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1.
对大洋27航次在西太平洋马里亚纳海沟挑战者深渊获取的3个多金属氧化物样品进行了X射线矿物衍射分析、穆斯堡尔谱分析及地球化学元素分析,研究其矿物、地球化学特征差异。结果表明,所取样品处于多金属氧化物发育的初始阶段,具有独特的矿物地球化学特征:(1)相较于太平洋CC区及中太平洋海盆获取的多金属结核样品,本研究样品的矿物组成中含有异常高的石英、斜长石以及黏土矿物,而水羟锰矿和钙锰矿含量较低。(2)样品中铁相矿物主要为正方针铁矿(91.6%),另含少量纤铁矿(8.4%),推测是纤铁矿向更加稳定的正方针铁矿衍变的结果。(3)由于样品中深海黏土组分以及氧化物核心物质的混入,加上吸附金属氧化物时间较短,导致SiO2和Al2O3含量均高于正常结核,而Fe、Mn、Cu、Co、Ni等其余金属元素含量较低。(4)由于形成时间较短,样品中稀土元素含量相对较低,ΣREE仅约为0.4×10-3(一般太平洋CC区及中太平洋结核中稀土含量均大于1.0×10-3);加之海水氧化还原作用的降低以及研究区海底热液活动的影响,Ce元素未表现出多金属结核中常见的正异常。  相似文献   
2.
This paper describes the petrology and geochemistry of rocks from the Yap Trench acquired by three dives of the Jiaolong research submarine. Combining the geophysical data and submersible observations, this paper describes the geomorphology, shallow structures, and sedimentology of the Yap Trench and further discusses the tectonics and activities of this region. Two obvious slope breaks are found on the landward slope, and horsts and grabens with small fault offsets are observed in the ocean-ward slope of the trench. Peridotites sampled from the Yap Trench inner wall are highly depleted subduction-related mantle residues. Volcanic rocks in the northern segment of the trench have subduction-related characteristics that Yap fore-arc rocks underwent metasomatism during Cenozoic subduction. The rocks with remarkable lithologic difference from lithospheric mantle and upper crust sampled in the break slopes suggest that the slope break area may represent a lithologic boundary or transition zone. The landward slope of the Yap Trench was removed by subduction erosion as a result of collision with the Caroline Ridge. The bending of the down-going plate caused normal faults, horsts, and grabens with little or no sediments indicating that the Caroline Ridge is subducting beneath the Yap arc along the trench even though the convergence rate is very slow.  相似文献   
3.
Hexi Corridor is located at the northeastern margin of the Tibetan plateau. Series of late Quaternary active faults are developed in this area. Numerous strong earthquakes occurred in history and nowadays. Jinta Nanshan fault is one of the boundary faults between the Qinghai-Tibet block and the Alxa block. The fault starts from the northwest of Wutongdun in the west, passes through Changshan, Yuanyangchi reservoir, Dakouzi, and ends in the east of Hongdun. Because the Jinta Nanshan fault is a new active fault in this region, it is important to ascertain its paleoearthquakes since late Pleistocene for the earthquake risk study. Previous studies were carried out on the western part, such as field geomorphic investigation and trench excavation, which shows strong activity in Holocene on the western segment of Jinta Nanshan fault. On the basis of the above research, in this paper, we carried out satellite image interpretation, detailed investigation of faulted landforms and differential GPS survey for the whole fault. Focusing on the middle-eastern part, we studied paleoearthquakes through trench exploration on the Holocene alluvial fan and optical luminescence dating. The main results are as follows:Early Pleistocene to late Pleistocene alluvial strata are widely developed along the fault and Holocene sediment is only about tens of centimeters thick. The Jinta Nanshan fault shows long-lasting activity since late Quaternary and reveals tens of centimeters of the lowest scarp which illustrates new strong activity on the middle-east segment of this fault. Since late Pleistocene, 4 paleoearthquakes happened respectively before(15.16±1.29) ka, before(9.9±0.5) ka, about 6ka and after(3.5±0.4) ka, revealed by 4 trenches, of which 2 are laid on relatively thicker Holocene alluvial fan. Two events occurred since middle Holocene, and both ruptured the whole fault.  相似文献   
4.
为了分析雅浦海沟中底栖生物群落的食物来源和营养级,本研究分析了雅浦海沟真光层中浮游植物和浮游动物、海底沉积物和巨型底栖生物(海绵、海参、海蛇尾、海星、海葵和钩虾)中的碳、氮稳定同位素组成。研究发现雅浦海沟真光层中的浮游植物和浮游动物δ13C值[(-22.8±0.4)‰和(-21.8±0.8)‰]和δ15N值[(5.4±0.4)‰和(6.8±0.2)‰]与巨型底栖生物的δ13C值(-20.1‰~-16.8‰)和δ15N值(11.9‰~17.9‰)的差异超过了一个营养级,表明作为底栖生物的初始食物来源的浮游植物和浮游动物在向下输送的过程中经历了食物链传递和细菌的降解。巨型底栖生物的δ15N和δ13C值之间无显著的相关性,此外不同物种之间营养级也存在明显差异,表现为海绵的营养级相对较高(3.4~4.7),海参(3.3~3.6)、海蛇尾(3.4~3.5)和海星(3.2~3.7)的营养级较为接近,钩虾(2.9~3.3)和海葵(3.1)的营养级则相对略低,反映了底栖生物不同物种之间食物来源的多样化。  相似文献   
5.
利用西太平洋地区的雅浦-马里亚纳海沟附近海域的多波束水深数据,获得了9.8°N—13.2°N、132.2°E—145°E矩形区域内的高精度水深地形图。通过对精细地貌进行研究发现,马里亚纳海沟南部的洋坡上发育有大范围的地垒、地堑型地貌,雅浦海沟北部存在明显的分段性特征,菲律宾海盆和帕里西维拉海盆内存在不同展布方向的大规模脊-槽地貌。研究结果表明此处复杂的地形地貌特征主要受板块运动的控制。最后结合已有研究成果,对该区域的地形地貌进行了分类。  相似文献   
6.
在马里亚纳海沟"蛟龙号"载人深潜器海试区约7000m水深的海底,发现了硅藻化石软泥沉积物,为中国首次在此大深度船载采集到硅藻化石软泥。室内硅藻化石分析显示,重力柱状样顶部约10cm厚的软泥为大筛盘藻Ethmodiscus rex硅藻软泥。化石主要由大筛盘藻组成,呈碎片状,数量巨大,并伴生有Azpeitia等热带远洋浮游种类。硅藻化石软泥发育表明,本区曾发生过E.rex勃发事件,具有重要的古海洋学和古生物学研究意义。  相似文献   
7.
日本海沟俯冲带热结构与深源地震   总被引:1,自引:1,他引:0       下载免费PDF全文
本文利用有限差分方法,计算了全地幔对流模式和双层地幔对流模式下日本海沟俯冲带热结构、浮力及P波速度异常分布,基于亚稳态橄榄石相变模型推测亚稳态橄榄石的存在范围,同时分析了热传导系数、热膨胀系数和热源对俯冲带热结构的影响,以及俯冲带所受浮力与俯冲带形态的关系.结果表明,双层地幔对流模式下模拟的P波速度异常分布与层析成像结果更为相符,也与深源地震的分布有较好的相关性.板块内部亚稳态橄榄石的存在范围随热传导系数和热膨胀系数的减小而增大,同时忽略相变潜热和剪切生热的影响也会造成模型所预测的亚稳态橄榄石范围偏大.俯冲带所受负浮力在400 km深度附近达到最大值,亚稳态橄榄石的存在使负浮力逐渐减小,甚至在板块内部产生正浮力,不利于俯冲带穿透660 km相变界面.  相似文献   
8.
Abstract

The Antarctic Bottom Water (AABW) current plays a crucial role in storing and transporting heat, water, and nutrients around the world. However, it is impossible to monitor AABW in the Plio-Pleistocene by direct measurement. Hence, abyssal erosion was usually chosen as an effective indicator of the presence of the AABW in the Indian and Eastern Pacific Oceans during that period. Here, we report a high-resolution magnetostratigraphy of a gravity core, the JL7KGC-01A from the south of the Mariana Trench, northwest Pacific Ocean. The main results are as follows: (1) polarity data suggest that the sequence recorded the late Gauss chron to the early Brunhes chron, including the Jaramillo, Cobb Mountain, and Olduvai normal subchrons; (2) the sedimentary processes in the study area since 2.9 Ma show three stages of sedimentation: 83 cm/Ma during 2.9–1.2 Ma, 183 cm/Ma during 1.2–0.7 Ma, and no sedimentation since ~0.7 Ma; (3) the area south of the Mariana Trench experienced a significant change in the deposition rate at 1.2 Ma, which could be correlated with the intensified desertification in inland Asia, and experienced a prominent depositional hiatus since the early middle Pleistocene, which likely resulted from the enhanced/expanded AABW. Based on these new polarity data and comparisons with previous studies around the Pacific Ocean, we therefore propose that the AABW experienced a notable change during the early–mid Pleistocene transition.  相似文献   
9.
黄庄—高丽营断裂是北京平原区一条重要的活动断裂,在庙城—高丽营段沿线发生地裂缝,造成大量房屋墙体开裂和道路破坏。在西王路村探槽揭示该断裂错断第四系地层,产生地表地裂缝。探糟断裂孢粉年龄测试,该断裂发生年龄大致在13~22ka,仍处于活动状态。  相似文献   
10.
蔚广盆地南缘断裂带唐山口段山前断层活动性研究   总被引:1,自引:0,他引:1  
蔚广盆地是山西地堑系北端京西北盆岭构造区内的一个半地堑盆地,蔚广盆地南缘断裂带为控制该盆地形成的边界断裂。该断裂带位于唐山口段的山前断裂在冲洪积扇体上形成了线性特征显著的断层陡坎。横跨断层陡坎开挖的探槽表明该条山前断裂属于全新世活动断裂,探槽揭示了2条活动断层以及相应的3次古地震事件。在距今约9ka时其中一条断层首次活动,之后在距今约7.3ka时该条断层再次活动并引发了另一条断层的形成与同步活动。最后它们又发生了第三次活动,而最新一次活动的时间由于相应地表沉积的缺失而无法获得。这3次古地震事件的累积垂直位错约为8.1m。估算出整条山前断裂的平均复发周期约为1.7ka、平均滑动速率约为1.6mm/a。此外还依据经验公式估算出了各次古地震的参考震级。  相似文献   
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