Middle Devonian monzonitic magmatism of the Sierra de San Luis

MARTINEZ DOPICO, C.I.; LÓPEZ DE LUCHI, M. G.,

Paris

Conferencia; Goldschmidt Conference 2017; 2017

Geochemical Society and the European Association of Geochemistry.

MiddleDevonian (393-382 Ma) batholiths are composed of I-to A-type hybrid shoshoniteand subordinated high-K series Monzonite (MS) and Granite suites (GS).SiO2(46?62%), Cr, Ni, V, Sc, LILE, LREE, Th, Zr and variable, Sr/Y, (La/Yb)Nand (Tb/Yb)N,, smooth Eu/Eu*, moderate Na2O (ca 3.5), and troughs at Nb and Tafor MS rocks suggest a subduction-related enriched lithospheric mantle source.Sm-Nd data (TDM=0.98-1.08 Ga, εNd(380Ma)=0.66-1.47) and87Sr/86Sri (0.703520-0.704203) are compatiblewith an enriched mantle source. GS rocks are characterized by relativelymoderate Al2O3, CaO, and 87Sr/86Sri, high LILE, Cr, variable Sr/Y, (La/Yb)N andEu/Eu* and low Rb/Sr (<1.2) which suggest a mafic source. TDM=1.20-1.28 Ga, εNd(380Ma)=3.02 to 3.3, 87Sr/86Sri=0.706578?0.707027 for porphyritic monzogranites and TDM=1.31 Ga, εNd(380Ma)=3.3, 87Sr/86Sri=0.707782for biotite monzogranites indicate a common source. TDM=1.36-1.38 Ga isconsiderably younger than the mean 1.8-1.6 Ga Eastern Sierras Pampeanas crustalresidence age. Equigranular alkali-calcic leucomonzogranites are characterizedby Rb/Sr >1.5, ASI 1.05-1.18, and Ga/Al 2.6-3.9, εNd(380Ma)=-3.74 to-3.95 and(87Sr/86Sr)i=0.710743-0.712955 which would point to metasedimentary or felsicigneous crustal sources. Middle Devonian magmatism record an episode of crustalgrowth by enriched mantle derived magma and variable degrees of partial meltingof a lower crustal source at the wanning stages of the Achalian orogeny.