Journal ArticleDOI
A model for Trondhjemite-Tonalite-Dacite Genesis and crustal growth via slab melting: Archean to modern comparisons
Mark S. Drummond,Marc J. Defant +1 more
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In this paper, the authors introduced the importance of subducted oceanic crustal age on arc petrogenesis and demonstrated that Archean TTD crustal generation processes are also present in selected high-Al Phanerozoic TTD terranes.Abstract:
The petrogenesis of trondhjemite-tonalite-dacite (TTD) involves all major petrologic models in various tectonic settings. A specific subtype of TTD, high-Al type, is the one most commonly associated with Archean gneiss terranes. During the Archean, continental crust formation was operating at an elevated rate relative to the Phanerozoic, and the generation of high-Al TTD played an integral role in its nucleation and growth. High heat flow, rapid convection, and subduction of hotter, smaller plates were unique tectonic elements to the Archean which optimized conditions required for transformation of subducted oceanic crust into sial via partial melting. Anatexis of Archean mid-ocean ridge basalt (MORB) under eclogitic to garnet amphibolitic conditions produced weakly peraluminous to metaluminous high-Al TTD with low heavy rare earth elements (HREE), Y, Nb, K/Rb, and Rb/Sr and high La/Yb and Sr/Y. This study demonstrates that Archean TTD crustal generation processes are also present in selected high-Al Phanerozoic TTD terranes. The Cenozpic high-Al TTD suites are commonly found in tectonic settings which are thought to recreate the elevated Archean thermal gradients, i.e., at sites of young, hot oceanic plate subduction. These relationships imply a petrologic continuity of TTD generation through time. A fertile zone of melting is envisioned at 23–26 kbar (75–85 km) and 700–775°C, where wet partial melting of the subducting slab occurs concurrently with dehydration reactions. At this depth, the converting mantle wedge continuously feeds hot mantle material to the wedge-slab interface, creating strong temperature gradients, intraslab fluid migration, and slab melting. In summary, in modern arc terranes where young ( 30 Ma) oceanic crust is subducted, mantle-derived magmas are dominant, giving rise to basaltandesite-dacite-rhyolite (BADR) fractionation suites. This study introduces the importance of subducted oceanic crustal age on arc petrogenesis.read more
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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 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).
Journal ArticleDOI
An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution
TL;DR: In this article, an analysis of an extensive adakite geochemical database identifies two distinct compositional groups: high-SiO2 adakites (HSA) which represent subducted basaltic slab-melts that have reacted with peridotite during ascent through mantle wedge and low-Si O 2 adakitic mantle wedge.
Journal ArticleDOI
Chemical composition and evolution of the upper continental crust: Contrasting results from surface samples and shales
TL;DR: The average chemical composition of the upper continental crust (UC) as a function of age is estimated from chemical analyses, geologic maps, stratigraphic sections and isotopic ages as discussed by the authors.
References
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Journal ArticleDOI
Distribution of the Elements in Some Major Units of the Earth's Crust
Karl K. Turekian,K. H. Wedepohl +1 more
TL;DR: A table of abundances of the elements in the various major units of the Earth's lithic crust with a documentation of the sources and a discussion of the choice of units and data is presented in this article.
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Orogenic Andesites and Plate Tectonics
TL;DR: In this article, the authors define Orogenic Andesite and discuss its properties and properties, including the following: 1.1 Topography, gravity, heat flow, and conductivity.
Journal ArticleDOI
Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks
TL;DR: In this paper, a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions were used to interpret variations of these elements, first in basalts and second during fractional crystallization from basic to acid magmas.
Journal ArticleDOI
An analysis of the variation of ocean floor bathymetry and heat flow with age
Barry Parsons,John G. Sclater +1 more
TL;DR: In this paper, a simple cooling model and the plate model were proposed to account for the variation in depth and heat flow with increasing age of the ocean floor. But the results were limited to the North Pacific and North Atlantic basins.
Journal ArticleDOI
Crustal contributions to arc magmatism in the Andes of Central Chile
Wes Hildreth,Stephen Moorbath +1 more
TL;DR: In this article, 15 andesite-dacite stratovolcanoes on the volcanic front of a single segment of the Andean arc show along-arc changes in isotopic and elemental ratios that demonstrate large crustal contributions to magma genesis.
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