Santa Lucia Range Research Articles

Habitat suitability assessment for tule elk in the San Francisco Bay and Monterey Bay areas

While California’s statewide tule elk (Cervus canadensis nannodes) population has recovered from two or three individual survivors in the late 19th century, the subspecies exists today in numerous widely disjunct populations, leaving vast areas of the species’ former range uninhabited. Large unoccupied areas of historic tule elk range include the Santa Cruz Mountains and the northern Diablo and northern Santa Lucia ranges. Natural range expansion by existing populations into these areas is blocked by major highways and urban development; although, before considering tule elk translocations, it is necessary to assess the habitat suitability there. To this end, we fit a resource selection function (RSF) using generalized linear mixed models to GPS collar data collected from nearby radio collared tule elk and used several environmental GIS layers to capture important habitat characteristics. We fit the RSF in a habitat use versus availability framework with only linear and quadratic terms and used stepwise model selection ranked by AICc to maximize its generalizability, enabling transferability to our unoccupied study area. We also used k-fold cross validation to evaluate our RSF and found it predicted habitat within the San Luis Reservoir herd well. The fit habitat relationships mostly followed expectations based on tule elk ecology, including positive responses to herbaceous vegetation cover and waterbody proximity, and negative responses to high tree cover and high puma habitat suitability. Our RSF accurately predicted currently occupied elk habitat as suitable and found well over 500,000 ha (2,000 mi2) of suitable but unoccupied habitat throughout the northern Diablo Range, the inland and coastal sides of the Santa Cruz Mountains, and the northern Santa Lucia Range. Assuming translocations, and construction and improvement of highway wildlife crossings, our results support the potential for re-establishing tule elk in these regions, which are more coastal and mesic than the species’ current habitat in the central Diablo and northern Gabilan ranges.

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

Review of the Purple Amole Chlorogalum purpureum (Agavaceae): a Threatened Plant in the Coast Ranges of Central California

The purple amole Chlorogalum purpureum (Agavaceae) is a bulbous, perennial soap plant endemic to central California and listed as threatened under the U.S. Endangered Species Act since 2000. Chlorogalum p. purpureum occurs in the rain shadow of the Santa Lucia Range on Fort Hunter Liggett, south Monterey Co., and on Camp Roberts, north San Luis Obispo Co. Chlorogalum p. reductum occurs in the rain shadow of the La Panza Range in central San Luis Obispo Co., mostly on Los Padres National Forest and with potential for a substantially larger occupied area on private land. We review and enhance the existing knowledge of C. purpureum, in particular its life history and ecology, distribution, population sizes, threats, current management and conservation status. In 2012, invasive plants are the primary threat to C. purpureum.

Tectonic underplating of trench sediments beneath magmatic arcs: the central California example

We summarize the post Late Cretaceous regional tectonic evolution of the central California Coast Ranges, west of the San Andreas fault system. The Monterey terrane of North American origin was laterally transferred to the Pacific plate via the San Andreas fault. The Monterey terrane is an assembly of three tectonic units, Salinia, Nacimiento and Sierra de Salinas blocks, two of which have been previously identified as separate terranes. These blocks are separated by two regionally important thrust faults: the Sur fault as well as the Salinas shear zone. Based on thermobarometric and thermochronologic constraints and the existence of a common younger cover sequence, these blocks were juxtaposed together after the latest Cretaceous. The Salinian assemblage represents a crustal section through the continental interior side of the Mesozoic California arc and formed during the Late Cretaceous, primarily during a regionally significant magmatic flare‐up between 95 and 80 Ma. In the Santa Lucia Range, parts of the arc are exposed to palaeo‐depths in excess of 30 km. The Nacimiento and Sierra de Salinas assemblages comprise basement rocks representing Late Cretaceous variants of the Franciscan Complex and are interpreted to be correlative. They represent the lower plate of a regionally important thrust system; the upper plate is the Salinian assemblage, whereas the Sur and Salinas faults are local exposures of the structure. We concur with previous estimates of 150 to 180 km of shortening during a brief time span (<6 my), at a rate of >3 cm/yr. This fault system corresponds to the megathrust of the Farallon subduction beneath North America during the early stages of the regionally extensive episode of shallow subduction (Laramide orogeny). As a result, trench sediment was thrust under North America and tectonically underplated to the lower crust of North America. The Salinas shear zone, in particular, is a ductile expression of shallow subduction; thermobarometry in the upper plate, lower plate and the shear zone itself indicate that this is the fossil subduction megathrust originating at depths of ∼35 km. The entire system collapsed extensionally soon after the trench sediment was underthrust, possibly because of the lack of strength of the lower plate. Arc magmatism in the upper plate ceased at the onset of underplating. This regional example illustrates the significance of tectonic underplating in shallow subduction systems. Accretion‐related trench sediment was shuffled from the trench to the sub‐arc region of the upper plate, but not recycled into the mantle. This process requires that the subduction megathrust be located solely within the North American crust. This geometry requires a sudden migration of the subduction interface toward the arc and may apply to other regional examples, including the modern shallow subduction of the Cocos plate beneath southern Mexico. The tectonically underplated trench sediment undergoes regional, Barrovian metamorphism, after initially following a high‐pressure/low‐temperature path. Moreover, the shear zone marking the fossil intracrustal megathrust was subject to granulite‐facies metamorphism and limited partial melting.

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.

Facies, Architecture, and Origin of a Reservoir-Scale Sand-Rich Succession Within Submarine Canyon Fill: Insights from Wagon Caves Rock (Paleocene), Santa Lucia Range, California, U.S.A.

Abstract Large submarine canyons incise most continental margins, but outcrops of comparably sized ancient examples are relatively rare. A preserved cross section of a filled Cretaceous–Paleocene submarine canyon, tens of kilometers wide by hundreds of meters deep and cut into granitic basement of the Salinian block, is exposed in the Santa Lucia Range of central coastal California. The exposure allows an opportunity for the detailed analysis of associated sand-rich deposits analogous to one type of petroleum reservoir. A succession of coarse-grained high-density turbidity current deposits present at Wagon Caves Rock (WCR), a 0.5 km2 mesa in the Indians Ranch area, is part of a lenticular sandstone body up to 75 m thick and several kilometers wide that accumulated within the confines of the submarine canyon. The facies architecture of the outcrop records canyon axial channel deposition in the middle reaches of the submarine canyon system. The uppermost beds at WCR record the catastrophic failure of the submarine-canyon wall, which was associated with the termination of coarse clastic deposition in the area. The modern Monterey submarine canyon, which incises Salinian block basement identical to that cut by the ancient canyon, provides a close analog for the depositional setting of the canyon deposits of the Indians Ranch area. The architectural analysis provides insight into facies and stratal architecture within a part of the deep-water slope environment that is relatively poorly known due to limited rock data from canyon successions and the inherent difficulty of recognizing large-scale submarine-canyon deposits in outcrop.

Net Dextral Slip, Neogene San Gregorio-Hosgri Fault Zone, Coastal California: Geologic Evidence and Tectonic Implications: (W. R. Dickinson, M. Ducea, L. I. Rosenberg, H. G. Greene, S. A. Graham, J. C. Clark, G. E. Weber, S. Kidder, W. G. Ernst, and E. E. Brabb)

One of the world's most dangerous faults, the San Andreas, lies along the “Ring of Fire,” yet is not directly influenced by modern subduction action and is in a region of California that is without the presence of active, or even intact, volcanoes. In the future, the behavior of this great fault system may jeopardize the lives of millions of people, and yet the nature of seismicity in this central section of the San Andreas has its own special character. It comes to this reviewer that the broad and segmented nature of the Santa Lucia Range likely absorbs and, perhaps, diffuses considerable transient tectonic stress with its own poorly understood potential for generating large, damaging earthquakes. Furthermore, this portion of California is one of the world's most highly complex tectonic jigsaw puzzles, and the authors have provided the first truly coherent interpretation of how the region is traversed by the San Andreas and its sister splay, the San Gregorio-Hosgri Fault Zone. This special paper offers great, broad value to those practicing in the field of engineering seismology, which is, in my opinion, a valid discipline of engineering geology. In this …

Variscan to eo-Alpine events recorded in European lower-crust zircons sampled from the French Massif Central and Corsica, France

Ion-microprobe U–Pb zircon dating of lower-crust metasedimentary granulite are reported on samples from two localities in Europe in order to determine (a) how this environment recorded the Variscan and eo-Alpine events, and (b) whether the transition between the two orogenic cycles was continuous or separated by a gap. The samples come from enclaves hosted by Miocene volcanoes at Bournac in the French Massif Central, and from the granulitic metasedimentary basement of the Alpine Santa Lucia nappe in Corsica, on the South European paleomargin of the Ligurian branch of the Tethys Sea. The zircon ages from Bournac range between 630 and 430 Ma and between 380 and 150 Ma with a major frequency peak at 285 Ma; the zircons older than 430 Ma are interpreted as detrital, whereas those younger than 380 Ma are considered to have formed by metamorphic processes after burial in the lower crust. Zircon ages from Santa Lucia range from to 356 to 157 Ma, with exception of one inherited Archean grain, and are interpreted like the younger Bournac zircons as having been formed by metamorphic processes. In a granulite metamorphic environment, as opposed to an anatectic environment, new zircon growth can occur in the solid state. Once Zr has been incorporated into zircon, however, it is difficult to remobilize without dissolution; thus Zr available for new zircon growth must result from the breakdown of Zr-bearing minerals during prograde and/or retrograde events. In this light, the U–Pb zircon-age probability curves are interpreted as markers for major tectonometamorphic events, as suggested by the close correspondence between peaks in the curve and geological events recorded in the upper-crust, such as magma emplacement and basin subsidence. Evidence of a tectonometamorphic gap between the Variscan and Alpine orogeneses is provided by the Santa Lucia zircon-age probability curve, which reveals a probable interlude during the Variscan–Alpine transition between 240 and 210 Ma. Here, the peak at 240 Ma is interpreted as the very beginning of crustal extension and the low at 210 Ma as a period of quiescence prior to the formation of an active margin and oceanization.

Moist Dynamics and Orographic Precipitation in Northern and Central California during the New Year’s Flood of 1997

Abstract The dynamics of moist orographic flows during the January 1997 floods in northern and central California are investigated using numerical simulations computed with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Early in the event (31 December 1996–1 January 1997), the low-level winds offshore of California’s central coast were blocked by the topography of the Santa Lucia Range, and the low-level winds in the Central Valley were blocked by the topography of the central Sierra Nevada Range. In contrast, moisture-laden winds along the northern Coast Ranges and the northern Sierra Nevada flowed over topographic barriers. As the core of humid air migrated to the south over 24 h, the low-level barrier jets weakened as the atmospheric stability decreased, bringing heavy rainfall to the central and southern Sierra Nevada at the end of the event. The heavy precipitation during this event was largely controlled by the interaction of the flow with topography, with little contribution from non–topographically forced dynamical uplift. Latent heating was essential for lowering the effective stability of the flow and allowing the winds to flow over mountainous terrain, particularly in the northern Coast Ranges, and for enhancing the low-level jet and associated moisture transport. The horizontal distribution of static stability played a key role in the event by setting up a complex combination of flow-over and flow-around regimes that enhanced uplift in the northern Sierra Nevada during the period of heaviest rainfall.

Report of the Sixty-Seventh Annual Meeting, San Luis Obispo, California, September 8-11, 2004

Report of the Sixty-Seventh Annual MeetingSan Luis Obispo, California September 8–11, 2004 Jim Keese, APCG 2004 Conference Coordinator The 67th Annual Meeting of the Association of Pacific Coast Geographers was held on the campus of Cal Poly State University, San Luis Obispo, September 8–11, 2004. Approximately 200 attendees enjoyed brilliant weather in the mid-80s on California's central coast. The Business Building complex was the meeting site and offered spectacular views of two of the Morros (Cerro San Luis and Bishop's Peak). The conference opened with tributes to Bill Loy (given by Alexander Murphy) and Tom McKnight (given by Lay Gibson). The opening session was titled "Conserving Open Space and Resources on the Central Coast." Neil Havlik (City of San Luis Obispo), Dan Berman (Morro Bay National Estuary Program), and Kara Blakeslee (American Land Conservancy) spoke on greenbelt land acquisition, watershed management, and conserving the 82,000-acre Hearst ranch. Four field trips highlighted the open spaces and the varied coastal and rural landscapes of the region. Jennifer O'Brien led a trip to the Hearst Castle, San Simeon, and Ragged Point. Jorge Lizarraga and Bob Hoover took a group to Mission San Antonio, which also included a transect of the Santa Lucia Range, a drive down the southern Big Sur coastline, and lunch at the former Hearst hunting lodge (which was designed by Julia Morgan). Cal Wilvert led a trip that blended themes in physical and cultural geography, with stops at the Pismo Dunes and the town of Guadalupe in the Santa Maria Valley. The final trip, led by Jim Keese, traveled through the emerging wine region of Paso Robles and explored the theme of the Spanish imprint on California and the new grapescape. Field-trippers returned to the Thursday evening dinner and reception on the creekside terrace at Novo Restaurant, adjacent to Mission San Luis Obispo and the city's world-famous farmers' market. Friday and Saturday featured 81 papers and 10 posters in 19 sessions. The quality of the papers was outstanding, and participation by students was high. The President's Plenary Session was titled "Major Directions in the Future of Population Geography of the Pacific [End Page 126] Coast." David Plane moderated a panel that included James Allen (California State University, Northridge), Patricia Gober (Arizona State University), and Waldo Tobler (University of California at Santa Barbara). At the President's Reception on Friday evening, AAG President Victoria Lawson gave an update on AAG issues. At the Saturday banquet, 101 participants were treated to a full-service dinner in the Garden Room at the fabulous Madonna Inn. APCG President David Plane enlightened and entertained us with his Presidential Address on "The Conditions of Coastality." The geographers at Cal Poly, San Luis Obispo, wish to thank the APCG and everyone who attended for the opportunity to host the 2004 annual meeting. We were honored to be chosen, and it was a pleasure for us to show off a place that we hold so dear. We look forward to seeing you at the 2005 meeting in Tempe. Respectfully submitted, Jim Keese, APCG 2004 Conference Coordinator Copyright © 2005 University of Hawai’i Press

Abstract: The Rocks Sandstone Member, Reliz Canyon Formation, Northern Santa Lucia Range, California: Internal Facies Architecture of a Sand-Rich, Deep-Sea Depositional System

Abstract: The Rocks Sandstone Member, Reliz Canyon Formation, Northern Santa Lucia Range, California: Internal Facies Architecture of a Sand-Rich, Deep-Sea Depositional System

Orthopyroxene‐bearing, mafic migmatites at Cone Peak, California: evidence for the formation of migmatitic granulites by anatexis in an open system

Abstract Orthopyroxene‐bearing migmatites, exposed at the summit of Cone Peak in the Santa Lucia Range, California, offer an opportunity to explore potential links between granulite facies metamorphism and migmatite formation. Geothermobarometry indicates that the metamorphic temperatures and pressures were in the approximate ranges of 700–750° C and 7.0–7.5 kbar. The rocks at the summit comprise three domains: relatively coarse‐grained, leucocratic veins; relatively fine‐grained, biotite‐enriched zones at the margins of the veins; and a biotite–hornblende‐bearing host rock. Orthopyroxene is concentrated in the veins, which have also the highest ratio of anhydrous to hydrous minerals of the three rock types. The composition of the veins, together with their textures and modes, suggest that they formed through anatexis involving a dehydration‐melting reaction which consumed hornblende and produced orthopyroxene. Variability in mineralogy and composition indicates that there was some local migration of magma along the veins before their final solidification. The biotite‐enriched zones formed either by the concentration of residual biotite at the margins of the vein, or through the metasomatic conversion of hornblende (and/or pyroxene) to biotite, or by a combination of the two processes. Significant differences in the chemistry of the neosome (vein + biotite‐enriched zone) and the host rock rule out simple dehydration melting in a local closed system. The model that explains best the mineralogical and chemical patterns involves triggering of melting by an influx of a low‐aH2O mixed fluid which added K and Si to and removed Ca from the neosome.

Late Cenozoic Fold and Thrust Belt of the Southern Coast Ranges and Santa Maria Basin, California (1)

Balanced cross sections across the Santa Maria basin and southern Coast Ranges of California show the Pliocene to Quaternary convergence to be a developing basement-involved fold and thrust belt. The fold and thrust belt is seismically active as evidenced by compressive earthquakes, geodetic measurements of present shortening, and folded Quaternary deposits. The Pliocene and Quaternary structure of the southern Coast Ranges is dominated by a series of large anticlinal structures that include the Lompoc-Purisima trend, the Casmalia-Orcutt trend, the Point San Luis anticline, the Santa Lucia Range anticlinorium, and the La Panza Range anticlinorium. The anticlinal trends are interpreted to be fault-bend and fault-propagation folds resulting from thrust ramps off thrust flat and a regional detachment at 11-14 km depth. Most of the thrust faults do not reach the surface (blind thrust). The southwestern range front of the San Rafael Mountains is interpreted to be the result of uplift above a ramp in the Point San Luis thrust. The cross section across the southern Coast Ranges shows 26.8 km of shortening from the edge of the continental margin to the San Andreas fault. Region-wide shortening is interpreted to have begun between 2.0 and 4.0 Ma, which yields an average regional convergence rate of 6.7-13.4 mm/yr. The late Pliocene and Quaternary convergence across the onshore Santa Maria basin is interpreted to be 9.2 km and the average convergence rate is 2.3-4.6 mm/yr. Compressive focal mechanisms and our structural analysis suggest that the ramp parts of the thrust system are the most likely sources for earthquakes. The historic seismic record and length of the anticlinal trends suggest that the thrust ramps probably are capable of generating moderate to large earthquakes (5.0<M[W]<7.5). Major thrust ramps underlie the city of San Luis Obispo and adjacent coastal towns. Cross section restoration reveals early formed hydrocarbon traps and accounts for the abundant hydrocarbon accumulations along the Casmalia-Orcutt anticlinal trend and under the Santa Maria Valley. The cross sections and restorations also illustrate the importance of Miocene and early Pliocene normal faults to oil maturation and trapping. Concealed normal faults along the flanks of the major anticlinal trends and the subthrust area along the north side of the Casmalia-Orcutt anticlinal trend form two relatively untested trap styles.

Phanerozoic granulites

Granulites can form at every stage of the Wilson cycle: during plate accretion (Mid-Atlantic Ridge), in active plate margins of island-arc and Andean type (Ivrea Zone, main complex in Kohistan in the Karakorums), in the roots of Andean-type batholiths (Coast Range Complex, British Columbia; Santa Lucia Range of California), during the closure of a marginal basin (Aracena belt, Spain), during Himalayan-type collision (Jijal Complex in the Karakorums of N Pakistan and at I’Agly in the Pyrenees) and during post-tectonic intrusion at depth(Sä0 Paulo, Brazil). Himalayan-type orogenic belts may, in principle, contain any of such granulites. The majority of granulites form along active plate margins in the roots of magmatic arcs, which are the main sites of crustal growth in the Phanerozoic. Layered stratiform complexes, formed largely by cumulate processes, are common in Phanerozoic granulites (Kohistan, Ivrea, Calabria in Italy, Cabo Ortegal in NW Spain, Brittany and N Pyrenees). Their granulite-grade parageneses may have formed during cooling from an igneous temperature, or during superimposed metamorphism. Variations in the types of granulites may help in understanding how different types of lower continental crust are constructed.

The Rocks Sandstone, an Eocene Sand-rich Deep-sea Fan Deposit Northern Santa Lucia Range, California

ABSTRACT The Rocks Sandstone of Thorup (1941), which crops out in the northern Santa Lucia Range, was deposited as a deep-sea fan in a restricted Eocene continental borderland basin. It is as thick as 640 m and consists primarily of medium-grained sandstone with interbedded mudstone and conglomerate. The average grain size and bed thickness increase toward the east, where The Rocks Sandstone is overlain by the nonmarine to shallow-marine Berry Formation and underlain by the deep-marine Lucia Mudstone of Dickinson (1965). To the west, The Rocks Sandstone thins and is overlain by the deep-marine Church Creek Formation and is underlain by the deep-marine Lucia Mudstone. Foraminifers from underlying and overlying units indicate a late early Eocene (Ulatisian) to middle Eocene (Narizian) age for Th Rocks Sandstone and deposition in a moderately deep basin connected to the open ocean. Thick channelized sandstone sequences typical of a middle-fan facies association characterize The Rocks Sandstone. Beds consist primarily of facies B and locally facies A of Mutti and Ricci Lucchi (1972, 1975) and contain graded beds, sole marks, dish structures, and other sedimentary structures indicative of deposition by sediment gravity flows. Amalgamated sequences of thick-bedded sandstone form fining- and thinning-upward channel deposits. These sequences appear to form anastomosing bodies of sandstone that directly overlie basin-plain deposits of the Lucia Mudstone. The middle-fan channel sequences are commonly superposed upon one another, forming thick sections that have very high sandstone-to-shale ratios. Interchannel deposits are relatively rare within these sandstone sequenc s, but where present consist of repetitive, thin, alternating beds of fine-grained sandstone, siltstone, and mudstone dominantly of Multi and Ricci Lucchi facies D and E beds. The minimal development of the outer-fan facies association and difficulties in separating the middle- and inner-fan facies associations characterize this sand-rich borderland-type deep-sea fan deposit. Deposition of large amounts of sand abruptly at the base of slope apparently resulted in a fan characterized chiefly by the middle-fan facies association. Without sufficient clay-sized sediment, turbidity currents that travel long distances and deposit outer-fan and basin-plain turbidites apparently did not develop. The petrographic data indicate derivation mainly from felsic plutonic rocks, with a minor contribution from volcanic rocks. Paleocurrent, thickness, and stratigraphic data indicate primarily northward and westward sediment transport. A granitic source terrane, located to the east and southeast, and probably comprising parts of the Salinian block and possibly part of the present Mojave Desert area, is suggested by the petrography and paleocurrents.

Age, origin, and thermal histories of some plutonic rocks from the Salinian block of California

U-Pb isotopic measurements on zircons from some granitic rocks of the Salinian block indicate emplacement and crystallization of these rocks about 104 m.y. ago (mid-Cretaceous). The relatively radiogenic nature of initial Sr and common Pb in these rocks, and the presence of an inherited component of zircon in some of them strongly suggest the involvement of continental crust in the genesis of the magmas. Possibly the magmas were generated in a zone of melting that overlapped the boundary between the mantle and the continental crust. U-Pb measurements on sphene, apatite, and feldspar from the plutons, along with previously published K-Ar and fission-track ages shed light on the post-emplacement thermal histories of the plutons. Most of the samples from the northern part of the Salinian block (Bodega Head, Point Reyes) show relatively simple thermal histories. Evidently these plutons were emplaced at moderate levels in the crust, crystallized, and cooled to moderate temperatures over an interval of about 10–15 m.y. Plutons from the central Salinian block (Santa Lucia Range) show more complex and prolonged thermal histories. These plutons evidently were emplaced at greater depths in the crust than were the plutons from the northern Salinian block. They remained at elevated temperatures for ca. 25 m.y., then cooled fairly rapidly, probably as a result of rapid uplift and erosion. One sample from the northern Salinian block shows an even longer span of time between emplacement and cooling. The thermal evolution of the Salinian plutonic rocks predates major offset along the San Andreas fault zone and thus reflects the thermal evolution of the undisrupted source terrane of the Salinian block. Isotopic measurements of the type reported here might therefore prove valuable in correlations across the San Andreas fault zone. Moreover, detailed study of thermal evolution within the Salinian block could shed light on major offsets within the block.

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

Research Article| November 01, 1974 Franciscan Rocks near Sur Fault Zone, Northern Santa Lucia Range, California: Reply 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 GSA Bulletin (1974) 85 (11): 1826. https://doi.org/10.1130/0016-7606(1974)85<1826: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: Reply. GSA Bulletin 1974;; 85 (11): 1826. doi: https://doi.org/10.1130/0016-7606(1974)85<1826: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 No Abstract Available. 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.

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

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

Modified Contour-Generalization Procedure As Applied to the Santa Lucia Range, California

Research Article| October 01, 1973 Modified Contour-Generalization Procedure As Applied to the Santa Lucia Range, California ARTHUR D. HOWARD ARTHUR D. HOWARD 1Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Author and Article Information ARTHUR D. HOWARD 1Department of Geology, Stanford University, Stanford, California 94305 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): 3415–3428. https://doi.org/10.1130/0016-7606(1973)84<3415:MCPAAT>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 ARTHUR D. HOWARD; Modified Contour-Generalization Procedure As Applied to the Santa Lucia Range, California. GSA Bulletin 1973;; 84 (10): 3415–3428. doi: https://doi.org/10.1130/0016-7606(1973)84<3415:MCPAAT>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 Contour generalization is an established procedure for restoring dissected landscapes to predissection forms. The modified generalization procedure herein proposed dispenses with most side-slope contours, leaving upland surfaces suspended at their individual levels. In addition, sequential cartographic patterns permit ready recognition of surfaces, and hachures emphasize abrupt peripheral slopes.Although the primary purpose is to discuss the proposed procedure, the bearing of the final map on the history of the Santa Lucia Range is briefly considered. The origin of the high-level surfaces has not yet been determined, although fragmentary evidence suggests they are probably fluvial. The multiple surfaces were presumably developed in response to changes in the elevation of base level. Simultaneous development of the surfaces due to differential lowering of rocks of varying resistance, independent of base level, is refuted by the similarity of the rock assemblages truncated by the different surfaces. The high surfaces in the northern part of the range are found to be sloping, rather than horizontal as previously supposed. Tilting of the northern area seems indicated. At their elevated southern ends, these surfaces hang above considerably lower terrain. Here, the relative horizontality of at least one extensive surface suggests simple vertical uplift. 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.

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.