Understanding the genesis of ore-bearing and ore-barren adakitic rocks: insights from geochronology and geochemical analysis of the Tuncang intrusion and enclaves along the South Tan-Lu Fault

IF 1.8 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Feng Zi, Wenzhou Xiao, Mabrouk Sami, Chenguang Zhang, Fenquan Xie, Ye Liu, Shuanglian Li
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Abstract

The relationships between metallogenic capacity and geochemical features of adakitic rocks along the South Tan-Lu Fault (STLF) remain unclear. In this study, the ore-barren adakitic rocks (Tuncang, Guandian and Wawuliu) exhibit higher K2O/Na2O ratios and lower Sr/Y ratios than the ore-bearing adakitic rocks (Chuzhou and Shangyaopu). These differences strongly suggest that the ore-barren adakitic rocks originated from the thickened lower continental crust (LCC), whereas the ore-bearing adakitic rocks were derived from oceanic slabs. Notably, the Tuncang granite exhibits higher Y/Yb and (Ho/Yb)N ratios than the Guandian granodiorite and Wawuliu intrusion. Accordingly, we suggest that the Tuncang granite likely originated from a delaminated eclogitic LCC, whereas the Guandian and Wawuliu intrusions were derived from a thickened basaltic LCC sources. The occurrence of diorite and gabbro mafic microgranular enclaves (MMEs) within the Tuncang granite strongly suggests a magma-mixing process. Considering their MgO contents and εNd(t) and (87Sr/86Sr)i values, we suggest that the gabbro MMEs were likely derived from an enriched mantle source previously metasomatized by subduction-related components and that the diorite MMEs were subsequently formed by magma mixing. Due to the slightly younger ages of the ore-bearing adakitic rocks, we propose a model in which the ore-barren adakitic rocks formed through LCC delamination at 130 Ma and the ore-bearing adakitic rocks formed through oceanic slab remelting at 125 Ma. Consequently, the exploration of Cu–Au mineralization along the STLF should focus on younger oceanic slab-derived adakitic rocks.

Graphical abstract

Abstract Image

了解含矿和贫矿赤铁矿的成因:对屯仓侵入体和南郯庐断层沿线飞地的地质年代和地球化学分析的启示
南郯庐断裂(STLF)沿线阿达克岩的成矿能力与地球化学特征之间的关系尚不清楚。在本研究中,与含矿阿达克岩(滁州和上窑铺)相比,贫矿阿达克岩(屯仓、官店和瓦屋刘)表现出较高的K2O/Na2O比值和较低的Sr/Y比值。这些差异有力地表明,贫矿金达基岩源于增厚的下大陆地壳(LCC),而含矿金达基岩则源于大洋板块。值得注意的是,屯仓花岗岩的Y/Yb和(Ho/Yb)N比值高于官店花岗闪长岩和瓦屋流侵入体。据此,我们认为屯仓花岗岩很可能源于脱层的蚀变岩LCC,而官店和瓦屋流侵入体则源于增厚的玄武岩LCC。屯仓花岗岩中出现的闪长岩和辉长岩岩浆微晶粒飞地(MMEs)强烈暗示了岩浆混合过程。考虑到它们的氧化镁含量和εNd(t)及(87Sr/86Sr)i值,我们认为辉长岩微晶飞地很可能来自富集的地幔源,之前被俯冲相关成分变质,而闪长岩微晶飞地则是随后由岩浆混合形成的。由于含矿闪长岩的年龄略小,我们提出了一个模型,即贫矿闪长岩是在130Ma时通过LCC分层形成的,而含矿闪长岩是在125Ma时通过大洋板块重熔形成的。因此,STLF沿线的铜金矿化勘探应重点关注更年轻的大洋板块衍生阿达克岩。
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来源期刊
International Journal of Earth Sciences
International Journal of Earth Sciences 地学-地球科学综合
CiteScore
4.60
自引率
4.30%
发文量
120
审稿时长
4-8 weeks
期刊介绍: The International Journal of Earth Sciences publishes process-oriented original and review papers on the history of the earth, including - Dynamics of the lithosphere - Tectonics and volcanology - Sedimentology - Evolution of life - Marine and continental ecosystems - Global dynamics of physicochemical cycles - Mineral deposits and hydrocarbons - Surface processes.
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