1) ◽  
pp. 39-47
Author(s):  
Zhou Yang ◽  
Shen Baoyun ◽  
Liu Hailing ◽  
Yan Yi ◽  
Yan Yan
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Frictional Heating ◽  
Hainan Island ◽  
Ductile Shear Zone ◽  
Spherical Nanoparticles ◽  
Pb Isotope ◽  
Tectonic Event ◽  
Isotope Geochronology ◽  
Early Devonian

U-Pb ages of zircons from the granitic gneisses in the Xiaomei shear zone, Hainan Island, provide constraints on the age of granitic gneisses and tectonic evolution of Caledonian orogeny in Hainan Island. Zircons extracted from granitic gneisses are rounded and subrounded and characterized by oscillatory overgrowths enclosing inherited cores. The Early Devonian (414–411 Ma) ages of inherited zircons from the Xiaomei granitic gneisses are consistent with tectonic event that uplifted the Hainan island, resulting in the absence of Devonian strata. Meanwhile, nanoparticles are found in the granitic gneisses, including agglomerated nanoparticles and spherical nanoparticles in the ductile shear zone. The spherical nanoparticles in the shear zone are believed to have experienced a two-stage formation, from the linear spherical nanoparticles to planar spherical nanoparticles. With rise in temperature due to frictional heating during the shearing, spherical nanoparticles are deformed to agglomerated nanoparticles and the inherited zircons probably are recrystallized at 411 Ma.

ISOTOPE GEOCHRONOLOGY OF METAMORPHIC PROCESSES

1986 ◽  
Vol 28 (5) ◽  
pp. 584-596
Author(s):  
L. N. Ovchinnikov ◽  
S. N. Voronovskiy ◽  
L. V. Ovchinnikova
Keyword(s):  
Isotope Geochronology
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