Ordovician back arc foreland and Ocloyic thrust belt development on the western Gondwana margin as a response to Precordillera terrane accretion

Abstract

The Famatina belt, southern central Andes, records a circa 470 m.y. shortening episode (Ocloyic orogeny) affecting the peri‐Gondwanan back arc basin in response to the accretion of the Precordillera terrane. Collision created distinct features across and along the margin, some of which persisted into the present Andean structure. From east to west, the Ocloyic deformation is recorded across the telescoped region of Famatina, represented by (1) an east vergent fold‐thrust belt (EVFTB) involving a major angular unconformity between Early and Middle Ordovician rocks, (2) a highly deformed volcano‐sedimentary belt, and (3) an east vergent ductile shear zone affecting Famatinian granites. Axis attitudes of Ordovician refolded anticlines in the EVFTB show west‐east tectonic transport, in agreement with kinematics of Ocloyic high‐strain belts, indicating shortening orthogonal to the present Pacific margin. Eastward displacement of the Ordovician volcanic arc at ∼27°S latitude together with a documented sinistral slip zone across the proto‐Andean margin suggests tectonic indentation.

Structural evolution of a composite middle to lower crustal section: The Sierra de Pie de Palo, northwest Argentina

“…This period is synchronous with voluminous magmatism within the Famatina arc (∼485-465 Ma) [Ducea et al, 2010], east vergent retro-arc thrusting (∼470 Ma) [Astini and Dávila, 2004], and initial collision of the Precordillera terrane (∼470 Ma) [Fanning et al, 2004] (Figure 18b).…”

The tectonic significance of K/Ar illite fine-fraction ages from the San Luis Formation (Eastern Sierras Pampeanas, Argentina)

“…1, Caminos 1979). This basement has registered the polyphase accretional history in the east of the Río de La Plata craton starting in the early Cambrian with the collision of the Pampean Terrane with the craton (Ramos et al 1986;Rapela et al 1998;Stuart-Smith et al 1999) followed by the amalgamation of the Precordillera/Cuyania Terrane to the newly formed margin of Gondwana during the Famatinian cycle (Astini and Thomas 1999;Rapalini et al 1999;Casquet et al 2001;Thomas et al 2002;Astini and Dávila 2004;Steenken et al 2006). The mode of emplacement of voluminous discordant granodioritic to syenogranitic batholiths throughout the Devonian is a matter of ongoing discussion.…”

Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin

“…Ramblones thrust sheet; LTS: Las Trancas thrust sheet; LDS: Los Damascos thrust sheet; LCS: Los Colorados thrust sheet; B. Cambro-Ordovician stratigraphy within the Famatina belt (modified from Astini and Dávila, 2004).…”

“…Samples for clay mineral X-ray analysis were prepared following the recommendations of Moore and Reynolds (1997 Astini et al (2007), Astini and Dávila (2004), and Collo et al (2009). …”

“…Within this belt, Middle-Upper Cambrian to Middle-Upper Ordovician deposits constitute an almost continuous succession affected by low-grade metamorphism. The well-constrained and mostly preserved Cambro-Ordovician stratigra phy in this region allows the reconstruction of the sedimentary history related to the evolution of the Ocloyic arc (Astini, 2003;Astini and Dávila, 2004). Three major stages of sedimentation re cord the period preceding the initiation of subduction up to the uplift and basin inversion in the final stages of the Ocloyic orogeny, which has been commonly related with the collision of the Precordillera terrane from the west (ca.…”