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71.
0.7Ma以来的念青唐古拉山脉隆升过程——来自冰川剥蚀作用的证据 总被引:1,自引:0,他引:1
通过对念青唐古拉山冰碛地层划分及冰碛物同位素测年,发现最早一期冰碛物形成于0.7~0.6MaBP,指示自中更新世以来念青唐古拉山脉开始隆升,主峰地区发生了大规模的冰川剥蚀作用,形成了大面积分布的冰碛高平台;0.2~0.14MaBP念青唐古拉山又快速隆升,并堆积了刚刚伸出各大沟谷口的高侧碛;0.07~0.03MaBP念青唐古拉山再次小规模隆起,形成各大沟谷内的侧碛和终碛垄;0.01Ma BP还有小规模冰川活动。念青唐古拉山主峰地区的冰川剥蚀作用反映出的山脉隆升过程,可较好地与青藏高原的隆起过程相对比,它应是青藏高原隆升的响应。 相似文献
72.
Bruno Dhuime Delphine Bosch Olivier Bruguier Renaud Caby Carlos Archanjo 《Comptes Rendus Geoscience》2003,335(15):1081-1089
The Borborema Province (BP) of northeastern Brazil is a complex crustal assemblage, which has undergone a polycyclic evolution during the Proterozoic. In the Piancó-Alto Br??gida belt, a metamorphosed leucosome vein inserted in amphibolites has a trace element pattern suggesting a T-MORB protolith. Apatites yield a REE pattern indicating growth in equilibrium with garnet, thus pointing to its metamorphic origin. UPb analyses yield an age of 540±5 Ma interpreted as a cooling age following amphibolite facies regional metamorphism associated with granitic emplacement at ca. 580 Ma. The resulting slow cooling rates (ranging from ca. 2.5 to 5 °C Ma?1) are consistent with underplating of mafic magmas, or crustal thickening caused by nappe stacking, as possible processes governing the metamorphic evolution of the BP. To cite this article: B. Dhuime et al., C. R. Geoscience 335 (2003). 相似文献
73.
The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system.
Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case
the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz.
The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic
zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing
type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that
these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent
low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of
this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type
A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there
were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important
chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun
Early Paleozoic.
Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program
“ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National
Geological Surveying Bureau. 相似文献
74.
Makoto Haruna Takahiro Hanamuro Kaoru Uyeda Hirokazu Fujimaki Hiroshi Ohmoto 《Resource Geology》2003,53(2):75-88
Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The δ18 O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of ∼ 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale. 相似文献
75.
金属成矿学研究的若干进展 总被引:15,自引:0,他引:15
主要讨论近10年来国内外在金属矿床地质研究中的若干进展,内容包括:成矿地质环境和深部背景;矿床、成矿带和全球的成矿作用演化;成矿系统和成矿动力学;地质流体与成矿作用以及超大型矿床的形成条件等。在这5个重点研究领域中,分别介绍了对它们的研究和已取得的一些进展,又展望了其在今后的研究前景。认为上述5个方面的系统深入研究,将构成21世纪上半世纪新的成矿理论基础,并将对金属矿产勘查工作有重大影响。 相似文献
76.
辽宁水泉金矿综合信息找矿模型及预测 总被引:1,自引:0,他引:1
通过对辽宁水泉金矿的基础地质研究和综合找矿信息分析,并根据该矿区资源危机,缺乏后备金矿储备的实际情况建立了水泉金矿综合信息找矿模型。对远景成矿靶区进行了初步圈定,为详细地质勘查、扩大金矿资源提供了依据。 相似文献
77.
试论会东大银厂铅锌矿找矿模式 总被引:2,自引:0,他引:2
对大银厂铅锌矿点分布区的地层、构造和成矿地质背景进行了论述,并与大梁子铅锌矿床作了对比,提出了寻找该类矿床的模式及找寻工业矿体最有希望的地段。找矿方法宜先化探后钻探。 相似文献
78.
79.
Chiyo Morimoto Yo-ichiro Otofuji Masako Miki Hidefumi Tanaka Tetsumaru Itaya 《Geophysical Journal International》1997,128(3):585-593
The geomagnetic field intensity during Archaean times is evaluated from a palaeomagnetic and chronological study of a dolerite dyke intruded into the 3000 Ma Nuuk Gneisses at Nuuk (64.2°N, 51.7°W), west Greenland. Plagioclase from the dolerite dyke yields a mean K-Ar age of 2752 Ma. Palaeomagnetic directions after thermal demagnetization of the dyke and the gneiss reveal a positive baked-contact test, indicating that the high-temperature-component magnetization of the dyke is primary. Thellier experiments on 12 dyke specimens yield a palaeointensity value of 13.5±4.4 μT. The virtual dipole moment at ca. 2.8 Ga is 1.9±0.6 × 1022 Am2 , which is about one-quarter of the present value. The present study and other available data imply that the Earth's magnetic field at 2.7 ∼ 2.8 Ga was characterized by a weak dipole moment and that a fairly strong geomagnetic field similar to the present intensity followed the weak field after ca. 2.6 Ga. 相似文献
80.
This paper investigates the role of housing age in constraining residential mobility, measured as the percent of households that have moved into their homes in the past 15 months. The leading explanation for why mobility rates differ so much among regions of the United States has been the overall level of growth. The present analysis shows that the growth effect operates through both the newness of population (migration) and the newness of housing available for occupancy by all local residents. The posited explanation for this housing age effect is that progressively older units contain increasingly settled occupants, yielding fewer opportunities for in-movers in areas with older housing. It is empirically demonstrated that households in older housing have lower likelihood of recent mobility even after controlling for age, tenure, migration status, and state location of residence. The analysis reveals the temporal interdependency of mobility, migration, person age, and housing age. 相似文献