MAGMA EMPLACEMENT AND FABRIC DEVELOPMENT IN THE WOOLEY CREEK BATHOLITH, KLAMATH MOUNTAINS, CA

The Wooley Creek batholith is a 158-155 Ma tilted intrusion emplaced into a series of accreted terranes in the Marble Mountains Wilderness, Klamath Mountains, N. CA. Previous work has demonstrated that the WCb is complexly zoned, with a structurally deeper section consisting of gabbro, diorite, quartz diorite, and tonalite, and a structurally shallower section consisting of diorite, quartz diorite, tonalite, granodiorite and granite.

New mapping and structural analysis in the interior as well as along the SW and SE margins has revealed the following:

1) The WCb may be divided into three structurally distinct units, a lower zone (northern) of marginally N-S striking hypersolidus foliations, an upper zone (southern) of both E-W and margin-parallel hypersolidus foliations, and an intensely deformed intermediate zone with NE striking hypersolidus foliations.

2) The lower portion of the pluton is sheeted at the metric to kilometric scale, with foliations parallel to sheet margins. In contrast, the upper portion of the pluton is texturally and compositionally much more homogeneous. New amphibole trace element geochemistry within the upper unit of the pluton indicates widespread chemical communication within a large partially molten chamber.

3) All structures within the WCb are magmatic in origin; aligned laths of plagioclase and amphibole define foliations where present. This is further supported by the presence of late, isotropic phenocrysts of biotite that grew over the magmatic foliation.

These observations are consistent with batholith-scale fabric formation due to emplacement-related processes. NS trending fabrics in the NE record magmatic flow within sheets. These sheets formed the conduits through which new material was injected into a large upper magma chamber, now exposed in the SW.