The Goldstein Peak Formation, central California: Record of a nonmarine intra-arc basin within the Early Cretaceous Sierra Nevada arc

摘要

New mapping in the Lake Kaweah pendant of the southwestern Sierra Nevada batholith reveals a previously unrecognized nonmarine sequence of metamorphosed sedimentary and volcanic strata, defined herein as the Goldstein Peak Formation. The nonmarine origin distinguishes the Goldstein Peak Formation from all other Sierra Nevada metasedimentary pendants and from virtually all other coeval deposits associated with the Sierra Nevada arc. Basic structural relations, supplemented by new U-Pb zircon ages, suggest an Early Cretaceous depositional age, a time that is poorly represented within the stratigraphic record of California. This unusual age makes the Goldstein Peak Formation the youngest sedimentary deposit preserved within the metamorphic framework of the exhumed batholith, one that was deposited concurrently with some of the earliest deposits in the Great Valley forearc basin and just preceding the mid-Cretaceous Sierra Nevada arc surge. Preserved sedimentary and volcanic structures, along with whole-rock geochemistry, are consistent with deposition of Goldstein Peak conglomerates and sandstones within fluvial and alluvial fan environments, deposition of mud-rich sediments and air-fall tuffs within a lacustrine(?) environment, and subaqueous to subaerial extrusion of basaltic to dacitic arc volcanic rocks. This volcano-sedimentary section was intruded soon after deposition, with peak hornblende hornfels to low-pressure amphibolite facies metamorphism ultimately driven by intrusion of the surrounding Early Cretaceous Stokes Mountain ring dike complexes. Deposition of the nonmarine Goldstein Peak Formation within a fault-bounded, possibly transtensional, intra-arc basin during the transition from the low-standing, moderately extensional, Late Jurassic fringing arc to the high-standing, compressional mid- to Late Cretaceous arc indicates that at least one section of the Sierra Nevada arc was a fully emergent continental margin arc by the Early Cretaceous Epoch.