Nacimiento Fault Research Articles

Forearc strike-slip displacement as an alternative to subduction erosion, with examples from Mexico and California (sinistral Nacimiento fault)

Slip on the Nacimiento fault of the central Coast Ranges of California has been variably interpreted as dextral, sinistral, or reverse. The currently prevailing interpretation is that the Nacimiento fault represents subduction erosion, by which the central to eastern part of the Cretaceous California batholith was thrust over the western part of the batholith and forearc basin, resulting in juxtaposition of the Salinian batholithic block against the Franciscan Complex, concurrently with Laramide flat-slab subduction (75–55 Ma) and underplating of the Pelona-Orocopia-Rand schist. No modern convergent plate margin includes such overthrusting. The closest modern analog to the likely configuration of the Salinian continental margin near the end of the Laramide deformation is southern Mexico, where arc plutons are exposed near the trench. Although commonly considered an example of subduction erosion, this margin is “missing” parts of the plutonic arc and forearc because they have been displaced to the southeast by sinistral slip. By analogy, the Nacimiento forearc was modified as a trench-trench-transform triple junction migrated southeastward along the continental margin during flat-slab subduction. This model makes testable predictions involving northwest-to-southeast younging of deep-marine deposits on batholithic crust underlain by contemporaneous schist. Correct restoration of later Cenozoic primarily dextral slip and Maastrichtian – Early Eocene primarily sinistral slip must result in realignment of north–south-trending belts of the Sierra Nevada – Salinia – Peninsular Ranges batholith, Great Valley forearc, and Franciscan Complex. These modern and ancient examples suggest that several “erosional” subduction zones are more plausibly explained by strike-slip truncation of forearcs.

Carbonic springs as distal manifestations of geothermal systems, highlighting the importance of fault pathways and hydrochemical mixing: Example from the Jemez Mountains, New Mexico

We examine a series of carbonic warm and hot springs in northern New Mexico, USA: 1) Tierra Amarilla springs 2) Penasco Springs and 3) Soda Dam, Jemez and Indian hot springs. Spring geochemistry is compared to waters from the Valles Caldera geothermal system and to groundwater in nearby sedimentary aquifers. Multiple hydrochemical tracers are applied to quantitatively evaluate flow paths and mixing at varying distances from the caldera. We test three hypotheses for source and transport of waters to Tierra Amarilla and Penasco Springs: San Juan basin origin, meteoric flow from the Nacimiento Mountains, and/or influence from the Valles Caldera geothermal system. Geochemically, carbonic spring groups are distinct from meteoric and sedimentary aquifer waters. Based on isotopes of He and Sr, and concentrations of Cl, SO4, Li and B, we interpret these carbonic springs to be distal manifestations of fluid circulation along faults with a mixture of Valles Caldera geothermal waters, local meteoric and Paleozoic aquifer waters, with the potential for small contributions from the San Juan Basin aquifers. Semi-confined fault conduits, the Jemez fault and Nacimiento fault systems, provide connectivity and help explain geochemical similarities and mixing trends within carbonic spring systems, and between these systems and the distal Valles Caldera. In addition, Penasco Springs are interpreted to reflect a component of outflow from the geothermal system that crosses the Nacimiento Mountain basement block along NE-trending faults. Input of deeply sourced waters can degrade water quality by contributing significant salinity and trace metals to groundwater at distances of >50 km from geothermal systems, with faults acting as conduits for subsurface fluid flow.

Salinia revisited: a crystalline nappe sequence lying above the Nacimiento fault and dispersed along the San Andreas fault system, central California

Salinia revisited: a crystalline nappe sequence lying above the Nacimiento fault and dispersed along the San Andreas fault system, central California

Kinematic analysis of mélange fabrics in the Franciscan Complex near San Simeon, California: Evidence for sinistral slip on the Nacimiento fault zone?

Asymmetric fabrics in Franciscan Complex shale matrix melange near San Simeon, central California, record synsubduction shear that has implications for the Late Cretaceous to early Tertiary tectonic evolution of the region. Outcrop-scale structural data including S-, C-, and C′-planes, slickenlines, block long axes, and offset blocks indicate that most asymmetric fabrics developed in a NE-dipping sinistral shear zone following Late Cretaceous chaotic mixing and accretion of the melange. Approximately 70% of C-planes strike within ∼45° of the major NW-striking structures in the region—the Neogene San Gregorio–Hosgri fault and the Late Cretaceous–early Tertiary Nacimiento fault zone. Slip vectors on these NW-striking C-planes consistently record sinistral or oblique sinistral shear. This dominant shear regime accommodated E-W to NE-SW shortening and N-S to NW-SE extension. Angles between S- and C-planes are typically ∼25°–35° and range up to ∼45°, suggesting dominantly simple shear. Sinistral shear in the melange is kinematically incompatible with Neogene to recent dextral faulting, indicating that these fabrics predate the early Miocene development of the Pacific–North America transform. We propose that sinistral shear in the melange is related to latest Cretaceous to early Tertiary slip on the adjacent Nacimiento fault zone. These kinematic data are compatible with previous studies that have suggested that the juxtaposition of the Salinian block against the Nacimiento block was accommodated by hundreds of kilometers of sinistral slip on the Nacimiento fault zone.

The influence of upper-crust lithology on topographic development in the central Coast Ranges of California

A fundamental geological tenet is that as landscapes evolve over graded to geologic time, geologic structures control patterns of topographic distribution in mountainous areas such that terrain underlain by competent rock will be higher than terrain underlain by incompetent rock. This paper shows that in active orogens where markedly weak and markedly strong rocks are juxtaposed along contacts that parallel regional structures, relatively high topography can form where strain is localized in the weak rock. Such a relationship is illustrated by the topography of the central Coast Ranges between the Pacific coastline and the San Andreas fault zone (SAFZ), and along the length of the Gabilan Mesa (the “Gabilan Mesa segment” of the central Coast Ranges). Within the Gabilan Mesa segment, the granitic upper crust of the Salinian terrane is in contact with the accretionary-prism mélange upper crust of the Nacimiento terrane along the inactive Nacimiento fault zone. A prominent topographic lineament is present along most of this lithologic boundary, approximately 50 to 65 km southwest of the SAFZ, with the higher topography formed in the mélange on the southwest side of the Nacimiento fault. This paper investigates factors influencing the pattern of topographic development in the Gabilan Mesa segment of the central Coast Ranges by correlating shortening magnitude with the upper-crust compositions of the Salinian and Nacimiento terranes. The fluvial geomorphology of two valleys in the Gabilan Mesa, which is within the Salinian terrane, and alluvial geochronology based on optically-stimulated luminescence (OSL) age estimates, reveal that the magnitude of shortening accommodated by down-to-the-southwest tilting of the mesa since 400 ka is less than 1 to 2 m. Our results, combined with those of previous studies, indicate that at least 63% to 78% of late-Cenozoic, northeast–southwest directed, upper-crustal shortening across the Gabilan Mesa segment has been accommodated within the Nacimiento terrane. This is significant because perpendicular to orogenic strike the Nacimiento terrane constitutes less than ¼ of the distance between the coast and the SAFZ, and the other ¾ (or greater) of the distance between the coast and the SAFZ is underlain by the granitic upper crust of the Salinian terrane. We propose that strain and mountain building are localized within the Nacimiento terrane because it consists predominantly of the relatively weak Franciscan Complex mélange, and because the upper crust of the Salinian terrane is composed of relatively strong granitic rocks. Our hypothesis is supported by the distribution of post-seismic surface uplift associated with the 2003, 6.5 M W San Simeon earthquake, which mimics the topography of the southwestern part of the Gabilan Mesa segment of the central Coast Ranges.

Late Cretaceous-early Cenozoic tectonic evolution of the southern California margin inferred from provenance of trench and forearc sediments

During the Late Cretaceous to early Cenozoic, southern California was impacted by two anomalous tectonic events: (1) underplating of the oceanic Pelona-Orocopia-Rand schists beneath North American arc crust and craton; and (2) removal of the western margin of the arc and inner part of the forearc basin along the Nacimiento fault. The Pelona-Orocopia-Rand schists crop out along a belt extending from the southern Sierra Nevada to southwestern Arizona. Protolith and emplacement ages decrease from >90 Ma in the northwest to <60 Ma in the southeast. Detrital zircon U-Pb ages imply that metasandstones in the older schists originated primarily from the western belt of the Sierran–Peninsular Ranges arc. Younger units were apparently derived by erosion of progressively more inboard regions, including the southwestern edge of the North American craton. The oldest Pelona-OrocopiaRand schists overlap in age and provenance with the youngest part of the Catalina Schist of the southern California inner continental borderland, suggesting that the two units are broadly correlative. The Pelona-OrocopiaRand-Catalina schists, in turn, share a common provenance with forearc sequences of southern California and the associated Salinian and Nacimiento blocks of the central Coast Ranges. This observation is most readily explained if the schists were derived from trench sediments complementary to the forearc basin. The schists and forearc units are inferred to record an evolution from normal subduction prior to the early Late Cretaceous to flsubduction extending into the early Cenozoic. The transition from outboard to inboard sediment sources appears to have coincided with removal of arc and forearc terranes along the Nacimiento fault, which most likely involved either thrusting or sinistral strike slip. The strike-slip interpretation has not been widely accepted but can be understood in terms of tectonic escape driven by subduction of an aseismic ridge, and it provides a compelling explanation for the progressively younger ages of the PelonaOrocopia-Rand schists from northwest to southeast.

Complex Faulting Associated with the 22 December 2003 Mw 6.5 San Simeon, California, Earthquake, Aftershocks, and Postseismic Surface Deformation

We use data from two seismic networks and satellite interferometric synthetic aperture radar (InSAR) imagery to characterize the 22 December 2003 M w 6.5 San Simeon earthquake sequence. Absolute locations for the mainshock and nearly 10,000 aftershocks were determined using a new three-dimensional (3D) seismic velocity model; relative locations were obtained using double difference. The mainshock location found using the 3D velocity model is 35.704° N, 121.096° W at a depth of 9.7±0.7 km. The aftershocks concentrate at the northwest and southeast parts of the aftershock zone, between the mapped traces of the Oceanic and Nacimiento fault zones. The northwest end of the mainshock rupture, as defined by the aftershocks, projects from the mainshock hypocenter to the surface a few kilometers west of the mapped trace of the Oceanic fault, near the Santa Lucia Range front and the >5 mm postseismic InSAR imagery contour. The Oceanic fault in this area, as mapped by Hall (1991), is therefore probably a second-order synthetic thrust or reverse fault that splays upward from the main seismogenic fault at depth. The southeast end of the rupture projects closer to the mapped Oceanic fault trace, suggesting much of the slip was along this fault, or at a minimum is accommodating much of the postseismic deformation. InSAR imagery shows ∼72 mm of postseismic uplift in the vicinity of maximum coseismic slip in the central section of the rupture, and ∼48 and ∼45 mm at the northwest and southeast end of the aftershock zone, respectively. From these observations, we model a ∼30-km-long northwest-trending northeast-dipping mainshock rupture surface—called the mainthrust—which is likely the Oceanic fault at depth, a ∼10-km-long southwest-dipping backthrust parallel to the mainthrust near the hypocenter, several smaller southwest-dipping structures in the southeast, and perhaps additional northeast-dipping or subvertical structures southeast of the mainshock plane. Discontinuous backthrust features opposite the mainthrust in the southeast part of the aftershock zone may offset the relic Nacimiento fault zone at depth. The InSAR data image surface deformation associated with both aseismic slip and aftershock production on the mainthrust and the backthrusts at the northwest and southeast ends of the aftershock zone. The well-defined mainthrust at the latitude of the epicenter and antithetic backthrust illuminated by the aftershock zone indicate uplift of the Santa Lucia Range as a popup block; aftershocks in the southeast part of the zone also indicate a popup block, but it is less well defined. The absence of backthrust features in the central part of the zone suggests range-front uplift by fault-propagation folding, or backthrusts in the central part were not activated during the mainshock.

Palinspastic reconstruction of Proterozoic basement-related aeromagnetic features in north-central New Mexico: Implications for Mesoproterozoic to late Cenozoic tectonism

Aeromagnetic maps from north-central New Mexico show east-northeast–trending linear features that are offset dextrally across the north-striking Picuris-Pecos, Tusas-Picuris, and (possibly) Nacimiento fault systems. Geologic structures that correspond to these regional aeromagnetic lineaments, where exposed in Phanerozoic uplifts, are major ductile shear zones of Proterozoic age that juxtapose folded metasedimentary rocks associated with areas of low aeromagnetic value with metavolcanic and metaplutonic rocks associated with areas of high aeromagnetic value. Regional aeromagnetic lineaments serve as piercing lines that suggest at least ∼55 km and perhaps as much as ∼90 km of net dextral separation since 1.4 Ga. The restored aeromagnetic lineaments are interpreted to represent a series of east-northeast–striking, dominantly north-vergent, thrust-sense shear zones that formed initially during the ca. 1.65 Ga Mazatzal orogeny and were variably reactivated during the ca. 1.4 Ga magmatic and deformational event.

Implications of Jurassic, Cretaceous, and Proterozoic piercing lines for Laramide oblique-slip faulting in New Mexico and rotation of the Colorado Plateau

Research Article| June 01, 1999 Implications of Jurassic, Cretaceous, and Proterozoic piercing lines for Laramide oblique-slip faulting in New Mexico and rotation of the Colorado Plateau Steven M. Cather Steven M. Cather 1New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar Author and Article Information Steven M. Cather 1New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1999) 111 (6): 849–868. https://doi.org/10.1130/0016-7606(1999)111<0849:IOJCAP>2.3.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 Steven M. Cather; Implications of Jurassic, Cretaceous, and Proterozoic piercing lines for Laramide oblique-slip faulting in New Mexico and rotation of the Colorado Plateau. GSA Bulletin 1999;; 111 (6): 849–868. doi: https://doi.org/10.1130/0016-7606(1999)111<0849:IOJCAP>2.3.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 Regional isopach patterns and pinch-out data for nine stratigraphic units of Jurassic and Cretaceous age are either permissive or supportive of significant dextral slip of Laramide age along the eastern Colorado Plateau boundary in New Mexico. The best-constrained dextral offset estimates are for the Sand Hill–Nacimiento fault system (20–33 km) and the previously published 13 km estimate for the Defiance monocline, which together yield a cumulative offset of 33–46 km. Mesozoic stratigraphic constraints for other Laramide fault systems are less precise, and typically provide only maximum limits for possible dextral offsets because of widely spaced control points and broad areas of Tertiary erosion. These less precise constraints allow as much as 40–60 km of Laramide dextral slip along what is now the Rio Grande rift and as much as 110 km across the entire breadth of the Laramide deformed zone in central and northern New Mexico.Well-documented dextral offsets of Proterozoic lithologies and structures across the Tusas-Picuris fault system (15 km) and Picuris-Pecos fault (37 km) probably represent minimum Laramide displacements because of the need to account for sinistral components related to other deformations. These displacements, when combined with dextral offsets along Sand Hill–Nacimiento and Defiance structures, yield a minimum dextral offset of ∼85 km for Laramide structures in northern New Mexico. This minimum dextral offset is approximately equivalent to the amount of Laramide crustal shortening on and northward of the Colorado Plateau, a result that argues against nearby Euler pole locations for Laramide rotation of the Colorado Plateau relative to cratonic North America. Geological constraints allow ∼0° to 3° of Laramide clockwise rotation of the Colorado Plateau. Additional clockwise plateau rotation during late Cenozoic development of the Rio Grande rift was 1° to 1.5°. Geological constraints thus indicate that clockwise rotation of the Colorado Plateau from combined Laramide and Rio Grande rift deformations was between about 1° and 4.5°. 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.

A Model for Evolution of Laramide Axial Basins in the Southern Rocky Mountains, U.S.A.

The structural, stratigraphic, and sedimentologic development of Laramide axial basins of the southern Rocky Mountains is inconsistent with previous models relating them to transpressional tectonics. Axial basins are better explained as broad synclinal troughs in the hanging walls of large pop-up structures, in contrast to perimeter and ponded basins formed in the footwalls of these same structures. Laramide faults in the southern Rocky Mountains can be divided into the E-dipping Park Range thrust system and the W-dipping Sangre de Cristo thrust system. The W-dipping Front Range fault is the backthrust of the Park Range system, and the E-dipping Nacimiento fault is the back-thrust of the Sangre de Cristo system. The broad synclinal troughs formed between these two pairs of oppositely verging thrust systems were the locations for sediment deposition in axial basins, as exemplified by the Galisteo-El Rito basin of northern New Mexico. The Eocene Galisteo and El Rito formations were deposited on a broad syncline of Phanerozoic strata with crystalline basement along the basin margins. Most sediment was derived from the northeast, north, and northwest, except near the NE-trending Tijeras-Canoncito transfer zone along the southeast margin of the basin. Uplift of the Sangre de Cristo Range occurred first, followed by backthrusting to uplift the Sierra Nacimiento. This model explains Laramide uplifts and basins as the direct response to rapid NE-SW convergence between the North American and Farallon plates, without multiple reorientation of Laramide stress fields, and without major strike-slip along the eastern side of the Colorado Plateau.

Structural Influences in Gavilan Mancos Oil Pool: Fractures, Dolomitization, Mineralization: ABSTRACT

The Gavilan Mancos oil pool produces from structurally induced naturally fractured intervals of the Mancos formation. Reservoir porosity is a combination of both fracture and matrix porosity. The matrix is characteristically of low porosity and permeability and consists of interbedded sandstones, siltstones, and shales of Niobrara and Carlile age. While the matrix is very consistent over the field, commercially productive wells rely on the concentration of natural fractures in the rock and are dependent on structural position related to the Gavilan dome. The Gavilan dome is a northwest-trending anticline with approximately 60 ft of closure existing at the Mancos level. Structural formation of the anticline and the major fracturing of the rock column are the result of Eocene tectonism that is responsible for the present structural configuration of the San Juan basin. Right-lateral transcurrent movements along the Nacimiento fault produced a series of northwest-trending anticlines and synclines. The stresses associated with the formation of the Gavilan dome were responsible for the creation of fractures within the more brittle zones of the Mancos formation.

Implications of upper Mesozoic conglomerate for suspect terrane in western California and adjacent areas

Several distinctive kinds of conglomerate occur in upper Mesozoic rocks in different regions of western California. Within each region, conglomerate in the accretionary-wedge Franciscan assemblage is similar to conglomerate exposed nearby in the fore-arc-basin Great Valley sequence, suggesting that both rock units were derived from the same source regions. Long-distance tectonic transport is not necessary to account for the detrital sedimentary rocks in the Franciscan. The types of conglomerate in the lower part of the Great Valley sequence relate to their place of deposition in the fore-arc basin. In the northern Coast Ranges, chert-rich conglomerate derived from the Klamath Mountains was transported longitudinally southward by a relatively large distribution system. Correlative conglomerate in the Diablo Range is rich in volcanic and detrital- sedimentary-rock clasts derived from the western edge of the Sierra Nevada and transported westward by relatively small distribution systems. Conglomerate rich in chert and quartzite in suspect terrane of the Golden Gate-Gilroy and Nacimiento blocks of central California may have been deposited by a large north-flowing system in the southern part of the same basin; an exotic origin is not required for the suspect terrane. In mid-Cretaceous time, the Nacimiento block may have been displaced southeastward along the Nacimiento fault and juxtaposed against the Salinian block, a deep and interior part of the magmatic arc in southern California. This displacement may be reflected in the clast composition of mid-Cretaceous conglomerate of the Nacimiento block, but stratigraphic documentation is still incomplete. Younger and approximately equal right-slip on the San Andreas fault system brought both the Nacimiento and Salinian blocks northwest to their present position. A southward increase in quartzite content in conglomerate of post-Nevadan age is broadly parallel to a similar increase in pre-Nevadan conglomerate of adjacent parts of the Klamath Mountains, Sierra Nevada, and Peninsular Ranges, making it unlikely that any of these rocks were tectonically derived from remote regions. Radiolarians from chert pebbles in Franciscan conglomerate are similar in age distribution and faunal composition to those from pebbles in the Great Valley sequence, from pebbles in pre-Nevadan conglomerate, and from bedded chert in presently adjacent source areas.

Earthquakes and associated tectonics in a part of coastal central California

Seismicity along a corridor 65 km wide and 100 km long across the central Coast Ranges of California, southwest from the San Andreas fault zone, is used to determine tectonic properties of the three constituent provinces: a region of horizontal shear along the San Andreas fault zone; a moderately active belt of compressional faulting along the coastline; and an intermediate low seismicity zone. Fault-plane mechanisms of 33 earthquakes in the corridor indicate that the three provinces are distinguished by characteristic tectonic features: directions of P (compression) axes; fault types; and fault-slip directions. Each interprovince transition appears to be less than 12 km wide. Across the boundary between the San Andreas fault zone and the low seismicity region, just SW of the San Andreas zone, P axes are rotated about 45°, and the dominant right-lateral slip directions also change by about 45°. Across the boundary between the low seismicity and the compressive regions, near the Nacimiento fault, a small rotation occurs in P axes and slips change from dominantly horizontal shear to the NE to oblique reverse to the SW. A remarkable result is that almost all inferred faults in the corridor can be interpreted as having moderate to steeply NE dipping planes along which horizontal components of slip are right-lateral and vertical components have the NE side moving up. The base of the seismogenic zone is about 12 km deep throughout the corridor. It is suggested that the seismicity and stress patterns in each of the three provinces reflect the relative strengths of upper crustal rocks in the seismogenic zone. The largest recorded earthquake ( ML = 6.0) in the corridor since 1941 is the Bryson earthquake of 1952. A reanalysis of the epicenter was made, based on the “calibration event” technique, in which readings of several newly collected seismograms were included; the revised location is just SW of the Nacimiento fault zone, about 6 km SW of Bryson. Displacement is right-lateral along a 55°NE dipping plane that strikes N55°W, in conformance with San Andreas-type faulting.

Cretaceous Sinistral Strike Slip Along Nacimiento Fault in Coastal California

The San Andreas and Nacimiento faults of coastal California both separate granitic and metamorphic basement rocks of the Salinian block from partly coeval but contrasting Mesozoic terranes underlain by the Franciscan subduction complex. By analogy with Neogene dextral strike slip along the San Andreas fault, Cretaceous sinistral strike slip can be inferred along the Nacimiento fault in preference to hypotheses for tectonic erosion during subduction or for dextral strike slip of unspecified amount. Following restoration of known San Andreas and inferred proto-San Andreas dextral displacements, reversal of about 560 km (350 mi) of postulated sinistral slip on the Nacimiento fault brings four major Mesozoic lithotectonic belts of California and Baja California into simple al gnment as subparallel terranes related to Mesozoic subduction along the continental margin. Neogene deformation within the San Andreas transform system involved (a) elongation of the Salinian block by dextral slip along subsidiary faults that branch from the San Andreas fault, and (b) dextral rotation of crustal panels within the Transverse Ranges. Latest Cretaceous and/or earliest Paleogene dextral slip along a proto-San Andreas fault followed the San Andreas course in central California, but diverged westward in southern California. Nacimiento sinistral displacements occurred in mid-Cretaceous to early or medial Late Cretaceous time, after Cretaceous emplacement of plutons now within the Salinian block but prior to deposition of uppermost Cretaceous sedimentary sequences in central California. Available data on Mesozoic relative and absolute plate motions in the Mesoameric n region support the likelihood of Cretaceous sinistral strike slip subparallel to the California continental margin. Paleotectonic reconstruction of crustal blocks in California and Baja California to their inferred mid-Cretaceous relative positions shows the Salinian block inserted on a bias between the flanking Mojave and Peninsular Ranges blocks. Salinian granitic rocks thus formed an interior part of the Mesozoic batholith belt, and their initial strontium isotopic ratios are compatible with the gradients displayed by values from the adjoining blocks. The similar Mesozoic terranes that now lie east and west of the Salinian block were then adjacent to one another west of the Sierra Nevada block. Available paleomagnetic data neither support nor preclude the reconstruction, but additional work together with future detailed lithotectonic comparisons potentially can confirm or refute the hypothesis i represents. A correct interpretation of the Nacimiento fault is important for understanding the overall tectonic framework of petroliferous basins both onshore and offshore in coastal California.

Rinconada Fault in Southern Coast Ranges, California and Its Significance: ABSTRACT

The Rinconada fault near Santa Margarita is a major northwest-trending, high-angle fault that separates a terrane of granitic basement on the northeast from one of Franciscan basement on the southwest. Southeastward from Santa Margarita this fault extends continuously into the fault across Cuyama Gorge to intersect the Big Pine fault in the San Rafael Mountains. Northwestward the Rinconada fault does not extend into the Nacimiento fault near the Nacimiento River, as presumed, but veers northward through Paso Robles into a line of faults locally called San Marcos, Jolon, and Espinosa faults, nearly to Reliz Canyon west of King City. Detailed mapping reveals that all these aligned faults are parts of one major fault, 160 mi long. Therefore, it is proposed to call it the Rinconada fault. It is separated by a 2-mi gap from the Reliz fault, aligned northwest along the base of Sierra de Salinas. The Rinconada fault, as defined herein, is nearly parallel with, and about 22 mi southwest, of the San Andreas fault. Southeastward from Santa Margarita the Rinconada fault is along the southwestern border of the Salinia block; northwestward from that town it extends into this block. Drag folding along and near the Rinconada fault indicates right-lateral movement. Much of this movement occurred before deposition of the Paso Robles Formation. Strata of Miocene and early Pliocene ages are offset about 11 mi near Paso Robles; tho e of Late Cretaceous-early Tertiary age are offset nearly 40 mi. End_of_Article - Last_Page 432------------

Nacimiento Fault and Related Structures, Northern New Mexico

Research Article| August 01, 1972 Nacimiento Fault and Related Structures, Northern New Mexico LEE A WOODWARD; LEE A WOODWARD Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 Search for other works by this author on: GSW Google Scholar WILLIAM H KAUFMAN; WILLIAM H KAUFMAN Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 Search for other works by this author on: GSW Google Scholar JOHN B ANDERSON JOHN B ANDERSON Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 Search for other works by this author on: GSW Google Scholar Author and Article Information LEE A WOODWARD Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 WILLIAM H KAUFMAN Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 JOHN B ANDERSON Department of Geology, University of New Mexico, Albuquerque, New Mexico 87106 Publisher: Geological Society of America Received: 17 Sep 1971 Revision Received: 17 Feb 1972 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (8): 2383–2396. https://doi.org/10.1130/0016-7606(1972)83[2383:NFARSN]2.0.CO;2 Article history Received: 17 Sep 1971 Revision Received: 17 Feb 1972 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation LEE A WOODWARD, WILLIAM H KAUFMAN, JOHN B ANDERSON; Nacimiento Fault and Related Structures, Northern New Mexico. GSA Bulletin 1972;; 83 (8): 2383–2396. doi: https://doi.org/10.1130/0016-7606(1972)83[2383:NFARSN]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 Initial development of the Nacimiento uplift occurred during the Laramide orogeny by what may have been shear folding of the brittle Precambrian basement rocks and stretching of the incompetent overlying sedimentary strata along a monoclinal fold on the west side of the uplift. Antithetic and synthetic normal faults formed in the strata along the monocline as it developed. The normal faults and the fold were cut by the Nacimiento fault which is nearly vertical at depth but flattens upward and has westward movement of the hanging wall block over the San Juan basin. Where the Nacimiento fault is preserved at high structural and stratigraphic levels it is gently dipping and has normal faults in the hanging wall block. These longitudinal normal faults formed as the uplift was arched and stretched.A model based on primary vertical uplift integrates the different stress fields that caused the complex sequence of monoclinal folding, normal faulting, and reverse faulting with concomitant tensional features in the hanging wall block. 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.

Early Tertiary Paleogeography of Central California

A continuously deposited, clastic sequence of Upper Cretaceous, lower and middle Eocene marine sedimentary rocks lies unconformably on granitic basement in the La Panza, southern Santa Lucia, and Sierra Madre Ranges of central California. The sequence is more than 30,000 ft thick and is bounded by the San Andreas and Nacimiento fault zones. Sediment accumulated in a steep-sided, troughlike basin southwest of the present San Andreas fault zone. The basin extended southeastward across the Big Pine and Pine Mountain faults into the Ventura basin in which the lower Tertiary sequence of the Santa Ynez Mountains accumulated. The wedge-shaped area, including the San Rafael Mountains, between the Sierra Madre trough and the Ventura basin, underwent uplift and erosion during Late Cretaceous and early Eocene time. During the late early Eocene, a marine transgression resulted in deposition of a thin limestone, followed by shales and sandstones, across the southeastern part of the San Rafael wedge-shaped area. The lower Tertiary strata of the Soledad area, north and east of Castaic and east of the San Gabriel fault, accumulated in the probable eastward extension of the Sierra Madre-Ventura composite basin. The composite basin may have extended as far south as the Channel Islands. Paleocurrent and stratigraphic studies in the lower Tertiary sequence deposited in the Sierra Madre basin indicate deposition mainly from a source area on the east, as in the Ventura basin. A possible source area may be the basement rocks of the Mojave Desert, San Bernardino Mountains, and the Orocopia Mountains. The Eocene of the Orocopias is a possible eastward extension of the composite basin that has been displaced along the San Andreas fault. The Poway conglomerate suite of Eocene sediments from southern California was probably deposited in a separate basin south of the Sierra Madre-Ventura composite basin.

Structure and Petrology of the Alpine-type Peridotite at Burro Mountain, California, U.S.A.

The alpine-type peridotite at Burro Mountain is a partially serpentinized harzburgite-dunite body approximately 2 km in diameter. It lies in a chaotic mélange derived from the Franciscan Formation (Upper Jurassic to Upper Cretaceous) of the southern Coast Ranges of California. The peridotite is bounded on the east by a vertical fault in the Nacimiento fault zone that brings sedimentary rocks of Taliaferro's (1943b) Asuncion Group (Upper Cretaceous) into contact with the peridotite. The peridotite appears to be one of a number of tectonic lenses, having a wide range in size, that make up the mélange. These lenses include metagraywacke, metachert, greenstone, amphibolite, and blueschist, as well as ultramafic rocks, and represent a wide range of pressure-temperature environments. The outer shell of the peridotite is a sheared serpentinite zone 10–15 m thick. The peridotite was tectonically emplaced at its present level as a cold solid mass and had little effect on the mineral assemblages of the Franciscan Formation. Local development of lawsonite and aragonite in shear zones may be related to the peridotite emplacement. Foliated harzburgite forms approximately 60 per cent of the peridotite. It is a lithologically uniform rock that has an olivine: orthopyroxene ratio of approximately 75:25. Accessory clinopyroxene and chromian spinel generally make up less than 5 per cent of the harzburgite. Dunite, composed of olivine, accessory chromian spinel (< 5 per cent), and trace amounts of pyroxene, makes up approximately 40 per cent of the peridotite and occurs as dikes, sills, and irregular bodies in the harzburgite. Olivine and pyroxene show small but significant compositional variations and chromian spinel shows a large range in the cation ratio Cr/(Cr+Al+ Fe3+). The compositional variations in these minerals are related to original differences in bulk chemical composition. The following compositional ranges were determined for minerals in the harzburgite: olivine, Fo91.1−Fo91.4; orthopyroxene, En89.8−En91.1; clinopyroxene, Ca47.0Mg50.0Fe3.0−Ca48.7Mg48.2Fe3.1; chromian spinel, Cr/(Cr+Al+Fe3+) 0.37−0.55. The pyroxenes have a range in A12O3 content of 1.3−3.0 wt per cent. Olivine from dunite ranges from Fo91 to Fo92 7 and the chromian spinel has a range in the Cr/(Cr+Al+Fe3+) ratio of 0.30−0.75. Although all the dunites are lithologically similar, three distinct types are recognized on the basis of composition of coexisting olivine and chromian spinel. Structural relations between the three types of dunite suggest three periods of emplacement (possibly overlapping) of dunite into harzburgite. The evidence indicates that the dunite, and probably also the harzburgite crystallized from an ultramafic magma, probably in the upper mantle. After the magmatic episode and crystallization, the peridotite was subjected to a deep-seated plastic deformation and recrystallization. The first phase of the deformation produced a pervasive, planar structural element (S1) that crosscuts many harzburgite-dunite contacts. It is probable that some of the dunite sills were emplaced during this deformation. The foliation, S1, is defined by layers of different orthopyroxene content in harzburgite, and by discontinuous layers of chromian spinel in dunite. Flow or slip along S1 produced slip folds in harzburgite—dunite contacts with axial planes parallel to S1. At a later stage, isoclinal folds developed in S1, and the present olivine microfabric was probably formed by recrystallization in the stress field that produced the isoclinal folding. In the olivine microfabric, X tends to be perpendicular to the axial planes (S2) of the isoclinal folds and Y and Z tend to form double maxima in S2 approximately 90° apart. Mg−Fe2+ distribution between coexisting mineral pairs yields a calculated temperature of formation of approximately 1200 °C. Although this temperature is only a nominal value, it indicates that the mineral pairs equilibrated at a significantly high temperature. In view of the deformation and recrystallization, the calculated temperature possibly represents subsolidus re-equilibration of the minerals during this event. The deformation and recrystallization probably occurred shortly after crystallization while the peridotite was still at a high temperature. A later deep-seated deformation produced small scattered kink folds in S1 that tend to disrupt the major olivine microfabric. The kink folding was accompanied or followed by the development of kink bands in olivine that reflect intragranular gliding on the system T = [Okl], t = [100]. The kink bands probably formed at a minimum temperature of 1000 °C. Following the deep-seated deformation, which probably took place in the mantle, the peridotite mass was tectonically detached and moved upward to its present level in the crust. Cleavages, joints, and faults provided channels for water to pervade the peridotite and allow alteration of the primary minerals.

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.

Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault

Research Article| April 01, 1970 Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault ROBERT A LONEY ROBERT A LONEY U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT A LONEY U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America Received: 29 Sep 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1970, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1970) 81 (4): 1249–1254. https://doi.org/10.1130/0016-7606(1970)81[1249:FITBMA]2.0.CO;2 Article history Received: 29 Sep 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ROBERT A LONEY; Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault. GSA Bulletin 1970;; 81 (4): 1249–1254. doi: https://doi.org/10.1130/0016-7606(1970)81[1249:FITBMA]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 northwest-striking Nacimiento fault, in the southern Coast Ranges of California, has generally been regarded as the boundary between two major structural blocks: the Nacimiento block to the southwest, in which the basement rocks belong to the Franciscan Formation (Upper Jurassic to Upper Cretaceous), and the Salinian block to the northeast, in which the basement rocks are granitic and high-grade metamorphic. It has been found, however, that in the Burro Mountain area of the southern Santa Lucia Range, the “Nacimiento” fault of Jennings (1959) is nearly vertical and is within the Nacimiento block. In this area, the Franciscan Formation crops out northeast of the “Nacimiento” fault through windows in an older, low-angle thrust fault that brings the Asuncion Group of Taliaferro (1943) (Upper Cretaceous) over the Franciscan Formation. The fault boundary between the Nacimiento and the Salinian blocks must therefore lie farther to the northeast, where it may be buried beneath the Asuncion Group and younger strata. This conclusion is supported by Hanna's recent aeromagnetic work (1969). 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.