177 Chronology of Orogenesis: Unlocking the Timelines of Mountain Building

The focus of this session is the use of geochronological methods (including but not limited to U-Pb, Ar/Ar, FT, (U/Th)-He) to establish the timing of key events in mountain building, including different orogenic phases, exhumation, and uplift rates.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 304C

Provenance and metamorphism of the Cuyania basement and peri-Gondwana blocks in the Sierras Pampeanas of Argentina: Evolution of a Paleozoic microcontinent-arc collision zone

Paper number: 177-9
Program: Technical Sessions
Time: 9:49 AM – 10:04 AM

Authors

Abstract

The proto-western Gondwanan margin (present-day Sierras Pampeanas region, Argentina) underwent tectonic convergence, magmatism, and lithospheric evolution during the early Paleozoic Famatinian orogenic cycle. The Famatinian arc phase (490–465 Ma) was characterized by Cordilleran-type magmatism and the formation of volcano-sedimentary successions. Subsequently, the collisional phase (465–400 Ma) involved the accretion of the Laurentia-derived Cuyania composite terrane, which was underplated beneath Gondwanan arc crust.  Today, uplifted blocks of the metamorphosed Cuyania basement and their cover sequences are exposed in the western region of the Sierras Pampeanas. However, uncertainty persists over the location of the Gondwana-Cuyania suture zone, as does the potential existence of peri-Gondwana blocks in the suture zone between Cuyania and the Famatinian arc crust. Moreover, the timing and magnitude of metamorphism and exhumation along the suture zone remain poorly constrained.

We present new whole rock X-ray fluorescence (XRF), zircon and monazite U-Th-Pb geochronology, and monazite trace/rare earth element geochemistry data to evaluate the provenance and metamorphic evolution of the Gondwana-Cuyania collision zone. Ten samples were collected from representative metamorphic complexes and intrusive rocks in ranges spanning ~29–32 °S (Sierras Maz, Espinal, and Ramaditas; Cerros Asperecito and Valdivia).

Zircon U-Pb ages reveal two clusters of Gondwanan versus Laurentian affinity and indicate that metamorphic rocks within the Sierra de Ramaditas, eastern Sierra del Espinal, and Cerro Asperecito have Cambrian protoliths with a Gondwanan provenance, confirming that they were part of the Gondwanan forearc before the arrival of Cuyania. Furthermore, XRF and zircon/monazite results indicate distinct stages of Famatinian metamorphism and tectonic assembly involving 1) migmatization of the Gondwanan forearc during arc emplacement and initial collision with Cuyania at ca. 470–460 Ma; 2) hard collision starting ca. 450–445 Ma that deformed both plates and lasted until 400 Ma; 3) pervasive syn-collisional (470–400 Ma) granite emplacement across downgoing and overriding plates; and 4) post-orogenic exhumation of underplated Cuyania basement beginning ca. 420 Ma. These results are significant for refining the timing of a major Paleozoic orogeny in South America and for recognizing the Gondwanan forearc preserved in the rock record, which has greater implications for the development and paleogeography of Gondwana.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414542

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