T291 Understanding the Interplay of Structural, Metamorphic, and Magmatic Processes in the Evolution of Convergent Margins: Lessons from the Proterozoic to Present-Day South American Andean Margin (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

REGIONAL PATTERNS TO LOCAL VARIATIONS IN PALEO-STRESS/STRAINS AND VERTICAL-AXIS ROTATIONS ACROSS PART OF THE ARGENTINIAN ANDES: DECIPHERING CONTRIBUTIONS FROM PLATE-MARGIN PROCESSES TO CRUSTAL ARCHITECTURE

Paper number: T291-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Anisotropy of magnetic susceptibility (AMS), minor fault, and paleomagnetic data collected for more than 300 sites in Triassic, Cretaceous, and syntectonic Neogene red beds located across the Principal Cordillera, thin-skin Precordillera, and thick-skin Sierras Pampeanas belts of Argentina reveal systematic regional variations in paleo-stress/strain directions and vertical-axis rotations across the normal to Pampean flat-slab segments. Sampling has focused on along-strike and across-strike variations in tectonic styles, including complications near transverse structures and relay zones. Results indicate an overall slight clockwise deflection of paleo-stress/strain directions compared to the relative motion direction between the Nazca and South American plates, partial correlation of shortening directions with changes in structural trend defined by major fault and fold traces, and minor net clockwise rotation, consistent with increased large-scale shortening toward the north. The gradient in shortening (and translation) is also consistent with deflection of paleostress/strain directions from the direction of relative plate motion. Paleo-stress/strain directions also locally refract near transverse zones and within relay zones between doubly plunging folds, which appear to partly follow pre-existing rift basins and basement shear zones. The inboard extent and magnitude of large-scale shortening, as well as internal strain, decrease south of the transition from flat-slab to normal subduction. These patterns are suggestive of partial coupling between flat-slab subduction and stress transfer in the retroarc, along with local modulation of the stress field related to heterogeneities in crustal architecture (basement shear zones, old sutures, former rift basins), development of relatively weak major faults, and evolving topography. Quantifying contributions from multiple processes that drive upper crustal deformation in Cordilleran orogenic systems, however, remains challenging. Continued work is underway to refine spatial sampling of AMS, minor fault, and paleomagnetic data, compare these data with seismic and GPS data sets, and integrate results with other ongoing thermochonologic and basin studies.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-305615

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