南海西部表层沉积物碎屑矿物分布特征及其物源

南海西部海域的物源研究程度相对较低,尤其对中段的物源有较大的争议。通常认为中部没有大河注入,其物源主要来自其南北的湄公河和红河。笔者通过对该区表层沉积物的系统取样及碎屑矿物分析鉴定认为,碎屑矿物主要分布于南部陆架区和中部陆坡区域。根据因子分析,南海西部碎屑矿物可以明显分为南部、中部、北部三区。南区陆架碎屑矿物主要由重矿物金红石、锐钛矿、白钛矿、锆石、透闪石、十字石及轻矿物石英、长石等组成,原岩应以岩浆岩类为主,包括部分变质岩;中区陆坡以十字石、透闪石、电气石、褐铁矿及黑云母、白云母为主,原岩可能主要为变质岩类;北区陆坡碎屑矿物少,组合特征不明显。各区不仅组合特征明显不同,且各区分界明显,表明其物质来源明显不同,南区物源主要来自红河和加里曼丹岛;中部海域的碎屑矿物组合与中南半岛大量出露的变质岩基本吻合,表明其物源主要来自中南半岛,而不是来自其南北的湄公河和红河。

Distribution of clastic minerals of surface sediments in the western China Sea and their provenance

The provenance of sediments in the western South China Sea (SCS) is less studied,and especially there is much dispute about the provenance of the central part of the sea area. Because of the absence of large river input,it is usually considered that the main material sources of the central part are the Red River in the north and the Mekong River in the south. In order to better understand the provenance in the western SCS,systematic surface sediment samples were collected and clastic minerals were analyzed. The results show that clastic minerals are mainly distributed in the continental shelf in the south and the slope in central part. Factor analysis shows that the south,central and north areas may be distinguished for the clastic minerals in the western SCS. The clastic minerals in the shelf of the south area consist predominantly of heavy minerals such as rutile,anatase,leucoxene,zircon,tremolite and staurolite and light minerals such as quartz,feldspar,which indicates that the protoliths are dominantly magmatic rocks and partly metamorphic rocks; those in the slope of the central area are mainly staurolite,tremolite,tourmaline,limonite,biotite and muscovite,which suggests that the protoliths might be mainly metamorphic rocks; and the clastic minerals in the slope of the north area are scarce and the characteristics of the mineral assemblage are not pronounced. The three areas not only show notably different mineral assemblage characteristics but also distinct boundaries between the areas,indicating that their provenances are markedly different. The provenance in the south area is the Mekong River and Kalimantan; the clastic mineral assemblage in the central area is in the main coincident with the metamorphic rocks exposed in large amount in the Indo-China Peninsula,suggesting that the provenance is mainly the Indo-China Peninsula rather than the Mekong River south of it and the Red River north of it.