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Early Mesozoic paleotectonic-paleogeographic reconstruction of the southern Sierra Nevada region

Saleeby, J. B. and Goodin, S. E. and Sharp, W. D. and Busby, C. J. (1978) Early Mesozoic paleotectonic-paleogeographic reconstruction of the southern Sierra Nevada region. In: Mesozoic paleogeography of the Western United States. Society of Economic Paleontologists and Mineralogists , Los Angeles, CA, pp. 311-336.

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Metamorphic country rocks of the southern Sierra Nevada occur as isolated roof pendants and as the western wall of the batholith. Metasedimentary rocks are primarily Triassic to early Jurassic in age as shown by fossil dates in conjunction with field and petrographic data. The lower Mesozoic strata were deposited across a complex paleo-basement consisting of two contrasting terranes. The western terrane is exposed along the foothills and consists of the Kings-Kaweah ophiolite belt, a latest Paleozoic to possibly earliest Mesozoic remnant of disrupted oceanic lithosphere. This belt appears to represent an oceanic fracture zone complex that was transported northward into the region by large-scale wrench faulting. The eastern terrane which can only be inferred from petrochemical studies on the batholith, was sialic in character. It may also have been displaced by wrench faulting, but to a lesser degree. The zone of joining between the eastern continental terrane and the western oceanic terrane is termed the foothill suture. Lower Mesozoic strata deposited on the oceanic terrane consist of: (1) chert-argillite olistostromes containing exotic blocks of upper Permian limestone and occasional blocks of quartzitic sandstone; (2) quartzitic to sub-arkosic flysch; (3) olistostromes derived from ophiolite basement rocks; and (4) basalt-andesite volcanic rocks. Strata deposited on the continental terrane consist of: (1) Quartzose to sub-arkosic flysch; (2) Quartzlte-arglllite olistostromes with large slide blocks of shallow water limestone; (3) massive quartzitic to sub-arkosic sandstones, limestone and calcareous sandstones; and (4) silicic tuffs and ash flows. The flysch sequences of each terrane are apparently correlative. The eastern sequence contains a more proximal facies and the western sequence contains a more distal facies. The western facies flysch was partly reworked with chert-argillite into olistostromes. The early Mesozoic paleogeography of the region was apparently controlled by a complex plate juncture that involved both large-scale wrench movements and oblique subduction. The Triassic was characterized primarily by tectonic truncation of the continental margin by wrench faulting. North-northeast structural and stratigraphic trends typical of the Paleozoic were overprinted by northwest trends. The major wrench zone had a dextral sense of motion and extended through the truncated margin and into the oceanic domain. The southern extension of this zone was a large fracture zone which extended to the equatorial and possibly southern proto-Pacific. During northward transport of the fracture zone complex, slide blocks of shallow water limestone were acquired from an equatorial oceanic faunal belt. As the fracture zone complex moved into the proximity of the truncated margin, slices of the continental margin were differentially transported northward. Some fragments were displaced as far as southeastern Alaska. During Late Triassic to Early Jurassic time a submarine fan complex was shed off the truncated continental shelf and dispersed across the fracture zone complex. The sands of this fan complex are believed to be in part an extension of the Navajo- Aztec sands which accumulated on the ancient shelf. At about the same time a change in relative plate motions resulted in a convergent component along the complex plate juncture. The fracture zone complex was accreted as the hanging wall of an oblique subduction zone. Eruption of oceanic arc-type rocks along the western terrane and ignimbrites along the eastern terrane indicate the onset of subduction related magmatism. Both volcanic assemblages were interstratified with Navajo-Aztec affinity sands. During arc volcanism both terranes of the southern Sierra underwent differential northward transport by intra-arc wrench faulting which dissipated the strike-slip component of oblique subduction. Volcanic centers and the submarine fan complex were dismembered as they were built. Slide blocks of shallow water limestone and sandstone were shed off the shelf edge and reworked as olistostromes. Basement uplifts in the western terrane shed ophiolite assemblage olistostromes and triggered reworking of the chert-argillite olistostrome complex along with flysch.

Item Type:Book Section
Additional Information:© 1978 Society of Economic Paleontologists and Mineralogists. Part of our work was supported by Geological Society of America Penrose funds. Special thanks to S.M. Curtis, L. F. Drake and F.J. Spera for assistance in mapping and collecting fossils, and to P.C. Bateman and O.T. Tobisch for spending time in the field with us. Conversations and written communications with B.C. Burchfiel, W.R. Danner, G.A. Davis, John Dillon, D.L. Jones, J.W. Monger, J.G. Hoore, and L.E. Weiss were also very helpful. Interpretations presented in this paper don't necessarily represent the views of these individuals.
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Geological Society of America Penrose Bequest Research GrantsUNSPECIFIED
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ID Code:48363
Deposited By: Tony Diaz
Deposited On:12 Aug 2014 17:55
Last Modified:03 Oct 2019 07:03

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