scholarly journals The largest plagiogranite on Earth formed by re-melting of juvenile proto-continental crust

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Hamed Gamal El Dien ◽  
Zheng-Xiang Li ◽  
Mohamed Abu Anbar ◽  
Luc S. Doucet ◽  
J. Brendan Murphy ◽  
...  
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
High Sodium ◽  
Melt Extraction ◽  
The Earth ◽  
Nubian Shield ◽  
Low Potassium ◽  
Juvenile Crust ◽  
Geochemical Analyses ◽  
Arabian Nubian Shield

AbstractThe growth of continental crust through melt extraction from the mantle is a critical component of the chemical evolution of the Earth and the development of plate tectonics. However, the mechanisms involved remain debated. Here, we conduct petrological and geochemical analyses on a large (up to 5000 km2) granitoid body in the Arabian-Nubian shield near El-Shadli, Egypt. We identify these rocks as the largest known plagiogranitic complex on Earth, which shares characteristics such as low potassium, high sodium and flat rare earth element chondrite-normalized patterns with spatially associated gabbroic rocks. The hafnium isotopic compositions of zircon indicate a juvenile source for the magma. However, low zircon δ18O values suggest interaction with hydrothermal fluids. We propose that the El-Shadli plagiogranites were produced by extensive partial melting of juvenile, previously accreted oceanic crust and that this previously overlooked mechanism for the formation of plagiogranite is also responsible for the transformation of juvenile crust into a chemically stratified continental crust.

scholarly journals Geoneutrinos

2012 ◽  
Vol 2012 ◽  
pp. 1-34 ◽  
Author(s):  
Ondřej Šrámek ◽  
William F. McDonough ◽  
John G. Learned
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Detection Methods ◽  
Heat Sources ◽  
Radiogenic Heat ◽  
Interdisciplinary Field ◽  
The Earth ◽  
Directional Detection ◽  
Under Construction ◽  
Current Detection

Neutrino geophysics is an emerging interdisciplinary field with the potential to map the abundances and distribution of radiogenic heat sources in the continental crust and deep Earth. To date, data from two different experiments quantify the amount of Th and U in the Earth and begin to put constraints on radiogenic power in the Earth available for driving mantle convection and plate tectonics. New improved detectors are under construction or in planning stages. Critical testing of compositional models of the Earth requires integrating geoneutrino and geological observations. Such tests will lead to significant constraints on the absolute and relative abundances of U and Th in the continents. High radioactivity in continental crust puts limits on land-based observatories' capacity to resolve mantle models with current detection methods. Multiple-site measurement in oceanic areas away from continental crust and nuclear reactors offers the best potential to extract mantle information. Geophysics would benefit from directional detection and the detectability of electron antineutrinos from potassium decay.

Old Continental Crust Underlying Juvenile Oceanic Arc: Evidence From Northern Arabian‐Nubian Shield, Egypt

2018 ◽  
Vol 45 (7) ◽  
pp. 3001-3008 ◽  
Author(s):  
Xian‐Hua Li ◽  
Yasser Abd El‐Rahman ◽  
Mohamed Abu Anbar ◽  
Jiao Li ◽  
Xiao‐Xiao Ling ◽  
...  
Keyword(s):  
Continental Crust ◽  
Nubian Shield ◽  
Arabian Nubian Shield

From Kenorland to modern continents: tectonics and metallogeny

2019 ◽  
pp. 3-32
Author(s):  
A. S. Yakubchuk
Keyword(s):  
Continental Crust ◽  
Tectonic Evolution ◽  
Plate Tectonics ◽  
Ferrous Metal ◽  
Time Intervals ◽  
Secular Changes ◽  
The Earth ◽  
Time Space ◽  
Long Time ◽  
Three Stages

There are three stages in tectonic evolution of the Earth: (1) nucleation — from origin of protocratons to their assembly into Supercontinent Kenorland (2.7–2.5 Ga); (2) cratonization — from breakup of Kenorland (2.45 Ga) to the assembly of Columbia (1.85 Ga) and its reorganization into Rodinia (1.0–0.72 Ga); (3) modern plate tectonics — from breakup of Rodinia at 720 Ma until present. Analysis of time-space reorganizations of Archean granulite-gneiss terranes, which correspond to continental lithospheric keels, reveals five groups of protocratons (Nena, Ur, Congo-Sahara, NAsia and Atlantica) that remained almost intact during long time intervals. After the breakup of Kenorland, the continental crust rotated counter-clockwise. NAsia and Atlantica the least rotated and drifted relative to Nena, however the latter was rotated by 180°. Congo-Sahara, Ur and Kalahari were the most rotated. The assembly and breakup of the supercontinents clearly correlates with secular changes in dominant types of base, precious and ferrous metal deposits, as well as formation and emplacement of diamonds.

A late Tonian plate reorganization event: Using a deep-time full-plate global model to unravel Neoproterozoic tectonic convulsions

2020 ◽  
Author(s):  
Alan Collins ◽  
Morgan Blades ◽  
Andrew Merdith ◽  
John Foden
Keyword(s):  
Plate Tectonics ◽  
Plate Motion ◽  
Deep Time ◽  
Geological Record ◽  
Plate Convergence ◽  
The Core ◽  
Nubian Shield ◽  
Plate Reconstructions ◽  
The One ◽  
Arabian Nubian Shield

<p>Plate reorganization events are a characteristic of plate tectonics that punctuate the Phanerozoic. They fundamentally change the lithospheric plate-motion circuit, influencing the planet’s tectonic-mantle system and both ocean and atmospheric circulation through changes in bathymetry and topography. The development of full-plate reconstructions for deep time allows the geological record to be interrogated in a framework where plate kinematic reorganizations can be explored. Here, the geological record of the one of the most extensive tracts of Neoproterozoic crust on the planet (the Arabian-Nubian Shield) is interpreted to reflect a late Tonian plate reorganization at ca. 800-715 Ma that switched plate-convergence directions in the Mozambique Ocean, bringing Neoproterozoic India towards both the African cratons and Australia-Mawson, instigating the closure of the intervening ocean and the future amalgamation of central Gondwana ca. 200 million years later. This plate kinematic change is coeval with constraints on break-up of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo.</p>

Fitting a new piece into the Precambrian puzzle: the detrital rutile record and its links to modern plate tectonics

2020 ◽  
Author(s):  
Inês Pereira ◽  
Craig D. Storey ◽  
Robin Strachan ◽  
Hugo Moreira ◽  
James Darling ◽  
...  
Keyword(s):  
Continental Crust ◽  
Detrital Zircon ◽  
Plate Tectonics ◽  
Secular Evolution ◽  
The Earth ◽  
Selective Preservation ◽  
Clastic Sedimentary ◽  
Detrital Zircon Ages ◽  
Orogenic Belts ◽  
Collisional Orogens

<p>Plate tectonics is responsible for shaping the Earth’s surface, influencing the geological, hydrological and atmospheric cycles. However, there is no consensus on when plate tectonics initiated: was it fully operational during the Archean or did it not develop until the Proterozoic?</p><p>Much of what is currently known about the secular evolution of Earth’s continental crust and its links to plate tectonics has been recovered from detrital minerals. This is related to the incomplete rock record; the detrital record allows access to information from eroded and unexposed terrains. Most studies have relied on the detrital zircon record, but it is still unclear if the coincidence in age peaks with periods of supercontinent assembly reflects episodic continental growth or bias due to selective preservation of new crust within collisional orogenic belts. Furthermore, because zircon mostly grows in high-temperature conditions, it mostly calibrates magmatic cycles. To understand the evolution of plate tectonics and to assess its influence on continental crust preservation, we developed a new proxy, relevant to a range of metamorphic conditions, including HP-LT.</p><p>We investigate the U-Pb distribution ages of detrital rutile, from a range of modern stream sediments and siliciclastic units at sub-amphibolite facies metamorphic grade. Rutile mostly forms in collisional orogens and, by comparison with the zircon record, we can test the existence of a preservation bias. Zircon and rutile age distributions from our sample sets show a significant correlation, both peaks and troughs, that can only be reconciled if the detrital zircon record reflects a preservation bias that occurred during supercontinent assembly.</p><p>We further present new U-Pb and trace element data from detrital rutile within two clastic sedimentary units, preserved at sub-greenschist facies conditions in NW Scotland. These are the Torridon (Tonian) and the Ardvreck (Cambrian) groups, whose detrital zircon ages span a significant period between 3 and 1 Ga. By applying Zr-in-rutile thermometry and comparing it to the preserved metamorphic record, we show that both low and high dT/dP conditions can be inferred since at least 2.1 Ga.</p><p>Combining the existence of paired metamorphism up to 2.1 Ga with the periodic preservation of the continental crust throughout most of the Earth’s history implies that one-sided subduction, a hallmark of plate tectonics, has operated since at least the late Paleoproterozoic, and that supercontinent assembly during and after this period has been driven by plate tectonic mechanisms.</p>

Ages and Hf isotopes of igneous zircons from Neoarchean TTG gneisses in the Eastern Block, North China Craton: Tectonic implications

2020 ◽  
Author(s):  
Guochun Zhao
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Plate Tectonics ◽  
Basic Research ◽  
Large Igneous Province ◽  
Main Body ◽  
Juvenile Crust ◽  
Block Based ◽  
Two Phases ◽  
T Values

<p class="BODYTEXT"><span lang="EN-GB">Available zircon ages indicate that the plutonic protoliths of Neoarchean TTG (tonalitic-trondhjemitic-granodioritic) gneisses in the Eastern Block were emplaced at two phases, with the earlier one at 2.75-2.65 Ga and the younger one at 2.55-2.50 Ga. Although the 2.75-2.65 Ga rock associations are only exposed in the Luxi and Qixia areas, the ~2.7 Ga igneous event must have occurred across the whole Eastern Block and was a major crustal accretionary or mantle-extraction event that formed a thick mafic crust beneath the whole Eastern Block based on the following lines of evidence: </span></p> <p class="BODYTEXT"><span lang="EN-GB">(1) The 2.75-2.65 Ga TTG rocks in the Luxi granite-greenstone terrane have positive εHf(t) values (+2.7 to +10.0), with most zircon Hf model ages close to the rock-forming ages, which provides robust evidence that the ~2.7 Ga event that formed the 2.75-2.65 rock associations was a crustal accretion (mantle extraction) event, not a crust-reworking event.</span></p> <p class="BODYTEXT"><span lang="EN-GB">(2) The 2.55-2.50 Ga TTG rocks in the Eastern Block possess mildly positive to slightly negative εHf(t) values, with most zircon Hf model ages pointing to 2.8-2.6 Ga, similar to rock-forming ages of the 2.75-2.65 Ga TTG gneisses in the Luxi granite-greenstone terrane, suggesting that the 2.55-2.50 Ga rocks in the Eastern Block were mainly derived from the partial melting of an early Neoarchean (2.75-2.65 Ga) juvenile crust that formed at ~2.7 Ga. As the 2.55-2.50 Ga TTG gneisses are ubiquitous over the whole Eastern Block, the 2.7 Ga event must have occurred over the whole Eastern Block, forming an early Neoarchean juvenile crust that experienced partial melting or reworking to form the 2.55-2.50 Ga TTG rocks. </span></p> <p class="BODYTEXT"><span lang="EN-GB">(3) TTG rocks are generally considered to have been derived from the partial melting of a thickened mafic crust (eclogite or rutitle/garnet-bearing amphibolite). This means that an early Neoarchean (2.75-2.65 Ga) juvenile crust formed by the ~2.7 Ga event should be a mafic-dominant crust, which is either a lower continental crust or an oceanic crust. In this case, the ~2.7 Ga event in the Eastern Block may have represented a Large Igneous Province event that formed the main body of the Eastern Block. This study was financially supported by the sub-project of a NSFC Major Project, entitled “Continental Crust Growth-Stabilization and Initiation of the Early Plate Tectonics” (Project Code: 41890831) and HKU Seed Fund for Basic Research (201811159089).</span></p>

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