莱州湾南岸入海河流重矿物特征及其物源意义

Characteristics of heavy minerals in rivers entering the sea from the south bank of Laizhou Bay and their provenance significance

  • 摘要: 在关注大河物源辨别和示踪的同时,“短源河流-瞬时大通量-快速物质转换”的源-汇体系值得重视。莱州湾南岸入海的中小河流沉积物来源明确,母岩、气候及水动力条件等复杂程度低,易于进行有限边界条件下的物质端元特征分析。本文对莱州湾南岸的小清河、弥河、白浪河、虞河、堤河、潍河、胶莱河等中小河流进行碎屑重矿物特征差异研究,判别分析不同河源物质来源。结果显示,莱州湾南岸中小河流沉积物中共鉴定出31种重矿物,以角闪石和绿帘石为主。重矿物含量较高(>5.5%)的小清河和潍河沉积物中褐铁矿含量高,而重矿物含量低(<1.5%)的其他河流沉积物中黑云母含量较高。石榴石-榍石-磷灰石组成的特征矿物组合以及标型矿物(硅灰石、矽线石、刚玉、十字石和红柱石等)反映物源区出露的酸性花岗岩、区域变质岩以及接触变质岩等不同岩性,它们是产生不同河流矿物特征组合差异的主控因素。另外,双标图和热力图显示来自黄河与莱州湾南部近岸海域重矿物特征差异较为显著。莱州湾南岸近海海区沉积物主要来自附近河流物质,而黄河来源物质的影响程度自西向东减弱。因此,对短源河流碎屑重矿物特征分析,可为山东半岛近海碎屑沉积物的物源辨识探究提供依据,对深入认识大陆边缘物质供应过程具有重要意义。

     

    Abstract: While focusing on identifying and tracing the sources of large rivers, the source-sink system of "short-source river flow – instantaneous large flux – rapid material transformation" deserves attention. The sediment sources of small- and medium-sized rivers entering the sea on the south bank of Laizhou Bay have clear sources, and low complexity in parent rocks, climate, and hydrodynamic conditions, which makes it easy to analyze the characteristics of material end-members under limited boundary conditions. We studied the differences in the characteristics of detrital heavy minerals from small- and medium-sized rivers, including Xiaoqing River, Mihe River, Bailang River, Yuhe River, Dihe River, Weihe River, and Jiaolai River on the south bank of Laizhou Bay, by which the sources of different river sources were analyzed and discriminated. Results show that a total of 31 heavy minerals were identified, mainly amphibole and epidote. The sediments of Xiaoqing River and Weihe River had a high heavy mineral content (>5.5%) typical of abundant limonite, while those of other rivers had a low heavy mineral content (<1.5%) typical of ample biotite. The characteristic mineral assemblages composed of garnet-sphene-apatite and standard minerals (wollastonite, sillimanite, corundum, staurolite, and andalusite, and so on) reflect different rock types such as acidic granites, regional metamorphic rocks, and contact metamorphic rocks exposed in the source area, which are the main controlling factors for the differences in the characteristic assemblages of different riverine minerals. In addition, the biplot and heatmap show that the spectra of heavy minerals from Huanghe River and the southern coastal waters of Laizhou Bay are quite different. The sediments in the offshore area of the southern coast of Laizhou Bay mainly come from nearby river materials, and the impact of Huanghe River materials weakens from west to east. Therefore, analyzing the characteristics of heavy minerals in short-source river sediments can provide a basis for identifying the sources of detrital sediments in the Shandong Peninsula, which is of great significance for a deeper understanding of the material supply process at the continental margin.

     

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