论文部分内容阅读
长期的华南地块研究取得了一系列重要成果,但是古太平洋俯冲作用于华南的地质记录不是很清晰,尚存争论。一派认为始于二叠纪,另一派认为中生代。本文试图通过华南中生代EW向特提斯构造域和NE向古太平洋构造域的构造转换过程及转换时间入手,探讨古太平洋俯冲启动。雪峰山地区早侏罗世地层以及侏罗纪类磨拉石建造呈NE或NNE向展布,燕山期主要发育2期褶皱变形,早期褶皱轴向为NE—NNE向,晚期为NNE或近南北向的隔槽式褶皱;而印支期也发育2期褶皱变形,D1期为EW—NEE向,D2期为NNE向的紧闭褶皱。这些都说明晚三叠世雪峰山地区已经从EW向特提斯构造域向NE—NNE向太平洋构造域的构造方向转换。而南岭地区,以及更南部的南海北部海域,构造转换时间相对较晚,为早—中侏罗世。综合前人的测年数据,德兴斑岩型铜矿三个含矿斑岩体形成于大约172 Ma,形成于古太平洋板块俯冲所形成的活动大陆边缘环境,成矿物质来源于俯冲洋壳的部分熔融,与地幔楔发生混染,推测与该时期古太平洋板块的平板俯冲、板片撕裂、拆沉和俯冲后撤一系列过程密切相关。同期,华南东南部发育了NE—NNE向、NW向和近EW向三组断裂,其中白垩纪(135~100 Ma)华南NE—NNE向的走滑断裂强烈活动,从东向西依次为:滨海断裂、长乐—南澳断裂、政和—大埔、邵武—河源—阳江断裂、吴川—四会断裂和合浦—北流断裂,主要表现为右旋走滑作用,在东南沿海地区形成一系列的拉分盆地,并非典型的“盆岭构造”。根据群速度和S波速度层析成像,华南地块总体上从西向东地壳的厚度整体上逐渐减薄;华南地块东部发生两次壳幔相互作用,对应两次岩石圈拆沉,这两次拆沉都与古太平洋板块的俯冲有关,第一次拆沉为古太平洋板块平板俯冲时板片撕裂所致,第二次拆沉为俯冲板片俯冲后撤和高角度俯冲造成。
Long-term research on the South China block has made a series of important achievements, but the geological records of the subduction of the South Pacific in the South Pacific are not very clear and remain controversial. One group believes that it started in the Permian and the other believed Mesozoic. This paper attempts to discuss the tectonic transformation process of the Tethys tectonic domain and the NE-trending Paleo-Pacific tectonic domain through the Mesozoic EW in South China and to explore the subduction of the Paleo-Pacific Ocean. The Early Jurassic strata and the Jurassic molasse in the Xuefeng Mountain area are characterized by NE or NNE distribution. The Yanshanian stage is characterized by two stages of fold deformation, the early fold axis is NE-NNE, the late stage is NNE or near North and South To the septate fold; while the Indosinian also developed two fold deformation, D1 EW-NEE to D2, NNE-oriented tight folds. All of these show that the Late Triassic Xuefeng Mountain region has been transformed from the EW to the Tethys tectonics to the NE-NNE tectonic tectonics. In the Nanling area and in the southern South China Sea, the tectonic transformation time is relatively late, which is Early-Middle Jurassic. Based on the previous dating data, the three ore-bearing porphyries of the Dexing porphyry copper deposit formed at about 172 Ma, forming on the active continental margin formed by the subduction of the Paleo-Pacific plate. The ore-forming materials are derived from the subducted oceanic crust And partially mixed with mantle wedges. It is presumed that there is a close correlation with a series of processes of plate subduction, tearing, delamination and subduction of Paleo-Pacific plate during this period. During the same period, three NE-NNE, NW and near EW faults developed in the southeastern South China. The NE-NNE strike-slip faults in South China during the Cretaceous (135 ~ 100 Ma) strongly moved from east to west in order: Coastal fault, Changle-Nan’ao fault, Zhenghe-Tai Po, Shaowu-Heyuan-Yangjiang fault, Wuchuan-Sihui fault and Hepu-Beiliu fault are characterized by dextral strike-slip and a series of pull in the southeastern coastal areas Sub-basin, not typical “basin ridge structure ”. According to the group velocity and S-wave velocity tomography, the thickness of the South China block generally decreases from west to east as a whole. Two crust-mantle interactions occur in the eastern part of South China block, corresponding to two times of lithosphere delamination The subsidence and sedimentation were related to the subduction of the Paleo-Pacific plate. The first detachment was caused by the tearing of the plate during subduction of the plate of the ancient Pacific Plate. The second subsidence was caused by subduction and subduction of the subducting plate and high-angle subduction.