The continental record and the generation of continental crust
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In this paper, detrital zircons have been used to estimate that at least 60% to 70% of the present volume of the continental crust had been generated by 3 Ga, which may have been linked to the onset of signifi cant crustal recycling through subduction at convergent plate margins.Abstract:
Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth’s record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and sea water and atmospheric proxies are distributed about a series of peaks and troughs. This distribution refl ects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physiochemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least ~60%–70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record , and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of signifi cant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic– and mantle-plume–dominated processes. The 60%–70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires on going destruction (recycling) of crust and subconti nental mantle lithosphere back into the mantle through processes such as subduction and delamination.read more
Citations
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Journal ArticleDOI
The supercontinent cycle: A retrospective essay
TL;DR: In this article, the authors trace the development of ideas concerning long-term episodic orogeny and continental crust formation, such as those embodied in the chelogenic cycle, through the first realization that such episodicity was the manifestation of the cyclic assembly and breakup of supercontinents, to the surge in interest in supercontinent reconstructions.
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Detrital Zircon U-Pb Geochronology Applied to Tectonics
TL;DR: Detrital zircon geochronology is rapidly developing into an essential tool in Earth science research because of the widespread occurrence of detrital minerals in sedimentary systems; the wide range of information that can be extracted from ZIRcon crystals; and the ability to determine ages with reasonable precision, accuracy, and efficiency as discussed by the authors.
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Detrital zircon U-Pb geochronology and Hf isotope geochemistry of Paleozoic and Triassic passive margin strata of western North America
George E. Gehrels,Mark Pecha +1 more
TL;DR: In this article, geochronologic and Hf isotopic analyses have been conducted on detrital zircons extracted from 36 samples of Neoproterozoic through Triassic passive margin strata from western North America.
Journal ArticleDOI
Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics
TL;DR: The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight as discussed by the authors.
References
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The continental crust: Its composition and evolution
TL;DR: In this paper, the authors describe the composition of the present upper crust and deal with possible compositions for the total crust and the inferred composition of lower crust, and the question of the uniformity of crustal composition throughout geological time is discussed.
Book ChapterDOI
Composition of the Continental Crust
Roberta L. Rudnick,Shan Gao +1 more
TL;DR: In this paper, the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories are discussed.
Journal ArticleDOI
The composition of the continental crust
TL;DR: In this paper, a new calculation of the crustal composition is based on the proportions of upper crust (UC) to felsic lower crust (FLC) to mafic lower-crust (MLC) of about 1.6:0.4.
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The geochemical evolution of the continental crust
TL;DR: A survey of the dimensions and composition of the present continental crust is given in this paper, where it is concluded that at least 60% of the crust was emplaced by the late Archean (ca. 2.7 eons).
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Nature and composition of the continental crust: A lower crustal perspective
TL;DR: In this article, a three-layer crust consisting of upper, middle, and lower crust is divided into type sections associated with different tectonic provinces, in which P wave velocities increase progressively with depth and there is a large variation in average P wave velocity of the lower crust between different type sections.