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61.
郯庐断裂带形成演化的年代学研究 总被引:11,自引:0,他引:11
通过对郯庐断裂带东侧张八岭蓝片岩带内白云母4 0 Ar - 3 9Ar年龄、断裂带内片麻状花岗岩中钾长石4 0 Ar- 3 9Ar年龄以及断裂带内断层泥K -Ar、ESR年龄的测定 ,并结合有关的地质和古地磁资料 ,厘定了郯庐断裂带形成和演化的过程 :(1)三叠纪 (2 44~ 2 0 9Ma)由于华北与扬子地块碰撞 ,郯庐断裂带形成为其主要左行平移时期 ;(2 )侏罗纪 (189~ 16 4Ma)时郯庐断裂东侧下扬子地块可能经历了逆时针转动 ;(3)白垩纪 (10 3~ 94Ma)开始郯庐断裂带伴随走滑平移而发生正断活动 ;(4)晚白垩—第三纪右旋平移阶段。郯庐断裂的形成与大别 -苏鲁变质带有关。 相似文献
62.
U-Pb isotopic thermochronometry of rutile, apatite and titanite from kimberlite-borne lower crustal granulite xenoliths has been used to constrain the thermal evolution of Archean cratonic and Proterozoic off-craton continental lithosphere beneath southern Africa. The relatively low closure temperature of the U-Pb rutile thermochronometer (~400-450 °C) allows its use as a particularly sensitive recorder of the establishment of "cratonic" lithospheric geotherms, as well as subsequent thermal perturbations to the lithosphere. Contrasting lower crustal thermal histories are revealed between intracratonic and craton margin regions. Discordant Proterozoic (1.8 to 1.0 Ga) rutile ages in Archean (2.9 to 2.7 Ga) granulites from within the craton are indicative of isotopic resetting by marginal orogenic thermal perturbations influencing the deep crust of the cratonic nucleus. In Proterozoic (1.1 to 1.0 Ga) granulite xenoliths from the craton-bounding orogenic belts, rutiles define discordia arrays with Neoproterozoic (0.8 to 0.6 Ga) upper intercepts and lower intercepts equivalent to Mesozoic exhumation upon kimberlite entrainment. In combination with coexisting titanite and apatite dates, these results are interpreted as a record of postorogenic cooling at an integrated rate of approximately 1 °C/Ma, and subsequent variable Pb loss in the apatite and rutile systems during a Mesozoic thermal perturbation to the deep lithosphere. Closure of the rutile thermochronometer signals temperatures of °C in the lower crust during attainment of cratonic lithospheric conductive geotherms, and such closure in the examined portions of the "off-craton" Proterozoic domains of southern Africa indicates that their lithospheric thermal profiles were essentially cratonic from the Neoproterozoic through to the Late Jurassic. These results suggest similar lithospheric thickness and potential for diamond stability beneath both Proterozoic and Archean domains of southern Africa. Subsequent partial resetting of U-Pb rutile and apatite systematics in the cratonic margin lower crust records a transient Mesozoic thermal modification of the lithosphere, and modeling of the diffusive Pb loss from lower crustal rutile constrains the temperature and duration of Mesozoic heating to °C for ka. This result indicates that the thermal perturbation is not simply a kimberlite-related magmatic phenomenon, but is rather a more protracted manifestation of lithospheric heating, likely related to mantle upwelling and rifting of Gondwana during the Late Jurassic to Cretaceous. The manifestation of this thermal pulse in the lower crust is spatially and temporally correlated with anomalously elevated and/or kinked Cretaceous mantle paleogeotherms, and evidence for metasomatic modification in cratonic mantle peridotite suites. It is argued that most of the geographic differences in lithospheric thermal structure inferred from mantle xenolith thermobarometry are likewise due to the heterogeneous propagation of this broad upper mantle thermal anomaly. The differential manifestation of heating between cratonic margin and cratonic interior indicates the importance of advective heat transport along pre-existing lithosphere-scale discontinuities. Within this model, kimberlite magmatism was a similarly complex, space- and time-dependent response to Late Mesozoic lithospheric thermal perturbation. 相似文献
63.
A palygorskite unit was discovered in a road cut of undifferentiated Tertiary limestone between the villages of El Pariso
and San Roman (18°49.309N, 88°37.861W) in the southeastern Yucatán Peninsula, Mexico. This is the southern most locality of
a clay-rich sedimentary unit reported in the literature for the Tertiary carbonates of the Yucatán Peninsula. This occurrence
indicates a much wider range of palygorskite-rich clay deposition than previously recognized. The lithology is 99% clay and
1% sand to silt size diagenetic quartz grains. The clay consists of approximately 85% palygorskite, 15% montmorillonite and
trace amounts of titanium oxides. EDS analyses on palygorskite are largely consistent with sedimentary palygorskites from
other coastal marine settings, however palygorskite has a low total Fe content (average = 0.40 wt% expressed as Fe2O3) compared to many other sedimentary palygorskites. Montmorillonite chemical compositions are typical and compared to the
palygorskite have substantially higher Fe2O3 concentrations (average = 3.90 wt%). The low percentage of coarse grains in the lithology combined with a high proportion
of palygorskite and lack of detrimental trace minerals suggest the deposit is of industrial grade; however, it has limited
reserves (6,000 m3). The unit could be potentially used in a wide array of environmental applications which are needed in the region including
liners for landfills and constructed wetlands. The unit is in a geographic location which would serve the expanding economy
of the region. This resource has the potential to have great impact on the quality of the local environment and the economy
of a region under great environmental threat. 相似文献
64.
Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano,Panama 总被引:3,自引:0,他引:3
Mare J. Defant Lee F. Clark Robert H. Stewart Mark S. Drummond Jelle Z. de Boer René C. Maury Hervé Bellon Thomas E. Jackson Juan F. Restrepo 《Contributions to Mineralogy and Petrology》1991,106(3):309-324
The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava
flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic
activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows
0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites.
The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young
group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed
in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent
among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or
polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples
from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics.
We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within
the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The
young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features
of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial
melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual
garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated
apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano
is related to the subduction of relatively hot lithosphere. 相似文献
65.
Particle composition and size distributions in and around a deep-pit swine operation,Ames, IA 总被引:1,自引:0,他引:1
Randal S. Martin Philip J. Silva Kori Moore Mark Erupe Vishal S. Doshi 《Journal of Atmospheric Chemistry》2008,59(2):135-150
The contribution of emissions from agricultural facilities is rapidly becoming a major concern for local and regional air
quality. Characterization of particle properties such as physical size distribution and chemical composition can be valuable
in understanding the processes contributing to emissions and ultimate fate of particulate matter from agricultural facilities.
A measurement campaign was conducted at an Iowa, deep-pit, three-barn swine finishing facility to characterize near-source
ambient particulate matter. Size-specific mass concentrations were determined using minivol samplers, with additional size
distribution information obtain using optical particle counters. Particulate composition was determined via ion chromatographic
analysis of the collected filters. A thermal-CO2 elemental/organic carbon analyzer measured particulate carbon. The chemical composition and size distribution of sub-micron
particles were determined via real-time aerosol mass spectrometry. Primary particulate was not found to be a major emission
from the examined facility, with filter-based impactor samples showing average near-source increases (~15–50 m) in ambient
PM10 of 5.8 ± 2.9 μg m−3 above background levels. PM2.5 also showed contribution attributable to the facility (1.7 ± 1.1 μg m−3). Optical particle counter analysis of the numerical size distributions showed bimodal distributions for both the upwind
and downwind conditions, with maximums around 2.5 μm and below the minimum quantified diameter of 0.3 μm. The distributions
showed increased numbers of coarse particles (PM10) during periods when wind transport came from the barns, but the differences were not statistically significant at the 95%
confidence level. The PM10 aerosols showed statistically increased concentrations of sulfate, nitrate, ammonium, calcium, organic carbon, and elemental
carbon when the samplers were downwind from the pig barns. Organic carbon was the major constituent of the barn-impacted particulate
matter in both sub-micron (54%) and coarse size (20%) ranges. The AMS PM1 chemical speciation showed similar species increases, with the exception of and Ca+2, the latter not quantified by the AMS. 相似文献
66.
The Chinese Tianshan belt of the southern Altaids has undergone a complicated geological evolution.Different theories have been proposed to explain its evolution and these are still hotly debated.The major subduction polarity and the way of accretion are the main problems.Southward,northward subduction and multiple subduction models have been proposed.This study focuses on the structural geology of two of the main faults in the region,the South Tianshan Fault and the Nikolaev Line.The dip direction in the Muzhaerte valley is southward and lineations all point towards the NW.Two shear sense motions have been observed within both of these fault zones,a sinistral one,and a dextral one,the latter with an age of 236-251 Ma.Structural analyses on the fault zones show that subduction has been northward rather than southward.The two shear sense directions indicate that the Yili block was first dragged along towards the east due to the clockwise rotation of the Tarim block.After the Tarim block stopped rotating,the Yili block still kept going eastward,inducing the dextral shear senses within the fault zones. 相似文献
67.
Mark Anglin Harris 《Environmental Geology》2009,56(8):1517-1522
Several years (7) after incidental lithification by added gypsum, the effect of crushing and phyto-organics on some physical
properties of red mud wastes (RMW) was examined under laboratory conditions. It was hypothesized that mechanically breaking
up the hardened masses would increase their permeability. However, on the contrary, crushing these rock-hard masses into <2-mm
particles did not increase permeability. A phyto-organic treatment on the other hand greatly improved permeability of the
crushed entities such that infiltration rates increased from 0 to 10 cm/h. After 24 weeks of incubation, the structure of
the newly formed phyto-organically treated gypsum-hardened RMW aggregates was also substantially improved over that of the
controls, as a >3-fold increase in resistance to disintegration during wet sieving was exhibited by the phyto-organically
treated samples. The increase in water infiltration by combining crushing with phyto-organic applications was ascribed to
a decrease in particle dispersion, creating more stable clay clusters, which in turn stabilized channels and pores. Conversely,
it was concluded that the singular crushing of gypsum-hardened bauxite waste in the waste dumps is potentially wasteful and
ineffective. 相似文献
68.
Jean-Jacques Peucat Johildo Salomão Figueiredo Barbosa Ivana Conceição de Araújo Pinho Jean-Louis Paquette Hervé Martin C. Mark Fanning Angela Beatriz de Menezes Leal Simone Cruz 《Journal of South American Earth Sciences》2011,31(4):397-413
This work provides five new U–Pb zircon dating and the corresponding Nd isotope data for felsic granulites from the south Itabuna-Salvador-Curaçá Block (ISCB), in the São Francisco Craton, Brazil. Three major sets of felsic granulites can be recognised. The oldest set is tonalitic in composition and of TTG affinity. It is Archaean in age with magmatic zircon cores dated at 2675 ± 11 Ma by LA-ICPMS and up to ca 2.7–2.9 Ga by SHRIMP on an other sample. It exhibits epsilon Nd values between ?8 and ?11 at 2.1 Ga. This Nd signature is similar to that of granulites found in the western Archaean Jequié Block. Cartographically, this set of Archaean terrains represents at least 50% of the granulites in the studied area. The second set corresponds to a Palaeoproterozoic calc-alkaline tonalitic suite with zircon ages from 2019 ± 19 Ma to 2191 ± 10 Ma and epsilon Nd values between ?3 and ?4 at 2.1 Ga, corresponding partially to a newly formed crust. The third set of granulites is also Palaeoproterozoic. It is shoshonitic to monzonitic in composition and synchronous with the high grade metamorphism dated by metamorphic zircons at 2086 ± 7 Ma (average of five samples). The Nd isotope signature for this alkaline set is similar to that of the Palaeoproterozoic calc-alkaline one. Nd isotopes appear to be a very efficient tool to distinguish Archaean from Palaeoproterozoic felsic protoliths in granulitic suites of the Itabuna-Salvador-Curaçá Block (ISCB). Finally, the southern part of the ISCB is composed of a mixture of Archaean and Palaeoproterozoic protoliths, in similar amounts, suggesting that it was probably an active margin between 2.1 and 2.2 Ga located on the eastern border of the Archaean Jequié Block. A major crustal thickening process occurred at ca 2.09 Ga in the ISCB and seems significantly younger towards the west, in the Jequié granulites, where an average of 2056 ± 9 Ma is determined for the high grade event. 相似文献
69.
Metrics to assess how longitudinal channel network connectivity and in‐stream Atlantic salmon habitats are impacted by hydropower regulation 下载免费PDF全文
Willem B. Buddendorf Iain A. Malcolm Josie Geris Mark E. Wilkinson Chris Soulsby 《水文研究》2017,31(12):2132-2142
Habitat fragmentation in channel networks and riverine ecosystems is increasing globally due to the construction of barriers and river regulation. The resulting divergence from the natural state poses a threat to ecosystem integrity. Consequently, a trade‐off is required between the conservation of biodiversity in channel networks and socio‐economic factors including power generation, potable water supplies, fisheries, and tourism. Many of Scotland's rivers are regulated for hydropower generation but also support populations of Atlantic salmon (Salmo salar L.) that have high economic and conservation value. This paper investigates the use of connectivity metrics and weightings to assess the impact of river barriers (impoundments) associated with hydropower regulation on natural longitudinal channel connectivity for Atlantic salmon. We applied 2 different weighting approaches in the connectivity models that accounted for spatial variability in habitat quality for spawning and fry production and contrasted these models with a more traditional approach using wetted area. Assessments of habitat loss using the habitat quality weighted models contrasted with those using the less biologically relevant wetted area. This highlights the importance of including relevant ecological and hydrogeomorphic information in assessing regulation impacts on natural channel connectivity. Specifically, we highlight scenarios where losing a smaller area of productive habitat can have a larger impact on Atlantic salmon than losing a greater area of less suitable habitat. It is recommended that future channel connectivity assessments should attempt to include biologically relevant weightings, rather than relying on simpler metrics like wetted area which can produce misleading assessments of barrier impacts. 相似文献
70.