冀东都山花岗岩基及相关花岗斑岩脉SHRIMP锆石U-Pb法定年及其意义

SHRIMP U-Pb zircon dating of the Dushan granitic batholith and related granite-porphyry dyke, eastern Hebei Province,

都山花岗岩体是冀东地区最大的花岗岩基,在其周边产有众多与其有关的“卫星”岩体和岩脉。采用先进的SHRIMP定年方法,测得都山花岗岩基的206Pb/238U年龄为(223±2)Ma,其东侧三家金矿区成矿前花岗斑岩脉的年龄为(222±4)Ma,二者在误差范围内一致,花岗岩基和花岗斑岩脉可视为同一次岩浆活动的产物。这种晚古生代末—早中生代印支期的花岗岩在华北克拉通北缘广泛分布,显示它是一次重要的构造-岩浆事件的产物。根据岩石化学和微量元素特征及有关判别图,都山等印支期花岗岩可能属中朝板块与西伯利亚板块碰撞造山作用的后碰撞花岗岩。花岗斑岩脉中发现有新太古代的继承锆石,表明花岗斑岩的部分源岩为区内新太古代八道河岩群变质岩。都山花岗岩与花岗斑岩脉同时、同源,推测其源岩也有部分为新太古代结晶基底的变质岩。花岗岩与区内金矿化有较大的时差,两者不存在直接的成因联系,仅表明成矿晚于早中生代印支期。

The Dushan granite is the biggest batholith in eastern Hebei Province. In the surroundings of the batholith, many satellite granites and dykes are occurred. The age of the Dushan batholith is (223± 2) Ma using the SHRIMP zircon U Pb method, and that of the pre mineralization granite porphyry dyke in the Sanjia gold deposit is (222± 4) Ma. Therefore, they could be considered as the product of the same magmatic activity. In the end of late Paleozoic to early Mesozoic, that is Indosinian, granites are widespread at the northern margin of the North China craton, showing that a major tectonic magmatic event took place in this period. Based on petrochemistry, trace element characteristics and the discrimination diagrams, the studied Indosinian granites, such as the Dushan granite are likely to be generated by the post collision between the Sino Korean plate and the Siberia plate. The Archean inherited zircons in the Sanjia granite porphyry dyke suggest that the Neo Archean metamorphic rocks of the Badaohe complex could be served as part of the granite source. Since the Dushan batholith and the granite porphyry dyke are cognate and simultaneous, it is inferred that the protolith of the batholith also contains the Archean crustal component. The granites mentioned above are quite temporally varied from the gold mineralization in the area, and no direct genetic relation exists between them. The present data indicate only that the gold mineralization took place no earlier than early Mesozoic Indosinian.<P>