拉脊山早古生代海沟-岛弧体系演化研究

The texture and evolution of trench-arc system can provide the most immediate evidence for reconstructing the formation of the orogen and plate tectonics. Lajishan Cambrian-Ordovician ophiolitic mélange and island arc were tectonically interlaid between the Central Qilian and South Qilian blocks, but tectonic evolution of Lajishan area and regional geology have still been debated because of particular lack of systemic studies on the texture, rock assemblages, and the spatial-temporal relationship of both units. Rock/block assemblage, patterns of deformation and spatial variation of Lajishan trench-arc system will be studied by field surveying, mapping, and comprehensive analyzing using multi-discipline methods in this project. Tectonic setting and evolution of the Lajishan ophiolite and island arc are systemically studied based on these new data together with regional data. These results can provide credible evidences for studying on the texture and tectonic evolution of the Lajishan Cambrian-Ordovician trench-arc system, which are also vital to discuss the relationship between the Paleozoic oceanic basin evolution of Lajishan area and the North Qilian belt. The results of this project can give more details about the temporal-spatial structure and evolution of the Lajishan Cambrian-Ordovician trench-arc system and provide some evidences for studying the relationship between tectonic evolution of the South Qilian belt and the Proto-Tethyan ocean.

沟-弧体系结构与演化研究可为造山带形成与古板块构造重建提供最直接证据。拉脊山寒武-奥陶纪蛇绿混杂带和岛弧带研究程度较低且其结构组成和时空对应关系缺乏系统研究，导致拉脊山及区域构造演化长期存在争议。本项目拟主要通过关键地段大比例尺填图和综合研究，运用构造、岩石、矿物、古生物、地球化学多种研究手段，结合区域地质资料，查明拉脊山寒武-奥陶纪蛇绿混杂带和岛弧带岩石/岩块组合、构造变形特征，综合研究蛇绿混杂带形成大地构造环境以及其与岛弧带构造演化过程，恢复拉脊山寒武-奥陶纪沟-弧体系时空对应关系，重塑古板块构造格局，探讨拉脊山与北祁连早古生代古洋盆演化之间关系。本项目研究的科学意义在于：深化南祁连拉脊山寒武-奥陶纪海沟-岛弧体系时空结构与演化，为南祁连构造演化与原特提斯洋之间关系研究提供直接依据。

沟-弧体系结构与演化研究可为造山带形成与古板块构造重建提供最直接证据。拉脊山寒武-奥陶纪蛇绿混杂带和岛弧带研究程度较低且其结构组成和时空对应关系缺乏系统研究，导致拉脊山及区域构造演化长期存在争议。本项目通过关键地段大比例尺填图和综合研究，运用构造、岩石、矿物、古生物、地球化学多种研究手段，结合区域地质资料，查明并研究了拉脊山寒武-奥陶纪蛇绿混杂带和岛弧带岩石/岩块组合、构造变形特征，综合分析了蛇绿混杂带形成大地构造环境以及其与岛弧带构造演化过程，在恢复拉脊山寒武-奥陶纪沟-弧体系时空对应关系基础上，探讨了拉脊山与北祁连早古生代古洋盆演化之间关系。研究表明，原特提斯洋在早古生代时期发生多方向俯冲-增生和弧-陆碰撞，初始俯冲时间早于535Ma，闭合时间为450Ma。这些认识可为深化南祁连拉脊山寒武-奥陶纪海沟-岛弧体系时空结构与演化以及南祁连构造演化与原特提斯洋关系研究提供直接依据。