Abstract: Tectonic Framework and Metallogenesis in California

John P. Albers

Since the development of the plate-tectonic theory, most geologists concerned with the tectonic framework of California have come to agree that various assemblages of oceanic lithosphere were accreted to older sialic crust during Mesozoic time, resulting in a westward or oceanward growth of the state. Great batholithic masses also were emplaced during the same time interval. The discrete geotectonic units that resulted from these events are characterized by rather specific types of mineral deposits.

From southeast to northwest, a simplified sequence of geotectonic components includes, (1) craton, consisting of Precambrian basement overlain by thin Paleozoic sedimentary rocks; (2) late Precambrian and Paleozoic miogeosynclinal rocks; (3) the Sierra Nevada batholith; (4) several slices or belts of oceanic crust, including island arc and melange, separated from each other by steeply dipping suture (subduction) zones marked by serpentinite; (5) continental shelf and slope rocks of the Great Valley sequence; and (6) another sequence of slices of oceanic crust, island arc, and melange mostly separated by serpentinite in sutures. These sutures dip eastward at moderate angles and are regarded as large thrust faults or fossil Benioff zones. Throughout the sutured terranes the slices of oc anic lithosphere are successively younger from east to west. The Sierra Nevada batholith, composed of numerous plutons that are generally more felsic from west to east, invades both miogeosynclinal rocks and rocks derived from oceanic lithosphere.

At least eight types of mineral deposits are closely associated with discrete geotectonic units and are characteristic of them. As examples, the Mother Lode gold quartz vein system, in accreted oceanic crustal terrane, is just west of, and partly coincident with, the easternmost subduction zone marked by the Melones fault system; all mercury deposits in the Coast Ranges are structurally within 1 km of the Coast Range thrust fault; and massive sulfide deposits, with one exception, are in silicic volcanic rocks of island-arc terranes. Recognition and delineation of terranes characterized by specific types of mineral deposits, can provide an important first step in planning exploration programs and in estimating the mineral potential of discrete large areas.

AAPG Search and Discovery Article #90962©1978 AAPG 2nd Circum-Pacific Energy and Minerals Resource Conference, Honolulu, Hawaii