Paleomagnetism and 40Ar/39Ar geochronology of gabbro sills at Mariscal Mountain anticline, southern Big Bend National Park, Texas: implications for the timing of Laramide tectonism and vertical axis rotations in the southern Cordilleran orogenic belt

Article Abstract:

The paleomagnetic data obtained from gabbro sills uncovered at Mariscal Mountain anticline demonstrate that Laramide folding predates sill emplacement. Isotopic dating by the 40Ar/39Ar method shows that sill intrusion took place roughly at 37 Ma and thus is dated to the late Eocene/early Oligocene ages, and not Late Cretaceous or early Eocene. Existing paleomagnetic evidence regarding the magnitude and timing of rotations associated with Basin and Range extension is shown to be equivocal.

Analysis, Geology, Structural, Structural geology, Paleomagnetism, Big Bend National Park, Texas

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Rapid uplift and rotation of mylonitic rocks from beneath a detachment fault: insights from potassium feldspar 40Ar/39Ar thermochronology, northern Snake Range, Nevada

Article Abstract:

Multiple diffusion domain analysis of potassium feldspar Arrhenius data and 40Ar/39Ar age spectra in studying the thermal histories of mylonitic rocks in the base region of the northern Snake Range decollement, NV, provided three case scenarios of rapid cooling. Of the three episodes, the middle Eocene scenario reveals an extensive unroofing period and the late Oligocene episode suggests a pulse of slip in the region.

Snake Range, Nevada

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Metamorphic soles from the Albanian ophiolites: petrology, 40Ar/39Ar geochronology, and geodynamic evolution

Article Abstract:

Research is presented concerning the use of 40Ar/39Ar geochronology and thermobarometry to investigate the ophiolite intrusives and metamorphic soles in young oceanic lithosphere between depths of 30- and 40-kilometers.

Plate tectonics, Albania, Ocean bottom, Ophiolites

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