Emplacement age of the Raohe Complex in eastern Heilongjiang Province and the tectonic evolution of the eastern part of Northeastern China.
Emplacement age of the Raohe Complex in eastern Heilongjiang Province and the tectonic evolution of the eastern part of Northeastern China.
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作者：
Cheng Rui
位于黑龙江省东部的饶河杂岩体是由大洋深源沉积物和镁铁质岩浆岩组成，被认为是洋壳的一个薄片，受蛤蟆河和太平村花岗岩侵入，锆石U-Pb定年表明，两岩体均侵位于早白垩世，蛤蟆河岩体形成于三个独立的阶段而饶河杂岩中辉长岩的形成时间为166± 1 Ma，而大洋沉积中最晚的放射虫年龄为160~ 150 Ma，因此，本区最晚的放射虫年龄为160~ 150 Ma。认为饶河杂岩的侵位时间为晚侏罗世-早白垩世150- 131 Ma，表明本区在晚侏罗世之前和期间存在太平洋板块俯冲和走滑作用-早白垩世。岩石学研究表明，这两个岩体含有岩浆堇青石，并显示过铝质特征，Hf同位素分析表明，该岩体中的锆石具有较高的~（176）Hf/~（长英质地壳岩石的Hf同位素模式年龄为500~ 780 Ma，表明其原岩为新元古代-早白垩世形成的幼年地壳，因此，在晚侏罗世-早白垩世之前，本区曾有明显的地壳抬升和风化作用。
Raohe Complex,located in the eastern Heilongjiang Province and composed of deep oceanic sediments and mafic igneous rocks,was considered as slice of oceanic crust and intruded by Hamahe and Taipingcun granites.Zircon U-Pb dating indicated that both of plutons were emplaced in Early Cretaceous,with the Hamahe pluton formed at three individual stages(131Ma,124Ma and≈115 Ma, respectively)and the Taipingcun pluton at 111-114Ma.However,the gabbro in Raohe Complex was formed at 166±1Ma,and the latest radiolarian in the deep oceanic sediments is about 160～150Ma.Therefore,it is concluded that the emplacement of the Raohe Complex took place at 150-131Ma of Late Jurassic-Early Cretaceous,indicating that there existed the Pacific plate subduction and striking-slip in this area before and during Late Jurassic-Early Cretaceous.Petrological studies indicate that both plutons contained magmatic cordierites and show peraluminous characteristics,suggesting their S-type affinity derived from partial melting of the sedimentary rocks.Hf isotopic analyses show that the zircons from plutons have high ~(176)Hf/~(177)Hf ratios and positivee_(HT)(t)values,and the Hf isotope model age with the felsic crust rocks is 500～780Ma,which indicates that their protolith should be the juvenile crust formed in Neo Proterozoic-Phanerozoic.Therefore,it is suggested that there existed significant crust uplift and weathering before Late Jurassic-Early Cretaceous in the area.