关键词: 瓮安穹隆, 早古生代构造事件, 构造变形, 角度不整合, 碎屑锆石分析

Abstract:

The Early Paleozoic, a key and widespread tectonic event, occurred between the Devonian and PreDevonian in the Yangtze Block. Different models on the event, such as the three episodes, two episodes and continued changing in paleogeographic patterns, have been proposed. This paper focuses on the Wengan Dome in the Southwest Yangtze Block, which has well preserved and exposed Early Paleozoic deformation. Six geologic crosssections of the Weng’an dome were used for the detailed divisions of the tectonic layers; analyses of structural styles, tectonic superposition and deformational sequence with chronological constraints were also performed. The results suggest that the Wengan Dome is essentially a tectonic superimposed dome. The dome experienced at least two deformations since the Paleozoic, namely the Early Paleozoic deformation D1 and Yanshanian deformation D2. The D1 deformation is represented by the EWtrending folds, strikeslip to thrust faults and EWtrending approximate to vertical interval cleavages—all resulted from SN vertical extrusion; it is seen in the CambrianSilurian and underlying tectonic layers. The EWtrending structures of the D1 deformation were intercepted and superimposed by the D2 deformation. This indicates that the D1 deformation formed before the angular unconformity between the tectonic layers of the CambrianSilurian and the Upper Devonian to Middle Triassic. According to the distribution of the detrital zircons, the Early Paleozoic era occurred later than ca. 438 Ma in the Wengan Dome. Geological investigation presented in this study, and numerous data published in recent years, further support the hypothesis that the Early Paleozoic tectonic deformation appeared first in the southern area of the South China Block before propagating to the north.

Key words: Key words: Weng’an Dome, Early Paleozoic tectonic event, deformation, angular unconformity, detrital zircon analysis