Mesozoic transpression, transtension, subduction and metallogenesis in northern and central California

Abstract

Middle Paleozoic to Middle Jurassic terrane assemblies in the Klamaths and Sierran Foothills consist of mafic-ultramafic complexes + fine-grained terrigenous strata derived from previously accreted continental-margin belts. Sutured oceanic terranes reflect c. 230 Myr of margin-parallel slip involving chiefly transtension and transpression. Quartzofeldspathic clastic rocks and blueschists ± eclogites are very rare. Little devolatilization occurred at magmagenic depths; hence, coeval hydrothermal ore deposits and granitoids are uncommon. In contrast, nearly head-on Cretaceous subduction of the Farallon plate generated the massive Klamath-Sierra Nevada volcanicplutonic arc, reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone. Immature Great Valley forearc and Franciscan trench deposits shed from the arc record c. 70 Myr. of rapid crustal growth. Au-bearing solutions rising from magmagenic depths, exsolved from plutons, and expelled from heated wall rocks were mobilized attending arc construction. Precipitation of gold-bearing quartz veins

Geochemical evidence for exhumation of eclogite via serpentinite channels in ocean-continent subduction zones

“…During the Jurassic and Early Cretaceous, when many of the Franciscan eclogites were formed and exhumed, subduction is thought to have been oblique (Wakabayashi, 1992). However, it has also been suggested that effusive continental arc magmatism during the mid-Cretaceous required more normal convergence (Ernst et al, 2008).…”

Guadalupe pluton–Mariposa Formation age relationships in the southern Sierran Foothills: Onset of Mesozoic subduction in northern California?

“…Through Middle Jurassic time, largely oceanic terranes that formed seaward and ultimately were assembled in the Klamaths and the Sierran Foothills, consist chiefly of intensely imbricated mafic-ultramafic complexes and superjacent, fine-grained terrigenous strata derived from previously accreted continental margin belts [e.g., Burchfiel and Davis, 1981;Wright, 1982;Dickinson, 2008;Ingersoll, 2008]. Although commonly regarded as products of convergent plate tectonic processes, sutured ophiolite + chertargillite terranes apparently reflect $230 Myr of dominantly margin-parallel slip, involving minor stages of transtension and transpression [Saleeby, 1981[Saleeby, , 1982[Saleeby, , 1983Silberling et al, 1987;Irwin, 2003;Ernst et al, 2008]. Felsic igneous units, quartzofeldspathic clastic rocks, and high-pressure metamorphic lithologies occur but are uncommon.…”

“…[2] Conducting new mapping and petrotectonic studies in medial belts of the Klamath Mountains and the southern Sierran Foothills, and building on the contributions of many earlier workers, Ernst et al [2008] proposed a plate tectonic scenario that described important aspects of the mid-Paleozoic -Mesozoic crustal growth of northern California. Through Middle Jurassic time, largely oceanic terranes that formed seaward and ultimately were assembled in the Klamaths and the Sierran Foothills, consist chiefly of intensely imbricated mafic-ultramafic complexes and superjacent, fine-grained terrigenous strata derived from previously accreted continental margin belts [e.g., Burchfiel and Davis, 1981;Wright, 1982;Dickinson, 2008;Ingersoll, 2008].…”

Late Mesozoic subduction‐induced hydrothermal gold deposits along the eastern Asian and northern Californian margins: Oceanic versus continental lithospheric underflow

“…Middle Paleozoic to Middle Jurassic sequential terrane dockings in the Klamath Mountains and the Sierra Nevada Foothills produced an amalgam consisting chiefly of mafic–ultramafic oceanic complexes, each overlain by fine‐grained terrigenous strata derived from previously accreted continental‐margin belts (Irwin 1981; Ernst et al. 2008).…”

“…Middle Paleozoic to Middle Jurassic sequential terrane dockings in the Klamath Mountains and the Sierra Nevada Foothills produced an amalgam consisting chiefly of mafic-ultramafic oceanic complexes, each overlain by fine-grained terrigenous strata derived from previously accreted continental-margin belts (Irwin 1981;Ernst et al 2008). In the Klamaths, from east to west, these include the Eastern Klamath terrane, the Central Metamorphic Belt, the Western Paleozoic and Triassic Belt, and the Western Klamath terrane.…”