Early Cretaceous gabbroic rocks from the Taihang Mountains: Implications for a paleosubduction-related lithospheric mantle beneath the central North China Craton   总被引：20，自引：0，他引：20  

Yuejun Wang  Weiming Fan  Hongfu Zhang  Touping Peng 《Lithos》2006,86(3-4):281-302

SHRIMP zircon U–Pb ages and geochemical and Sr–Nd–Pb isotopic data are presented for the gabbroic intrusive from the southern Taihang Mountains to characterize the nature of the Mesozoic lithospheric mantle beneath the central North China Craton (NCC). The gabbroic rocks emplaced at 125 Ma and are composed of plagioclase (40–50%), amphibole (20–30%), clinopyroxene (10–15%), olivine (5–10%) and biotite (5–7%). Olivines have high MgO (Fo = 78–85) and NiO content. Clinopyroxenes are high in MgO and CaO with the dominant ones having the formula of En_42–46Wo_41–50Fs_8–13. Plagioclases are dominantly andesine–labradorite (An = 46–78%) and have normal zonation from bytownite in the core to andesine in the rim. Amphiboles are mainly magnesio and actinolitic hornblende, distinct from those in the Precambrian high-pressure granulites of the NCC. These gabbroic rocks are characterized by high MgO (9.0–11.04%) and SiO₂ (52.66–55.52%), and low Al₂O₃, FeOt and TiO₂, and could be classified as high-mg basaltic andesites. They are enriched in LILEs and LREEs, depleted in HFSEs and HREEs, and exhibit (⁸⁷Sr/⁸⁶Sr)_i = 0.70492–0.70539, ε_Nd(t) = − 12.47–15.07, (²⁰⁶Pb/²⁰⁴Pb)_i = 16.63–17.10, Δ8/4 = 70.1–107.2 and Δ7/4 = − 2.1 to − 9.4, i.e., an EMI-like isotopic signatures. Such geochemical features indicate that these early Cretaceous gabbroic rocks were originated from a refractory pyroxenitic veined-plus-peridotite source previously modified by an SiO₂-rich melt that may have been derived from Paleoproterozoic subducted crustal materials. Late Mesozoic lithospheric extension might have induced the melting of the metasomatised lithospheric mantle in response to the upwelling of the asthenosphere to generate these gabbroic rocks in the southern Taihang Mountains.  相似文献   

Coulomb stress triggering of earthquakes along the Atalanti Fault, central Greece: Two April 1894 M6+ events and stress change patterns     

A. Ganas  E. Sokos  A. Agalos  G. Leontakianakos  S. Pavlides 《Tectonophysics》2006,420(3-4):357-369

Two M6+ events occurred 15–20 km apart in central Greece on April 20 and April 27, 1894. We identify the April 27, 1894 rupture (2nd in the sequence) with the Atalanti segment of the Atalanti Fault Zone because of unequivocal surface rupturing evidence reported by Skouphos [Skouphos, T., 1894. Die swei grossen Erdbeben in Lokris am 8/20 und 15/27 April 1894. Zeitschrift Ges. Erdkunde zu Berlin, vol. 24, pp. 409–474]. Coulomb stress transfer analysis and macroseismic evidence suggest that the April 20, 1894 event (1st in the sequence) may be associated with the Martinon segment of the same fault zone. Our stress modelling suggests that this segment may have ruptured in an M = 6.4 event producing a 15-km long rupture which transferred 1.14 bar in the epicentral area of the April 27th, 1894 event, thus triggering the second M = 6.6 earthquake along the Atalanti segment and producing a 19-km long rupture. We also examined three alternative fault sources for the first event; however, all these produce smaller stress stresses for triggering the second event. The proposed slip model for the second earthquake is capable of producing coastal subsidence of the order of centimetres to decimetres, which fits the geological data. The 1894 earthquake sequence was followed by a difference in the timing of subsequent M > 5 events in each of the “relaxed” areas (stress shadows; a negative change in Coulomb failure stress > − 0.6 bar), which terminated between 22–37 years (north) and 80 years (south).  相似文献   

The determinants of primary health care utilization: a comparison of three rural clinics in Southern Honduras   总被引：2，自引：0，他引：2  

Jonathan B. Baker  Lin Liu 《GeoJournal》2006,66(4):295-310

Primary health care utilization is poorly understood in many parts of the developing world. This is especially true in rural places, such as Santa Lucia, Intibuca, Honduras, where there are only three primary health care facilities servicing almost 12,000 people, and generally speaking access to care is limited. This study examines the factors that can be used to explain primary health care utilization, and aims to improve the understanding of patient utilization behavior. A better understanding of utilization can be used by health service planners to improve primary health care delivery in this and similar locations. The findings of this research indicate that utilization can be explained, to a large extent, by factors relating to economic status and walking time to clinic. These findings are consistent with findings from prior research. In addition, a home territory variable is used to examine spatial variations of utilization behavior. This variable has not been considered in previous utilization research, and is found to be a very significant determinant of health facility utilization in the study area.  相似文献   

15,000 Years of mass-movement history in Lake Lucerne: Implications for seismic and tsunami hazards   总被引：2，自引：0，他引：2  

Michael Schnellmann  Flavio S. Anselmetti  Domenico Giardini  Judith A. Mckenzie 《Eclogae Geologicae Helvetiae》2006,99(3):409-428

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Sulfur Isotope Geochemistry of the Supergiant Xikuangshan Sb Deposit, Central Hunan, China: Constraints on Sources of Ore Constituents   总被引：2，自引：0，他引：2  

Dong-sheng Yang    Masaaki Shimizu  Hidehiko Shimazaki    Xian-hua Li  Qing-lin Xie 《Resource Geology》2006,56(4):385-396

Abstract. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ³⁴S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ³⁴S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ³⁴S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ³⁴S_pyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.  相似文献   

Temperature and density of the Tyrrhenian lithosphere and slab and new interpretation of gravity field in the Tyrrhenian Basin     

F. Cella  S. de Lorenzo  M. Fedi  M. Loddo  F. Mongelli  A. Rapolla  G. Zito   《Tectonophysics》2006,412(1-2):27-47

The gravity anomaly field of the Tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the Oligocene–Miocene. They can resume in lithospheric thinning and asthenospheric rising beneath the Tyrrhenian Basin, coexisting with the roll-back subduction of the African plate margin westward sinking beneath the Calabrian Arc. The geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects.A model of the litho-asthenospheric structure of this region is suggested, showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro-physical features of the mantle. The first phase of this study consisted of the computation of the isotherms in the crust–mantle system beneath the Tyrrhenian Basin and, afterwards, of the density distribution within the partially melted upwelling asthenosphere. The second phase consisted of a temperature/density modelling of the slab subducting beneath the Calabrian Arc. Finally, a 2^1 / 2 interpretation of gravity data was carried out by including as constraints the results previously obtained. Thus, the final result depicts a model matching both gravity, thermal and petrographic data. They provide (a) a better definition of the thermal regime of the passive mantle rise beneath the Tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and (b) a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works.  相似文献   

Earthquake-induced deformation structures in lake deposits: A Late Pleistocene to Holocene paleoseismic record for Central Switzerland   总被引：1，自引：0，他引：1  

Katrin Monecke  Flavio S. Anselmetti  Arnfried Becker  Michael Schnellmann  Michael Sturm  Domenico Giardini 《Eclogae Geologicae Helvetiae》2006,99(3):343-362

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Modeling of Regional High Ozone Episode Observed at Two Mountain Sites (Mt. Tai and Huang) in East China   总被引：3，自引：0，他引：3  

Zifa Wang  Jie Li  Xiquan Wang  Pakpong Pochanart  Hajime Akimoto 《Journal of Atmospheric Chemistry》2006,55(3):253-272

A high O₃ episode was observed during 23–25 May 2004 at two high-mountain sites reflecting the regional pattern of air pollutants over East China. This episode lasted about three days with the maximum hourly O₃ mixing ratios reaching 111 and 114 ppbv at Mt. Tai and Huang, respectively. Backward trajectories and meteorological analysis indicated that regional transport, associated with a weak high pressure system over the East China Sea, might play an important role in the formation of this high ozone episode. The nested air quality prediction modeling system (NAQPMS) was applied to investigate the formation and evolution of this high O₃ event. The comparison of model results with observations showed that NAQPMS successfully reproduced the main observed patterns of O₃ and meteorological parameters during the simulated period. The model results with emission over the Yangtze Delta and the East Central China switched on/off clearly showed that ozone and its precursors transported from the Yangtze Delta and the East Central China enhanced the high ozone episode at two sites, with a contribution of 20%–50% during the episode. In addition, based on process analysis with the model, chemical production and regional transport appeared to be the main causes of high ozone episode involving a large amount of high-ozone air masses and precursors transported from the surrounding areas. The horizontal transport is more active during the period of high ozone episode than that during the non-episode at Mt. Tai as well as Mt. Huang.  相似文献   

大地电场日变化特征   总被引：7，自引：0，他引：7  

解用明  韩和平  高登平  孙澎涛  薛志芳  鞠永 《山西地震》2006,(3):1-4,37

利用后土桥等地震台的大地电场分钟值资料,分析了各方向的日变形态和特征。结果发现,一般各方向日变与地磁场日变近似,出现双峰单谷。而后土桥地震台有别于其他地震台,东西向以半日波为主,出现双峰双谷。  相似文献   

河北省地热资源分布特征、开发利用现状、存在问题与建议   总被引：4，自引：0，他引：4  

张国斌 《中国煤田地质》2006,(Z1)

河北省境内赋存和分布有多种成因的地下热水资源,按地质构造和地貌可初步划分冀北山地区、冀西山地区、冀西北山间盆地区、河北平原区等四大地下热水区,各地已将地热直接用于地热供暖、浴疗保健、温泉洗浴、旅游、地热种植、养殖及工业利用等,但地热利用中存在着勘查评价程度差、开发利用程度低、资源浪费严重等问题。为了保护地下热水资源,做到有序、合理开发,还应加强我省地热资源开发利用管理力度。  相似文献