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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Neoproterozoic bimodal magmatism in the Cathaysia Block of South China and its tectonic significance
TL;DR: The Mamianshan felsic rocks were most likely generated by partial melting of the regional Paleoproterozoic Mayuan amphibolites as mentioned in this paper, with an eruption age of 818 ± 9 Ma.
327
Recognizing mantle plumes in the geological record
TL;DR: In this article, geochemistry and isotopes can be used to test and characterize the plume origin of a large igneous province (LIP), dominated in the Phanerozoic by flood basalts and in the Proterozoic by the exposed plumbing system of dykes, sills, and layered intrusions.
325
The Petrogenesis of A-type Magmas from the Amram Massif, Southern Israel
TL;DR: The Amram mafic dikes of the Amram Massif, southern Israel as discussed by the authors have been used to model the chemical evolution of the suite and reveal a correlation between decreasing stratigraphic age and increasing silica content.
320
Origin of Mesoproterozoic A-type granites in Laurentia: Hf isotope evidence
TL;DR: In this article, the authors measured the Hf isotope composition of zircons from 31 previously dated A-type granites intruding Proterozoic basement provinces from the southwest U.S. to the upper mid-continent.
314
Permian peralkaline, peraluminous and metaluminous A-type granites in the Panxi district, SW China : Their relationship to the Emeishan mantle plume
J. Gregory Shellnutt,Mei-Fu Zhou +1 more
TL;DR: In this article, the permian granitic intrusions (plutons) in the Panxi region, SW China are spatially and temporally associated with the Emeishan large igneous province (ELIP).
305
References
Trace element discrimination diagrams for the tectonic interpretation of granitic rocks
TL;DR: In this article, a data bank containing over 600 high quality trace element analyses of granites from known settings was used to demonstrate using ORG-normalized geochemical patterns and element-SiO2 plots that most of these granite groups exhibit distinctive trace element characteristics.
Tectonic setting of basic volcanic rocks determined using trace element analyses
Julian A. Pearce,J.R. Cann +1 more
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Nature and origin of A-type granites with particular reference to southeastern Australia
TL;DR: In the Lachlan Fold Belt of southeastern Australia, Upper Devonian A-type granite suites were emplaced after the Lower Devonian I-type granites of the Bega Batholith as mentioned in this paper.
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