267 Tectonics: Exhumation, Erosion, Subsidence, and Rotation

Wednesday, 4 November 2015
8:00 AM - 12:00 PM
Room 347/348

CENOZOIC ACCRETION AND MORPHO-TECTONIC RESPONSE IN THE NORTHERN ANDES (COLOMBIA) THROUGH LOW-TEMPERATURE THERMOCHRONOLOGY ANALYSES/MODELING

Paper number: 267-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The Northern Andes exhibit a litho-tectonic and orogenic configuration strongly influenced by accretionary processes of lithospheric blocks taking place since the Late Cretaceous. A set of major crustal structures in Colombia (e.g., Cauca-Romeral Fault System, CRFS) mark the limit between a Paleozoic-Precambiran(?) domain of continental affinity to the east and Cretaceous accreted terrenes to the west. This boundary is well displayed along the Cauca River, which occupies a major Inter-Andean trough between the Central and Western cordilleras.

Structurally, the region is dominated by the N-S trending CRFS as a structure that can be traced to southern Ecuador. Relationships between the CRFS and W-SW verging thrust system are unknown, although they represent key components of a transpressional orogeny. To understand timing of accretion and morphptectonic respose (mountain building, uplift, exhumation) of various crustal blocks, we used (U-Th)/He and fission track thermochronology analyses (dating and modeling). Samples were collected along four vertical profiles on two distinct litho-tectonic units: (1) three vertical profiles in the eastern-continental realm on Paleozoic metamorphic-basement rocks and associated Cretaceous intrusives, and (2) one vertical profile in the Mande batholith (MB), an Eocene pluton on the Panama Chocó Block magmatic arc accreted to the margin in Oligocene-Miocene times.

Zircon helium ages (ZHe) show a clear contrast between the eastern domain (ca. 53-60 Ma) and the Mande Batholith (ca. 30-40 Ma). Apatite helium ages (AHe) also illustrate a marked contrast with ca. 23-42 Ma for the eastern sections and a distinct cluster at ca. 4 Ma for the MB. Our results suggest contrasting cooling histories for the two litho-tectonic blocks: The MB (western block) records Late Eocene and Pliocene events while the older eastern block does not. Paleocene morphotectonic pulses recorded by the eastern block are related to the Laramic Orogenetic phase. Elevation-invariant ZHe ages from the ancient eastern block suggest rapid uplift-exhumation during the Paleogene. This information is modeled via PeCube® to better constraint morphotectonic histories.