MINERALOGY AND PETROGRAPHY OF THE POLYMETAMORPHIC KINGS SEQUENCE, LAKE KAWEAH PENDANT, WEST-CENTRAL SIERRA NEVADA BATHOLITH, CA

The Lake Kaweah pendant, located ≈40 km northeast of Visalia, CA in the western Sierra Nevada foothills, is composed dominantly of the Kings Sequence, a Late Triassic to Middle Jurassic marine metasedimentary to calcsilicate unit. Protoliths of the Kings Sequence were deposited in a submarine fan system containing craton-derived sand, silicic volcaniclastic units, silicic tuff, and ash-flow tuff, all interbedded with mudstone, carbonate, and marl (Saleeby et al., 1978). Few petrologic studies of the Kings Sequence have been undertaken, presumably due to its complex metamorphic and deformational history. The goal of the current study is to produce a detailed mineralogic description of the Kings Sequence exposed in the northernmost part of the Lake Kaweah pendant. Preliminary petrographic analysis, coupled with scanning electron microscopy, suggests that mineral assemblages were equilibrated in the greenschist facies then partially reequilibrated in the hornblende hornfels facies. The Late Jurassic history of the Kings Sequence was undoubtedly complex, including deformation events associated with convergent margin tectonics as well as metamorphism during construction of a superimposed Late Jurassic arc. The roots of this arc are preserved in the Mill Creek Complex that is represented in the Lake Kaweah pendant by a 163±1.5 Ma quartz diorite pluton surrounded by a tungsten skarn. By ≈139 Ma, these Kings Sequence rocks resided at the surface where they formed the depositional basement for the nonmarine Goldstein Peak formation. The two units were metamorphosed together in the hornblende hornfels facies during the Early Cretaceous (locally ~115±5 Ma) intrusion of the tonalitic to granitic plutons that surround the Lake Kaweah pendant.

Saleeby, J.B., S.E. Goodin, W.D. Sharp and C. J. Busby, 1978, Early Mesozoic Paleogeographic Recontruction of the Southern Sierra Nevada Region in D.G. Howell and K.A. McDougall, eds., Mesozoic Paleogeography of Western United States: Pacific Coast Paleogeography Symposium 2, Society for Sedimentary Geology (S.E.P.M.) Pacific Section, p.311-336.