Late Cretaceous to Paleocene Terrane Accretion in the Colombian Andes: Paleomagnetic and Sedimentary Evidence

Abstract:

The formation of the Northern Andean Orogen include the accretion of various oceanic related terranes that have been accreted to the continental margin since the Late Cretaceous. The origin, drift and collisional history of such terranes can be addressed with an integrated magmatic, paleomagnetic and sedimentary perspective.

The Barroso Formation is a Cretaceous volcano-sedimentary sequence that outcrops in the western Cordillera. It is made of basaltic lava flows with interbedded pillow and marine sediments that was formed as part of an oceanic plateau associated to the Caribbean plate. Limited paleomagnetic results have suggested the existence of significant south to north terrane translation of this block from the Pacific.

This unit is intruded by numerous gabbroic, tonalitic and granodioritic plutons that record the formation of an oceanic arc on top of the plateau unit that finally collide with the continental margin in the Late Cretaceous.

The sedimentary record associated to this magmatic units has been included in the Penderisco Formation which widely outcrop as a series of lenses tectonically intermixed with the basaltic rocks of the Barroso Formation. Despite its extension, the tectonostratigraphic meaning of such record has been scarcely address.

Two different sedimentary members have been recognized within the Penderisco Formation. The Nutibara member include mostly pelagic and chemical sedimentary rocks and the Urrao member characterized by intercalation of sandstones mudstones and chert that resembles a turbiditic facies. The sedimentary provenance of sandstones beds associated to the Urrao member include mainly monocrystallyne quartz with undulose and straight extinction, plagioclase, minor volcanic and metamorphic lithics and significant contents of muscovite.

Whereas the Nutibara member is interpreted as related to the oceanic drift of the volcanic terrane that include the Barroso formation, the turbidites from the Urrao member that include a bimodal arc and metamorphic ensialic provenance can be interpreted as a sealed sequence formed associated to the collision of the oceanic unit with the continental margin. Fourteen new paleomagnetic sites have been recently collected on the Barroso formation to refine the understanding of the origin and intra-oceanic drift phases.