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
The 1.75-1.68Ga anorthosite-mangerite-alkali granitoid-rapakivi granite suite from the northern North China Craton: Magmatism related to a Paleoproterozoic orogen
TL;DR: The AMGRS is a suite of anorthosite-mangerite-alkali granitoid-rapakivi granite in the northern North China Craton (NCC) as mentioned in this paper.
201
Petrogenesis of Neoproterozoic Granitoids and Related Rocks from the Seychelles: the Case for an Andean-type Arc Origin
TL;DR: The Seychelles islands consist of undeformed and unmetamorphosed basaltic magmas derived from metaluminous monzogranites and granodiorites of Neoproterozoic depleted mantle, variably contaminated by Archaean age (> 750 Ma.
200
The geochemistry of phosphorus in granite rocks and the effect of aluminium
TL;DR: In this paper, a systematic study of the distribution of P2O5 in granitoids from all over the world shows that there are two modes to describe phosphorus enrichment in peraluminous granitic rocks: (1) the Hoyos-type trend, which is parallel to the one in Harrison and Watson's (HW) model and (2) the Pedrobernardo type trend, implying an increase in phosphorus in the most SiO2-rich differentiates, low-Ca granites.
199
Cenozoic Qaidam basin, China: A stronger tectonic inversed, extensional rifted basin
TL;DR: The geologic history of the Cenozoic Qaidam basin can be divided into two megastages on the basis of stratigraphy and structure as discussed by the authors, which is demonstrated by two tectono-sequences formed by the rifting, the synrifting magmatic thermal activity, and the control of protobasin development by syndepositional faults.
197
Geochemistry and U-Pb zircon geochronology of the Alvand plutonic complex in Sanandaj-Sirjan Zone (Iran): New evidence for Jurassic magmatism
Hossein Shahbazi,Wolfgang Siebel,M. Pourmoafee,Majid Ghorbani,Ali Asghar Sepahi,C. K. Shang,M. Vousoughi Abedini +6 more
TL;DR: In this paper, the Alvand plutonic complex in the Sanandaj-Sirjan zone (SSZ), Western Iran, was analyzed using geochemical, Sr-Nd isotopic, and U-Pb zircon geochronological data.
195
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