由秦巴泥盆纪岩相古地理研究探讨古构造活动

PALAEOTECTONIC ACTIVITIES: AN INVESTIGATION OF DEVONIAN SEDIMENTARY FACIES AND PALAEOGEOGRAPHY IN THE QINLING—BASHAN AREA

摘要:

秦巴地区位于华北地块与扬子地块两个相对稳定地质单元之间,处于南、北方的过渡地带。泥盆纪是秦巴地区由活动转向相对稳定的关键时期。现通过地层古生物、沉积相古地理、古地磁、古构造演化及化探等学科的研究,诸多资料均说明这一过渡地带的存在。

Abstract:

This paper elucidates, on the basis of the reconstruction of sedimentary facies and palaeogecgraphy, the Devonian palaeoenvironmental vicissitudes in the Qinling—Bashan area, which were characterized by the gradual transgression from south to north and from west to east; the migration of depositional or subsidence centres from south to north; the northward migration of the volcanic zones and the variations from basic to intermediate-acidic compositions; the northward migration of the ancient islands; the variations in ancient submarine topography lower in the south and higher in the north in the early stage, or vice versa in the later stage, and the extensional faulting which led to the transgression all over the region. It is believed that all the regular changes mentioned above may be attributed to the external factors. And internally, the Qinling-Bashan area lay between the North China and Yangzi plates. The increasing suturing of the southern and northern plates during the Caledonian allowed the disappearance of the oceanic crust, the elevation of the crust and the retreat of sea water. Later in the Devonian, as a result of the northward shifting of the North China plate, the study area is thought to be in an extensional and faulted environment where the continental crust became thinner and elongated. The crust downwarped slowly and thus the transgression occurred, accompanied by faulting and weak volcanic activities. It follows that the Devonian time represents a transitional stage, i. e. a relatively stable stage between active Caledonian and Indo-Chinese epochs.