The role of crustal thickness on magma composition in arcs: An example from the pre-Andean, South American Cordillera

ALASINO, P.H.; PATERSON, S.R.; KIRSCH, M.; LARROVERE, M.A.

GONDWANA RESEARCH

ELSEVIER SCIENCE BV

Año: 2022 vol. 106 p. 191 - 210

1342-937X

We explore the temporal evolution of pre-Andean Cordilleran arcs in central and northwestern Argentinaand northern Chile (27?34S) with a focus on the geochemical characteristics of the episodic magmatismand the relationship with crustal thickness. A compilation of ca. 5000 U-Pb bedrock and detrital zirconages, with ages from 600 to 130 Ma, reveals seven temporal magmatic accretions with main peaksat 526 Ma (Pampean); 471 Ma (Famatinian); 340 and 305 Ma (Early Gondwanan); 253and 221 Ma (Gondwanan); and 160 Ma (Early Andean). We show that most of the magmatic episodeswere developed in 30?50 km thick crust. Magmatism experienced fractional crystallization (r = 0) combined with variable degrees of assimilation (r > 0) that mostly did not exceed 30% crust. We conclude thatincreasing crustal thickness not only promotes more extensive differentiation by fractionation but alsoestablishes conditions near host rock solidi at shallow crustal levels promoting further contaminationin magmas.