西藏尕尔穷-嘎拉勒铜金矿集区两套火山岩浆源区及其地质意义——来自Hf同位素特征的指示

MAGMA ORIGIN OF TWO SERIES OF VOLCANIC ROCKS FROM GAERQIONG-GALALE Cu-Au ORE CONCENTRATED AREA OF TIBET AND ITS GEOLOGICAL SIGNIFICANCE:IMPLICATION FROM Hf ISOTOPE CHARACTERISTICS

尕尔穷-嘠拉勒铜金矿集区位于班公湖-怒江缝合带西段,区内发育有早白垩世及晚白垩世两套中酸性火山角砾岩。通过锆石Hf同位素测定,识别出矿集区两套火山岩浆源区。早白垩世朗久组英安质火山角砾岩ε_(Hf)(t)值变化于-13.93^-4.93之间,地壳模式年龄(t_(DM))变化于1 006Ma^1 354Ma之间,负的ε_(Hf)(t)值及老的模式年龄表明其岩浆源区起源于古老的成熟地壳,形成于古拉萨地体陆缘弧环境,与班公湖-怒江特提斯洋向南俯冲有关。晚白垩世多爱组安山质火山角砾岩ε_(Hf)(t)值变化于5.19~8.86之间,地壳t_(DM)模式年龄变化于404Ma^546Ma之间,其正的ε_(Hf)(t)值及相对较年轻的地壳模式年龄表明其形成于新生下地壳的部分熔融,与班公湖-怒江特提斯洋消亡后,南羌塘陆块与北冈底斯陆块碰撞闭合有关。通过对比南冈底斯及班公湖-怒江成矿带北缘典型矿床成矿岩体Hf同位素组成及相应的成矿作用,表明班公湖-怒江缝合带西段可能是区域上最具潜力的Cu,Au成矿地带,同时缝合带南缘具有寻找斑岩型铜金矿的巨大潜力。

Two series of early-late Cretaceous intermediate-acid volcanic breccias occur in the Ga＇ erqiong-Galale Cu-Au ore concentrated area in the western segment of the Bangonghu-Nujiang suture zone. Study of magma origin of these volcanic rocks is carried out by means of the Hf isotope determination. It shows that the zircon εHf （t） values of the Early Cretaceous dacitie volcanic breccias of Langjiu Formation range from -13.93 to -4. 93, and the tDM model ages range from 1 006 Ma to 1 354 Ma,indicating that the volcanic breccias are derived from the old and mature crust and formed in the continental margin arc environment related to the southward subduction of the Bangonghu-Nujiang Tethy Sea. The Late Cretaceous volcanic breccias of Duoai Formation show a narrow range of zircon εHf（t） values from 5. 19 to 8. 86 with the tDM model ages from 404 Ma to 546 Ma,indicating that the magma origin of volcanic breccias of Duoai Formation are the newly formed crust related to the collision of the Qiangtang block and the Gangdese block. A comparative study of the Hf isotope of the magmatic rock in the typical deposits in the southern Gangdese and the northern Bangonghu-Nujiang suture zone shows that the western Bangonghu-Nujiang suture zone has the potential to the Cu-Au mineralization,and the southern Bangonghu-Nujiang suture zone possesses the greatest potential to the prospecting of porphyry Cu-Au deposit.