Garnet trace element geochemistry as a sediment provenance indicator: An example from the Qaidam basin, northern Tibet
Garnet trace element geochemistry as a sediment provenance indicator: An example from the Qaidam basin, northern Tibet
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石榴石微量元素地球化学作为沉积物物源指标：以藏北柴达木盆地为例
DOI：
10.1016/j.marpetgeo.2020.104316
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发表时间：
2020-06
影响因子：
4.2
通讯作者：
Zhang Wei
中科院分区：
文献类型：
--
作者：
Hong Dongming;Jian Xing;Fu Ling;Zhang Wei
碎屑石榴子石常量元素地球化学是一种广泛应用的沉积物源分析方法，特别是在揭示硅质沉积物的母岩岩性方面。然而，长英质结晶岩石中的石榴石（例如，中酸性火成岩和变岩）通常具有相似的主元素组成。这在大多数情况下导致了来源解释的模糊性。本文收集了不同岩石类型石榴石的微量元素数据，探讨碎屑石榴石微量元素地球化学在沉积物物源分析中的可行性。以西藏北方柴达木盆地为例，根据碎屑岩石榴石微量元素组成解释了盆地新生代沉积岩的物源。中酸性岩浆岩中石榴石的重稀土元素丰度（HREE > 600 ppm）和钇丰度（Y > 800 ppm）远高于变岩中石榴石（HREE < 300 ppm，Y < 500 ppm）。高级变岩（如麻粒岩相）中的石榴石通常比低级、中级变岩（直至角闪岩相）中的石榴石具有更高的轻稀土元素（HREE> 4ppm）和锌（Zn > 150 ppm）丰度。据此，我们认为，柴北方新生代沉积岩中富Fe、Mn的碎屑石榴子石可能来源于中低品位的变岩，而富Mg、贫Ca的碎屑石榴子石可能来源于麻粒岩相的变岩。这一物源解释支持了北祁连山是北方柴达木盆地的主要物源，阿尔金断裂沿着向西的主要变形方式是大幅度的侧向错动和挤压，而不是地壳增厚和隆升。研究表明，碎屑岩石榴石微量元素地球化学在碎屑沉积盆地物源分析和构造-沉积演化重建中具有重要的应用价值。
Major element geochemistry of detrital garnet is a widely-used approach for sedimentary provenance analysis, in particular for unravelling parent-rock lithology of siliciclastic sediments. However, garnets from felsic crystalline rocks (e.g., intermediate–acidic igneous rocks and metapelites) often have similar major element composition. This results in ambiguity of provenance interpretation in most cases. Here, we collect trace element data of garnets from different rock types to explore the feasibility of detrital garnet trace element geochemistry in sediment provenance analysis. The Qaidam basin in northern Tibet is taken as an example and provenance of Cenozoic sedimentary rocks therein is interpreted based on detrital garnet trace element composition. We find that garnets in intermediate–acidic igneous rocks have much higher heavy rare earth element (ΣHREE > 600 ppm) and yttrium (Y > 800 ppm) abundances than garnets in metapelites (ΣHREE < 300 ppm, Y < 500 ppm). Garnets in high-grade metapelites (e.g. granulite facies) usually have higher light rare earth element (ΣLREE > 4 ppm) and zinc (Zn > 150 ppm) abundances than garnets in low-, medium-grade metapelites (up to amphibolite facies). Based on these findings, we suggest that Fe- and Mn-rich detrital garnets in the Cenozoic sedimentary rocks from the northern Qaidam basin were probably derived from low-, medium-grade metapelites and Mg-rich, Ca-poor detrital garnets therein were most likely derived from granulite-facies metapelites. This provenance interpretation supports that the Qilian Mountains to the north was the major source for the northern Qaidam basin and major deformation style along the Altyn Tagh Fault to west have been dominated by large-amplitude lateral offset and extrusion, rather than crustal thickening and uplift during the early Cenozoic. This study emphasizes high potential of detrital garnet trace element geochemistry in provenance analysis and reconstruction of tectono-sedimentary evolution of clastic sedimentary basins.
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