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991.
992.
Two types of tectonic deformations indicating different geodynamic settings are defined in the southwestern Primorye region. Near-latitudinal compression forces were responsible for the oldest, Late Paleozoic deformations. The Permian stratified complexes host a near-meridional system of folds and zones of dynamothermal metamorphism, cleavage, and foliation oriented orthogonally relative to the compression. Late Proterozoic (?) mafic-ultramafic rocks are characterized by similar deformations. In the Late Permian, the deformations were accompanied by granitoid magmatism controlled by fold and cleavage structures. The younger, Mesozoic deformations produced by near-meridional compression are represented by NE-trending sinistral strike-slip faults and their structural parageneses: an ENE-trending system of folds and downdip-thrusts both superimposed on Paleozoic protostructures and manifested in Mesozoic and Cenozoic sequences. It is inferred that, at the Paleozoic-Mesozoic boundary, near-latitudinal compression was replaced by near-meridional compression, probably, in response to the corresponding change in direction of the lateral displacement of the interacting Asian continent and (or) Pacific Plate. 相似文献
993.
柴达木盆地北缘(以下简称柴北缘)—东昆仑地区已经勘查发现了一批造山型金矿,它们是加里东和晚华力西—印支复合造山作用的产物。通过柴北缘—东昆仑地区12处造山型金矿中流体包裹体研究发现,该区造山型金矿中发育两种不同的成矿流体:低盐度的H2O-CO2-NaCl-CH4流体和低盐度的H2O-CO2-NaCl±CH4。前者的XCH4、XCO2和XH2O分别为0.14~0.34(平均值0.24)、0.11~0.59(平均值0.34)和0.64~0.31(平均值0.42),温度变化为180~270℃,压力为180~560Mpa,是晚加里东期碰撞造山作用的产物,主要沿加里东碰撞造山带边界的上地壳底部-中地壳上部的塑性变形带大规模流动,并在本区形成了广泛的金矿化;后者的XCH4、XCO2和XH2O分别为0~0.12(平均值0.06)、0.18~0.25(平均值0.21)和0.79~0.69(平均值0.73),温度变化为280~449℃(主要在280~360℃),压力为80~230Mpa,主要与晚华力西—印支期碰撞造山作用有关,其中不少矿床还受侵入岩浆作用的影响,其沿晚华力西—印支期碰撞造山带边界的上地壳大规模流动,导致了本区造山型金矿的最终定位。上述两期成矿流体的盐度相差不大,总体变化在1.4%~11.4%(NaCl)(大部分集中于2.7%~9.1%)。压力-深度换算结果显示,本区晚华力西—印支期碰撞造山作用表现出地壳强烈隆升过程,其最大隆升幅度达12km。这说明该区大规模的造山型金成矿作用发生在地壳隆升的背景之下。 相似文献
994.
张明华 《大地构造与成矿学》2007,31(4):418-423
东喜马拉雅南迦巴瓦峰地区地质构造十分复杂,对该区板块缝合带的空间位置问题,长期以来,一直认为沿雅鲁藏布江呈弧形展布。笔者以ETM+为主要信息源,以遥感与GIS为技术支撑,对南峰地区的断裂构造进行了详细的遥感解译分析,从构造统计分析的角度对断裂构造进行定量研究,从分维值及趋势值的空间分布及变化特征分析,认为缝合带的南东段、北段大致沿雅鲁藏布江展布,而北西段位于雅鲁藏布江的北西侧,沿东久-米林(断裂带)展布,这也与近几年来开展了1∶25万区域地质调查获得的新认识相一致。 相似文献
995.
Yoshiyuki Kaneko Shigenori Maruyama Ade Kadarusman Tsutomu Ota Masahiro Ishikawa Tatsuki Tsujimori Akira Ishikawa Kazuaki Okamoto 《Gondwana Research》2007,11(1-2):218
The Timor–Tanimbar islands of eastern Indonesia form a non-volcanic arc in front of a 7 km deep fore-arc basin that separates it from a volcanic inner arc. The Timor–Tanimbar Islands expose one of the youngest high P/T metamorphic belts in the world, providing us with an excellent opportunity to study the inception of orogenic processes, undisturbed by later tectonic events.Structural and petrological studies of the high P/T metamorphic belt show that both deformation and metamorphic grade increase towards the centre of the 1 km thick crystalline belt. Kinematic indicators exhibit top-to-the-north sense of shear along the subhorizontal upper boundaries and top-to-the-south sense in the bottom boundaries of the high P/T metamorphic belt. Overall configuration suggests that the high P/T metamorphic rocks extruded as a thin sheet into a space between overlying ophiolites and underlying continental shelf sediments. Petrological study further illustrates that the central crystalline unit underwent a Barrovian-type overprint of the original high P/T metamorphic assemblages during wedge extrusion, and the metamorphic grade ranged from pumpellyite-actinolite to upper amphibolite facies.Quaternary uplift, marked by elevation of recent reefs, was estimated to be about 1260 m in Timor in the west and decreases toward Tanimbar in the east. In contrast, radiometric ages for the high P/T metamorphic rocks suggest that the exhumation of the high P/T metamorphic belt started in western Timor in Late Miocene time and migrated toward the east. Thus, the tectonic evolution of this region is diachronous and youngs to the east. We conclude that the deep-seated high P/T metamorphic belt extrudes into shallow crustal levels as a first step, followed by doming at a later stage. The so-called ‘mountain building’ process is restricted to the second stage. We attribute this Quaternary rapid uplift to rebound of the subducting Australian continental crust beneath Timor after it achieved positive buoyancy, due to break-off of the oceanic slab fringing the continental crust. In contrast, Tanimbar in the east has not yet been affected by later doming. A wide spectrum of processes, starting from extrusion of the high P/T metamorphic rocks and ending with the later doming due to slab break-off, can be observed in the Timor–Tanimbar region. 相似文献
996.
The Chinese Loess Plateau is suffering from severe soil erosion. The eco-environmental changes of the plateau are believed
to have an important influence on global eco-environmental sustainability; hence, this problem has attracted considerable
attention from scientists around the world. This study has two purposes; application of remote sensing (RS) and geographic
information system (GIS) techniques in the dynamic analysis of eco-environmental changes in the semiarid zone; and using the
Longdong region of the Chinese Loess Plateau as an example, to make dynamic analysis of the eco-environmental changes of the
region during the 1986–2004 period and identify controlling factors. Landsat Thematic Mapper (TM) data at a spatial resolution
of 30 m were used for analysis. Two training areas were selected in Jingning and Qingcheng counties for analysis using 10-m
resolution SPOT and Landsat TM data. The satellite RS images were obtained from the Institute of Remote Sensing Application
(IRSA), Chinese Academy of Sciences (CAS). Each images was rectified by Albers Equal Area Conic projection based on 1:50,000
scale topographic maps after spectrum preparation of the images. To make the precision within 1 or 2 pixels, the accurate
coordinative control points of the two systems were identified. Then the interpretation key was established based on the land
use/cover survey in the study area. The images were classified into six primary environmental types (farmland, forest, grassland,
water, construction area, and desert) and 25 sub-types using a visual image interactive interpretation method to obtain vector
and attribute data. The resultant accuracy of the land use/cover classification reached 95%. Finally, the transformation areas
and ratios of various eco-environmental types in the region were calculated to obtain the transition matrixes of eco-environmental
types in the two training areas, Jingning and Qingcheng. This study demonstrates that satellite RS and GIS techniques are
effective tools to monitor and analyze the eco-environmental changes in the semiarid region. Visual image interactive interpretation
based on GIS technique provides comprehensive information on the direction, rate, and location of eco-environmental changes.
The transition matrix model can be used to precisely analyze the variation and rates of the eco-environmental types and their
spatial distribution. Great land use changes have taken place Longdong during the 1986–2004 period. These eco-environmental
changes were driven by natural and human factors. Natural factors influencing the Longdong region of the Chinese Loess Plateau
mainly include temperature, water condition, terrain, soil, and erosion; while human activities include over-cultivation,
overgrazing, and fuelwood cutting. As viewed from the extent and severity of the influences, human activities play a very
important role in altering the eco-environment of the semiarid region. The study results indicate a need for future research
and observation in the semiarid region. 相似文献
997.
On the basis of geological observations and the study of conodont and radiolarian microfauna, a new stratigraphic scheme was proposed for the Mesozoic deposits of the Komsomolsk district of the Amur region. The lower Khorpy Group (T2-J3) consists of two units: the Boktor (T2-J2) and Kholvasi (J2–3). The Boktor Sequence (400 m thick) is represented by pelagic cherts with an admixture of cherty-clayey shales and volcanic rocks. The Kholvasi Sequence (500 m thick) is built up of the predominant siltstones and clayey shales with rare intercalations and lenses of clayey cherts and cherty-clayey shales. The upper Komsomolskaya Group (K1) has a terrigenous composition and includes the Gorin, Pionerskaya, and Pivan formations of 5 km total thickness. It is made up of intercalated sandstones, siltstones, mudstones, and often turbidites (proximal to distal). The rocks contain abundant buchia fauna of Volgian-Valanginian age, as well as carbonized plant detritus and flora of the Early Cretaceous habit. The described complex is characterized by a nappe-fold structure typical of the accretionary prisms in the ocean-continent convergence zones. The predominance of the coherent type of accretionary prisms reflects the simple morphology of the oceanic plate. 相似文献
998.
极端干旱荒漠区典型晴天大气热力边界层结构分析 总被引:3,自引:1,他引:3
利用极端干旱区敦煌野外观测试验资料,分析了极端干旱荒漠区夏季典型晴天位温、风速、比湿等主要物理要素的垂直结构特征及其地表热力和近地层大气运动特征的日变化规律。发现在极端干旱地区夏季晴天大气热力边界层结构十分独特。在夜间,贴地逆温层最低在900 m以上,最厚可以达到1 750 m,逆温层上面的残余层一般能达到4 000 m左右的高度。在白天,位温超绝热递减层高达1 000 m,超绝热递减层上面的混合层最高达3 700 m,混合层顶上还有大约450 m甚至更厚的夹卷层。当白天对流层发展达到残余层以后,混合层的发展明显加快。风速和比湿垂直廓线特征很好地印证了大气热力边界层独特的结构特征,地表热力和近地层大气运动特征也为这种独特的大气热力边界层结构提供了较好的物理支持。 相似文献
999.
利用架设在珠峰北坡4475m高度处的一套开路涡动协方差测量系统,对曲宗地区的大气状况进行了连续观测.分析了近地层气象要素、辐射平衡各分量和能量平衡各分量在高原雨季前(5月),雨季中(7月)和雨季后(11月)的变化特征.通过分析,发现曲宗地区气温和相对湿度日平均变化均呈单峰单谷型特征,气压则呈双峰双谷型特征,风速日变化为单峰型特征,风速一般在午后突然增大.伴随着雨季的爆发,曲宗地区气温升高,相对湿度增大,气压升高,风速减小.主导风向由东北风转换成西南风.雨季前后,辐射平衡各分量及能量平衡各分量均具有明显的变化趋势. 相似文献
1000.
南岭山地高速公路雾区恶劣能见度研究 总被引:13,自引:8,他引:13
使用2003年10月-2005年3月南岭山地京珠高速公路粤北段云岩雾区路段5套能见度仪的每分钟能见度资料和3套自动气象站的每分钟温度、湿度、风向、风速等气象要素资料, 分析研究了南岭山地高速公路雾区浓雾的能见度特征.结果表明, 南岭山地高速公路雾区各月雾日频率以1月最多, 近一半的天数都有雾; 3月次之, 7月最少.11月到次年5月雾日占全年雾日的80%以上, 形成明显的"雾季".南岭山地高速公路雾区浓雾存在日变化, 雾的频率在一天内凌晨最高, 午后最低, 明显比辐射雾的日变化小, 说明夜间辐射降温虽然不是南岭山地高速公路雾区起雾的主要原因, 但还是起到了一定的加强作用.虽然南岭山地雾区大气中含有丰富的凝结核, 南岭山地形成浓雾还是需要较高的相对湿度, 相对湿度至少要达到91%以上才能形成雾.在雾区出现5.2 m/s的大风时仍然有雾, 有雾时90%以上的风速在3 m/s以下, 有几乎一半的浓雾出现时风速在2 m/s左右, 这与辐射雾形成时大都是静小风的情况形成了鲜明对照.南岭山地高速公路雾区浓雾受地形影响比较大, 迎风坡出现雾的频率比背风坡高. 相似文献