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Transverse Ranges Province: a Unique Structural-Petrochemical Belt Across the San Andreas Fault System

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Transverse Ranges Province: a Unique Structural-Petrochemical Belt Across the San Andreas Fault System A. K. BAIRD ^ A o' WOODFORD | Geology DePartment, Pomona College, Claremont, California 91711 K. W. BAIRD ' Transverse Ranges Province: A Unique Structural-Petrochemical Belt across the San Andreas Fault System ABSTRACT relate the system to concepts of global or plate tectonics (Atwater, 1970; Suppe, 1970; Hill, 1971b; Yerkes and Campbell, 1971). The San Gabriel and San Bernardino mountain ranges of Though these latest concepts have been widely discussed, only southwestern California, and associated mountains and basins diagrammatic interpretations that relate directly to problems of the westward to the Pacific Ocean, make up a unique east-trending Transverse Ranges Province have appeared so far in the literature geomorphic, stratigraphic, petrologic, and structural belt 400 km (for example, Anderson, 1971). Implicit or explicit in some of these long that is offset only a few tens of kilometers right laterally by discussions, which interpret the San Andreas zone as a plate northwest-striking faults of the San Andreas type. Spot correlations boundary (and a transform fault), is the idea that the Transverse across these faults, suggesting displacements of hundreds of Ranges are a geologically new feature, rotated and uplifted by the kilometers, perhaps have other explanations. Within the transverse most recent movements associated with southern and Baja ranges and basins, the east trend is shown by the general petrology, California tectonism and opening of the Gulf of California. the crystalline rock patterns, pre- and post-batholithic structural It is not the intent of this paper to redescribe, evaluate, and features, and batholithic chemical patterns. The east-west unity is criticize earlier studies. Rather, we wish to examine some of the especially striking west of the San Andreas fault, but it is also evident evidence bearing on the antiquity of the Transverse Ranges Province in the central and southern San Bernardino Mountains, east of that and how this province is related through time to adjacent provinces fault. of southern California. We conclude that this belt has existed for a The Salton Trough and the southern boundary of the Transverse long time with the same transverse orientation, and that no great Ranges Province appear to be the most important provincial lateral separation — certainly not hundreds of kilometers — has boundaries in southwestern California. West of the San Jacinto occurred across this belt along any or all of the faults of the San fault, which is just southwest of the San Andreas fault and nearly Andreas system acting singly or together. To substantiate this parallel to it, the Transverse Ranges Province is bounded on the conclusion, we describe the geology under four headings: (1) south by the Malibu Coast-Cucamonga fault zone. At and just east pre-batholithic rocks and structure; (2) batholithic rocks and of the San Jacinto fault, the southern boundary fault zone is structure, chemical and age distributions; (3) post-batholithic rocks displaced by faulting 30 to 40 km to the southeast, and is continued and structure; and (4) structural development through time. as the Banning fault. East of the eastern (Mission Creek) branch of Much of the information assembled is not new, and most of it is the San Andreas fault, east-trending faults are present, but the San the work and resultant ideas of others. Most of the pertinent earlier Bernardino Mountains rocks and structures merge into the work was summarized by Bailey and Jahns (1954) and Jahns (1954). southeast-trending Little San Bernardino Mountains. Some of our compilations have relied heavily upon the mapping of T. W. Dibblee, Jr., of the U.S. Geological Survey. Most of the more INTRODUCTION general stratigraphic and structural features on which we rely are Along the entire mapped length of the San Andreas fault zone, shown on the Santa Ana, San Bernardino, and Los Angeles sheets of from northern California to Mexico, no other belt of rocks, the Geologic Map of California (Rogers, 1965, 1967; Jennings and structure, and geomorphology similar to the Transverse Ranges Strand, 1969). Province crosses the zone. This has been clearly stated earlier by Allison (1964) and Gilluly (1970). No offset equivalent of the GEOGRAPHIC NOMENCLATURE eastern (San Bernardino Mountains) part of the Transverse Ranges Province is known across the San Andreas fault zone to the The Transverse Ranges Province is usually described on a northwest. No offset equivalent of the western (San Gabriel—Santa geomorphic basis as made up of the chains of ranges and valleys Ynez Mountains) part of the Transverse Ranges Province is known extending from the Santa Ynez Mountains and Channel Islands across the fault zone to the southeast. The western part of the eastward through the San Bernardino Mountains (Fig. 1). Problems Transverse Ranges Province appears to offset, left laterally, a major arise, however, in defining accurate limits. The southern boundary boundary (the Newport-Inglewood zone) between granitic and from the coast to the San Jacinto fault is sharply delineated against oceanic basement terrains, though the northward continuation of the Peninsular Ranges Province (including the Los Angeles Basin) by the wholly crystalline oceanic bedrock has not been discovered. The the Malibu Coast—Cucamonga fault zone (Fig. 2); east of the San province, therefore, has crucial implications for understanding the Jacinto fault, no line so prominent is evident. The northern structural evolution of southern California. boundary is poorly defined on both the extreme west, where the Development of ideas about the movement history of the San province joins the Coast Ranges Province, and on the extreme east, Andreas fault (and the other parallel faults that, with it, make up the where the San Bernardino Mountains merge with the Mojave Desert San Andreas system) has proceeded from the original concept of Province. The north edge of the San Gabriel Mountains, at and near large-scale right-lateral slip proposed by Hill and Dibblee (1953), the San Andreas fault, and the north edge of the San Bernardino through numerous studies along various segments of the faults in Mountains, however, provide a sharp geomorphic contrast with the attempts to document offset through time, to the current efforts to considerably lower Mojave Desert plateau to the north. It is unclear how far eastward the province extends. Some of these boundary * Present address: U.S. Geological Survey, Menlo Park, California 94025. problems are considered later in this paper. Geological Society of America Bulletin, v. 85, p. 163-174, 9 figs., February 1974 163 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/2/163/3428744/i0016-7606-85-2-163.pdf by guest on 29 September 2021 164 BAIRD AND OTHERS ! SIERRA NEVADA •- \ GREAT COAST VALLEY RANGES ••..'*.?••" MOJAVE DESER1 Figure 1. Natural provinces and major physiographic features, southern California. AlAMO LAKE HJÌMES ' -. RANGES 8ERNARO.NO MTNS. *'.. PIMTO MTNS l SANTA MONICA Ml?!?. Tr(f LOS ANGCLfS ftfVTffSlDE *'•. ^'V _ \aN .ES »A*» ^ * \ l0S 0E1 \ ^ vV %% v \ X % RANGES PRE-BATHOLITHIC ROCKS conglomerate dips gently north and overlies gneiss. This east-west line of unconformity has been traced for more than 6 km, in and out Distribution of the ravines on the; south slope of Sugarloaf Mountain (J. F. One of the more striking aspects of areal geology in southern Richmond, 1973, personal commun.). Westward in the San California is the absence of rocks of known or suspected Bernardino Mountains and San Gabriel Mountains, east-striking Precambrian age in the Peninsular Ranges Province. In view of the carbonate and quartzite sequences occur, but no fossils have been extensive radiometric dating programs (carried out mainly by the found (Alf, 1948; Baird, 1956; Ehlig, 1958). South of the Malibu California Inst. Technology and the U.S. Geol. Survey), this absence Coast-Cucamonga fault zone, in the Peninsular Ranges Province, appears to be real. All known, or suspected, exposures of rocks of this type are unknown, except for small bodies such as those Precambrian rocks lie north of the Malibu Coast-Cucamonga fault in the Riverside area, in the San Jacinto—Santa Rosa Mountains, and zone or north or east of the Banning fault (Fig. 3; see Silver, 1971, for in northern Baja California. a discussion of the ages of the Precambrian rocks). Precambrian In contrast, in the western part of the Peninsular Ranges Province, rocks crop out on both sides of both branches of the San Andreas thick sections of lowei (?) and middle Mesozoic rocks, consisting of fault in the Cajon Pass-San Gorgonio Pass region, but do not appear argillaceous, volcanic, and graywacke assemblages, crop out south of the Banning fault. The southern boundary of Precambrian (Larsen, 1948; Schwarcz, 1969, p. 6). The Bedford Canyon rocks is interrupted at and near the San Jacinto fault, with about 30 Formation of the Peninsular Ranges; (at least in part Callovian) and to 40 km of right-lateral separation (Allen, 1957; Sharp, 1968). One the Santa Monica Slate of the Santa Monica Mountains have been of the most distinctive units within the Precambrian is tentatively correlated across the Malibu Coast-Cucamonga fault syenite-anorthosite and related rocks exposed in the San Gabriel zone (Hoots, 1931; Woodford, 1960; Imlay, 1963). Exposures of Mountains (Higgs, 1954), Mojave Desert (Crowell and Walker, these two units are separated, however, by extensive Tertiary and 1962, p. 262-264), Colorado Desert (Crowell and Walker, 1962; Quaternary cover in the Los Angeles Basin. Silver, 1971), and Sonora, Mexico (Merriam, 1972). Steeply dipping east-trending structures, primarily foliation and The eastern Transverse Ranges contain known and presumed late layering, prevail in pre-batholithic rocks throughout most of the Paleozoic quartzite and marble in relative abundance. The largest, Transverse Ranges Province (Fig. 4). These structures are in addition least deformed, and least recrystallized masses occur in the eastern to the prevalence of elongate east-trending roc.c units ranging in age part of the north flank of the San Bernardino Mountains (Woodford from Precambrian to late Paleozoic.
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