应用6.7μm水汽图像分析一次特大暴雨的大气环境特征

本文所采用的资料是日本GMS-5卫星每天1小时一张的6.7μm水汽图像资料和常规的探空资料，卫星图像资料等，对2000年4月14日发生的一场特大暴雨的大气环境特征进行了分析。分析指出，造成此次特大暴雨主要是由于由副高西侧南支槽和西风槽同位相叠加，造成强烈和持续的深厚水汽输送，使得MCS猛烈发展，带来强降雨。     

Platform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)

High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport.During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian.From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite.This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin.     

Geochemistry of Sulfide Chimneys and Basement Pillow Lavas at the Southern Mariana Trough (12.55°N–12.58°N)

Three submarine hydrothermal sites (Snail, Y and Pika sites) in the southern Mariana area were investigated to clarify the geochemical difference between off-axis and on-axis submarine hydrothermal activities and volcanic rocks. The Snail and Y sites are located on the axis of the spreading ridge, and the Pika site is located on the off-axis region. Low-temperature venting of submarine hydrothermal fluids was observed at the Snail and Y sites. High-temperature black smoker activities were found at the Pika site. For further geochemical study, sulfide chimneys and mounds were collected from each site by manned submersible Shinkai 6500 . Basement short drill cores of volcanic rocks and sulfides were also obtained from the Snail and Pika sites using a multi-coring system. All drilled pillow lavas were tholeiitic andesite with a narrow range of chemical variation. Significant enrichments of Rb, Ba and Th were absent in both on-axis (Y and Snail sites) and off-axis (Pika site) samples, suggesting the least incorporation of subducting sediments to the magmatic system. Concentrations of Au and Ag in the sulfide chimney were within the range of massive sulfides at the mid-ocean ridge rather than typical arc-type massive sulfides. It is found that sulfur isotope compositions of sulfides were different between the on-axis and off-axis samples: on-axis samples had heavy δ³⁴S (+2.9–+8.7‰) and off-axis samples (–0.3 to +3.8‰) were similar to the local magmatic value. Such a regional difference probably results from changes of deep hydrothermal processes during the water–rock interaction rather than differences in tectonic settings.     

东海地区新构造运动研究

文中涉及的东海地区主要包括东海大陆架和冲绳海槽。该区的地质构造基本属于中国东部大陆向海域延伸的部分,新生代发育东海陆架盆地、钓鱼岛隆褶带和冲绳海槽盆地。由于东海位于大陆板块及其与菲律宾海板块接合的地带,中新世中期以来的新构造运动及其产生的地质构造具有独特性和复杂性。在充分解读前人有关资料和研究成果的基础上,从构造地貌、地质构造、岩浆活动和地震活动性等方面,对东海地区新构造运动的特征进行了较为系统而深入的分析研究,并在此基础上探讨了该区新构造运动的动力条件,取得了一些初步认识。东海地区新构造运动开始于中新世中期,构造应力作用由原先左旋剪切拉张转为左旋剪切挤压;区内新构造运动性质具有非一致性,东海陆架盆地表现整体微向SE倾斜下沉活动,冲绳海槽为主动机制的地壳拉张裂陷运动,钓鱼岛褶皱带具侧向挤压拱曲隆升活动;活动断裂以NNE和NE向为主,基本分布在东海陆架盆地以东地区,尤其是冲绳海槽;岩浆作用和地震活动也主要分布在东海陆架盆地东边,特别是冲绳海槽;东海地区的新构造运动,是菲律宾海板块往东海陆架之下俯冲导致弧后地幔隆起,引起冲绳海槽NWSE向扩张,及与青藏高原东边地块被侧向挤出推动华南地块往东南运动共同作用的结果。     

Evolution of West Rota Volcano, an extinct submarine volcano in the southern Mariana Arc: Evidence from sea floor morphology, remotely operated vehicle observations and 40Ar–39Ar geochronological studies

Abstract West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 × 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE‐trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal arc crust to the east from subsiding, thin back‐arc basin crust to the west. The WRV is distinct from other Mariana Arc volcanoes: (i) it consists of a lower, predominantly andesite section overlain by a bimodal rhyolite‐basalt layered sequence; (ii) andesitic rocks are locally intensely altered and mineralized; (iii) it has a large caldera; and (iv) WRV is built on a major fault. Submarine felsic calderas are common in the Izu and Kermadec Arcs but are otherwise unknown from the Marianas and other primitive, intraoceanic arcs. ⁴⁰Ar–³⁹Ar dating indicates that andesitic volcanism comprising the lower volcanic section occurred 0.33–0.55 my ago, whereas eruption of the upper rhyolites and basalts occurred 37–51 thousand years ago. Four sequences of rhyolite pyroclastics each are 20–75 m thick, unwelded and show reverse grading, indicating submarine eruption. The youngest unit consists of 1–2 m diameter spheroids of rhyolite pumice, interpreted as magmatic balloons, formed by relatively quiet effusion and inflation of rhyolite into the overlying seawater. Geochemical studies indicate that felsic magmas were generated by anatexis of amphibolite‐facies meta‐andesites, perhaps in the middle arc crust. The presence of a large felsic volcano and caldera in the southern Marianas might indicate interaction of large normal faults with a mid‐crustal magma body at depth, providing a way for viscous felsic melts to reach the surface.     

Variations in sediment thickness and type along the northern Philippine Sea Plate at the Nankai Trough

Abstract   We documented regional and local variations in basement relief, sediment thickness, and sediment type in the Shikoku Basin, northern Philippine Sea Plate, which is subducting at the Nankai Trough. Seismic reflection data, tied with ocean drilling program drill cores, reveal that variations in the incoming sediment sequences are correlated with basement topography. We mapped the three-dimensional seismic facies distribution and measured representative seismic sequences and units. Trench-parallel seismic profiles show three regional provinces in the Shikoku Basin that are distinguished by the magnitude of basement relief and sediment thickness: Western (<200–400 m basement relief, >600 m sediment thickness), Central (>1500 m relief, ∼2000 m sediments), and Eastern (<600 m relief, ∼1200 m sediments) provinces. The total thickness of sediment in basement lows is as much as six times greater than that over basement highs. Turbidite sedimentation in the Shikoku Basin reflects basement control on deposition, leading to the local presence or absence of turbidite units deposited during the middle Oligocene to the middle Miocene. During the first phase of sedimentation, most basement lows were filled with turbidites, resulting in smooth seafloor morphology that does not reflect basement relief. A second phase of turbidite deposition in the Eastern Province was accompanied by significant amounts of hemipelagic sediments interbedded with turbidite layers compared to the other provinces because of its close proximity to the Izu–Bonin Island Arc. Both regional and local variations in basement topography and sediment thickness/type have caused lateral heterogeneities on the underthrusting plate that will, in turn, influence lateral fluid flow along the Nankai accretionary prism.     

海斗深渊沉积物组成特征及其物质来源研究进展

海斗深渊是海洋中最深的区域,由水深范围在6000～11000 m范围内的深部海沟组成,以极端的物理化学条件为特征,其沉积物以深海黏土为主。基于目前关于马里亚纳海沟及其沉积物的研究进展,总结了海斗深渊的地貌、物理化学和水动力等方面的特征;归纳了海斗深渊沉积物的粒度特征、矿物组成和古生物特征;探讨了海斗深渊沉积物的物质来源及主要分析方法。海斗深渊沉积物的物质来源具有多源性,综合多种方法示踪是准确揭示其物质物源的关键。     

Element enrichment and U-series isotopic characteristics of the hydrothermal sulfides at Jade site in the Okinawa Trough

The geochemical and U-series isotopic characteristics of hydrothermal sulfide samples from the Jade site (127°04.5′E, 27°15′N, water depth 1300–1450 m) at Jade site in the Okinawa Trough were analyzed. In the hydrothermal sulfide samples bearing sulfate (samples HOK1 and HOK2), the LREEs are relatively enriched. All the hydrothermal sulfide samples except HOK1 belong to Zn-rich hydrothermal sulfide. In comparison with Zn-rich hydrothermal sulfides from other fields, the contents of Zn, Pb, Ag, Cd, Au and Hg are higher, the contents of Fe, Al, Cr, Co, Ni, Sr, Te, Cs, Ti and U lower, and the ²¹⁰Pb radioactivity ratios and ²¹⁰Pb/Pb ratios very low. In the hydrothermal sulfide mainly composed of sphalerite, the correlations between rare elements Hf and U, and Hf and Mn as well as that between dispersive elements Ga and Zn, are strongly positive; also the contents of Au and Ag are related to Fe-sulfide, because the low temperature promotes enrichment of Au and Ag. Meanwhile, the positive correlations between Fe and Bi and between Zn and Cd are not affected by the change of mineral assemblage. Based on the ²¹⁰Pb/Pb ratios of hydrothermal sulfide samples (3.99×10⁻⁵-5.42×10⁻⁵), their U isotopic composition (²³⁸U content 1.15–2.53 ppm, ²³⁸U activity 1.07–1.87 dpm/g, ²³⁴U activity 1.15–2.09 dpm/g and ²³⁴U/²³⁸U ratio 1.07–1.14) and their ²³²Th and ²³⁰Th contents are at base level, and the chronological age of hydrothermal sulfide at Jade site in the Okinawa Trough is between 200 and 2000 yr. Supported by the Pilot Project of Knowledge Innovation Project, Chinese Academy of Sciences (Grant No. KZCX2-YW-211), National Natural Science Foundation of China (Grant Nos. 40830849, 40176020), and Special Foundation for the Eleventh Five Plan of COMRA (Grant No. DYXM-115-02-1-03)     

The Crustal Structure Character of East China Sea

This paper presents actuality of investigation and study of the crustal structure characters of East China Sea at home and abroad. Based on lots of investigation and study achievements and the difference of the crustal velocity structure from west to east, the East China Sea is divided into three parts - East China Sea shelf zone, Okinawa Trough zone and Ryukyu arc-trench zone. The East China Sea shelf zone mostly has three velocity layers, i.e., the sediment blanket layer （the velocity is 5.8-5.9 km/s）, the basement layer （the velocity is 6.0-6.3 km/s）, and the lower crustal layer （the velocity is 6.8-7.6 km/s）. So the East China Sea shelf zone belongs to the typical continental crust. The Okinawa Trough zone is located at the transitional belt between the continental crust and the oceanic crust. It still has the structural characters of the continental crust, and no formation of the oceanic crust, but the crust of the central trough has become to thinning down. The Ryukyu arc-trench zone belongs to the transitional type crust as a whole, but the ocean side of the trench already belongs to the oceanic crust. And the northwest Philippine Basin to the east of the Ryukyu Trench absolutely belongs to the typical oceanic crust.     

Structural control of the Gagua “Wedge” Zone east of Taiwan Island on the southern Okinawa Trough

The sea area east of Taiwan Island is a unique ac-tive arc-continental collision margin in China and even in the world with the NE-nearly EW extending Ryu-kyu trench-arc-backarc basin system on the east and the nearly N-S extending Manila trough and Luzon arc on the west. The sea area east of Taiwan Island differs from the Ryukyu trench-arc-basin system in structural property, but there is a certain genetic relation between the two (Fig. 1)[1-3]. Since the 1990s, many investigations and …