Late Permian kuroko-type mineralization in the Bully Hill area of the East Shasta district formed along two horizons within the Bully Hill rhyolite. In the Bully Hill, Rising Star, and Copper city mine areas, syngenetic mineralization is underlain by alteration zones characterized by addition of SiO₂ and K₂O, loss of NaCO, CaO, and Fe₂O₃* , and the assemblage quartz + sericite + pyrite. Quartz precipitation in the upper portion of the zones led to cyclic sealing of fluid flow, rupturing of the seal, quartz supers aturation, focused fluid discharge, and formation of sulfide mounds on the seafloor. Syngenetic mineralization occurred in several stages: (1) deposition of fine-grained banded sulfides and gangue; (2a) recrystallization of Stage 1 minerals, and void-filling by pyrite + weakly chalcopyrite-diseased sphalerite ± barite; (2b) deposition of coarsely-crystalline pyrite + heavily chalcopyrite-diseased sphalerite; (3a) void-filling and replacement by galena + chalcopyrite + tetrahedrite-tennantite; (3b) replacement by chalcopyrite; and (4) replacement by barite. ΣSO₄⁼ and H₂S contents of hydrothermal fluids decreased from Stages 2a to 3a. δ³⁴S values of sulfides increased successively from Stages 1 (-15.8 per mil) to 3a (3.0 per mil), reflecting variable inputs of biogenic sulfur and deep-seated fluid evolution. δ³⁴S values of syngenetic barites range from 12.4 to 22.5 per mil, reflecting cold seawater and hydrothermal sulfur sources, respectively. δ³⁴S values of epigenetic pyrite and barite within the alteration zones range from -0.7 to 2.7 per mil and 12.4 to 24.1 per mil, respectively. Primary and pseudosecondary fluid inclusions in epigenetic minerals have filling temperatures of 240 to 260 °C and salinities of 3 to 12.3 equivalent weight percent NaCl. Lower limits of fluid salinities and δ³⁴S values of barite indicate that seawater was a primary component of the hydrothermal fluid, and that seawater also mixed with discharging fluids on the seafloor. High fluid salinities, the lack of a silica source, and the close link of magmatism with mineralization indicate that magmatic fluids may have been an important component of the hydrothermal fluids.

Different patterns of uniform-uplift periods associated with passage of the Mendocino triple junction (MTJ) and a change in tectonic regime are based on altudinal spacing analyses of nine flights of marine terraces. Rates of uplift appear to increase from <1 m/ka to 4-5 m/ka, with periods of most rapid uplift that are progressively younger toward the triple junction. The MTJ was about 55 km to the south at about 1 ma ago, where uplift has been uniform at about 1.3 m/ka during the last 300 ka. Maximum uplift of about 4 m/ka is occurring 20-40 km south of the MTJ; prior to about 100-150 ka uplift was slow, being only 0.2-0.5 m/ka. Ten km to the north of the MTJ, accelerated uplift has occurred only during the last 60 ka. Relative strength of soil development in sandy marine deposits on five Pleistocene and Holocene (1.7 to 120 ka) marine terraces near the MTJ is one basis for relative age estimates and correlation of terrace soils. Organic carbon content in the upper 70 cm of the soil profile increases exponentially, and pH decreases exponentially; for both properties steady state is attained by 40 ka. Whole profile content of clay, total free iron oxyhydroxides (Fe(d)), and total free and para-crystalline aluminum oxyhydroxides increase nearly linearly until at least 120 ka. Comparison of these soils with four marine terrace soils (103-405 ka) 100-120 km to the south indicates that maximum percent values of clay and Fe(d) increase exponentially, with highest values reached at about 120 ka. Analysis of three-dimensional morphological properties of 25 coastal drainage basins that have evolved in areas of low (<1 m/ka), intermediate (1-3 m/ka), and high (>3 m/ka) rates of uplift near the MTJ identified channel slopes as the best indicator of tectonism in the landscape. Lower order tributaries reflect tectonically-controlled differences best. The largest streams examined, of third order, are able to adjust to most base-level change and maintain their profile form, whereas lower order streams farther upstream tend to accumulate the effects of net base-level fall, and have steepest profiles in the areas of highest uplift. Although first order streams are excellent indicators of highest uplift rate areas and regional differential tilting, they are less useful in distinguishing between low and intermediate uplift rate areas. Analysis of the longitudinal profile of the main trunk stream of 10 of the 25 drainage basins with the stream-gradient index (Hack, 1957) was useful to broadly categorize uplift rates, and to distinguish between low and intermediate uplift rate streams.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The Diligencia Formation comprises approximately 1600 meters of OligoMiocene continental siliciclastic sedimentary rocks and intercalated basaltic lavas, located in the eastern Orocopia Mountains of southeastern California. These deposits exhibit characteristics which may link them to tectonic processes diagnostic of both the Basin and Range physiographic province of North America, and the Transverse Ranges province of California. These different processes were active, however, during different periods in the history of the formation. The early Diligencia Basin had an asymmetric half-graben geometry, and formed in response to presently north-south directed extension along a listric detachment located along the northern basin margin. Facies associations determined from five measured sections through the lower Diligencia Formation reveal a distinctly asymmetric distribution of facies across the basin. The deposits along the northern margin of the basin are characterized by cobble and boulder conglomerates and very coarse-grained sandstones unconformably overlying marine sedimentary rocks of the Eocene Maniobra Formation. These sedimentary rocks represent a high-gradient alluvial fan system which developed against the steep escarpment of the listric detachment fault. These deposits contrast with those present along the southern basin margin. The sedimentary rocks on the southern margin are characterized by pebble and cobble breccias, pebble conglomerates, very coarse- to fine-grained sandstones and gypsiferous mudstones. These facies define a system of low-gradient alluvial fans/fluvial braidplain that were deposited on the relatively gently sloping hangingwall block of the detachment, and that interfingered with deposits of a playa lake complex that formed in the basin interior. The age of these deposits, basin geometry, and the style of sedimentation are very reminiscent of half-graben basins known from the Colorado River Extensional Corridor of the Basin and Range. Paleomagnetic studies indicate that the block containing the Diligencia Formation may have been rotated more than 90° about a vertical axis since deposition ceased. In addition, regional palinspastic reconstructions indicate that the basin may have been significantly further north and east in the Miocene. These observations suggest that the Diligencia Basin may be genetically related to similar basins in the western Basin and Range, and that Diligencia Formation can be better understood if viewed in this tectonic context. Sometime after deposition had ceased, the rocks of the Diligencia Formation were deformed under an imposed compressional stress field in association with activity along the Clemens Well Fault, a major, dextral wrench fault in the region. The action of the Clemens Well Fault also juxtaposed the Diligencia Basin with distinctive crystalline terranes of the central and western Orocopia Mountains, including the Mesozoic Orocopia Schist. The association of these rock types with structures characteristic of dextral strike-slip deformation have led most workers to tie the Orocopia Mountains to similar complexes in the Transverse Ranges province of southern California. In fact, the post-depositional history of the Diligencia Formation can best be understood only in the context of Transverse Ranges-style tectonic processes. The complicated history of the sedimentary and volcanic rocks of the Diligencia Formation has made it difficult for previous workers to sort out an appropriate tectonic context in which to describe them. Recent advances in our understanding of the sedimentary responses to Tertiary rifting in the western Basin and Range, provide a new opportunity to evaluate the history of these deposits and this work has determined that the Diligencia Formation has had close ties to both the Basin and Range and the Transverse Ranges at different times during its complex history. / Master of Science