Interpretation and tectonic implications of cooling histories: An example from the Black Mountains, Death Valley extended terrane, California

Details Interpretation and tectonic implications of cooling histories: An example from the Black Mountains, Death Valley extended terrane, California Interpretation and tectonic implications of cooling histories: An example from the Black Mountains, Death Valley extended terrane, California

Apr 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.116...63h&link_type=abstract

Earth and Planetary Science Letters, Volume 116, Issue 1-4, p. 63-80.

Mathematics

Logic

16

Scientific paper

In the Death Valley extended terrane of California, the Black Mountains have long been considered unique because they largely lack the miogeoclinal cover rocks characteristic of the surrounding ranges. Fission-track ages presented here are combined with published 40Ar/39Ar ages and used to construct cooling path envelopes for samples of Precambrian crystalline basement and Miocene plutonic rocks collected across the entire range. The cooling history reconstructions are used to differentiate between contrasting Miocene unroofing histories proposed for this range. Apatite and zircon fission-track ages from the southeastern portion of the range suggest unroofing occurred there at ~ 13-8.5 Ma from temperatures well below 300°C. Cooling age data from the central Black Mountains indicate major unroofing at 8.5-6.0 Ma from temperatures greater than 300°C. Old cooling ages from directly beneath the highly extended Amargosa chaos rocks are consistent with the chaos rocks being part of an allochthonous slice that was tectonically transported from high crustal levels onto deeper crustal levels.
Scenarios for the Miocene unroofing history of this range rely heavily on interpretations of the depth of emplacement of Miocene plutons in the core of the range. Thermochronologic and geobarometric data and thermal modeling of intrusion cooling suggest emplacement of an 11.6 Ma pluton into the crystalline core at a depth of 10-15 km. Both the cooling-age data and considerations of the local geology seem to preclude an unroofing history dominated by erosion of the overlying miogeoclinal section. The morphology of the cooling path envelopes constructed here are similar to those constructed for detachment fault terranes. The data are most consistent with unroofing involving tectonic denudation (10-15 km) along a single, westerly dipping detachment zone. Diachronous rapid cooling from southeast to northwest within the range is interpreted as a result of the lower plate undergoing flexural deformation as it pulls out from underneath a relatively rigid, scoop-shaped hanging wall block (the `rolling-hinge' model). Migration of unroofing and tilting within the range mimics the overall east to west sequential tilting and unroofing of range blocks in the Death Valley extended terrane. Similar thermochronologic evidence for sequential range-scale tilting has been obtained from the Lake Mead extended region, suggesting that this style of extension might provide an explanation for strongly extended domains in the Basin and Range Province.

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