海洋地质与环境重点实验室知识库

西菲律宾海是全球海-气和海-陆相互作用的关键区域之一，是全球物质和能量交换的重要场所，因而在研究区域的源-汇过程和全球气候变化中扮演重要角色。菲律宾岛弧是西菲律宾深海碎屑沉积物的主要源区，然而对于其碎屑沉积物的沉积特征还缺乏系统的研究，因而缺少可供物源对比研究的基础数据；对于岛弧物质向深海输入的变化及其控制因素也缺乏清晰的认识。2006年“国际海洋全球过去气候变化(IMAGES)”MD155航次在吕宋岛东侧比科尔岛架MD06-3052站采集到了高质量的沉积岩心，为开展上述问题提供了很好的材料。本论文对该岩心碎屑沉积物的矿物组成、粒度、放射性成因Sr、Nd同位素等特征进行了研究，分析了碎屑沉积物的来源、输运方式，探讨了碎屑物质向海输入变化规律及其控制因素。

通过X-射线衍射分析(XRD)和综合矿物分析仪(Tescan Integrated Mineral Analyser, TIMA)分析方法，在比科尔岛架正常海相沉积物中识别出的主要矿物包括方解石、文石、电气石、斜长石、石英、绿帘石。浊流层矿物组成与正常海相沉积层类似，火山灰层以含有火山玻璃为特征，但不同火山灰层的火山玻璃含量和形态存在差异。研究区中的文石和方解石主要是生物成因的，而石英、斜长石、电气石等代表了陆源碎屑组分。150 ka以来碳酸盐的含量在间冰期增加而冰期时减少，石英、斜长石以及电气石的含量变化与其相反，表现为冰期高而间冰期低。石英/碳酸盐比值具有冰期高而间冰期低的变化趋势，指示了研究区冰期时陆源碎屑物质输入增加，间冰期时输入减少。

在MD06-3052孔中，正常海相沉积层位的碎屑物质主要由黏土和粉砂组成，砂含量较低，而火山灰层和浊流层中砂含量明显增加。利用粒度参数化端元分析方法，在正常海相沉积层位的碎屑组分中分离出EM1(众数2 μm)、EM2(众数10 μm)和EM3(众数45 μm)三个端元。根据各端元粒径分布，对不同粒级(<4 µm和 >20 µm)碎屑进行了Sr、Nd同位素分析，结果表明MD06-3052孔不同碎屑端元主要来源于菲律宾岛弧。此外，通过火山灰层中火山玻璃主微量元素的对比分析，结果表明MD06-3052岩心中约18 ka(A1)和76 ka(A3)堆积的火山灰来源于皮纳图博(Pinatubo)火山的喷发，而103 ka的火山灰(A4)来自于比科尔弧火山活动区的安山-英安质岩浆喷发。

结合碎屑沉积物的来源和粒级进一步分析了各端元输运方式，其中EM1和EM2碎屑端元分别通过表层流和底层流搬运到比科尔岛架，EM3粗粒碎屑端元则是低海平面时期裸露的岛架碎屑沉积物在重力流作用下再沉积形成的。

风化碎屑总含量和各端元含量变化，以及粗碎屑(EM2和EM3)质量堆积速率(MAR)的变化相同，并与全球海平面协同变化，150 ka以来表现为冰期低海平面时(40~14 ka和150~130 ka)高而间冰期高海平面时低，而细粒EM1碎屑端元的MAR在40~14 ka低海面时并未明显增加。我们认为，海平面变化是控制吕宋岛粗碎屑物质向比科尔岛架输入的主要因素。冰期海平面大幅度降低使大部分岛架裸露并成为新的物源区，这导致菲律宾岛弧碎屑物质在从源到汇系统中的搬运距离大大缩短，从而使粗碎屑向研究站位的输入明显增加。细粒碎屑端元的输入除了受到海平面变化的影响外，还可能受到洋流和区域降水的影响。

The West Philippine Sea is one of the key areas for global sea-air and sea-land interactions, and it is also an important place of global material and energy exchange, so it plays an important role in the study of regional source-sink process and global climate change. The Philippine island arc is the main source area of deep sea detrital sediments in the West Philippine. However, there is still no systematic research on the sedimentary characteristics of the detrital sediments, so there is a lack of basic data for the comparative study of the prevenance. There is also a lack of clear understanding of the changes and control factors of the island arc material input to the deep sea. A high-quality sediment core was collected at MD06-3052 station of Bicol Shelf on the east side of Luzon Island during MD155 cruise of "International Ocean Global Past Climate Change (IMAGES)" in 2006, which provides a good material for the above problems. In this dissertation, the characteristics of mineral composition, grain size, radiogenic Sr and Nd isotopes of the detrital sediments are studied. The source and transport mode of the detrital sediments are analyzed, and the variation and controlling factors of the input of detrital material to the seaare discussed.

Through the combination of X-ray diffraction analysis (XRD) and Tescan Integrated Mineral Analyser (TIMA), the main minerals identified in the normal marine sediments of Bicol Shelf include calcite, aragonite, tourmaline, plagioclase, quartz, and epidote. The mineral composition of the turbidite is similar to the normal marine sedimentary layer. The tephra layers are characterized by volcanic glass, but the content and shape of volcanic glass in different tephra layers are different. Aragonite and calcite in the study area are mainly biogenetic, while quartz, plagioclase and tourmaline represent terrigenous detrital components. Since 150 ka, the content of carbonate increased in interglacial period and decreased in glacial period, while the content of quartz, plagioclase, and tourmaline changed in the opposite direction, showing high in glacial period and low in interglacial period. The quartz/carbonate ratio has a trend of high in glacial period and low in interglacial period, indicating that the input of terrigenous detrital materials increased in glacial period and decreased in interglacial period.

In core MD06-3052, the detrital material in the normal marine sedimentary layers is mainly composed of clay and silt, the sand content is relatively low, while the sand content in the tephra layers and turbidity current layers is significantly increased. Three endmembers (EM1, mode at 2 μm), EM2 mode at 10 μm, and EM3, mode at 45 μm) were separated from the detrital components of the normal marine sedimentary layers by using the particle size parameterized end-member analysis method. According to the grain-size distribution of each end member, Sr and Nd isotopic compositions of different grain size (<4 µm and >20 µm) were analyzed. The results show that different detrital end members in the core MD06-3052 are mainly from the Philippine island arc. In addition, through the comparative analysis of the main and trace elements of the volcanic glass in the tephra layer, the results show that the volcanic ash of 18 ka (A1) and 76 ka (A3) in the core MD06-3052 originates from the eruption of Pinatubo volcano, and the volcanic ash of 103 ka (A4) comes from the eruption of andesitic-dacitic magma in the Bicol arc active area.

Combined with the the source and grain size of the detritla sediments, the transport mode of each end member is further analyzed. Among them, the EM1 and EM2 are transported to the Bicol Shelf through the surface and bottom currents, respectively. The EM3 coarse-grained detritus is formed by the redeposition of the exposed island shelf detrital sediments in the low sea level period under the action of gravity flow.

The trends of the total content of weathering detritus, the content of each detrital end member, and the the mass accumulation rate (MAR) of coarse detritus (EM2 and EM3) are the same, as that of global sea level, which is highin glacial low sea level periods (40~14 ka and 150~130 ka) and low in interglacial high sea level periods. However, the MAR of fine-grained EM1 detrital end member did not increase significantly at 40~14 ka low sea level period. We argue that sea level change is the main factor controlling the coarse detritus input from Luzon Island to Bicol Shelf. During the glacial period, the sea level was greatly reduced, which made most parts of the island shelf exposed and became a new source area, which led to a significant reduction in the transportation distance of detrital material from the source to the sink system in the Philippine island arc, thus significantly increasing the input of coarse detritus to the research area. The input of fine-grained detrital end member is not only affected by sea level change, but also by ocean current and regional precipitation.