东秦岭—大别造山带及两侧晚古生代构造环境与油气意义

LATE PALEOZOIC TECTONICS ENVIRONMENT AND HYDROCARBON SIGNIFICANCE OF EAST QINLING-DABIE OROGENIC BELT AND ITS BOTH SIDES

通过对秦岭—大别造山带及两侧火山岩地球化学分析认为,略阳庄科和大西洋中脊的岩石可归为一类,其特征是K2O/SiO2比值低,TiO2/SiO2比值高,其∑REE值低,稀土模式平缓,不富集轻稀土,介于大陆和大洋拉斑玄武岩之间;略阳三岔子、石泉两河和日本岛弧地区的岩石其特征是K2O/SiO2比值高,TiO2/SiO2比值低,其∑REE值高,稀土模式为陡右倾,富轻稀土。综合研究认为晚古生代西秦岭(勉略—阿尼玛卿—索托湖—麻扎)为古特提斯大洋环境,往东经镇巴—城口—青峰—襄樊—周家湾—广济为坳拉槽特征。同时期造山带南侧主要受古特提斯洋的影响处于海相沉积的伸展环境;北侧处于隆起状态下的陆内坳陷沉积。南侧二叠系碳酸盐岩、泥页岩及煤系是主要烃源岩,以生气为主;北侧石炭—二叠系煤系地层是主力烃源岩,晚燕山—喜山期二次生烃具有重要的油气意义。

On the basis of geochemical analysis for volcanic rocks from East Qinling--Dabie Orogenic Belt and its both sides： Zhuangke of Ltieyang County and mid-Atlantic ridge can be classified as the same type of rocks characterized by low ratio of K2O/SiO2, high ratio of TiO2/SiO2, low value of ∑REE, with flat REE pattern and not enriched LREE, which are between the continental and the oceanic tholeiire. The rock characteristics from Sanchazi of Lueyang County, I.ianghe of Shiquan County and the Japanese island arc are high ratio of K2O/SiO2, low ratio of TiO2/SiO2, high value of EREE and richment of LREE, the REE distribution pattern showed steep right-dip. This paper considers that the environment of West Qinling Mountain （Mianlue--Animaqing--Soto Lake--Mazha） is the Paleo-Tethys Ocean in the Irate Paleozoic, the east area（passed by the Zhenba--Chengkou--Qingfeng--Xiangfan-- Zhoujiawan--Guangji） is aulacogen sediments. The south side of Qinling--Dabie Orogenic Belt is mainly in the extended environment affected by Paleo Tethys Ocean which main hydrocarbon source rocks are Permian carbonate, shale and coal, and enriched gas. While the north side is in a state of intracontinental depression accompanying the uplifting, and the Carboniferous--Permian coal-bearing strata are the main hydrocarbon source rocks, secondary hydrocarbon generation in Late Yanshanian--Himalayan has important significance for oil and gas accumulation.