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991.
Lamprophyric lavas in the Colima graben,SW Mexico 总被引:2,自引:3,他引:2
The Colima graben, located in SW Mexico, is one of three grabens which intersect about 50 km SSW of Guadalajara, forming a triple junction. The 90 km long, 20–60 km wide Colima graben represents a N-S rift of the E-W trending Mexican Volcanic Belt. Since the Early Pliocene, the Colima graben has served as a locus for the eruption of alkaline lavas, the most recent of which are basanites and minettes erupted from Late Pleistocene cinder cones (Luhr and Carmichael 1981). In this paper, we report on older alkaline lavas which crop out in the graben's walls. These rocks include phlogopite- and hornblende-bearing lamprophyres, a phlogopite-kalsilite-ankaratrite, and high-K andesites. These lavas crop out throughout the Colima graben area, and are intimately associated with calc-alkaline lavas in the field. Compared to these, the alkaline rocks are strikingly enriched in the incompatible elements, particularly Ba, Sr, P, and the LREE. Unlike the younger Late Pleistocene alkaline cinder cone lavas, most of the graben wall lamprophyres and the high-K andesites represent magmas that appear to have undergone significant evolution since their generation, including fractionation, crustal contamination, and possible magma mixing. Least-squares modeling indicates that the cinder cone minettes represent reasonable parental magmas for the graben lamprophyres. The occurrence of these alkaline lavas in an active calc-alkaline volcanic arc is unusual, and we suggest that they are a manifestation of the rifting processes which produced the Colima graben. 相似文献
992.
Two methods are compared for estimating the shape parameters of Pareto field-size (or pool-size) distributions for petroleum
resource assessment. Both methods assume mature exploration in which most of the larger fields have been discovered. Both
methods use the sizes of larger discovered fields to estimate the numbers and sizes of smaller fields: (1) the tail-truncated
method uses a plot of field size versus size rank, and (2) the log–geometric method uses data binned in field-size classes
and the ratios of adjacent bin counts. Simulation experiments were conducted using discovered oil and gas pool-size distributions
from four petroleum systems in Alberta, Canada and using Pareto distributions generated by Monte Carlo simulation. The estimates
of the shape parameters of the Pareto distributions, calculated by both the tail-truncated and log–geometric methods, generally
stabilize where discovered pool numbers are greater than 100. However, with fewer than 100 discoveries, these estimates can
vary greatly with each new discovery. The estimated shape parameters of the tail-truncated method are more stable and larger
than those of the log–geometric method where the number of discovered pools is more than 100. Both methods, however, tend
to underestimate the shape parameter. Monte Carlo simulation was also used to create sequences of discovered pool sizes by
sampling from a Pareto distribution with a discovery process model using a defined exploration efficiency (in order to show
how biased the sampling was in favor of larger fields being discovered first). A higher (more biased) exploration efficiency
gives better estimates of the Pareto shape parameters. 相似文献
993.
994.
995.
Preface: Proceedings of the 5th International Symposium on Lithographic Limestone and Plattenkalk 总被引:1,自引:0,他引:1
Daniel Marty Jean-Paul Billon-Bruyat Christian A. Meyer Loïc Costeur Basil Thüring 《Swiss Journal of Geoscience》2011,104(1):1-29
Magmatic rocks from the pre-Mesozoic basements of the Sambuco and Maggia nappes have been dated by U–Pb zircon ages with the LA-ICPMS technique. Several magmatic events have been identified in the Sambuco nappe. The mafic banded calc-alkaline suite of Scheggia is dated at 540 Ma, an age comparable to that of mafic rocks in the Austroalpine Silvretta nappe. The Sasso Nero peraluminous augengneiss has an age of 480–470 Ma, like many other “older orthogneisses” in Alpine basement units. It hosts a large proportion of inherited zircons, which were dated around 630 Ma, a Panafrican age indicating the Gondwanan affiliation of the Sambuco basement. The calc-alkaline Matorello pluton yielded ages around 300 Ma, similar to numerous Late Carboniferous intrusions in other basement units of the Lower Penninic (Monte Leone, Antigorio, Verampio) and Helvetic domains (Gotthard and other External Crystalline Massifs). Associated lamprophyric dykes are slightly younger (300–290 Ma), like similar dykes sampled in gneiss blocks included in the sedimentary cover of the underlying Antigorio nappe (290–285 Ma). The Cocco granodiorite and Rüscada leucogranite, both intruding the basement of the neighbouring Maggia nappe, yielded ages of ca. 300–310 Ma, identical within errors to the age of the Matorello pluton. They are significantly older than former age determinations. This age coincidence, coupled with remarkable petrologic similarities between the Cocco and Matorello granodiorites, strongly suggests paleogeographic proximity of the Sambuco and Maggia nappes in Late Carboniferous times. In recent publications these two nappes have been interpreted as belonging to distinct Mesozoic paleogeographic domains: “European” for Sambuco and “Briançonnais” for Maggia, separated by the “Valais” oceanic basin. In this case, the similarity of the Matorello and Cocco intrusions would demonstrate the absence of any significant transcurrent movement between these two continental domains. Alternatively, according to a more traditional view, Sambuco and Maggia might belong to a single large Alpine tectonic unit. 相似文献
996.
V CHOWKSEY D M MAURYA PARUL JOSHI N KHONDE ARCHANA DAS L S CHAMYAL 《Journal of Earth System Science》2011,120(6):979-999
The Kachchh Mainland Fault (KMF) is a major E–W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic
evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed
as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow
zone between the E–W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable
heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are
exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The
deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary
sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring
below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic
rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small
coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF.
The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated
from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite.
These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest
deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite
time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The tectonically controlled incision
and dissection of the Quaternary deposits is the result of neotectonic activity that continues at present day. The overall
nature, sedimentary characteristics and geomorphic setting of the sediments suggest that the KMF remained neotectonically
active throughout the Quaternary period. 相似文献
997.
Hussein Mustapha 《Computational Geosciences》2011,15(3):385-397
We present G23FM, a mesh generation tool for discretizing two- and three-dimensional complex fractured geological media. G23FM
includes different techniques to generate finite element grids that maintain the geometric integrity of input surfaces, and
geologic data and produce optimal triangular/tetrahedral grids for flow and transport simulations. G23FM generates grid for
two-dimensional cross-sections, represents faults and fractures, for three-dimensional fractured media, and has the capability
of including finer grids. Different examples are presented to illustrate some of the main features of G23FM. 相似文献
998.
Chemical and Strontium Isotopic Compositions of the Hanjiang Basin Rivers in China: Anthropogenic Impacts and Chemical Weathering 总被引:1,自引:0,他引:1
The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route
of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are
determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs
on river solutes, as well as the associated CO2 consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by
the dominance of Ca2+ and HCO3
−, followed by Mg2+ and SO4
2−. The increase in TDS and major anions (Cl−, NO3
−, and SO4
2−) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities
over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone,
and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load
are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates
weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic
contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for
the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 106 and 6.1 × 106 ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately
38.5 ton/km2/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO2 consumption by carbonate and silicate weathering are estimated to be 56.4 × 109 and 12.9 × 109 mol/year, respectively. 相似文献
999.
Since the early 1980s, the Dead Sea coast has undergone a near catastrophic land deterioration as a result of a rapid lake-level
drop. One conspicuous expression of this deterioration is the formation of sinkholes fields that puncture the coastal plains.
The evolution of sinkholes along nearly 70-km strip has brought to a halt the regional development in this well-known and
toured area and destroyed existing infrastructures. Great efforts are being invested in understanding the phenomena and in
development of monitoring techniques. We report in this paper the application of airborne laser scanning for characterization
of sinkholes. We demonstrate first the appropriateness of laser scanning for this task and its ability to provide detailed
3D information on this phenomenon. We describe then an autonomous means for their extraction over large regions and with high
level of accuracy. Extraction is followed by their detailed geometric characterization. Using this high-resolution data, we
show how sinkholes of 0.5 m radius and 25 cm depth can be detected from airborne platforms as well as the geomorphic features
surrounding them. These sinkhole measures account for their embryonic stage, allowing tracking them at an early phase of their
creation. 相似文献
1000.
Prediction of Floor Water Inrush: The Application of GIS-Based AHP Vulnerable Index Method to Donghuantuo Coal Mine,China 总被引:6,自引:0,他引:6
Qiang Wu Yuanzhang Liu Donghai Liu Wanfang Zhou 《Rock Mechanics and Rock Engineering》2011,44(5):591-600
Floor water inrush represents a geohazard that can pose significant threat to safe operations for instance in coal mines in
China and elsewhere. Its occurrence is controlled by many factors, and the processes are often not amenable to mathematical
expressions. To evaluate the water inrush risk, the paper proposes the vulnerability index approach by coupling the analytic
hierarchy process (AHP) and geographic information system (GIS). The detailed procedures of using this innovative approach
are shown in a case study in China (Donghuantuo Coal Mine). The powerful spatial data analysis functions of GIS was used to
establish the thematic layer of each of the six factors that control the water inrush, and the contribution weights of each
factor was determined with the AHP method. The established AHP evaluation model was used to determine the threshold value
for each risk level with a histogram of the water inrush vulnerability index. As a result, the mine area was divided into
five regions with different vulnerability levels which served as general guidelines for the mine operations. The prediction
results were further corroborated with the actual mining data, and the evaluation result is satisfactory. 相似文献