In the Santa Clara Avenue oil field, the nonmarine Sespe Formation of Oligocene age has produced 4 million barrels of oil trapped by a Miocene mafic igneous intrusion that cuts across bedding. Throughout most of the oil field, the Miocene and older beds dip about 15° northwest. The intrusion may be related to the outpouring of Conejo Volcanics throughout much of the southern Ventura basin. The Pacific Farms #1 well penetrated 1000 feet of igneous rocks below 5100 feet, whereas wells less than 500 feet to the northwest penetrated Sespe Formation over this interval. The western wall of the intrusion is located by 10 wells which pass repeatedly through the Sespe-intrusive contact. Structure contours on the intrusive contact with the Sespe on the northwest show Redacted for Privacy that the contact varies from N20°E,80°SE in the southern portion of the field, to N90°E,85°S in the northern end of the field. The southeast wall of the intrusion is not cut by wells, but its location is controlled by a well about 1200 feet southeast of the northwest wall. If the intrusive contact is rotated to its position when it was intruded prior to tilting of the middle and late Miocene Modelo Formation, the Sespe overhangs the igneous body along a contact with a paleo-dip of 80°NW. Lateral closure in the field may be due to early Miocene normal faulting of the Sespe Formation. In the Las Posas area, two faults are documented. Both faults cut the entire Miocene section but do not cut the Pliocene-Pleistocene Pico Formation. The Miocene Vaqueros is found only on the south side of the Las Posas fault. Intra-Sespe correlations show that the upthrown block of the Las Posas fault lost to erosion 1000 feet of Sespe in addition to the Vaqueros Formation. The Epworth syncline and Beryiwood anticline were folded prior to the deposition of the Pico Formation. / Graduation date: 1986

Surface and subsurface data indicate that Cretaceous strata in the southern Ventura basin are part of the northward prograding Chatsworth submarine fan. The fan extends westward as far as Trancas Beach in the Santa Monica Mountains and wells in the Oxnard Plain and on Oak Ridge. The eastern edge of the fan is constrained by wells in western San Fernando Valley which contain fine-grained strata which may have been deposited east of the Chatsworth fan. The Nonmarine Simi Conglomerate overlies the Cretaceous and is itself overlain by Paleocene marine beach sandstone and siltstone. These marine strata do not extend eastward into the San Fernando Valley. The lower Paleocene and Cretaceous strata were overlapped by the upper Paleocene Santa Susar1a and middle Eocene Liajas Formations. Sedimentation patterns for the Santa Susana and Llajas may be explained by two models: (1) A northwest-trending submarine ridge on which muds and silts were deposited, was flanked on the northeast and southwest by troughs receiving deep-water sands. (2) Both formations were deposited on a southwest-facing shelf, slope, and turbidite trough. Subsurface data important in basin analysis include 1) bathyal paleo- bathymetry for the entire Santa Susana, 2) sand channels in the Santa Susana which possibly funneled sediment westward down a submarine slope, 3) shelf-facies(?) Eocene strata with neritic to upper bathyal paleobathymetry in Oxnard Plain, and 4) Llajas fades in northern Simi Valley suggesting gradation upward from a shallow marine to outer shelf or slope environment. Facies correlations across the Simi fault indicate no large-scale post- Paleogene strike-slip displacement. If these sequences were rotated, as suggested by paleomagnetic data, the restored Cretaceous fan would come from the east and the restored Paleocene shoreline would face south. Thus paleogeography for the Cretaceous is simplified by the rotation hypothesis, but Paleocene paleogeography is made more complicated. / Graduation date: 1983

Five lithologic units, ranging in age from Middle Miocene to Recent, are defined on the basis of continuous seismic reflection profile records. Two of the units are Miocene sedimentary and volcanic rocks that have been truncated to form a major unconformity (post-orogenic surface) related to the most recent major tectonism of the region. The remaining units are post-orogenic unconsolidated sediments. The fault pattern offshore is generally related to that exhibited on the island. The pattern conforms to a wrench-fault system hypothesized by Moody and Hill (1956) modified by a general north-south tensional fracturing. The San Clemente Fault is assumed to be the primary wrench fault of the system. Anomalies in the thicknesses and the structure of the unconsolidated sediment and rock units tend to confirm the structural model. A canyon (Eel Ridge Canyon) off the west side of San Clemente Island appears to have been caused by pivotal faulting and erosion, and represents a boundary between different structural trends north and south. A prominent terrace around the island is postulated to have been wave-cut during and since the Late Pleistocene. The island has been tilted slightly to the west by Recent tectonism. A steep magnetic gradient off the east side of the island is considered the consequence of faulted volcanic flows comprising the island itself and a deep basic rock mass responsible for a large positive magnetic anomaly off the northwest side. Other magnetic anomalies reflect major structural trends. Earthquake epicenter data suggest a recent and possibly cyclical occurrence of fault activity in the northern Continental Borderland region and the study area. Fault offsets at the sea floor and earthquake epicenters along the San Clemente fault zone imply recent adjustments along the fault. Wrench-fault movement resulting from a simple shear or shear couple is considered to have caused the zone of brecciation along the San Clemente Fault and produced the fault-trace curvature so evident in a series of en echelon, northwest-striking major faults of the Borderland. Tensile release during periods of wrench-fault development has been a fundamental factor in the structural development of the Borderland basins. The entire structure of the Continental Borderland is believed to have developed by right-lateral movement along the series of wrench faults. These faults are believed to have resulted from a translation of force by sea-floor spreading originating on the East Pacific Rise in the Gulf of California region. This force is considered to have moved a northern Continental Borderland crustal plate westward by east to west release along major wrench faults bordering the north and south ends of this plate. Sediments, transported along channels developed along faults in the island block, were deposited in basins developed by faulting and folding of the pre-orogenic rocks. Transportation appears to have been by means of turbidity-current flows, sand flows, and slides. A maximum average depositional rate of 35 to 47 centimeters per 1,000 years is estimated for post-orogenic sediments. The following findings are suggested for inclusion in the Neogene history of the island: (1) the top 365 meters of Miocene andesitic lavas were deposited above sea level and tend to become slightly more basic in composition with depth; (2) subsidence of the island region and temporary sea-level stand(s) occurred after the deposition of the volcanic rocks, with possible periods of foundering to about the Late Pliocene; (3) emergence, lengthy subaerial exposure, and a period of partial submergence took place from about Late Pliocene through Early Pleistocene; (4) a north-south compressive force developed or recurred across the Borderland during Late Pliocene, developing the present northwest-southeast and east-west wrench-fault systems that have been intermittently active to the present time; (5) much of the present Borderland topography formed during the Pleistocene to Recent. / Graduation date: 1969

Detailed mapping and geochemical analysis of Oligocene to early Pliocene volcanic rocks in the Little Walker volcanic center, Mono County, California have revealed a complex eruptive history. After eruption of widespread rhyolitic ash flows of the Valley Springs Formation in the Oligocene, Miocene to early Pliocene volcanism of the western Great Basin and northern Sierra Nevada was dominated by eruption of calc-alkalic, andesitic lavas bearing abundant hydrous mafic phenocrysts, and, thus, high H���O contents. These kinds of calc-alkaline magmas are associated with most of the major epithermal Au-Ag districts of the western Great Basin. A highly potassic latitic pulse of volcanism occurred at the Little Walker volcanic center about 9.5 m.y. ago during the ongoing calc-alkalic activity. The latitic series is unusually enriched in K and other incompatible elements, as well as Fe compared to the surrounding calc-alkaline rocks. The latites have mineralogic evidence of much lower H���O content than the calc-alkaline lavas; yet early latitic magmas were rich enough in volatiles to produce very large, welded ash-flow sheets (e.g., the Eureka Valley Tuff). Rapid evacuation of the magma reservoir beneath the Little Walker center during the ash-flow activity resulted in formation of the Little Walker caldera. Intracaldera volcanism culminated with extrusion of viscous, phenocryst-rich plug domes and coulees of transitionally calc-alkaline, low-K latite lava of the Lavas of Mahogany Ridge. The low-K latite series is severely depleted in all incompatible elements relative to early latitic rocks and has mineralogic, geologic, and trace element evidence of higher H���O content relative to early latites. Significant phenocrystic hornblende, association with hydrothermal alteration, and high Eu����� /Eu����� all suggest significant H���O concentration in the low-K latite magmas. These rocks probably come from a source region intermediate between that of the calc-alkaline and latite series. Trace and major element data favor generation of latitic magmas from a primitive mantle diapir. The diapir rose into a subduction zone that was actively generating widespread calc-alkalic lavas throughout the region from hydrous mantle and, possibly, lower crustal sources. The latite magmas were drier and hotter than the calc-alkaline magmas, but were also enriched in volatiles, particularly CO���, and incompatible elements from their undepleted mantle source. Rising latitic magmas may have gained additional incompatible elements by wall rock reaction and zone refining of upper mantle and lower crustal rocks. Extensive qualitative trace element evidence of crystal fractionation shows that incompatible elements may have been further concentrated by variable amounts of crystal settling. High-pressure (plagioclase-poor, pyroxene-rich) fractionation of the early, dry latitic series produced low-Ca-Mg latites with high Fe/Mg and A1���0��� but low Si0���. Low-pressure (plagioclase rich) differentiation of the early latitic magmas produced quartz latite ash flows with high Si0��� and moderate Fe/Mg, while low-pressure differentiation of hydrous low-K latite magmas yielded silicic low-K latite and quartz latite lavas with low Fe/Mg. More extensive separation of olivine relative to pyroxenes at low pressures and increased stability of subsilicic hydrous crystals and Fe-Ti oxides in the hydrous magmas account for changes in differentiation trends caused by Ptotal and PH���O variations. Lack of giant welded ash-flow sheets in the hydrous calc-alkaline series and common eruption of such ash flows from volcanic centers with rather anhydrous magmas led to the conclusion that H���0/CO��� as well as total volatile content are critical controls on the likelihood of large scale, hot ash-flow eruptions. Giant, hot ash-flow sheets and associated calderas are favored in magmas with low H���0/CO��� and high total volatile content. Basaltic and latitic volcanism in areas of thick sialic crust, where crystal fractionation is extensive are, therefore, the best sources of giant ash-flow sheets. H���0/CO��� and total volatile content were also critical controls of the probability of hydrothermal ore deposition. Magmas with high H���0/CO��� and moderate total volatile contents are most favored for ore deposition, because such magmas tend to form mesozonal or epizonal plutons rather than volcanic rocks. Plutonic crystallization of hydrous magma will yield a fluid phase capable of transferring incompatible metals and geothermal heat to ground water. If permeable structures and rocks are present, as in a caldera, widespread mineralization will be favored, but there may be no genetic relation between ore-forming magmas and magmas which produce calderas. / Graduation date: 1980 / For master (tiff) digital images of maps contained in this document contact scholarsarchive@oregonstate.edu

A multidisciplinary investigation into the timing, distribution, and intensity of tectonothermal events has resulted in an understanding of the tectonic evolution of the northeast Sacramento Mountains, in particular, and of the northern Sacramento Mountains in general. The application of geologic, structural, geochemical, and thermochronologic techniques has provided the relative and absolute timing of crustal and tectonic processes, leading to the development of a petrogenetic model for the evolution of the Sacramento Mountains metamorphic core complex. The metamorphic core complex was uplifted and cooled during Miocene detachment faulting (-23- 12 Ma). The Eagle Wash Intrusive Complex, a calc-alkalic granodioritic intrusion, was emplaced during detachment faulting at -20 Ma, at -3 kb and ~680°C. The EWIC records rapid cooling and uplift following emplacement, at rates of >100°C/Ma and 1.5-3 km/Ma, respectively. The EWIC was below ~100°C (the closure temperature of fission tracks in apatite) by 15 Ma. The structural and thermal history for the syntectonic intrusive suite is best explained via an evolving simple shear zone. The EWIC was intruded into, or proximal to, a mylonitic shear zone. The SW dip of the myonitic foliation in the EWIC could represent a primary feature of the shear zone, or the capture of a relatively older feature by a younger detachment fault splay. The later interpretation is consistent with the thermochronologic data, which suggests that faulting continued in the east after its termination in the west. Using the thermochonologic data to develop a thermal profile of the crust, the angle of faulting was calculated to be <30°C. The slip-rate associated with the detachement fault, though poorly constrained, was determined to be -4 mm/yr. This value is about half that determined from other core complexes and suggests that extension was slower here than elsewhere in the region.

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Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 309-324. / Ph.D.