徐宿地区震旦纪地质事件及其成因讨论

Study on Sinian Geologic Events in Xuzhou-Suzhou Area and Discussion on Their Origin

徐宿地区震旦系为陆表浅海沉积 ,沉积相以碳酸盐台地相为主。在潮上 -潮下低能沉积中 ,常间有阵发性高能沉积 ,并伴生有异常沉积构造。这些异常沉积构造及同生阶梯状小断裂多为古地震遗迹 ,据此可识别出五个古地震遗迹密集分布层段。在研究区至少有两次浅成 超浅成基性岩浆侵入活动 ,分别发生在早震旦世和晚震旦世。地震事件、岩浆侵入事件与海平面升降有成因联系。研究表明 ,研究区震旦纪地质事件受控于伸展构造 ,地质事件发生于 738.6～ 60 4Ma之间。这一时限与中 -新元古代超大陆Rodinia在 780～ 60 0Ma逐步裂解的时间是一致的 ,因而徐宿地区震旦纪地质事件的起因可能与Rodinia的裂解过程有关。由“古郯庐裂陷带”

The Sinian strata in Xuzhou Suzhou area are deposits of the epicontinental sea. They are mainly referred to the carbonate platform facies. In the supratidal to subtidal low energy sedimental environments, sudden, violent high energy sedimentation occasionally occur, which are often associated with some abnormal sedimentary structures. These structures along with step like small faults may indicate the ancient seismic traces. In the studied area, the Sinian seismic traces mainly include densely spaced veins of micritic calcites, strongly scouring and erosion structures of 'bag gutter' like, plastic rudites, earthquake breccias, inter formation folds and step like small faults. Five distinguished stratomeres with closely spaced seismic traces represen ting five earthquakes phases have been recognized, which might include dozens, even hundreds of strong earthquakes. At least two phases of hypabyssal to subsurface basic magmatic intrusions can be distinguished, occurring respectively in the early and late Sinian period. The seismic events, magmatic intrusions and sea level changes are related in origin. Frequent, strong earthquake activities caused the sea level rise. The magmatic intrusions occurred in the interval between tow seismic phases and in the sea level fall times. The research results showed that the Sinian geologic events in the studied area might be controlled by extensional structures. The ages of these events are 738.6-604Ma, corresponding to the breakup times (780-600Ma) of global supercontinent Rodinia. Therefore it is deduced that the origin of the Sinian geologic events in Xuzhou Suzhou area might relate to the breakup processes of Rodinia. The area from 'Plaeo Tanlu zone' to the north of boundary fault zone in the northern side of North Qinling Mountains might be the breakup zone within the North China Plate margin.