信江盆地上饶段结构特征与成矿前景——来自大地电磁的证据
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摘要
信江盆地处于赣东北武夷山脉和怀玉山脉之间近东西向狭长的谷地内,大地构造处于扬子古板块和华夏古板块接合部,中生代以来经历了由裂陷盆地到断陷盆地的演化历程,沉积了一套"下灰上红"的陆相碎屑岩系.白垩纪之后经历了喜山期构造及新构造运动的作用,随而沉积了厚达数千米的红砂岩,俗称"红层".为了较全面、客观地认识盆地上地壳的电性结构,研究成矿规律与深部地球物理、地质结构的对应关系,依托钦杭结合带及邻区深部地质调查项目在上饶地区探测廊带部署的大地电磁(MT)和高频大地电磁(HMT)剖面,对其中33个MT和43个HMT测深点进行数据处理和反演,结合MT反映的深部信息和HMT反映的浅层信息,对信江盆地上饶段的边界、内部结构及成矿前景进行分析,得出以下几点认识:(1)MT和HMT反演剖面均能较好的反映盆地边界,红层盆地在上饶段跨度达40 km以上,且呈现浅宽深窄的形态,厚度从几百米到2 km左右不等.(2)盆地南侧发现一个产状较陡的低阻带,一直延伸到近10 km以深,推测为华夏和扬子板块边界,也即钦杭结合带的南边界—江绍断裂.(3)盆地内部多为陆相红色砂岩,除前人已发现的火山岩型热液铀矿和石膏矿以外,推断盆地内几大结构完整的凹陷为成油有利区.
The Xinjiang basin is located in the narrow east-west valleys between the Wuyi and Huaiyu Mountains in northeastern Jiangxi, which the tectonic structure lies in the junction of the Yangtze paleo plate and the Cathaysia plate. Since Mesozoic, it has experienced the evolution process from rift basin to fault basin, and a set of continental clastic rock series with "lower ash and upper red" has been deposited. After Cretaceous, it underwent the Himalayan tectonic and Neotectonic Movement. Subsequently, red sandstone with a thickness of several kilometers has been deposited, commonly called the red layer". In order to understand the electrical structure of the upper crust of the basin more comprehensively and objectively, and to study the corresponding relationship between metallogenic regularity and deep geophysics and geological structure. Data processing and inversion of 33 MT and 43 HMT sounding points were carried out, which was based on the MT and the high frequency electromagnetic(HMT) profiles deployed in the Qing-Hang belt and the adjacent geological survey project in the vicinity of the exploration corridor in Shangrao region. Combined with the deep information from MT and the shallow information from HMT, the boundary, internal structure and metallogenic prospect of the Shangrao section of the Xinjiang basin are analyzed, and the following conclusions are obtained. First, the MT and HMT inversion profiles can well reflect the basin boundaries. The red-bed basin has a span of more than 40 km in Shangrao section and has a shallow, deep and narrow shape with thickness varying from a few hundred meters to two kilometers. Next, a steep low resistivity zone was found on the south side of the basin, which extends to the depth of nearly 10 km. It is presumed to be the boundary between the Cathaysian and the Yangtze plates, that is, the southern boundary of the Qinhang belt-Jiang Shao fault. Third, the interior of the basin is mostly continental red sandstone.In addition to the volcanic hydrothermal uranium deposits and gypsum deposits discovered previously,it is inferred that the main depressions and the existing depressions and valleys in the basin are favorable areas for oil production.