A-type granites: geochemical characteristics, discrimination and petrogenesis
TL;DR: A-type granites as mentioned in this paper were found to have high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr.
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Abstract: New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites. A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.
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Citations
Early Paleozoic Tectonic Evolution of the South Tianshan Collisional Belt: Evidence from Geochemistry and Zircon U-Pb Geochronology of the Tie’reke Monzonite Pluton, Northwest China
TL;DR: An Early Paleozoic hornblende quartz monzonitic pluton from the Tie-reke region in the central South Tianshan Collisional Belt (STCB) was reported in this article.
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Geochronology, petrogenesis, and tectonic setting of Mesozoic volcanic rocks, southern Manzhouli area, Inner Mongolia
TL;DR: In this paper, major and trace element analyses of volcanic rocks in Northeast China, as well as U-Pb dating and Hf isotopic analysis of their zircons, were undertaken to determine the petrogenesis and tectonic setting of the volcanics.
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Geochemical and isotopic constraints on island arc, synorogenic, post-orogenic and anorogenic granitoids in the Arabian Shield, Saudi Arabia
TL;DR: The Arabian Shield preserves a protracted magmatic record of repeated amalgamation of juvenile subduction terranes that host granite intrusions ranging in age from the early Neoproterozoic to the Cambrian, which were emplaced into convergent and within-plate settings.
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Geochronology, elemental and Nd–Hf isotopic geochemistry of Devonian A-type granites in central Jiangxi, South China: Constraints on petrogenesis and post-collisional extension of the Wuyi–Yunkai orogeny
Shang-Jie Feng,Kui-Dong Zhao,Kui-Dong Zhao,Hong-Fei Ling,Pei-Rong Chen,Wei-Feng Chen,Tao Sun,Shao-Yong Jiang,Shao-Yong Jiang,Wei Pu +9 more
TL;DR: In this paper, the authors reported a systematic study on two Devonian A-type granites in the central Jiangxi Province, which indicated that the Wuyi-Yunkai orogeny in South China had changed from syncollisional crustal thickening to post-collisionally extension at least from 415-Ma.
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High-K calc-alkaline to A-type fissure-controlled volcano-plutonism of the São Félix do Xingu region, Amazonian craton, Brazil: Exclusively crustal sources or only mixed Nd model ages?
Carlos Marcello Dias Fernandes,Caetano Juliani,Lena Virgínia Soares Monteiro,Bruno Lagler,Carlos Mario Echeverri Misas +4 more
TL;DR: In the Sao Felix do Xingu region, southern portion of Amazonian craton, voluminous well-preserved Late Paleoproterozoic volcanic and plutonic rocks are grouped in the Sobreiro and Santa Rosa formations.
58
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