大兴安岭东坡中北段六九山斑岩铜成矿系统浅成岩成因与地球动力学背景

Genesis and Geodynamic Setting of Hypabyssal Intrusive Rocks in the Liujiushan Porphyry Cu Ore System,Eastern Edge of the Northern Great Hinggan Range

六九山铜矿床产在大兴安岭地区东坡中北段,位于中亚造山带东端。为了探讨该区浅成岩成因与地球动力学背景,对六九山斑岩铜成矿系统内与成矿密切的闪长玢岩、二长斑岩两类浅成岩进行了地质、岩相学、锆石U-Pb同位素定年和元素地球化学等方面的研究。结果表明:闪长玢岩和二长斑岩内岩浆锆石加权平均年龄分别为(132.6±2.6)Ma(n=5)和(132.4±1.3)Ma(n=22),岩浆就位发生在约132 Ma,结合辉钼矿Re-Os同位素年龄((134.1±0.8)Ma),限定成矿作用发生在早白垩世;闪长玢岩(w(SiO_(2))为52.98%~59.83%)和二长斑岩(w(SiO_(2))为66.90%~67.56%)为典型的中—酸性浅成斑岩,富集大离子亲石元素,亏损高场强元素,分别为典型岛弧钙碱性岩和埃达克质岩石;岩浆起源于与大洋板块俯冲有关的以流体交代为主的富集地幔部分熔融;成岩成矿作用适值中生代早白垩世库拉板块向欧亚板块俯冲的大陆边缘岩浆弧背景。

The Liujiushan Cu deposit is located in the eastern end of the northern Great Hinggan Range,part of the easternmost edge of Central Asian orogenic belt.This study presents detailed field geology,petrography,elemental geochemistry and geochronology of diorite porphyry and monzonite porphyry to reveal the petrogenesis and geodynamic setting of these intrusive rocks.Magmatic zircons from diorite porphyry and monzonite porphyry yielded a weighted average age of(132.6±2.6)Ma(n=5)and(132.4±1.3)Ma(n=22),respectively.The LA-ICP-MS zircon U-Pb ages show these intrusive rocks were emplaced at~132 Ma,consistenting with the molybdenite Re-Os isotopic dating of(134.1±0.8)Ma,which constrains Cu mineralization to the Early Cretaceous.The diorite porphyry(52.98%-59.83%w(SiO_(2)))and monzonite porphyry(66.90%-67.56%w(SiO_(2)))are classified as intermediate to acidic hypabyssal intrusive rocks,enriched in the large ion lithophilic elements and deleted in high field strength elements,representing island arc alkaline and of adakitic rock types,respectively.Their parental magmas originated from an enriched mantle.All these studies show that the diagenesis and mineralization resulted from subduction of the Kula slab beneath Eurasian continent.