The distribution of radiogenic heat production as a function of depth in the Sierra Nevada Batholith, California   总被引：4，自引：0，他引：4  

Robert J. Brady  Mihai N. Ducea  Steven B. Kidder  Jason B. Saleeby 《Lithos》2006,86(3-4):229-244

Geochemical analyses and geobarometric determinations have been combined to create a depth vs. radiogenic heat production database for the Sierra Nevada batholith, California. This database shows that mean heat production values first increase, then decrease, with increasing depth. Heat production is 2 μW/m³ within the 3-km-thick volcanic pile at the top of the batholith, below which it increases to an average value of 3.5 μW/m³ at 5.5 km depth, then decreases to 0.5–1 μW/m³ at 15 km depth and remains at these values through the entire crust below 15 km. Below the crust, from depths of 40–125 km, the batholith's root and mantle wedge that coevolved beneath the batholith appears to have an average radiogenic heat production rate of 0.14 μW/m³. This is higher than the rates from most published xenolith studies, but reasonable given the presence of crustal components in the arc root assemblages. The pattern of radiogenic heat production interpreted from the depth vs. heat production database is not consistent with the downward-decreasing exponential distribution predicted from modeling of surface heat flow data. The interpreted distribution predicts a reasonable range of geothermal gradients and shows that essentially all of the present day surface heat flow from the Sierra Nevada could be generated within the 35 km thick crust. This requires a very low heat flux from the mantle, which is consistent with a model of cessation of Sierran magmatism during Laramide flat-slab subduction, followed by conductive cooling of the upper mantle for 70 m.y. The heat production variation with depth is principally due to large variations in uranium and thorium concentration; potassium is less variable in concentration within the Sierran crust, and produces relatively little of the heat in high heat production rocks. Because silica content is relatively constant through the upper 30 km of the Sierran batholith, while U, Th, and K concentrations are highly variable, radiogenic heat production does not vary directly with silica content.  相似文献   

Mercury mobility at the Carson River Superfund Site, west-central Nevada, USA: Interpretation of mercury speciation data in mill tailings, soils, and sediments     

Paul J. Lechler  Jerry R. Miller  Liang-Chi Hsu  Mario O. Desilets 《Journal of Geochemical Exploration》1997,58(2-3)

The Carson River Superfund Site in west-central Nevada is an area of Hg-contaminated soil, sediment, water, air, and biola resulting from the amalgamation milling of Ag-Au ores of the Comstock lode worked approximately a century ago. In order to develop an understanding of the behavior, transport, and fate of Hg at this site, a technique was developed to estimate the proportions of total, elemental, exchangeable, organic, and sulfide Hg in soils, sediments, and tailings.Results of this analysis performed on active Carson River sediments indicate that Hg is selectively dissolved out of Hg-Au amalgam particles and subsequently adsorbed to fine-grained sediments which are then deposited in downstream, low-energy reaches of the Carson River and Labontan Reservoir. In the relatively more-reducing environment of the reservoir Hg appears to be converted, in large part, to relatively-insoluble HgS.The original elemental form of Hg released to the environment is the chemical form which is still dominant in most highly-contaminated soils, sediments, and tailings. Deeper, more-reducing soil horizons, however, appear to fix a significant portion of the Hg as HgS, analogous to the Lahontan Reservoir example described above. This fixation as HgS is documented to be largely limited to higher-sulfur areas where sulfide minerals from the Comstock ores increase the total sulfur concentrations of contaminated soils, sediments, and tailings.  相似文献   

Characteristics and origin of sediment-hosted disseminated gold deposits: a review   总被引：4，自引：0，他引：4  

Greg B. Arehart 《Ore Geology Reviews》1996,11(6):383-403

Sediment-hosted disseminated gold (SHDG) deposits comprise a major portion of the gold production and reserves in the US. Although presently known to be common only in western North America, SHDG deposits are a significant source of world gold production. These deposits are characterized by extremely fine-grained disseminated gold, hosted primarily by arsenian pyrite. Other metals show very little enrichment although in addition to As, anomalous concentrations of elements such as Sb, Hg, Tl and Ba are utilized as exploration tools. The host rocks are dominantly silty carbonates, but ore concentrations are also present in siliceous and silicified rocks as well as intrusive rocks. Alteration consists of decarbonatization, silicification (jasperoid formation) and argillization, which are arranged both spatially and temporally in that order. Argillic alteration is zoned from kaolinite-dominated cores to sericite-dominated margins. The deposits commonly exhibit significant structural (faults) and stratigraphic (composition/permeability) controls. Until the last few years, SHDG deposits were considered as near-surface, epithermal type deposits in origin. Because of their fine-grained nature and the lack of macroscopic features such as veins, it has proven quite difficult to extract geochemical data that are clearly related to their genesis. However, fluid inclusion data indicate pressures corresponding to depths of 2–4 km under lithostatic conditions. Temperatures are constrained by fluid inclusions and phase equilibria to near 225°C. Stable isotope data from alteration minerals and fluid inclusions indicate that the ore fluids were dominated by meteoric waters, some of which had clearly exchanged oxygen with wallrocks during their passage through the crust. Although the data vary, most ore fluids probably had δD values near −150‰ and δ¹⁸O values ranging from −10 to +5‰. Sulfur isotope values reported from SHDG deposits span a wide range, from −30 to +20‰ (sulfides) and 0 to >45‰ (sulfates). Ore-related sulfides (pyrite, realgar) fall at the upper end of the range reported for sulfides. The alteration and mineral assemblage indicate the ore fluids were probably near neutral and gold was likely carried as a bisulfide complex. The depositional mechanism(s) probably included mixing, cooling and oxidation. These mechanisms are consistent with the observed alteration features, i.e. quartz precipitation, calcite dissolution and sericite-kaolinite coexistence. It also explains the presence of both siliceous ores containing native Au and sulfide ores containing Au in pyrite. The extreme variations in sulfur isotopes as seen at Post and fluid inclusion data from Carlin may be indicative of some phase separation (‘boiling’), but such relations have not been documented in other deposits and the importance of phase separation to gold deposition appears minimal.  相似文献   

Fabric studies within the Cascade Lake shear zone, Sierra Nevada, California   总被引：1，自引：0，他引：1  

Basil Tikoff  Matthew R. Davis  Christian Teyssier  Michel de St. Blanquat  Guillaume Habert  Sven Morgan   《Tectonophysics》2005,400(1-4):209-226

The Cascade Lake shear zone occurs on the eastern margin of the Tuolumne Intrusive Suite, Sierra Nevada Batholith, California. Foliation in the zone is NNW trending and subvertical, and lineation is moderately south plunging. Deformation is syn-tectonic with emplacement of the Cathedral Peak granodiorite. A deformation gradient exists toward the NE margin of this pluton, with higher strains and lower temperatures of deformation found near the contact. We compare fabric data collected very densely in this shear zone using several techniques: field fabrics, 3D orientation of K-feldspar megacrysts, and AMS (anisotropy of magnetic susceptibility) analysis. In general, the results from the three different methods are in agreement. Deformation in this shear zone is part of a larger pattern of deformation within the Cathedral Peak granodiorite, as recorded by AMS analysis, and dextral shearing associated within the last stage of plutonism within the Sierra Nevada magmatic arc.  相似文献   

Spatiotemporal estimation of snow depth using point data from snow stakes,digital terrain models,and satellite data          下载免费PDF全文

Antonio‐Juan Collados‐Lara  Eulogio Pardo‐Igúzquiza  David Pulido‐Velazquez 《水文研究》2017,31(10):1966-1982

Snow availability in Alpine catchments plays an important role in water resources management. In this paper, we propose a method for an optimal estimation of snow depth (areal extension and thickness) in Alpine systems from point data and satellite observations by using significant explanatory variables deduced from a digital terrain model. It is intended to be a parsimonious approach that may complement physical‐based methodologies. Different techniques (multiple regression, multicriteria analysis, and kriging) are integrated to address the following issues: We identify the explanatory variables that could be helpful on the basis of a critical review of the scientific literature. We study the relationship between ground observations and explanatory variables using a systematic procedure for a complete multiple regression analysis. Multiple regression models are calibrated combining all suggested model structures and explanatory variables. We also propose an evaluation of the models (using indices to analyze the goodness of fit) and select the best approaches (models and variables) on the basis of multicriteria analysis. Estimation of the snow depth is performed with the selected regression models. The residual estimation is improved by applying kriging in cases with spatial correlation. The final estimate is obtained by combining regression and kriging results, and constraining the snow domain in accordance with satellite data. The method is illustrated using the case study of the Sierra Nevada mountain range (Southern Spain). A cross‐validation experiment has confirmed the efficiency of the proposed procedure. Finally, although it is not the scope of this work, the snow depth is used to asses a first estimation of snow water equivalent resources.  相似文献   

Centuries of artificial recharge on the southern edge of the Sierra Nevada (Granada,Spain)   总被引：1，自引：0，他引：1  

A. Pulido-Bosch  Y. Ben Sbih 《Environmental Geology》1995,26(1):57-63

In the Alpujarra (southern Spain), every year between the March and June, an ancestral practice continues in the form of diverting water from the rivers by way of an extensive network of irrigation channels (acequias) to well-defined, highly permeable areas. This practice, known ascareos, constitutes an ancient example of artificial recharge. The objective is to guarantee a supply of drinking water during the dry months, as well as improve the physicochemical characteristics of the water. In addition, this system helps maintain moisture in the immediate environment, and thus has a positive effect on local vegetation.  相似文献   

Paleofire reconstruction for high-elevation forests in the Sierra Nevada, California, with implications for wildfire synchrony and climate variability in the late Holocene     

Douglas J. Hallett  R. Scott Anderson 《Quaternary Research》2010,73(2):180-190

Here, we present two high-resolution records of macroscopic charcoal from high-elevation lake sites in the Sierra Nevada, California, and evaluate the synchroneity of fire response for east- and west-side subalpine forests during the past 9200 yr. Charcoal influx was low between 11,200 and 8000 cal yr BP when vegetation consisted of sparse Pinus-dominated forest and montane chaparral shrubs. High charcoal influx after ∼ 8000 cal yr BP marks the arrival of Tsuga mertensiana and Abies magnifica, and a higher-than-present treeline that persisted into the mid-Holocene. Coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the Sierra Nevada after 3800 cal yr BP. Independent fire response occurs between 9200 and 5000 cal yr BP, and significant synchrony at 100- to 1000-yr timescales emerges between 5000 cal yr BP and the present, especially during the last 2500 yr. Indistinguishable fire-return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late Holocene. Fires after 1200 cal yr BP are often synchronous and corroborate with inferred droughts. Holocene fire activity in the high Sierra Nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the El Niño-Southern Oscillation.  相似文献   

Scale of pluton/wall rock interaction near May Lake,Yosemite National Park,CA, USA     

Ryan D. Mills  Allen F. Glazner  Drew S. Coleman 《Contributions to Mineralogy and Petrology》2009,158(2):263-281

Interaction of magma with wall rock is an important process in igneous petrology, but the mechanisms by which interactions occur are poorly known. The western outer granodiorite of the Cretaceous Tuolumne Intrusive Suite of Yosemite National Park, California, intruded a variety of metasedimentary and igneous wall rocks at 93.1 Ma. The May Lake metamorphic screen is a metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation, disaggregation, and partial melting. The chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure of pluton/wall rock interactions. Wall rock xenoliths (mostly pelitic quartzite) are predominantly located in an elongate horizon surrounded by a hybridized fine-grained granodiorite. Initial Sr and Nd isotopic ratios of the hybridized granodiorite indicate significant local incorporation of crustal material. Major- and trace-element geochemical data indicate that contamination of the granodiorite occurred via selective assimilation of both high-K and low-K, high-silica partial melts derived from pelitic quartzite. Although the hybridized granodiorite shows significant amounts of contamination, adjacent to xenoliths the proportion of contamination is undetectable more than a meter away. These results indicate that the chemical and isotopic variability of the Tuolumne Intrusive Suite is not caused by magma contamination via in situ wall rock assimilation.  相似文献   

The role of aridification in constraining the elevation range of Holocene solifluction processes and associated landforms in the periglacial belt of the Sierra Nevada (southern Spain)     

Marc Oliva  Antonio Gómez Ortiz 《地球表面变化过程与地形》2011,36(10):1279-1291

Climate variability during the Mid‐Late Holocene has influenced the activity of geomorphic processes in the current periglacial belt of the Sierra Nevada. We studied two types of sedimentary records that reveal a synchronous timing for slope instability in this high semi‐arid massif: solifluction landforms and mountain lake sediments. Lithological and sedimentological properties of both records have recorded numerous cycles of different magnitude of slope processes in the massif. Solifluction deposits record seven phases of solifluction activity and soil development during the last 7 ka bp and lake sediments show evidence of eight periods with increased geomorphic activity in the catchments over the last 6 ka bp . Although present‐day climate conditions do not promote active solifluction processes in the Sierra Nevada, colder and wetter periods during the Holocene triggered solifluction and transported coarse‐grained sediments into the lakes. By contrast, warm phases favoured soil formation and spread an incipient vegetation cover over the headwaters of the highest valleys, diminishing the grain size of the particles reaching the lakes. Lake sediments record an aridification trend in the massif intensifying since 4·2 ka bp that has conditioned solifluction activity to shift gradually to higher elevations. During major cooler phases such as the Little Ice Age active solifluction was recorded back down to 2500 m altitude. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A Comparison of Carlin-type Gold Deposits:Guizhou Province,Golden Triangle,Southwest China,and Northern Nevada,USA   总被引：2，自引：0，他引：2  

Jean S.CLINE  John L.MUNTEAN  Xuexiang GU  Yong XIA 《地学前缘》2013,20(1):1-18

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