RT Journal Article
T1 Fault controlled Carboniferous A-type magmatism in the proto-Andean foreland(Sierras Pampeanas, Argentina): Geochemical constraints and petrogenesis
A1 Dahlquist, Juan A.
A1 Alasino, Pablo H.
A1 Eby, G. Nelson
A1 Galindo Francisco, Mª del Carmen
A1 Casquet, César
AB The intrusion of granitoids into the Eastern Sierras Pampeanas in the Early Carboniferous took place after along period of mainly compressional deformation that included the Famatinian (Ordovician) and Achalian(Devonian) orogenies. These granitoids occur as small scattered plutons emplaced in a dominant extensionalsetting, within older metamorphic and igneous rocks, and many of them are arranged along a reactivatedlarge shear zone. A set of 46 samples from different granitic rocks: Huaco granitic complex, San Blas pluton,and the La Chinchilla stock from the Sierra de Velasco, Zapata granitic complex from Sierra de Zapata, and theLos Árboles pluton from Sierra de Fiambalá, display high and restricted SiO2 contents between 69.2 and76.4 wt.%. On both FeO/(FeO+MgO) vs. SiO2 and [(Na2O+K2O)−CaO] vs. SiO2 plots the samples plot in theferroan and alkaline-calcic to calco-alkaline fields (FeO/(FeO+MgO)=0.88–1.0%;[(Na2O+K2O)−CaO]=6.3–8.3%), thus showing an A-type granitoid signature. The high concentrations for the High Field StrengthElements (HSFE), such as Y, Nb, Ga, Ta, U, Th, etc. and flat REE patterns showing significant negative Euanomalies are also typical features of A-type granites. Our petrogenetic model supports progressivefractional crystallization with dominant fractionation of feldspar and a source mineral assemblage enrichedin plagioclase. Biotites have distinctive compositions with high FeO/MgO ratios (7.8–61.5), F (360–5610 ppm), and Cl (120–1050 ppm). The FeO/MgO ratios together with the F and Cl content of igneousbiotites seem to reflect the nature of their parental host magmas and may be useful in identifying A-typegranitoids. The isotopic data (Rb–Sr and Sm–Nd) confirm that the A-type granites represent variablemixtures of asthenospheric mantle and continental crust and different mixtures lead to different subtypes ofA-type granite (illustrating the lack of consensus about A-type magma origin). We conclude that prominentshear zones play an important role in providing suitable conduits for ascending asthenospheric material andheat influx in the crust, a hypothesis that is in accord with other recent work on A-type granites.
PB Elsevier Science B.V., Amsterdam
SN 0024-4937
YR 2010
FD 2010
LK https://hdl.handle.net/20.500.14352/41884
UL https://hdl.handle.net/20.500.14352/41884
LA eng
DS Docta Complutense
RD 15 may 2024