Sur-Nacimiento Fault Research Articles

Geologic map and structural development of the northernmost Sur-Nacimiento fault zone, central California coast

Geologic map and structural development of the northernmost Sur-Nacimiento fault zone, central California coast

Assembling the world’s type shallow subduction complex: Detrital zircon geochronologic constraints on the origin of the Nacimiento block, central California Coast Ranges

Temporal and spatial patterns in the architecture of the Franciscan Complex provide valuable insights into the subduction processes through which such patterns arise. The Nacimiento Franciscan belt is an allochthonous sliver of subduction assemblages in the central California Coast Ranges displaced either: (1) from southern California by >300 km of Neogene dextral slip along the San Andreas fault system or (2) from central California to southern California and back again, by >500 km of Late Cretaceous–Paleocene sinistral slip along the Sur-Nacimiento fault followed by San Andreas–related motion. New U-Pb detrital zircon data from 20 (meta)clastic samples indicate that the Nacimiento Franciscan section was assembled between ca. 95 and 80 Ma. Abundant Cretaceous (particularly Late Cretaceous) and diminishing amounts of Jurassic and Proterozoic zircon grains point to a southern California origin for Nacimiento Franciscan protoliths, precluding significant sinistral strike-slip along the Sur-Nacimiento fault. Furthermore, the suite of detrital zircon ages reported here bears a strong resemblance to new and existing data from subduction complexes in southern California that were emplaced during Laramide shallow subduction (i.e., Sierra de Salinas, Portal Ridge, Quartz Hill, Rand, San Emigdio, and Tehachapi schists). Hence, the Nacimiento Franciscan is distinct from Franciscan rocks in central and northern California and more likely represents an outboard element of the Late Cretaceous southern California low-angle subduction system. Upon restoring the Nacimiento block to its Late Cretaceous position, an inboard-younging trend is apparent in the composite Nacimiento–southern California schist belt, suggesting that progressively younger accretionary materials were underplated farther inboard by tectonic erosion. We posit that arc and forearc elements absent from southern California were removed by a combination of physical and tectonic erosion attending shallow subduction, interleaved in the subduction complex, and recycled into the mantle. Steepening of the Laramide slab was marked by a phase of crustal extension in the overriding plate. During this phase, the Sur-Nacimiento fault likely functioned as a segment of a low-angle normal fault system spanning the southern Sierra Nevada batholith to the Nacimiento accretionary system.

Jurassic through Oligocene Pre-Basin Stratigraphy in the Santa Maria Basin Area, California

Compilation from published records of 30 pre-Miocene stratigraphic columns in the Santa Maria basin area of California (west of the Sur-Nacimiento fault and north of the Santa Ynez fault) reveals two basement units and 22 overlying sedimentary units. This article displays the stratigraphic columns and includes descriptions and environmental interpretations of the 24 rock units. The basement rocks include an Upper Jurassic ophiolite sequence and the Lower Jurassic through Upper Cretaceous Franciscan Complex. Most of the 22 sedimentary units were deposited along a subduction-type margin prior to development of the late Tertiary Santa Maria basin. Overlying and generally in fault contact with the basement rocks are four Upper Jurassic through Lower Cretaceous units that were deposited in basin plain and out continental margin environments. Unconformably overlying these units are eight Upper Cretaceous units that were deposited in a wide range of environments that ranged from trench, slope, and submarine fan up through shelf and nonmarine fluvial environments. Lower Tertiary units onlap unconformably onto the Cretaceous rocks and were deposited only in the southernmost part of the area. These rocks include lower Eocene basin plain and outer submarine fan deposits; middle Eocene mid-fan and slope deposits; upper Eocene inner fan, shelf,more » shoreface, and foreshore deposits; and Oligocene shoreface, foreshore, and nonmarine fluvial deposits.« less

Paleogeographic implications of an erosional remnant of Paleogene rocks southwest of the Sur-Nacimiento fault zone, southern Coast Ranges, California

A small tract of heretofore-unrecognized Paleogene rocks lies about 30 km northeast of Santa Maria and 1 km southwest of the Sur-Nacimiento fault zone near upper Pine Creek. This poorly exposed assemblage of rocks is less than 50 m thick, lies unconformably on regionally distributed Upper Cretaceous submarine-fan deposits, and consists of three units: fossiliferous lower Eocene mudstone, Oligocene(?) conglomerate, and basaltic andesite that has a radiometric age of 26.6 ± 0.5 Ma. Both the sedimentary and igneous constituents in the Paleogene sequence are unlike those of known sequences on either side of the Sur-Nacimiento fault zone. Conventional paleogeographic restorations need to be modified to accommodate the conditions of deposition and emplacement represented by the three rock units. The Paleogene sedimentary rocks near upper Pine Creek presumably are remnants of formerly widespread early Eocene bathyal deposits and locally distributed Oligocene(?) fluvial deposits southwest of the fault zone. The 26.6 Ma basaltic andesite, however, may not have extended much beyond its present outcrops. Although the history, nature, and amount of pre-Miocene slip along the Sur-Nacimiento fault zone are not resolved, an episode of Oligocene(?) displacement is required by the contrast in thicknesses; depositional patterns, and paleobathymetry of the juxtaposed rock sequences.

Distribution of Disharmonic En Echelon Folds in Siliceous Beds of the Miocene Monterey Formation East of San Luis Obispo, California

A discontinuous series of tight, locally en echelon, northwest-trending folds in largely siliceous shales of Miocene Monterey Formation were delineated by recent detailed geologic mapping in the Lopez Mountain 7.5-min. quadrangle, San Luis Obispo County, California. Complexly folded strata within the informally named Lopez Mountain syncline represent the northern terminus of the broader and more gently folded Huasna syncline, which is located 25 km to the southeast. Flank dips on many folds in the Lopez Mountain syncline generally range from 60 to 70{degree} and locally are vertical or slightly overturned. Distances between fold axes range from as little as 100 m to as much as 1 km. Some folds can be traced for only a few hundred meters, whereas others extend for as much as 3 km. Folding of the siliceous upper part of the Monterey appear to be disharmonic with respect to stratigraphically lower calcareous and/or phosphatic shales. Unconformably underlying Mesozoic and Tertiary strata tend to be less deformed than most Monterey strata, with the exception of highly deformed Franciscan assemblage melange and serpentine that from the basement beneath the Lopez Mountain syncline. The Lopez Mountain syncline lies between the Sur-Nacimiento fault zone on the east and the Westmore » Huasna fault zone on the west. Although the timing, magnitude, and sense of motion on the fault zones are poorly constrained, much of Monterey Formation deformation in the Lopez Mountain area probably occurred in latest Miocene or early Pliocene time, possibly as a result of differential wrench movement along the two adjacent fault zones.« less

Correlation and provenance of upper Mesozoic chert-rich conglomerate of California

In the central coastal region of California, conglomerate that is rich in chert and quartzite clasts occurs as channel deposits in thin-bedded turbidites of the lower part of the Great Valley sequence of Late Jurassic and Early Cretaceous age (Tithonian to Valanginian). Very similar conglomerate occurs in displaced blocks in melange of the Franciscan assemblage. The Franciscan conglomerate, however, is richer by about 8% in vein-quartz pebbles and requires a slightly different source area. Thick-bedded lithic sandstone in Franciscan melange is also petrographically similar to sandstone of the lower part of the Great Valley sequence, but it is less rich in lithic grains, and, likewise, requires a slightly different source area. The Franciscan conglomerate and sandstone compare most closely with the southernmost exposures of the lower part of the Great Valley sequence near Santa Barbara and may have had a more southerly source area. Younger Franciscan sedimentary rocks are less similar to rocks of the Great Valley sequence, possibly because of the influence of an enlarging subduction complex. Correlative conglomerates of the Great Valley sequence of the Sacramento Valley are very rich in chert clasts, whereas those of the San Joaquin Valley contain more clasts of other sedimentary and volcanic rocks. A speculative model, similar to one proposed previously, suggests that the Great Valley forearc basin formed in an embayment with promontories north and south. The promontories contributed pebbles rich in chert that were transported longitudinally north and south into the basin, then westward. Less extensive, volcanic-rich conglomerates were derived from the east. Comparisons of clast compositions suggest that the chert-rich conglomerates of the Great Valley sequence of the central coast area were deposited about 300 km north of their present positions. Deposition was followed by 700 to 800 km of mid-Cretaceous sinistral strike slip on the Sur-Nacimiento fault and 400 to 500 km of Cenozoic dextral strike slip on the San Andreas fault.

Franciscan-type rocks off Monterey Bay, California: Implications for western boundary of Salinian Block

Serpentinites and spilitic basalts recovered at depths of 1000 m from Ascension Submarine Canyon northwest of Monterey Bay, California indicate that Franciscan basement is present immediately to the west of the San Gregorio Fault. This new information, together with published geological/geophysical data, support previous suggestions that the offshore western boundary of the Salinian block (Sur-Nacimiento Fault) has been tectonically truncated by the San Gregorio Fault and has been displaced by as much as 90 km to the northwest since the mid-late Miocene.

Stratigraphic and Structural Relations to Pre-Tertiary Rocks on Perimeter of Santa Maria Basin: ABSTRACT

On the perimeter of the Santa Maria basin three tectono-stratigraphic terranes of pre-Tertiary rocks are recognized. In ascending stratigraphical and structural order, these are: the Franciscan assemblage, the Coast Range Ophiolite, and the Great Valley sequence. Where exposed in the western Santa Ynez and San Rafael Mountains, the Franciscan assemblage is a melange of chiefly graywacke, argillite, chert, and blueschist rocks. The Coast Range Ophiolite forms a discontinuous tectonized belt of outcrops along the southwest edge of the San Rafael Mountains; parts of the dismembered ophiolite are exposed at Cuyama Gorge, Tepusquet-Colson Canyon, north side of Figueroa Mountain, Little Pine Mountain, and Santa Ynez River west of Gibraltar Dam. Rock types include harzburgite, p roxenite, gabbro, diorite, pillow basalt, tuff, and serpentinite. Throughout the ophiolite belt, serpentine-rimmed cold intrusions invade sedimentary strata as young as middle Miocene. The Great Valley sequence includes Tithonian through Maestrichtian submarine-fan strata as well as fluviodeltaic strata of probable Campanian age. The latter crop out in the Sisquoc River area directly west of the Sur-Nacimiento fault zone. Along the north flank of the Santa Ynez Mountain, structural superposition resulting from truncation along thrust planes has juxtaposed beds as young as Valanginian above the Franciscan assemblage. The structural and stratigraphic relations of the three terranes support the concept of a regionally persistent late Mesozoic forearc basin and accretionary subduction complex that may have extended from the Klamath Mountains of Oregon to as far south as the Vizcaino Peninsula of Baja California, Mexico. End_of_Article - Last_Page 450------------

An experimental study of granitoid rocks related to the San Andreas and Sur-Nacimiento fault systems

An experimental study of granitoid rocks related to the San Andreas and Sur-Nacimiento fault systems

Franciscan Rocks near Sur Fault Zone, Northern Santa Lucia Range, California

Research Article| October 01, 1973 Franciscan Rocks near Sur Fault Zone, Northern Santa Lucia Range, California WYATT G. GILBERT WYATT G. GILBERT 1Geology Department, University of Alaska, Fairbanks, Alaska 99701 Search for other works by this author on: GSW Google Scholar Author and Article Information WYATT G. GILBERT 1Geology Department, University of Alaska, Fairbanks, Alaska 99701 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1973) 84 (10): 3317–3328. https://doi.org/10.1130/0016-7606(1973)84<3317:FRNSFZ>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WYATT G. GILBERT; Franciscan Rocks near Sur Fault Zone, Northern Santa Lucia Range, California. GSA Bulletin 1973;; 84 (10): 3317–3328. doi: https://doi.org/10.1130/0016-7606(1973)84<3317:FRNSFZ>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Sur fault zone is a complex series of high-angle and low-angle faults that juxtapose a northeast block of competent crystalline rocks against a southwest block of generally sheared Franciscan rocks. The Franciscan rocks are an assemblage of sandstone, siltstone, greenstone, and chert. This assemblage can be divided into a northwestern terrane characterized by unmetamorphosed sheared and unsheared units containing detrital K-feldspar and a southeastern terrane with a pervasive dip-slip tectonite fabric throughout, metamorphic mineral assemblages indicative of high-pressure, low-temperature metamorphism, and no K-feldspar. A lawsonite isograd in Franciscan sandstone crosses the southeastern terrane. K-Ar dates indicate a minimum age of Late Cretaceous for high-pressure metamorphism of the Franciscan.During mid- to Late Cretaceous time, accumulation of Franciscan rocks was closely followed by subduction and high-pressure, low-temperature metamorphism. Low-pressure, high-temperature metamorphism and plutonism occurred concurrently in the Salinian block. In Late Cenozoic time, the San Andreas fault probably offset the Sur-Nacimiento fault from the Great Valley subduction zone. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Faults and Earthquakes in Monterey Bay Region, California: ABSTRACT

The structure of the continental margin, between Monterey Bay on the south and Point Reyes on the north, is dominated by a northwest-trending belt of rocks composed of continental crust (Salinian block) that is separated from oceanic crust on the east by the active San Andreas fault system, and on the west by the Sur-Nacimiento fault zone. Recent marine geophysical End_Page 781------------------------------ investigation have shown extensive faulting within this crustal block--some of which appears to have locally offset Holocene deposits. Most of the faults within the Salinian block in the Monterey Bay region occur in two major intersecting fault zones; the northward-trending Carmel Canyon fault zone, extending offshore from Point Sur (oriented N25°W), and the northwest-trending Monterey Bay fault zone, extending offshore from the town of Monterey (oriented N50°W). The Carmel Canyon fault zone appears to connect the Palo Colorado fault in the south with the San Gregorio fault in the north. The Monterey Bay fault zone appears to be the offshore continuation of the Sur-Nacimiento fault zone. Epicenters of many recent earthquakes are concentrated at the intersection of the Carmel Canyon and Monterey Bay fault zones, in the central part of Monterey Bay. First-motion studies of 8 earthquakes indicate right-lateral strike-slip displacement on these offshore faults. The cessation of a 10-day period of rapid tectonic creep along the adjacent San Andreas fault in 1970 coincided with a 4.3-magnitude earthquake in the Monterey Bay fault zone. This, as well as first-motion studies of the earthquakes and mapping of the offshore faults and seismicity, suggests a direct coupling between the San Andreas fault and the adjacent fault zones. End_of_Article - Last_Page 782------------

Pre-Cenozoic Tectonic History of the Salinian Block, Western California

The Salinian block is the elongate segment of the California Coast Ranges that lies between the Sur-Nacimiento and San Andreas fault zones. Known basement rocks within this block consist of Cretaceous and older granitic and high-grade metamorphic rocks that contrast sharply with Franciscan Group rocks of overlapping age east of the San Andreas and west of the Sur-Nacimiento fault zones. The metamorphic rocks of the Salinian block (often termed Sur series) are probably in part Paleozoic in age and appear to have been derived from a relatively shallow-water shelf-type sequence of psammitic rocks with subordinate calcareous and pelitic rocks. A graphite- and pyrite-bearing unit, mapped for more than 20 mi in the northern Santa Lucia Range, defines two sets of folds. Mineral lineations and mesoscopic folds indicate that major folding about northeast-trending axes occurred prior to prominant folding about north-northwest-trending axes. Assuming approximately 300 mi of post-Cretaceous right slip along the San Andreas fault, the metamorphic rocks of the Salinian block are tentatively correlated with similar Paleozoic and, perhaps in part, Precambrian rocks of the Mojave Desert and southwestern Tehachapi Mountains. The age of the early northeast-trending folds is unknown, but they may be a southwestward extension of Paleozoic tectonic and stratigraphic trends that head from Nevada into southern California. The north-northwest-trending folds are in part Cretaceous as indicated by the syntectonic emplacement of Cretaceous granitic rocks.

Sur-Nacimiento Fault Zone of California: Continental Margin Tectonics

The Sur-Nacimiento fault zone extends northwest through the southern and central Coast Ranges of California, and presumably continues offshore on the Continental Shelf. In part, or perhaps in its entirety, it forms the approximate boundary between the Franciscan trench(?) assemblage on the southwest and the granitic and regionally metamorphosed basement rocks of the Salinian block on the northeast. The Sur-Nacimiento fault zone includes the Sur fault zone, the Nacimiento fault, and a number of other faults of various kinds and various ages. There has been a long history of recurrent activity characterized by sequential changes in the types of movement. The Sur fault zone is here considered to have originated at the former margin of the continent during latest Cretaceous or Early Tertiary time as the culmination of processes that operated during the entire Late Mesozoic. Throughout the latest Jurassic, Early Cretaceous, and mid-Cretaceous, Franciscan deposits were probably carried into a trench and pushed against or partly beneath the crust to the east, by ocean-floor spreading. The Franciscan assemblage has a melange-like aspect which is appropriate to this kind of disturbance. Some rocks within the assemblage are about the same age (Early or mid-Cretaceous) as the adjacent Salinian granite, but they are unaffected by the granite. The postulated trench containing the Franciscan assemblage was probably far offshore during the time of granitic intrusion, but westward drift of North America narrowed the intervening distance. Conveyor-belt action of eastward-moving oceanic crust impinging against and beneath the edge of the continent may have ripped off and carried downward blocks of sialic crust. Perhaps this was the mechanism that eventually brought the Franciscan assemblage against the Salinian granite, creating the ancestral Sur fault zone. The Franciscan terrain is locally tectonically covered by allochthonous masses of Great Valley-type Late Mesozoic clastic sedimentary rocks predominantly of two ages: (1) Tithonian-Valanginian, and (2) Campanian-Maestrichtian(?). It is tentatively suggested that these allochthonous rocks were deposited between the continent and the trench in which the Franciscan accumulated, and that they were underthrust by the Franciscan during the same action that produced the Sur fault, in latest Cretaceous or Early Tertiary time. In the Tertiary, normal faulting occurred along the Sur-Nacimiento zone, following the annihilation of the active trench system. There are indications that strike-slip faulting and reverse faulting ensued at various times.

Stratigraphic Variations in Sandstone Petrology, Great Valley Sequence, Central California Coast

West of the Sur-Nacimiento fault zone in the Southern Coast Ranges of California, strata of the Great Valley sequence are exposed in thrust plates resting tectonically on the underlying Franciscan assemblage as is the case east of the San Andreas fault. Detrital modes of sandstones from different horizons in the local sequence show the same systematic variations with Stratigraphic position as do correlative late Mesozoic strata in the main outcrop belt along the west side of the Great Valley. The similar tectonic setting and sandstone petrology suggest the rocks in the two areas are parts of a single extensive terrane separated by fault offset in the Cenozoic.