T9 Linking Fault Zone Deformation Processes, Kinematic Indicators, and Geochronology through the Brittle and Brittle-Ductile Regimes of the Earth’s Crust

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

FAULT GOUGE DATING IN THE SPANISH PYRENEES: SHORTENING RATES, THERMAL CONSTRAINTS ON CLAY GOUGE FORMATION, AND CATACLASTIC AGE INTERPRETATION

Paper number: T9-2
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

Dating brittle faults by the growth of authigenic illite in fault gouge allows for direct testing of kinematic models of orogenic evolution, such as in-sequence vs. out-of-sequence thrusting, and the presence of orogenic ‘pulses’ of deformation on multiple thrusts simultaneously. We present ages of authigenic illite in fault gouge from 5 thrust faults along the Ter and Freser rivers in the south-eastern Pyrenees fold-and-thrust belt dated by Illite Age Analysis. The ages suggest broadly in-sequence thrusting for the prowedge of the eastern Pyrenees during the Eocene and early Oligocene, ranging from 49.5 + 4.4 Ma for the inboard Freser Antiformal Stack to 31.9 +/- 3.9 Ma for the frontal L’Escala thrust. Unlike many other foreland fold-and-thrust belts, foreland progression of ages is preserved, although overlapping of ages of the frontal thrusts suggests that the interpretation of a pulse of orogenic activity around 35 Ma is also possible, similar to coeval fault activity observed elsewhere in the Pyrenees. We also provide interpretations of the age of the cataclastically-derived component in gouges, often difficult to interpret. The latest Paleozoic ages of the cataclastically-derived component of many of the foreland basin thrusts indicate that Hercynian-age micas were deposited in the Southern Pyrenean foreland basin as early as the late Cretaceous. Recently published thermochronometer and D47 temperatures from syn-faulting calcite veins at the same outcrops allows the temperature of clay gouge formation to be constrained at 50 - 210°C, with the most likely range of temperatures of 90 - 160°C. Shortening rates for the Ter-Freser section range from 1.6 – 3.0 km/Ma, with bulk strain rates ranging from 7.0 x 10-16 s-1 to 1.6 x 10-15 s-1.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359921

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