Terrane

About: Terrane is a research topic. Over the lifetime, 11025 publications have been published within this topic receiving 442596 citations. The topic is also known as: tectonostratigraphic terrane.

Cenozoic tectonics of the western United States

Abstract: The Cenozoic structures of the western United States are interpreted here as being products mostly of horizontal motion of the crust. The distribution of strike-slip faulting, tensional fragmentation of the brittle upper crust or rupturing of the entire continental crust, and compression define a pattern of northwestward motion increasing irregularly southwestward toward coastal California. Hans Becker, in 1934, and S. W. Carey, in 1958, are among those who have suggested such a tectonic system. The aggregate Cenozoic right-lateral displacement of Cretaceous and older rocks and structures by the northwest-trending strike-slip faults of coastal California is about 500 km. The greater part of this movement has occurred along the San Andreas fault, but many other faults share in it. At least six earthquakes within the past century have been accompanied by lateral displacements at the surface along faults of the San Andreas system. Successively greater offsets of successively older geologic terranes demonstrate continuing motion throughout Cenozoic time. Late Miocene materials have been displaced at least 160 km; Oligocene, at least 260 km. The present velocity of regional shear strain, about 6 cm/yr, demonstrated by geodetic resurveying in southern and central California, is about 8 times faster than the average needed to account for the total movement within the Cenozoic. The faults are in general associated with structures formed by oblique tension south of Los Angeles and with structures due to oblique compression north of that city. The opening of the Gulf of California and the Salton Trough by the oblique rifting of Baja California and the Peninsular Ranges away from mainland Mexico is the greatest of the tensional effects. The strike-slip faults may be confined to the crust. Earthquake foci extend no deeper than 16 km. The faults end to the south in the Gulf of California, whose crustal structure is oceanic. To the north, the San Andreas turns seaward as the north-facing Gorda scarp, west in line of which in deeper water is the south-facing Mendocino escarpment, produced apparently by an inactive left-lateral oceanic fault. The continental sliver of coastal and Baja California, west of the faults of the San Andreas system, may be drifting northwestward independently over the ocean floor and the mantle, and the leading point of the sliver may have been deflected westward when it hit the Mendocino scarp on the sea floor. East of this coastal movement system is the Basin and Range province, whose obvious Cenozoic structures are dominated by block faulting. The present ranges have formed mostly since early Miocene time, similar older ranges having been destroyed by erosion and deformation. The normal faulting, which is not associated within the region with any complementary tectonic compression, requires crustal extension as its basic cause. If the faults maintain their average 60° dips at depth, extension is half the dip-slip amount; but probably the major faults flatten downward, and the amount of extension about equals that of shallow dip-slip. Total Cenozoic extension in northern Nevada and Utah may have been 300 km. Concurrent volcanism much augmented the thinned and fragmented crust, and the volcanic terranes in turn have been fragmented by block faulting. Right-lateral strike-slip faults trend northwestward in lanes between normal-fault maintain blocks in the southwestern part of the Basin-Range province. Cenozoic displacements reach 50 km on the Las Vegas fault and 80 km on the Death Valley-Furnace Creek faults. Northeast of the strike-slip faults, ranges and basins trend north-northeastward in tension-gash orientation. Within the belt of lateral faulting, ranges undergoing active normal faulting mostly trend north-northwestward in oblique pull-apart orientation. The Sierra Nevada and Klamath Mountains have moved northwestward and rotated counterclockwise, thus moving away from the continental interior more in the north than in the south, and the extension distributed behind them has formed the Basin-Range province. The narrow block-fault Rio Grande valley system of New Mexico and southern Colorado is structurally and topographically similar to the rift valleys of East Africa and reflects localized crustal extension. The Idaho batholith, like the Sierra Nevada batholith, is drifting northwestward as an unbroken plate. Extension east of the Idaho batholith is taken up by normal-fault fragmentation in south-central Idaho and southwestern Montana, whereas extension south of the batholith has produced a rift through the continental crust, the Snake River Plain, filled deeply by lava. Seismic velocities indicate granitic crust to be lacking in at least the western part of the plain. Right-lateral faults of the Osburn system bound the batholithic plate on the north, and the motion they represent is taken up north of them by extension forming fault troughs. Integration of geologic and geophysical information shows that large regions of the Northwest are lava accumulations of continental crustal thickness, not old continental crust covered by lava. The volcanic terrane of northwestern Oregon and southwestern Washington forms new volcanic crust in a region which was oceanic before Cenozoic time. The volcanic terrane of southeastern Oregon, northeastern California, and northwestern Nevada fills an irregular tension rift through the Mesozoic continental crust. This rift resulted from the westward motion of the Klamath Mountains region, which was sundered from a position south of the Mesozoic terrane of northeastern Oregon and which was bent oroclinally as it moved westward in post-middle Eocene time. The Mesozoic terrane of northeastern Oregon pivoted away from the Idaho batholith to form a smaller orocline and left a triangular rift since filled by lava. Independent motion of continental crust over mantle and oceanic crust seems to be indicated. Inertial forces due to redistribution of rotational momentum among crustal fragments, mantle, and core may provide the motive power.

The early Paleozoic evolution of the Argentine Precordillera as a Laurentian rifted, drifted, and collided terrane: A geodynamic model

Abstract: Paleontologic and stratigraphic evidence points to the early Paleozoic Precordilleran terrane of western Argentina as being the conjugate rift pair of the Appalachians. Stratigraphic similarities of the Cambrian and early Arenig carbonate series and very strong affinities among trilobite, conodont, and brachiopod faunas show their close relationship. The most probable provenance areas are the Appalachian-Ouachita rifted margin and the Newfoundland Appalachians, although the former fits better with geometric and drifting paths suggested by faunal affinities. Increasing Celtic and Baltic brachiopod genera and divergent stratigraphy since the Arenig indicate the drifting of the Precordilleran terrane. Collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed. The collision of the Precordillera with western Gondwana occurred during the mid-Llanvirn to Llandeilo. A magmatic arc related to eastward subduction (present coordinates) was active in the Famatina Range east of the Precordillera. This region of Celtic affinity shows faunal exchange with the Precordilleran terrane since the late Arenig and may represent accreted intra-Iapetus volcanic island-arc complexes. The rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the Precordilleran terrane from periequatorial to peripolar latitudes between the Cambrian and latest Ordovician. The deep ocean to the west of the Precordillera started to close by the Late Ordovician with the eastward drift of the Chilenian terrane. Absence of volcanic or pyroclastic arc-derived rocks in the Precordillera indicate west-dipping subduction. As Chilenia approached the continental margin, a new forebulge was established on the former collided Precordilleran terrane, developing an erosional unconformity in central Precordillera (Talacasto-Tambolar arch). A Gondwanic signature was fully developed by the Middle Silurian when the Malvinokaffric Clarkeia Fauna flourished. Before then, the Late Ordovician glacial record and associated Hirnantia Fauna were the first clear tie to Gondwana. During the Silurian the marginal basin behaved as a foreland, with lithosphere rheology and eustasy governing the sequence stratigraphy. Wrench faulting along its eastern boundary displaced the Precordillera toward the south. Continued shortening during closure with the Chilenian terrane in the mid-Devonian produced thrust loading of the basin and generated a thick graywacke succession. Final accretion of Chilenia (Late Devonian) generated a regional angular unconformity between the lower and upper Paleozoic. New eastward subduction was initiated west of the accreted Chilenian terrane during the Late Permian–Triassic as indicated by the Choiyoi volcanic complex, which presently outcrops in the Frontal Cordillera.