Portal de Periódicos da CAPES

Wallrocks of the central Sierra Nevada batholith, California: A collage of accreted tectono-stratigraphic terranes

1983; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp1255

2330-7102

Warren J. Nokleberg,

Geological formations and processes

Structural and stratigraphic analysis of the wallrocks of the central Sierra Nevada batholith, California, supports the hypothesis that the wallrocks constitute a collage of tectono-stratigraphic terranes that were accreted along an actively deformed continental margin.The terranes, represented by well-known pre-middle Cretaceous belts of wallrocks, with north-northwest trends, were successively accreted during Triassic and Jurassic time.Successive pulses of magmatism were interspersed with successive accretions of terranes and with successive deformations and movements along interarc faults.From east to west, the terranes consist of: (1) early Paleozoic metasedimentary rocks (Owens terrane); (2) late Paleozoic metasedimentary and unconformably overlying Permian and Triassic metavolcanic rocks (High Sierra terrane); (3) Jurassic metavolcanic rocks (Goddard terrane); (4) Late Triassic and Early Jurassic miogeosynclinal metasedimentary rocks and sparse metavolcanic rocks of the Kings sequence (Kings terrane); (5) late Paleozoic slate, marble, and metaquartzite of the Calaveras Formation and rocks similar to the Shoo Fly Formation and underlying late Paleozoic ophiolite (Merced River terrane); and (6) Jurassic andesite and basalt flows, breccias, epiclastic mudstone, siltstone, volcanic graywacke, and conglomerate representing a volcanic arc suite and underlying Jurassic and older ophiolite west of the Melones fault (Foothills terrane).Each terrane generally has: (1) a distinct stratigraphic sequence with a narrow age range; (2) no nearby sediment source; (3) bounding thrust, reverse, or strike-slip faults; and (4) a distinct structural history.After accretion, adjacent terranes were welded together and their boundaries locally obliterated by episodic intrusion of granitic magmas.Major thrust, reverse, or strike-slip faults representing accretionary sutures separate the various terranes.The Owens Valley fault, a vertical, predominantly right lateral strike-slip fault, separates the Owens terrane from bedrock units to the east in the White-Inyo Mountains.The Laurel-Convict fault, an originally west dipping thrust, separates the Owens and High Sierra terranes.Triassic accretion and deformation along this suture defines the Sonoman orogeny in the eastern Sierra Nevada.The San Joaquin River fault, a major strike-slip fault, separates the High Sierra and Goddard terranes.The Kings River fault, a major right-lateral strike-slip fault, separates the Goddard and Kings terranes.Late Jurassic accretion and deformation along the Kings River and San Joaquin River faults between the High Sierra, Goddard, and Kings terranes defines the Nevadan orogeny in the eastern part of the central Sierra Nevada.The Foothill suture, originally a major left-lateral strike-slip fault, separates the Kings and Merced River terranes.Middle Jurassic accretion along this suture marks the accretion of the Tethyan-derived Merced River terrane to the western margin of North America.The collision of the Merced River terrane with the western margin of North America may have caused the contemporaneous left-lateral offset of Precambrian crystalline terranes from southeastern California to Sonora, Mexico.The Foothill suture may be the continuation of the left-lateral megashear in the central Sierra Nevada.The Melones fault separates the Merced River and Foothills terranes.Late Jurassic accretion and deformation along this suture, along with reactivation of the Foothill suture, defines the Nevadan orogeny in the western metamorphic belt.Comparison of the tectonics of the Mesozoic Sierra Nevada with that of Cenozoic southern Alaska reveals many similarities.The Mesozoic Sierra Nevada may represent an Alaskan-type volcanic and plutonic arc that formed along a tectonically active continental margin.