Active faulting and climate history in the northern Walker Lane and Ruby Mountains, Nevada, United States of America.

摘要

Up to 25% of Pacific-North America plate relative motion is accommodated by faults east of the Sierra Nevada. Most of that 25% is taken up by deformation in the Walker Lane, a discontinuous zone of strike-slip and normal faults parallel to the San Andreas in the westernmost Basin and Range province. I present the results of active fault studies in the northern Walker Lane (Pyramid Lake and Olinghouse fault zones) and central Basin and Range (Ruby Mountains fault zone) and compare the displacement histories of these faults to geodetically measured strain accumulation in these regions. The NW-trending, right-lateral Pyramid Lake fault zone has been the source of at least four post-Lake Lahontan (∼15.5 ka) earthquakes and accommodates at least 2.6 +/- 0.3 mm/year, or ≥25%--70%, of ∼6 +/- 2 mm/year of right-lateral shear measured geodetically across the northern Walker Lane. The NE-trending, left-lateral Olinghouse fault zone has been the source of multiple Holocene earthquakes and shows a variable displacement history along strike that may reflect interaction with the conjugate Pyramid Lake fault zone. These studies together demonstrate that NW-trending, right-lateral faults and NE-trending, left-lateral faults of the northern Walker Lane work together to accommodate plate-boundary related shear. In the central Basin and Range, the Ruby Mountains fault zone has accommodated ∼0.2--0.3 mm/year of horizontal strain during the late Pleistocene, implying a rate of strain accumulation across the fault zone that is at odds with characterization of this region as a geodetic microplate.; Deposits in the northern Walker Lane and Ruby Mountains that are deformed by active faulting also record significant late Pleistocene and Holocene climate variations. During the late Holocene in the Pyramid Lake subbasin of Lake Lahontan a transgression began at or after 3595 +/- 35 14C yr B.P. and continued, perhaps in pulses, through 2635 +/- 40 14C yr B.P., resulting in a lake as high as 1199 m. During the Younger Dryas period of the late Pleistocene a lake stood at approx. 1212 m at around 10,890 +/- 35 14C yr B.P. and a geomorphically and stratigraphically distinct suite of constructional shorelines associated with this lake can be traced to 1230 m. In the Ruby Mountains, 10Be cosmogenic radionuclide (CRN) exposure dating is used to quantify the timing of late Pleistocene glacial advances. The Angel Lake terminal moraine in Hennen Canyon was deposited between 15.4--23.1 ka, an interval that coincides with the Tioga glacial advances in the Sierra Nevada and Pinedale advances in the Rocky Mountains. The termination of the Angel Lake glaciation is nearly synchronous with the final highstand and subsequent rapid desiccation of Lake Lahontan. The average 10Be model age of samples from the Lamoille moraine in Hennen Canyon is 30.7 ka (range 19.3--66.5 ka), implying deposition during MIS-3.