铜陵矿集区舒家店矿区正长花岗岩的年代学和地球化学特征及其指示意义

舒家店岩体位于长江中下游成矿带中部的铜陵断隆区,与繁昌断凹区(盆地)临近,主要的岩浆岩岩石类型有辉石闪长岩、石英闪长斑岩和花岗闪长岩等。正长花岗岩为舒家店岩体深部新发现的岩石类型,其矿物组合与岩体内其他类型岩石明显不同,其形成的背景存在争议。本文通过对岩体中正长花岗岩的锆石LA-ICP MS精确定年、Hf同位素和地球化学组成分析,研究舒家店岩体正长花岗岩的年代学、岩浆源区等问题。研究显示舒家店岩体为"异源同体"的复式岩体,岩体中的正长花岗岩的侵入时间为126.5±1.6Ma~129.8±2.4Ma,明显晚于早期的辉石闪长岩和石英闪长斑岩(138.2±4.6Ma~143.7±1.7Ma),也明显晚于舒家店斑岩型铜矿床的形成时代。全岩元素地球化学和锆石Hf同位素组成指示舒家店岩体中正长花岗岩为叠加到早期辉石闪长岩及石英闪长斑岩之上的后期岩浆活动的产物,可能与繁昌盆地内花岗岩有相同的源区,为新元古代新生地壳(类似新元古花岗岩)部分熔融的产物,其岩浆源区处于高温低压的环境,相较于辉石闪长岩和石英闪长斑岩起源更浅,指示长江中下游成矿带在145~123Ma地壳处于不断减薄的过程。

Chronological, geochemical characteristics of the K-feldspar granite from Shujiadian intrusion, Tongling ore district: Its significance

Shujiadian intrusion, consisting of pyroxene diorite, quartz diorite porphyry and granodiorite, locates in the Tongling uplift zone, adjacent to Fanchang basin, which is in the Middle and Lower Yangtze River metallogenic belt. K-feldspar granite, the new discoveried intrusive rock, the mineral assemblages of which is different from other intrusive rocks in the Shujiadian intrusion. There is debate about the ownership of the K-feldspar granite of Shujiadian intrusion. The paper focuses on zircon U-Pb dating, Hf isotopes and geochemistry, and aim to constrain the geochronology and origin of the K-feldspar granite. Our results indicate that Shujiadian intrusion is complex intrusion, and the K-feldspar granite formed from 129.8±2.4Ma to 126.5±1.6Ma, which is later than early quartz diorite porphyry, pyroxene diorite (from 138.2±4.6Ma to 143.7±1.7Ma) and the formation of Shujiadian porphyry copper deposit. Whole-rock geochemistry and zircon Hf isotope study show that the K-feldspar granite is the product of later magmatic activity, and the source is similar to granite in Fanchang basin, both of which produced by anatexis of the middle and upper crust represented by the Neoproterozoic granites. Compare with quartz diorite porphyry and pyroxene diorite, the magma source of K-feldspar granite is shallower, which maybe suggest that the Middle and Lower Yangtze River metallogenic belt under an extension setting with increasing intensity during 145~123Ma.