Formation of the Yazi Spring Stream and its significance on tectonics-climate on the northern slope of Kunlun Mountains

IEECAS SKLLQG

Tectonics of the southern tip of the Parece Vela Basin, Philippine Sea Plate

We report new geophysical and petrological data collected at the southern tip of the Parece Vela Basin in the Philippine Sea. The Parece Vela Basin, which was formed as a backarc basin behind proto Mariana arc-trench system from late Oligocene to middle Miocene, provides us a good opportunity to study the nature of successive backarc basin formations in the Philippine Sea and the relationship between are and backarc magmatisms. Regional bathymetric map derived from satellite altimetry shows that the southern tip of the basin, now located just west of the Yap arc-trench system, has unique morphological and tectonic features which include: 1) the absence of spreading center or its trace, 2) shallow average depth, and 3) enigmatic curved structures. Our newly collected high-resolution bathymetric data reveal that the spreading fabric similar to the central Parece Vela Basin exists to the north of 9 degrees 20'N. Thus it appears that the present-day Yap arc and backarc region represent the western half of the seafloor that was produced by the early E-W and the following NE-SW spreading in the northern and central Parece Vela Basin, and that the eastern counterpart now lies west of the West Mariana Ridge. Unlike the northern Parece Vela Basin, there appears to be no evidence for a systematic propagation of spreading center in the southern part. Instead two rift segments, one which extends from the central Parece Vela Basin and the other which lies within the western remnant arc (Kyushu-Palau Ridge), overlap at the southern tip of the basin, producing a complex seafloor that includes curvilinear deeps and deformed topographic highs. (c) 2007 Elsevier B.V. All rights reserved.

Tectonics in the northwestern West Philippine basin

The West Philippine basin (WPB) is a currently inactive marginal basin belonging to Philippine Sea plate, which has a complex formation history and various crust structures. Based on gravity, magnetic and seismic data, the tectonics in West Philippine basin is characterized by amagma spreading stage and strike slip fractures. NNE trending Okinawa-Luzon fracture zone is a large fracture zone with apparent geomorphology and shows a right-handed movement. The results of joint gravity-magnetic-seismic inversion suggest that the Okinawa-Luzon fracture zone has intensive deformation and is a transform fault. Western existence of the NW trending fractures under Ryukyu Islands Arc is the main cause of the differences between south and north Okinawa Trough. The Urdaneta plateau is not a remained arc, but remnant of mantle plume although its lava chemistry is similar to oceanic island basalt (OIB).

根据特有植物的分布探讨中国冰期避难所

第三纪晚期和第四纪全球变冷对植物类群现在的分布式样有着重要的影响。植物特有现象出现的地区或中心一般都和一些适宜植物生存的避难所相联系，在这些避难所，众多植物类群得以保存、同时不断多样化形成新的类群。尽管中国区系中包括了丰富的特有类群，对特有类群丰富的地区也开展了一些初步的研究，但迄今我们对中国特有地区的数量、具体位置及其地理式样的了解仍然有限，对特有现象形成的原因更是所知甚少。为此，本研究通过选择555种中国特有植物类群（包括种、亚种和变种）为代表，对中国维管植物的特有中心及其地理式样进行了研究，并在此基础上探究了中国的冰期避难所。我们首先将这些特有类群的分布描绘在1  1纬度/经度的方格里，计算了特有现象的两个基本参数：总特有和加权特有，将那些特有参数值在前5%的单元确定为特有中心。 为了进一步了解中国的特有中心主要是植物的保存地（“植物博物馆”）还是植物新类群发生和物种形成（“植物摇篮”）的场所，或二者兼而有之，我们又根据化石证据、分子和形态系统树，以及生物地理等一系列数据，把555个特有类群分为古特有和新特有两个级别，探讨了这两个特有级别各自的分布式样。结果显示，具有特有现象的地区有20个，这些地区位于华中和华南，大致对应于这些地区的山系。特有中心主要位于青藏高原的东部（横断山和大雪山）、云贵高原、华中山脉、南岭山脉和东南山脉;海南和台湾也具有很多特有种。通过特有种所在的地区界定冰期避难所与第四纪植被重建的结果在很大程度上相一致，后者显示在这些地区在冰期有泛温带和亚热带森林出现。因此，山脉地区可能通过复杂的地形和更新世极端气候条件的局域缓冲为这些特有类群提供稳定生存的生境;这既保存了这些孑遗类群（“植物博物馆”），又使得新的类群得以不断出现（“植物摇篮”）。 中国特有中心既包含孑遗的类群（古特有）也包含近期新形成的类群（新特有）。然而，它们的分布和密度却非常不同，这可能与这些地区的地质分化和构造历史有关。尤其值得注意的是，青藏高原东部边缘是中国最重要的“进化前沿”，这可能与晚第三纪青藏高原的不断隆升有关。相反，在第三纪多数时候，华中和华南（除了海南和台湾）在地质构造上的相对稳定，使得孑遗植物谱系得以最大程度地保存。两种特有级别在全国水平上的比例（古特有为39.1%，新特有为60.9%）说明，尽管不同地区间存在一定的差异，但华中和华南既是晚第三纪和第四纪全球变冷后植物得以保存的避难所，也是植物分化和新类群形成的重要中心。 这些研究结果对特有植物、尤其对具有不同保护要求的孑遗类群和新类群的保护有着重要意义。我们可以针对富有古特有的地区以及有更多新类群产生的“植物摇篮”制定不同的保护策略和措施。

Tectonic and geodynamic pattern of marginal seas on the West Pacific inferred from multi-satellite altewetry geoid

With the rapid development of satellite observations, we can use the altimetry geoid to study submarine tectonics and geodynamics. On the basis of the 4' x 4' geoid undulation calculated from altimeter data of Geosat, ERS-1/2 and Topex/Poseidon on the West Pacific, located between 0degreesN similar to 45degreesN, 100degreesC similar to 150degreesE, Bouguer, Glenni and isostatic geoid undulation are obtained from correction of gravitational potential of the global topography and isostacy. Moho discontinuity depth is inversed by the Glenni geoid undulation, and the stress field from small-scale mantle convection is reasonably calculated from the isostatic geoid undulation. The results show that within the Philippine Sea and the South China Sea, short-wavelength lineations of the geoid undulation are parallel or cross to magnetic lineations and rifting ridges. The Moho depth of marginal sea basins becomes shallow southward, and its values are similar to that of the Philippine Sea. These facts show that strength of tectonic activities are almost the same on the both sides of the Ryukyu-Taiwan-Philippine are. Various kinds of tectonic features with different driving mechanisms of small-middle and large-scale of mantle convection, however, display a special pattern of tectonics and geodynamics of the continental marginal seas distinguished from oceans and continents.

Os isotope dating and growth hiatuses of Co-rich crust from central Pacific

Up to now, accurate determination of the growth age and hiatuses of the Co-rich crust is still a difficult work, which constrains the researches on the genesis, growth process, controlling factors, regional tectonics, paleo-oceanographic background, etc. of the Co-rich crust. This paper describes our work in determining the initial growth age of the Co-rich crust to be of the late Cretaceous Campanian Stage (about 75-80 Ma), by selecting the Co-rich crust with clear multi-layer structures in a central Pacific seamount for layer-by-layer sample analysis and using a number of chronological methods, such as Co flux dating, dating by correlation with Os-187/Os-188 evolution curves of seawater, and stratigraphic division by calcareous nannofossils. We have also discovered growth hiatuses with different time intervals in the early Paleocene, middle Eocene, late Eocene and early-middle Miocene, respectively. These results have provided an important age background for further researches on the Co-rich crust growth process and the paleo-oceanographic environment evolution thereby revealed in the said region.

Seismic profiles across the middle Tan-Lu fault zone in Laizhou Bay, Bohai Sea, eastern China

The stratigraphic architecture, structure and Cenozoic tectonic evolution of the Tan-Lu fault zone in Laizhou Bay, eastern China, are analyzed based on interpretations of 31 new 2D seismic lines across Laizhou Bay. Cenozoic strata in the study area are divided into two layers separated by a prominent and widespread unconformity. The upper sedimentary layer is made up of Neogene and Quaternary fluvial and marine sediments, while the lower layer consists of Paleogene lacustrine and fluvial facies. In terms of tectonics, the sediments beneath the unconformity can be divided into four main structural units: the west depression, central uplift, east depression and Ludong uplift. The two branches of the middle Tan-Lu fault zone differ in their geometry and offset: the east branch fault is a steeply dipping S-shaped strike-slip fault that cuts acoustic basement at depths greater than 8 km, whereas the west branch fault is a relatively shallow normal fault. The Tan-Lu fault zone is the key fault in the study area, having controlled its Cenozoic evolution. Based on balanced cross-sections constructed along transverse seismic line 99.8 and longitudinal seismic line 699.0, the Cenozoic evolution of the middle Tan-Lu fault zone is divided into three stages: Paleocene-Eocene transtension, Oligocene-Early Miocene transpression and Middle Miocene to present-day stable subsidence. The reasons for the contrasting tectonic features of the two branch faults and the timing of the change from transtension to transpression are discussed. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.

柴达木盆地西区新生代构造演化

The Qaidam Basin constitutes a major portion of the northeastern Tibetan Plateau, and an understanding of its tectonic development will help decipher how the Tibetan Plateau was formed. It is shown that Late Cretaceous–Paleocene deposits of the western Qaidam Basin can be well correlated with their counterparts of the southwestern Tarim Basin, implying that the two regions were originally connected or were in the same depositional basin during that period of time. The Qaidam Basin commenced subsiding due to crustal shortening in the Eocene, and it has subsequently evolved into an independent basin since the Miocene. The main depocenter was noticeably persistent in the middle of the western Qaidam Basin from Eocene to Miocene time, and then it shifted to the east. On the basis of spatial stratigraphic correlation and restoration of sedimentary processes, we surmise that there existed a proto–Qaidam Basin during the Paleogene, where the Suhai and Kumukol Basins represent its northern and southern margins, respectively. The Suhai and Kumukol Basins were subsequently isolated from the Qaidam Basin as a result of basinward thrusting in basin-margin areas. It is shown that the western Qaidam Basin experienced three distinct stages: the first stage was characterized by a simple synclinal depression; the second stage was marked by occurrence of reverse faults at inflection points of the megafold and continuous subsidence in the middle of the basin; and the third stage featured intrabasinal deformation and uplift. The eastern Qaidam Basin underwent a diverse evolution and became the main depositional area in the Quaternary. It is suggested that the Qaidam Basin should be generated as a result of crustal buckling or folding, manifesting itself as a synclinal depression. The crustal folding model can account for a number of observations, including localization of the depocenter in the middle of the basin, nearly concomitant deformation on the south and north sides of the Qaidam Basin, occurrence of major high-angle reverse faults at basin margins, and generation of adjacent intermontane Suhai and Kumukol Basins. A tectonic model is accordingly advanced to illustrate Cenozoic tectonics of the Qaidam Basin.

西秦岭新生代火山岩中的地幔捕虏体和捕虏晶研究

Western Qinling, a conjunction region of the North China Craton, the Yangtze Craton and the Tibetan Plateau, has very complicated history of geologic and tectonic evolution. Previous studies mainly focus on tectonics and petrology of volcanic rocks in the western Qinling. Therefore, little is known about the Cenozoic lithospheric mantle beneath the western Qinling. Mafic, ultramafic and/or alkaline volcanic rocks and their entrained mantle peridotitic xenoliths and xenocrysts are known as samples directly from the lithospheric mantle. Their petrological and geochemical characteristics can reflect the nature and deep processes of the lithospheric mantle. Cenozoic volcanic rocks in the western Qinling contain abundant mantle xenoliths and xenocrysts, which provide us an opportunity to probe the lithospheric mantle beneath this region and a new dimension to insight into geologic evolution. Cenozoic volcanic rocks (7-23 Ma) from the western Qinling are sparsely distributed in the Lixian-Dangchang-Xihe Counties, Gansu Province, China. Volcanic rocks contain plenty of mantle-derived xenoliths, including spinel lherzolites with subordinate wehrlite, dunite, olivine websterite, clinopyroxenite and garnet lherzolite, and few olivine, clinopyroxene and spinel xenocrysts. These peridotitic xenoliths show clear deformed textures and their major minerals show excellent orientation. Thus, these peridotites are typical deformed peridotites. Olivine xenocrysts have clearly-zoned textures. The peridotitic xenoliths can be divided into two groups based on their compositions, namely, the H-type and L-type. The H-type peridotites are characterized by high Fo (>90) in olivines in which fine-grained ones have higher Fo than the coarse grains, low CaO (<20 %) in clinopyroxenes, high Cr# (>40) in spinels and high equilibration temperatures. They may represent the refractory lithospheric mantle. In contrast, the L-type peridotites contain low Fo (<90) olivines (with lower Fo in fine-grained olivines), high CaO (>20 %) clinopyroxenes, low Cr# (<20) spinels and low equilibration temperatures. They experienced low degree of partial melting. The Cenozoic lithospheric mantle beneath the western Qinling was refractory in major element compositions based on the mineral compositions of xenoliths and xenocrysts and experienced complicated deep processes. The lithospheric mantle was modified by shear deformation due to the diapirism of asthenosphere and strong tectonic movements including the collision between North China Craton and Yangze Craton and the uplift of Tibetan Plateau, and then underwent metasomatism with a hydrous, Na, Ti and Cr enriched melt.

鄂尔多斯盆地子洲气田二叠系山西组储层特征与天然气富集规律研究

In this thesis, detailed studies on the sedimentology and petrophysical properties of reservoir rocks in the Shan#2 Member of Shanxi Formation, Zizhou gas field of Ordos Basin, are carried out, based on outcrop description, core description, wireline log interpretation and analysis of petrophysical properties. In the context of stratigraphic division scheme of the Upper Paleozoic in Ordos Basin, the Shan#2 Member is further divided into three subintervals: the Shan#23, Shan#22 and Shan#21, based on the marker beds，depositional cycles, wireline log patterns. Subaqueous deltaic-front distributary channels, distributed from the south to north, is identified，which is the main reservoir sand bodies for gases of Shan#2 Member at Zizhou gas field. Quartzose and lithic-quartzose sandstones, commonly with a high volume of cement, but a low volume of matrix, are the major reservoir rocks in the studied area. All sandstones have been evolved into the late diagenetic stage (referred to as diagenetic stage B) during the burial, experiencing compaction, cementation, replacement and dissolution, in which the compaction and cementation could have reduced the porosity, while dissolution could have improved the petrophysical properties. The pore types in the reservoirs are dominated by intergranular-solutional, intergranular-intercrystal and intercrystal-solutional porosity. According to the parameters and capillary pressure curves of test samples, five types of pore texture (I-V) are differentiated, in which types II and III pore textures displayed by low threshold pressure-wide pore throat and moderate threshold pressure-moderately wide pore throat, exist widespread. Sandstone reservoirs in the studied area are characterized by exceptionally low porosity and permeability, in which the petrophysical properties of those in Shan#23 horizon are relatively better. The petrophysical property of reservoirs was influenced both by the sedimentation and diagenesis. In general, the coarse quartzose sandstones deposited in subaqueous distributary channels show the best petrophysical property, which tends to be worse as the grain size decreases and lithic amount increases. Three types of gas reservoirs in Shan#23 horizon are classified according to petrophysical properties (porosity and permeability), which could have been influenced by the initial depositional facies, diagenesis and tectonics. On the basis of the study on the geological conditions of reservoirs in the area, it is concluded that sedimetary facies, diagenesis and tectonic actions can provide an important foundation for gas pool formation, which can also control the accumulation and distribution of gas reservoirs.