胶莱盆地早白垩世莱阳群沉积物源及地质意义

Provenance of Early Cretaceous Laiyang Group in Jiaolai Basin and its significance

应用古流向、砾石成分及砂岩碎屑锆石定年方法,综合分析了胶莱盆地早白垩世莱阳群沉积时期的物源组成及其地质意义。古流向,五莲—诸城显示较稳定的N向,莱阳—乳山一带由早期的E-SE向逐渐转变为晚期W-NW向。砾石成分,五莲—诸城—胶州地区以花岗片麻岩、花岗岩、大理岩和石英岩为主,莱阳—乳山早期花岗岩砾石成分含量高,晚期成分复杂。碎屑锆石年龄分布主要集中在110~145 Ma,150~180 Ma,200~250 Ma,600~950 Ma和1700~2600 Ma。由此推断胶莱盆地在早白垩世莱阳群沉积期的物源主要由三部分组成：①盆地南缘苏鲁造山带超高压-高压变质岩和浅变质杂岩;②盆地周缘燕山期（J2-3-K1）花岗岩;③北侧胶北隆起基底（亲华北型）变质岩。并且盆地物源组成表现出明显的区域差异性,这种差异说明当时苏鲁造山带的南、北段在抬升及抬升后可能存在着差异性的隆起和改造,表现为苏鲁造山带南段（南苏鲁造山带）隆升幅度大并且稳定,北段（北苏鲁造山带）表现出较为低缓的隆起或者局部的小隆起并且后期经历大规模的塌陷。另外,物源也指示早白垩世莱阳群沉积时期,胶莱盆地呈现出西高东低的古地貌特征,直到莱阳群沉积晚期,盆地东部才有所抬升。

Using the paleocurrents, gravels composition and detrital zircons age spectrum, the authors analyzed the provenance ofEarly Cretaceous Laiyang Group in Jiaolai basin and its geological significance. The paleocurrents show a stable northward direction in Wulian-Zhucheng, but gradually change from E-SE at the early stage to W-NW at the late stage in Laiyang-Rushan.Gravels in Wulian- Zhucheng- Jiaozhou comprise mainly granite gneiss, granite, marble and quartzite; in Laiyang- Rushan,however, granites are dominant at the early stage and multiple gravels are present at the late stage. Detrital zircons ages are primarily distributed in the ranges of 110-145 Ma, 150-180 Ma, 200-250 Ma, 600-950 Ma and 1700-2600 Ma, whereas Paleozoic zircons are rarely seen. All these features indicate that there existed three main sources for Early Cretaceous Jiaolai Basin： 1 HP- UHP metamorphic rocks and shallow metamorphic complex of Sulu orogen, 2 Yanshanian granites（J2-3-K1）, and 3 Metamorphic rocks from the Jiaobei uplift. Additionally, the regional difference of provenance is apparent, which suggests the southern part and the northern part of Sulu orogenic belt experienced different orogenic processes. The southern Sulu orogenic belt experienced largescale uplift and was stable, whereas the northern Sulu orogenic belt was subjected to small- scale uplift and collapsed at the late stage. It is also concluded from the provenance that the ancient landform of Jiaolai basin in the southwest was higher than in the east during the sedimentation of Early Cretaceous Laiyang Group until the late stage of the sedimentation when the east part of the basin was uplifted.