Offset of Late Mesozoic Basement Terrains by the San Andreas Fault System
01 Nov 1970-Geological Society of America Bulletin (Geological Society of America)-Vol. 81, Iss: 11, pp 3253-3258
TL;DR: In this paper, the authors proposed a new generalized reconstruction of California and Baja California prior to the major Tertiary strike-slip faulting of the San Andreas system.
Abstract: Two assumptions provide the basis for a new generalized reconstruction of California and Baja California prior to the major Tertiary strike-slip faulting of the San Andreas system. (1) The contrasting Franciscan and batholith basement types originally formed two parallel belts such as are found elsewhere around the Pacific margin; and (2) rhombochasms or zones of extension must be found to account quantitatively for any major displacement of crustal blocks along these strike-slip faults, and conversely, zones of Tertiary extension must be closed in any Mesozoic reconstruction. The Gulf of California rhombochasm of Carey (1958) and Hamilton (1961) is large enough to account for all of the apparent offset in southern California but only half of that in central and northern California. It is here proposed that this additional offset may be accounted for in the deep-water region of the continental borderland of northern Baja California. This region is thus considered to be analogous to the Gulf of California rhombochasm. This implies a two-stage movement history of the San Andreas system with an intervening change in direction of block movement by about 25° and related left-lateral faulting in the Transverse Ranges. Salinia would have moved twice for a total of approximately 600 km and would once have lain off southern California and northern Baja California, while southern and Baja California would have moved only once for approximately 300 km.
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TL;DR: In the Yerington district, western Nevada, pre-Tertiary rocks are overlain by an Oligocene ignimbrite sequence and Miocene andesites as discussed by the authors.
Abstract: In the Yerington district, western Nevada, pre-Tertiary rocks are overlain by an Oligocene ignimbrite sequence and Miocene andesites. Basin and Range normal faulting began in Miocene time, as andesitic volcanism died out (17 to 18 m.y. ago), and has continued to the present. The faults dip east and are curved, concave upward, with net displacements in a nearly east-west direction. Movement on the curved faults has resulted in steep westward tilting of the Miocene andesites and of all older rocks. Alluvium and 8- to 11-m.y.-old basalt flows deposited during the period of faulting are tilted gently west. The oldest faults, which dipped steeply east when they were active, are now inactive and dip gently eastward as a result of westward tilting on other faults. Younger faults dip more steeply east, and the youngest faults, those responsible for present Basin and Range topography, are the steepest. More than 100 percent of east-west extension has taken place across the district because of normal faulting. The rate of extension was most rapid between 17 and 11 m.y. ago and was slower after 11 m.y. ago. The extension is deep seated rather than thin skinned and apparently involves thinning of the crust. Several theories of origin for Basin and Range structure can be rejected because of the field data at Yerington, and the theory that Basin and Range structure was caused by a continental spreading axis best fits the data. Basin and Range spreading seems to have been most active between the projections of the Mendocino and Murray fractures. It may have first started south of the Great Basin, when these fractures were farther south relative to the continent and when the oceanic spreading axis that had been between these fractures was interacting with the continent.
486 citations
TL;DR: In this article, conditions favoring this sort of tectonic response are shown to be 1) a high angle of oblique convergence, 2) a low angle of subduction, and 3) relative thermal softening of the magmatic arc.
228 citations
17 Mar 2013
TL;DR: A preliminary look at sea-floor glasses from active spreading centers suggests that the FETI basalt group (high FeO and TiO2, low MgO) is more common at rapidly spreading ridges (East Pacific rise system) than at slower spreading ridge systems (mid-Atlantic ridge system) as mentioned in this paper.
Abstract: The abundant glassy rinds and chilled contacts of submarine extrusions and intrusions provide the most reliable indicators of primary magmatic compositions of deep-sea igneous rocks. They are homogeneous at the precision of electron microprobe analyses, so that even small sub-samples are reliable indicators of the composition of larger eruptive units. Analyses of such sea-floor glasses by electron microprobe techniques for Si, Al, Fe, Mg, Ca, Na, K, Ti, P reveal an extremely diverse compositional spread, ranging form highly differentiated basalt to varieties extremely depleated in large ion lithophile elements. A preliminary look at glasses from active spreading centers suggests that the FETI basalt group (high FeO and TiO2, low MgO) is more common at rapidly spreading ridges (East Pacific rise system) than at slower spreading ridges (mid-Atlantic ridge system). The data presented here appear for the most part inadequate for meaningful assessment of chemical gradients along spreading centers. There is strong evidence, though, that some segments of spreadings centers have erupted similar lava compositions over tens of millions of years. These similar chemical groups are symmetrically distributed on each side of spreading segments as is expected from sea-floor spreading models. There is very little overlap in the compositions of the basaltic chemical groups at the level precision of the electron probe analyses. However, there are a few Atlantic chemical groups that occur both in the North and South Atlantic. Even these intra-ocean matches of chemical groups from one locality to another are, however remarkably few. This survey shows the great predominance of various basalt types at spreading centers, but other rock types, including soda rhyolite from the Galapagos rise, occur rarely.
222 citations
17 Mar 2013
177 citations
TL;DR: In this article, the development of Mesozoic and Cenozoic sedimentary basins in western North America was linked to the overall geodynamics of an active continental margin.
Abstract: Development of Mesozoic and Cenozoic sedimentary basins in western North America was linked to the overall geodynamics of an active continental margin. The Cordilleran margin, now largely of Califo...
172 citations