Cenozoic provenance history of synorogenic conglomerates in western Argentina (Famatina Belt): Implications for Central Andean foreland development

DAVILA, F.M., ASTINI, R.A.

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

Año: 2007 vol. 119 p. 609 - 622

0016-7606

In Famatina, at the modern northern flat-slab segment of the Central Andean belt, synorogenic conglomerate facies provide a unique opportunity to reconstruct paleogeography and tectonic setting. Stratigraphically constrained provenance analyses record a multi-event history of the Andean foreland and a complex pattern of exhumed uplands that, in turn, controlled the depocenter history. Western and eastern sources can be differentiated. The western domain was composed of equigranular granitoids and lower and upper Paleozoic volcano-sedimentary and sedimentary units, whereas the eastern domain was mainly formed by porphyrytic granitoids and minor slightly metamorphosed lower Paleozoic clastic rocks. The surrounding regions expose medium- to high-grade metamorphic rocks, which are not recorded in any Cenozoic conglomerate of Famatina. Unroofing sequences are deduced from the compositional trends. Conglomerate composition and paleocurrent data show input from intrabasinal sources and important participation of basement since the beginning of the Neogene. An early Miocene broken foreland is interpreted during deposition of the Del Crestón Formation. A significant source inversion, with clasts supplied from the eastern basement domain, is recorded ~2000 m from the base, within the Middle Miocene Del Abra Formation; reactivation of western granitic thrust sheets occurred by the late Middle Miocene and Late Miocene, as indicated by provenance studies of the Santo Domingo and El Durazno formations. In contrast to simple asymmetric foreland models, provenance analysis documents early participation of crystalline rocks, suggesting early development of intra-foreland basement highs within the southern Central Andes. At a regional scale, basement thrusting and associated intermontane basin development was diachronous. This interpretation is supported by broad propagation of basement thrusting from the northern Sierras Pampeanas (and Famatina) toward the central and eastern Sierras Pampeanas between Early-Middle Miocene and Late Miocene-Pliocene time. Early Miocene reconstructions of the Juan Fernandez Ridge position on the Central Andean margin suggest that during this interval, shallow subduction was unlikely related to oceanic plateau subduction under the Sierras Pampeanas.