中新世以来奄美三角盆地沉积物中粘土矿物的来源

IOCAS-IR > 海洋地质与环境重点实验室

	中新世以来奄美三角盆地沉积物中粘土矿物的来源
	刘华华1,2
学位类型	硕士
导师	蒋富清
	2016-05-24
学位授予单位	中国科学院大学
学位授予地点	北京
学位专业	海洋地质
关键词	粘土矿物物源奄美三角盆地中新世
摘要	位于菲律宾海西北部的奄美三角盆地是亚洲大陆风尘物质的重要“汇”，因此从奄美三角盆地沉积物中提取亚洲大陆风尘物质输入的信号对于追溯亚洲大陆古气候、古环境的演化具有重大意义。“国际大洋发现计划”（IODP）351航次在奄美三角盆地采集了高质量的岩芯沉积物，为开展该海域风尘记录的研究提供了很好的机会。本文对该航次采集的两个岩芯U1438A孔和U1438B孔沉积物中的粘土矿物进行了系统的研究，通过X-射线衍射和扫描电镜分析，研究了中新世以来沉积物中粘土矿物的种类、含量、结晶学参数，以及粘土矿物的形态特征。结果显示，中新世以来奄美三角盆地沉积物中粘土矿物主要是由蒙皂石、伊利石、绿泥石和高岭石组成，其中蒙皂石（~55%）和伊利石（~35%）为主要组分，绿泥石（7%）和高岭石（~3%）含量较低，为次要组分。伊利石的化学指数绝大部分小于0.5，平均值为0.3，伊利石结晶度指数在0.18-0.43°Δ2θ之间变化，平均0.3°Δ2θ，绝大部分都<0.4°Δ2θ。扫描电镜分析结果显示蒙皂石多呈不规则状，如絮状、朵状、卷片状；伊利石和绿泥石则为不规则片状，边缘清晰，角钝圆，有被磨蚀的痕迹。通过将研究区粘土矿物组成、结晶学特征和形貌特征与可能源区（亚洲大陆、吕宋岛、西菲律宾海、四国海盆等）粘土矿物进行对比分析，对四种主要粘土矿物的来源进行了分析，蒙皂石的高含量（~55%）以及典型的自生形态（花朵状、絮状等）表明其主要来自研究区周围火山岛弧物质的风化蚀变；伊利石的结晶度指数与化学指数指示其产生于寒冷干燥、物理风化占主导的环境条件下，而且伊利石结晶度值与黄土、古土壤中伊利石的结晶度值基本一致，伊利石形态呈不规则片状，棱角钝圆，未发现细针状的自生伊利石，由此说明伊利石应该来自亚洲大陆；绿泥石和高岭石中新世以来的变化趋势同伊利石基本一致，而且二者与伊利石之间具有很好的正相关性，因此认为绿泥石和高岭石也主要来自亚洲大陆。中新世以来，四种主要粘土矿物的含量表现为阶段性变化：阶段1，早中新世（23-16.0Ma），以蒙皂石为主，含量90%，伊利石含量次之，9%，基本不含绿泥石和高岭石；阶段2，中中新世-晚中新世（16.0-5.3Ma），蒙皂石含量有所减少，平均61%，伊利石、绿泥石以及高岭石含量显著增加，伊利石平均含量达到30%，绿泥石和高岭石总含量为10%；阶段3，上新世至今（5.3Ma-至今），伊利石含量（46%）明显增加，绿泥石和高岭石含量也增至13%，而蒙皂石的含量明显降低（41%）。中新世以来，引起粘土矿物显著变化的主导因素是构造活动和气候变化：早中新世（23-16Ma）主要受构造活动影响，频繁的火山活动产生大量的火山物质，这些火山物质的蚀变使得奄美三角盆地蒙皂石含量很高；中中新世至今（16Ma至今）全球气候变冷驱动了亚洲内陆干旱，以及大气环流的增强，导致伊利石、绿泥石、高岭石输入明显增加。伊利石含量的变化记录了东亚冬季风在大约15Ma、8Ma以及3Ma时出现的三次增强。晚更新世以来，（伊利石+绿泥石）/蒙皂石、（伊利石+绿泥石）/高岭石冰期高的特点指示了亚洲物质输入的增加，在一定程度上响应了冰期亚洲大陆干旱和东亚季风的增强。
其他摘要	Amami Sankaku Basin (ASB), located in northwestern Philippine Sea, is a major sink area of Asian dust. Therefore, Asian dust signal obtained from the sediment in the ASB is very important to trace the paleoclimatic and envrionmental evolution of the Asian continent. High quality sediment section, recovered from ASB during International Ocean Discovery Program (IODP) Expedition 351, provides a unique opportunity to study the paleoclimate of this area. In this paper, the clay minerals in hole U1438A and U1438B retrieved during Expedition 351, were systematically analyzed. The clay mineral assemblages, content, mineralogical and micromorphology characteristics were investigated with X-ray diffraction and scanning electron microscopy. The analysis results show that the clay minerals in the Amami Sankaku Basin are mainly composed of smectite, illite, chlorite and kaolinite. The smectite (average 55%) and illite (average 35%) are the major component, and chlorite (average 7%) and kaolinite (average 3%) are the minor component in the clay minerals. The chemical index of illite in most samples is less than 0.5, and with an average of 0.3. The illite crystallinity values vary between 0.18 and 0.43°Δ2θ, and with an average of 0.3°Δ2θ. The illite crystallinity values in most samples are less than 0.4°Δ2θ. Scanning electron microscopy (SEM) images show that the morphology of smectite is irregular, with flocculent, flower-shaped, curled flake, and illite and chlorite are irregular flake, with clear edges, round corners and abrasion marks. Based on comparison of clay mineral assemblages, crystallographic and microscopic morphological features between ASB and the potential sources area (e.g. Asian continent, Luzon islands, western Philippine Basin, Shikoku Basin), the provenance of the four clay minerals is analyzed. The high content and typical authigenic morphology (flower-shaped, flocculent) for semctite indicate that smectite was mainly derived from weathering and alteration of volcanic materials around ASB. The crystallinity and chemical index of illite indicates it was formed in a cold and dry environment dominated by physical weathering. The crystallinity of illite is similar with that of Chinese loess and paleosol. In addition, the morphology of illite is irregular flake with round corner and abrasion mark. All above evidences indicate that illite originated from Asian continent. The variation of chlorite and kaolinite since Miocene is similar with illite, and the three minerals show a high positive correlation. Therefore, we argue that chlorite and kaolinite are also derived from Asian continent. The variation of the content of the four clay minerals can be divided into three stages since Miocene, Stage 1(early Miocene, 23-16Ma), the clay mineral is dominantly composed of smectite(90%), with minor illte(8%). and chlorite and kaolinite are too low to be identified. Stage 2 (middle to late Miocene, 16-5.3Ma), the content of smectite decreased to 61%, whereas illite (30%), chlorite and kaolinite (10%) increased. Stage 3 (Pliocene to present, 5.3Ma-present), the content of illite (46%) increased significantly, and the content of chlorite and kaolinite also increased (up to 13%), whereas the content of smectite (41%) decreased significantly. The significant variation of clay minerals in Amami Sankaku Basin since Miocene was resulted from the tectonic activities and climate change. In the early Miocene (23-16Ma), the variation of clay mineral is mainly influenced by the tectonic activities. Frequent volcanism related to the tectonic activities produce large amounts of vocanic materials. The alteration of the volcanic material resulted in the relatively high conent of semctite. Since middle Miocene (16Ma to present), global cooling forced the aridity of Asia continent, and intensification of atmosphere circulation, caused the increase of illite, chlorite and kaolinite. The variation of illite content revealed the strengthening of East Asian winter mosoon for three times (approximately 15Ma, 8Ma and 3Ma) since Miocene. In late Pleistocene, high ratios of (illite+chlorite)/ smectite and (illite+chlorite)/ kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.
学科领域	海洋地质学
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/117000
专题	海洋地质与环境重点实验室
作者单位	1.中国科学院海洋研究所 2.中国科学院大学
第一作者单位	中国科学院海洋研究所
推荐引用方式 GB/T 7714	刘华华. 中新世以来奄美三角盆地沉积物中粘土矿物的来源[D]. 北京. 中国科学院大学,2016.

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