Abstract

The Cambrian Long Mountain Granite, exposed in the western Wichita Mountains, Oklahoma, is red, granophyric, alkali feldspar granite. The red granite abruptly transitions into a green granite in the subsurface; both red and green granites have similar geochemical signatures. Anisotropy of magnetic susceptibility analysis shows that the green granite retains a primary magnetic fabric that is consistent with the sill-like emplacement of the Wichita Granite Group. Demagnetization of green granite specimens yields a characteristic remanent magnetization (ChRM) residing in magnetite with east declinations and moderate down inclinations. The paleopole (9.0°N, 314.6°E) is interpreted as a primary Cambrian thermal remanent magnetization or an early magnetization related to deuteric/hydrothermal alteration. The paleopole position is consistent with some other poles for Cambrian igneous rocks in southern Oklahoma but is to the southwest of the Cambrian part of the apparent polar wander path. The red granite contains abundant secondary hematite that occurs in fractures, as grain boundary coatings, and along cleavage and exsolution planes in alkali feldspars. The iron in the hematite appears to be sourced from the oxidation of primary magnetite and ilmenite and the breakdown of silicate ferromagnesian minerals. The red granite has about two orders of magnitude lower magnetic susceptibility and natural remanent intensity than the green granite. The magnetic fabric is interpreted as an alteration fabric. The ChRM of red granite has southeast declinations and shallow inclinations and is interpreted as a chemical remanent magnetization (CRM) residing in hematite. The paleopole (44.9°S, 304.9°E) falls near the 290–300 Ma segment of the North American apparent polar wander path, which is consistent with inferred timing of exposure of the Long Mountain Granite. The CRM is interpreted to have been acquired during alteration by low-temperature weathering fluids near the surface during the late Paleozoic. The results from the red granite are not consistent with alteration caused by widespread paleoclimatic conditions in the Late Permian, and they are interpreted as related to local tectonic and/or weathering events.

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