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No description available.

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No description available.

The Kootenay Arc in northeastern Washington and southeastern British Colunbia is transitional between: (1) lower Paleozoic autochthonous miogeoclinal strata and Paleozoic to Mesozoic eugeoclinal terranes of uncertain paleogeographic affinity (e.g., the Quesnel terrane): and (2) areas where Devono-Mississippian tectonism was of a compressional nature (Antler Orogeny in central Nevada), and areas in northern British Columbia and southern Yukon Territory where coeval deformation was evidently of an extensional nature. The nature of these transitions was addressed by study of lower Paleozoic eugeoclinal strata comprising the portions of the Kootenay terrane, the most inboard of the terranes in the Canadian Cordillera, and it's contact relations with miogeoclinal strata. Stratigraphic, structural, and U-Pb geochronologic studies focussed primarily on portions of the Lardeau Group in the Trout Lake area in the northern Kootenay Arc and the Covada Group in the southern Kootenay Arc. As a result of these studies, the following concepts are proposed: (1) lower Paleozoic eugeoclinal strata can be correlated along the length of the Arc; (2) these strata are in fault contact with miogeoclinal strata along the length of the Arc: (3) a contractional event of pre-Mississippian and perhaps Devono-Mississippian age is recorded in the Kootenay Arc: (4) despite faulted oontacts, the eugeoclinal strata are parautochthonous and derived from adjacent portions of North America; and (5) structures and stratigraphy in the Kootenay Arc are broadly correlative with those in the Roberts Mountains allochthon in central Nevada. Two important implications of this study, requiring revisions to theories regarding the more general problem of Cordilleran accretion are that: (1) through a series of stratigraphic linkages it can be demonstrated that the Quesnel terrane, a Mesozoic arc-related assemblage often regarded on the basis of faunal evidence to be "exotic", is parautochthonous; and (2) the Antler Orogeny, often regarded as a localized disturbance, affected at least 1200 km of the Cordilleran margin, and perhaps the entire Cordilleran margin.

Geologic mapping and analysis of Oligocene-Miocene sedimentary rocks in the upper plate of the Buckskin-Rawhide detachment fault system (west-central Arizona) reveal a complex paleogeographic history during fault displacement, involving shifting sediment-source areas and multiple drainage reversals. Within the study area, four upper-plate fault blocks are capped by homoclinal sedimentary sections that display fanning dip relationships indicating concurrent tilting and sedimentation. Four sedimentary assemblages can be correlated between fault blocks on the basis of lithologic similarity, stratal position, provenance, paleocurrent data, and sparse geochronologic constraints. Detritus within the basal assemblage was derived from the granitic terrane surrounding the northern part of the study area. The overlying lower assemblage contains voluminous quantities of sedimentary breccia that were derived from source areas consisting mainly of Mesozoic and Paleozoic rocks exposed to the south of the study area. Middle-assemblage sediments were deposited by an extensive south-directed stream system that probably flowed off undistended parts of the hanging wall. Upper-assemblage sediments were deposited by a northeast-directed system of broad, shallow streams; these deposits display a variety of clast types, including Tertiary mylonitic rocks that were eroded from the upwarped footwall of the metamorphic core complex. During deposition of these sedimentary rocks, upper-plate sedimentation was intermittently confined to separate half-graben, while at other times rapid rates of aggradation relative to fault-displacement resulted in burial of ridges separating sub-basins. Evaluation of sedimentary breccia bodies contained within the lower assemblage in the Artillery Peak area indicates that r,nany are of rockavalanche origin. Some are sufficiently large to have represented large rock avalanches (that is, sfurzsfroms) at the time of emplacement and display features consistent with descriptions of such lobes. Some rockavalanche deposits interbedded with lacustrine sediments represent initially subaerial lobes that flowed into lakes. These bodies locally "are intruded by substrate-derived injection structures and contaminated by lakebed mud; mud contamination was initially concentrated along the bases of lobes, but affected a progressively greater proportion of the flows with increasing subaqueous runout. Contaminated portions of rockavalanche lobes exhibit features consistent with decreased shear strength, and thoroughly contaminated lobes appear to have transformed into slowmoving, slurry-like flows that experienced internal cycling of debris.

This research evaluates models of earthquake behavior and fault segmentation, by quantifying the rupture-magnitude pattern along the trace of coseismic surface rupture for each of four earthquakes. One is the 1983 (Ms = 7.3) Borah Peak, Idaho, earthquake and three are prehistoric. Two earthquakes occurred along each of the adjacent Thousand Springs and Mackay Segments (TSS and MS) of the Lost River fault in east-central Idaho, and within their intervening segment boundary. The apparent vertical slip-component (throw) was measured as the vertical separation of surveyed longitudinal profiles of faulted stream floodplains, terraces, and alluvial fans, and relative uncertainty in the measurements was obtained. The true vertical slip-component (VD) was calculated to account for geometric distortion in throw data. Knowledge of fault dip is required, and was estimated using structural contour models of the fault. The preferred model relies on the measured orientation of the 1983 net-slip vector at a faulted-fence site, but the calculation is more dependent on profile gradient then on fault dip. The ages of faulted landforms are constrained by a dated soil chronosequence (in calibrated calendar years BP). The period of record is approximately ≈ 17 ky, the age of ubiquitous late-glacial fans. The Borah Peak surface rupture is 5 km longer than previously thought. 1983 rupture VD was uniformly approximately ≈ 2 m along the southeastern half of the TSS and penetrated the segment boundary with uniform VD of 0.5 m. The penultimate earthquake on the TSS occurred between 10 and 11 ka, and had rupture magnitude and location nearly identical to the 1983 earthquake. On the Mackay Segment (MS), an earthquake occurred at approximately ≈ 5 ka with ruptures penetrating the segment boundary. Apparently a previous event occurred between 12 and 17 ka. The cumulative VD for the period of record is uniform 4 to 4.5 m on both the TSS and the MS, but only 2 m ofVD in the segment boundary. There is no evidence for medium sized earthquakes. All the evidence can be explained by four nearly identical, large magnitude characteristic earthquakes on a segmented fault.

Chimney Creek is a sediment-hosted disseminated precious metal deposit located in the Osgood Mountains, Humboldt County, Nevada. It is the first large deposit of this type discovered in rocks affected by the Antler, Sonoma, and Nevadan orogenies and by Tertiary extension. The orebody is in alkalic basalts of the Mississippian Goughs Canyon Formation and the Etchart Limestone, a mixed siliciclastic-carbonate shallow-water sequence of Pennsylvanian- Permian age. These strata are bounded by the Devonian-Mississippian Roberts Mountain Thrust and the Permo-Triassic Golconda Thrust and are dissected by Nevadan and Basin and Range block faulting. The mid-Cretaceous Osgood Mountains Granodiorite intruded these rocks and a complex hydrothermal system evolved in which the Chimney Creek deposit and the other ore deposits of the Osgood Mountains developed. A magmatic-metasomatic auriferous CO₂-H₂O-CH₄ fluid of pH = 4 to 5 flowed upward along fractures in the Goughs Canyon Formation and spread out laterally along permeable beds in the lower member of the Etchart Limestone under a minimum pressure of 800 bars. Pathways in the basalt were armored with wide phyllic selvages and the carbonates were dissolved. Resulting space in the Etchart Limestone was partially filled by stratabound and stratiform silicification when the CO₂-H₂O-CH₄ fluid mixed with a dilute aqueous meteoric fluid and Au was deposited. On average, high enthalpy silica undersaturated solutions removed quartz from the deposit core and low enthalpy silica saturated solutions deposited quartz at the margin, so an outer annulus of bedded jasperoid surrounds a sanded core. This acid-sulfate alteration converted detrital feldspars and illite to phyllosilicates and sulfates in an area at least one kilometer in diameter coincident with conodont CAIs of 4 to 5 and fracture densities greater than 0.2 cm⁻¹. Chimney Creek is a mesothermal fluid mixing acid sulfate sediment-hostel precious metal deposit that formed along with skarn and hot spring type deposits as the Osgood Mountains Granodiorite cooled.

The effect of altitude on individual storm precipitation in some of the San Dimas experimental watersheds is investigated. It is found that there is a well-defined increase of storm precipitation with altitude for storms greater than one inch. This increase is a linear function of storm depth. Using 41 storms of different magnitudes, a precipitation-altitude relationship is derived for a small area in the San Dimas Experimental Forest. The regionalization of this relationship and its transferability are tested by analyzing differences (errors) between computed and observed storm precipitation values in each case. In testing the regionalization of the precipitation-altitude relationship by computing mean areal storm precipitation over a larger area the standard error of estimate is around 11 percent. In transfering the same relationship the results are not as good and give a standard error of 16 percent. For individual points, however, the error is much higher. A rainfall-runoff model is used as a tool for evaluating the effect of precipitation errors, on simulated streamflow, in a watershed of 4.5 square miles. For annual flows, errors range between 3.4 and 12. 8 percent while errors in simulated monthly flows are as high as 22 percent. It is also evident that there is a strong dependence of the error magnitude on the state (wet, dry, etc.) of the preceding year or months, whichever is applicable. An error propagation is observed as a result of consistently over-estimating the precipitation input to the model. This evaluation is more of a qualitative nature and the values of error given should he viewed in this sense.