Structural Styles and Chronological Evidences from Dulong-Song ChayTectonic Dome: Earlier Spreading of South China Sea Basin due toLate Mesozoic to Early Cenozoic Extension of South China Block
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摘要: 南海盆地的扩张经历了早期(中生代晚期至新生代早期)和晚期(32~17Ma)2个快速阶段,但2阶段在时间上相继,在形成机制上也可能是一致的.然而由于南海盆地与周围板块侧向作用的关系复杂,对扩张机制的认识一直极具争议,新的构造分析和测年资料表明“弧后扩张”及“走滑扩张”模式均与事实有出入.对位于华南地块西南缘的都龙SongChay变质穹隆体的研究表明,在中生代至新生代时期,至少经历了2期重要的伸展构造: D1期(237~228Ma)穹隆的隆升与表露阶段,代表了印支期造山作用前的伸展构造; D2期(86~78Ma)叠加和改造阶段,并有可能始于176~146Ma,致使穹隆进一步隆升和表露.D2期构造在发育时间、伸展方向及变形方式等上既与华南地块同时期区域伸展构造特征相一致,也与南海盆地北缘早期扩张特征相一致.因此,作为华南地块的组成部分,南海盆地北缘的早期扩张也是华南中生代晚期至新生代早期伸展构造的构成部分.由此推测,南海盆地扩张的动力学机制可能主要来自于华南地块的板内变形作用,而哀牢山-红河断裂带的左行走滑作用对南海盆地新生代的扩张起到推动和加强作用.
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关键词:
- 南海盆地北缘 /
- 都龙-Song Chay变质穹隆体 /
- 华南地块 /
- 伸展构造 /
- 构造年代
Abstract: The South China Sea basin expanded firstly from Late Mesozoic to Early Cenozoic,and then at 32-17 Ma.The second stage of extension formed immediately after the first stage,and both extensions are consistent with the forming mechanism.New structural analysis and geochronological data are both inconsistent with the current models of backarc extension and extension by strike-slip fault.New data of structural styles and geochronometry in the Dulong-Song Chay metamorphic dome indicate at least two epoches of major extensional tectonics: the D2 deformation of the rising and exhumation of the dome occurred at 237-228 Ma; and the D2 deformation overprinted and re-deformed on the dome at 86-78 Ma.Of them,the D2 deformation shows a consistent forming time,extensional direction and tectonic regime amongst the Dulong-Song Chay dome,South China block and the north margin of the South China Sea basin.Regional geology shows that the north margin of the South China Sea basin belongs to the South China block.Therefore,we interpret that the Late Mesozoic to Early Cenozoic extensional tectonics occurred in the north margin of the South China Sea basin as a result of the interplate deformation of the South China block The Ailaoshan-Red River sinistral slip strengthened the Cenozoic extension in the South China Sea. -
图 1 华南地块、印支地块区域构造略图(Chung et al., 1997;胥颐等, 2003)
Fig. 1. An outline tectonic map of South China block and Indochina block
图 2 都龙变质穹隆体地质图
南部完整的Song Chay变质穹隆体参见Roger et al.(2000)和Maluskia et al.(2001)
Fig. 2. Geological map of Dulong metamorphidome
图 4 DL-2锆石SHRIMPⅡ离子探针分析结果
a.15个分析点的不一致曲线; b.17个点的Th/U比值; c.3个点的206Pb/238U平均年龄; d.6个点的206Pb/238U平均年龄
Fig. 4. SHRIMPⅡ U-Pb zircon dating results from sample DL-2
表 1 DL-2锆石SHRIMP Ⅱ U-Pb分析结果
Table 1. SHRIMP Ⅱ U-Pb isotopic analyses for zircon from sample DL-2
表 2 DL-1黑云母40Ar/39Ar同位素年龄测试结果
Table 2. 40Ar/39Ar analyses of the biotites from the DL-1
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