即墨地区莱阳群底部止凤庄组地质特征及其碎屑锆石LA-ICP-MS U-Pb年龄地质意义

为了了解盆地沉积初期的物源特征,对位于胶莱盆地东缘即墨地区早白垩世莱阳群止凤庄组沉积特征、物质组成及碎屑锆石进行了U-Pb同位素测年研究。野外调查表明,止凤庄组为一套陆源碎屑沉积,具有近源沉积的特点。南泊一带止凤庄组底部碎屑岩碎屑锆石LA-ICP-MS U-Pb年龄介于233~734 Ma,年龄分布于5个区间,呈现明显的幕式特征,至少记录了2次重要的构造热事件。侵入于止凤庄组石英二长岩的锆石U-Pb加权平均年龄为(123.50±0.95)Ma,限定了止凤庄组地层沉积上限年龄为123.50 Ma。综合分析认为,止凤庄组物源主要来自苏鲁造山带,部分来自扬子板块。这有助于了解胶莱盆地沉积初期其物源区苏鲁造山带的地体情况。

Geological Characteristic and Significance of LA-ICP-MS U-Pb Detrital Zircon Ages of Zhifengzhuang Formation in Lower Part of Laiyang Group in Jimo Area

In order to know characteristics of ore forming materials at the beginning of basin deposition, sedimentation characteristics, material compositon, and detrital zircon U-Pb isotope age of Zhifengzhuang formation in early Crataceous in eastern Jiaolai basin have been studied. As showed by field survey results, Zhifenghzuang formation belongs to the land sources clastic deposition and has the characteristics of proximal deposition. Detrital zircon LA-ICP-MS U-Pb isotope age of clastic rocks in lower part of Zhifengzhuang formation in Nanbo area is 233~734Ma. Isotope ages distributed in five groups and showed an obvious curtain type characteristics. It at least recorded two tectonic thermal events. Zircon U-Pb weighted average age of adamellite intruded in Zhifengzhuang formation is (123.05±0.95)Ma. It delimits the upper age limit of Zhifengzhuang formation to123.50Ma. According to comprehensive analysis, material source of Zhifengzhuang formation mainly came from Sulu orogenic belt, and partly from Yangzi palte. It is helpful for understanding geological circumstance in material source area at the beginning of sedimentary age in Jiaolai basin.