闽西南地区天池塘花岗闪长岩地质年代学和地球化学特征:对区域成矿作用的指示

Geochronological and Geochemical Characteristics of the Tianchitang Granodiorite in Southwestern Fujian Province:Indications for the Regional Metallogeny

早白垩世与晚白垩世更替之际的花岗闪长岩类是闽西南地区铜多金属最主要的成矿岩体。紫金山火山盆地与闽西南坳陷过渡地带的白垩纪岩体成因及相关成矿过程尚不明确,制约了对成岩成矿规律的认识和区域成矿潜力评价。本文选择该地区与矽卡岩铁铜矿化相关的天池塘花岗闪长岩为研究对象,进行了LA-ICP-MS锆石U-Pb定年和全岩元素组成分析。结果显示,岩浆锆石^(206)Pb/^(238)U加权平均年龄为(100.7±1.0)Ma和(99.6±0.7)Ma,指示岩体形成于晚白垩世早期。岩石表现准铝质-过铝质特征,属高钾钙碱性-钾玄岩系列,富集Rb、Th、Zr和Hf等大离子亲石元素,亏损Nb、Ta、Sr、Ti和P等高场强元素,具Eu弱负异常。综合分析认为,岩体形成于伸展构造背景,由受到先期俯冲组分改造或影响的幔源岩浆与中下地壳物质部分熔融形成的花岗质岩浆混合形成。天池塘岩体与紫金山矿田成矿岩体具有相似的地球化学特征和年龄,指示形成于100 Ma左右的花岗闪长岩类在不同环境中可形成多种矿化类型,是闽西南地区重要成矿岩体,应作为铜多金属矿的关键成矿要素和预测标志。

Granodiorite,emplaced at the transition of Early to Late Cretaceous,is the most important Cu-polymetallic metallogenic intrusion in southwestern Fujian province.The Tianchitang granodiorite,located in the transition zone between the Cretaceous Zijinshan volcanic basin and the Late Paleozoic SW Fujian depression,presents a Cu-Fe skarn affinity at the outer contact zone.LA-ICP-MS magmatic zircon U-Pb dating of the granodiorite has been conducted to understand the regional magmatic mineralization,yielding weighted average^(206)Pb/^(238)U ages of(100.7±1.0)Ma and(99.6±0.7)Ma.The result indicate that the granodiorite was emplaced early Late Cretaceous.Petrogeochemistry shows the intrusion is metaluminous-peraluminous and high-K calc-alkaline.The rocks are enriched in LILEs(Rb,Th,Zr and Hf)and depleted in HFSEs(Nb,Ta,Sr,Ti and P)with a weak negative Eu anomaly.The comparison with ore-forming intrusions in the Zijinshan orefield indicates that all of these intrusions were simultaneously formed in an extensional tectonic setting,and were the products of mixing of the granitul magma by partial melting of crustal material and mantle-derived mafic magma modified/influenced by subduction components.The ca.100 Ma granodiorite could resultsin different forms of mineralization in various locations.Therefore,it is a critical factor for the mineralization and prospecting of Cu-polymetallic deposits in southwestern Fujian province.