【作者】 徐先兵；

【导师】 张岳桥；

【作者基本信息】 南京大学 ， 构造地质学， 2011， 博士

【摘要】 本文选择对武夷山地区韧性剪切带、中生代褶皱和断裂以及显生宙火成岩进行综合研究,探讨了显生宙构造-热事件的形成时代和构造变形样式,并讨论了华南早古生代造山带的构造演化、印支期构造变形与动力学以及中生代构造体制的转换。华南东部武夷山地区前寒武纪基底出露广泛。四个变沉积-火山岩样品的锆石U-Pb年代学表明武夷山地区麻源群大金山组形成时代晚于879 Ma,马面山群东岩组形成于818土14Ma,万全群杜潭组和黄潭组分别形成于825±18 Ma与746.0±6.2Ma。根据区域上前寒武纪地层岩性和时代的对比研究,认为武夷山地区新元古界可以划分为三期,早期由麻源群的大金山组和马面山群的龙北溪组的陆源碎屑沉积岩构成,形成时限为879-825 Ma；中期包括麻源群的南山组,马面山群的东岩组和大岭组,万全群和龙泉群,以及交溪组,迪口组和桃溪组下段,以火山-沉积岩系列为主,可以分为两期,即825-800 Ma和751-728 Ma。晚期由原天井坪组主体、桃溪组上段以及楼子坝群下部的沉积岩组成,其形成时限为620-542 Ma。武夷山地区前寒武纪变质基底中韧性剪切带发育,局部卷入中上泥盆统石英砾岩。野外地质调查表明,韧性剪切带断续出露于武平、长汀-清流以及将乐地区,走向由北北东向、北东向转换为近东西向。剪切带记录了两期韧性变形,早期为由北西向南东方向的逆冲剪切,晚期为右旋走滑变形。武平韧性剪切带内发育早古生代同构造片麻状花岗岩和混合岩,是同变形地壳深熔作用的结果。三个同构造片麻状花岗岩样品的锆石U-Pb年龄分别为440.8±4.8 Ma,435.6±6.2 Ma与431.2±3.2 Ma,混合岩中锆石变质增生边形成于433.8土6.8 Ma,指示武平韧性剪切带的早期逆冲剪切形成于441-431 Ma。武夷山地区韧性剪切带在印支期发生活化,发生右旋走滑。剪切带中两个糜棱岩样品的云母40Ar/39Ar坪年龄分别为235.3±2.8 Ma与238.5±2.8 Ma,侵入剪切带的花岗岩脉锆石U-Pb为229.8±2.2Ma,表明右旋走滑形成于239-230 Ma。根据糜棱岩中矿物变形组合和电子探针分析,右旋走滑韧性剪切带形成的温压条件分别为400℃-500℃和7～10kbar。闽西玮埔岩体形成于447.1土4.7 Ma-440.8±3.4 Ma,赣南菖蒲混合岩形成于445.9±3.8 Ma,指示武夷山地区在447-441 Ma遭受强烈的热作用。武夷山地区遭受强烈动力作用形成的片麻状花岗岩和混合岩形成于441-431 Ma。再结合区域上早古生代角度不整合、花岗岩年代学以及构造变形年代学,可以认为早古生代造山作用形成于465-420 Ma,自420 Ma之后进入后造山伸展垮塌阶段。闽北铁山正长岩锆石U-Pb年龄为169.3±1.6 Ma,粤北同构造片麻状花岗岩为165.4±1.2 Ma,侵入燕山早期北东向褶皱的河田岩体年龄为152.9±1.4 Ma,且逆冲断裂带白云母40Ar/39Ar坪年龄为162±2 Ma,表明武夷山地区燕山早期挤压构造形成于169-162 Ma。晚侏罗世至早白垩世,中国东南部发育大量断陷盆地。盆地内发育大量的早白垩世火山岩,锆石U-Pb年代学表明武夷山地区火山岩形成于141-135.8±1.1 Ma。盆地边界断层和同沉积断层矢量反演古构造应力场指示武夷山地区早白垩世伸展方向为NW-SE向,区域上早白垩世火山岩指示NW-SE向伸展持续到-130 Ma。早白垩世晚期,挤压作用导致下白垩统翘倾和长乐-南澳断裂带的左旋走滑。长乐-南澳断裂带断层矢量反演的构造应力场为NW-SE挤压。左旋走滑卷入的最新地层为早白垩世火山岩,侵入断裂带的未发生构造变形的花岗岩年龄为108±2 Ma,表明挤压作用形成于130 Ma之后,结束于108Ma之前。此后,强烈的伸展作用造成晚白垩世火山岩喷发和断陷盆地形成。武夷山地区晚白垩世火山岩形成于100.4±1.5-97.6±1.1 Ma。区域上还发育同期的碱性花岗岩与基性岩墙活动。岩墙展布方向和盆地断层矢量反演的构造应力场指示晚白垩世早期为NW-SE向伸展。由此可见,中国东南部在晚中生代遭受NW-SE向挤压和伸展作用交替控制,可能是太平洋板块俯冲角度调整、俯冲方向转变以及俯冲板片断离和俯冲带后撤的产物。系统的地质编图结果表明华南印支期褶皱轴向以近东西向为主,燕山期褶皱则表现为北东-北北东走向。武夷山地区印支期北东走向韧性剪切带表现为右旋走滑剪切,而燕山早期北东向断裂则以由北西向南东方向逆冲为主。武夷山地区印支期构造变形表现为近东西向褶皱和沿北东向韧性剪切带的右旋走滑,是近南北向陆陆碰撞作用的结果；而燕山早期构造变形表现为北东向褶皱和沿北东向断裂的逆冲剪切,是太平洋板块俯冲作用的产物。华南东部地区早、晚中生代构造变形、岩浆作用以及动力学等方面都存在明显的差异,表明其经历了构造体制转换。综合研究表明,华南板块中生代构造体制转换形成于早侏罗世。更多还原

【Abstract】 Based on researches of ductile shear zones, Mesozoic folds and faults as well as Phanerozoic igneous rocks in Wuyishan area, we studied the timing and structural deformational styles of Phanerozoic tectono-thermal events. In addition, we discussed the tectonic evolution of the Early Paleozoic orogen in South China, Indosinian structural deformation and geodynamics, and transformation of Mesozoic tectonic regime.The Precambrian strata are widespread in the Wuyishan area, South China. This study presents four zircon La-ICPMS U-Pb ages of meta-volcano-sedimentary rocks. The new data indicate that the Huangtan and Dutan formations of the Wanquan Group were deposited at 746.0±6.2 Ma and 825±18 Ma, respectively, the Dongyan Formation of the Mamianshan Group was deposited at 818±14 Ma, whereas the Dajinshan Formation of the Mayuan Group was deposited after 879 Ma. Three episodes of Neoproterozoic deposition are identified according to lithologic stratigraphic and geochronological data. The early episode is between 879 Ma and 825 Ma, which is characterized by terrigenous sedimentary rocks in t he Dajinshan Formation of the Mayuan Group and the Longbeixi Formation of the Mamianshan Group. The middle episode consists of the Nanshan Formation of the Mayuan Group, the Dongyan and the Daling Formation of the Mamianshan Group, the Wanquan and the Longquan groups, and the Jiaoxi, Dikou and Lower Taoxi formations. These deposits are dominated by volcanic-sedimentary rocks and can be further subdivide into two sub-episodes. The early sub-episodes is between 825 Ma and 800 Ma, whereas the later sub-episodes between 751Ma and 728 Ma. The late episode is between 620Ma and 542 Ma, which is characterized by the sedimentation of the main body of t he original Tianjinping Formation, the upper Taoxi Formation, and the lower Louziba Group.Ductile shear zones have been well documented in Pre-Devonian meta-volcanic and meta-sedimentary rocks in the Wuyishan area, South China. Field investigation shows that these shear zones are discontinuously distributed in the area from Wuping County to Jiangle County, and their strikes changes from NNE-trending, to NE-trending and nearly E-W-trending. Two stages ductile deformations had been found in these shear zones. The early deformation is top-to-SE thrust shearing, whereas the late is dextral strike-slip motion. Early Paleozoic gneissic granites and migmatites developed in the Wuping ductile shear zone are the result of syn-deformation crust anatexis. Zircon La-ICPMS U-Pb ages of three syn-orogeny gneissic granites are 440.8±4.8 Ma,435.6±6.2 Ma and 431.2±3.2 Ma, respectively. Moreover, the metamorphic growth rims of zircons in migmatite developed at 433.8±6.8 Ma. These aforementioned data shows that the early thrust shearing formed between 441 Ma and 431 Ma. These top-to-SE thrusting shear zones moved again in Indosinian period, and changed into dextral strike-slip shearing.40Ar/39Ar step-heating dating of biotite and muscovite separated from two mylonites yields ages of 235.3±2.8 Ma and 238.5±2.8 Ma, respectively; and an undeformed granitic dyke intruded into the shear zone was dated,229.8±2.2 Ma, by La-ICP-MS U-Pb zircon method. These dates reveal that dextral shearing developed at the time span between 230 Ma and 239 Ma, during the Triassic Indosinian tectono-thermal event. Deformation temperature is estimated in 400～500℃and the pressure between 7 kbar and 10 kbar by syn-mylonitization mineral assemblages, mineral deformation behavior and electron microprobe analysis on muscovite in mylonitic rocks.Geochronology of zircon La-ICPMS U-Pb method suggests that Weipu grantic pluton formed between 447.1±4.7 Ma and 440.8±3.4 Ma, and Changpu magmatite developed at 445.9±3.8 Ma, which indicating that a intense thermal event (447～441 Ma) occurred in Wuyishan area. Combining with Paleozoic angular unconformity, geochronology of granites and structural deformation, we thought that Early Paleozoic orogeny in South China occurred between 465 Ma and 420 Ma, followed by extension and collapse after 420 Ma.Syenite in Tieshan, Zhenghe County, formed in extensional environment, gives an age of 169.3±1.6 Ma, as the lower bound of Early Yanshanian event. While Bachi granitic gneiss in Pingyuan, northern Guangdong Province, formed in compressional environment, yields an age of 165.4±1.2 Ma. This indicates the main timing of deformation. In contrast,40Ar/39Ar plateau age of syn-deformation muscovite in Changting, western Fujian Province, is 162±2 Ma. This is interpreted as cooling age of the thrust shear, supplying the upper bound of Early Yanshanian event. This is also supported by the Hetian granite crystallized at 152.9±1.4 Ma, which intruded the Early Yanshanian NNE-trending folds in Changting basin. These above data indicated that Early Yanshanian event formed between 169 Ma and 162 Ma. From Late Jurassic to Early Cretaceous, a lot of faulted-depression basins developed in southeast China, filled mainly by volcanic rocks in Early Cretaceous. Volcanic rocks in Wuyishan area erupted between～141 Ma and 135.8±1.1 Ma by La-ICP-MS U-Pb zircon method. Paleostress field analyses of slip vectors from normal boundary faults and syn-deposition faults indicated that NW-SE-striking extension dominated in Early Cretaceous and tilled to～130 Ma. In late Early Cretaceous, structural compression led the Lower Cretaceous to be tilted and Changle-Nan’ao fault to ductile sinistral motion. Paleostress field analyses of slip vectors from Changle-Nan’ao fault showed that NW-SE-striking compression. The youngest strata involved in the shear zone were Early Cretaceous volcanic rock. And the sinistral fault was intruded by Shanxia granitic pluton (108±2 Ma), indicating that NW-SE-striking compression occurred between 130 Ma and 108 Ma. Thereafter, intense extension dominated southeast China again, and led to Late Cretaceous volcanic action and normal faulting. Two volcanic samples erupted in 100.4±1.5 and 97.6±1.1 Ma by La-ICP-MS U-Pb zircon method. Meanwhile, alkaline granite and mafic dykes developed in southeast China. The strike of mafic dykes and slip vectors analyses of boundary normal faults of Late Cretaceous basins indicated that southeast China suffered from NW-SE-trending extension. In short, the late Mesozoic tectonic evolution of southeast China was alternated between extension and compression, maybe as the result of the slab dip angle increased from a very low angle to a median angle, the rotation of slab direction, the slab break-off and roll-back.Systematic geological map compilation shows that the axes of Indosinian folds in South China strikes E-W-trending, whereas the axes of Yanshanian folds is NNE-NE-striking. Moreover, in Wuyishan area, Indosinian NE-striking ductile shear zones are characterized by dextral motion, while Yanshanian faults are featured by top-to-SE thrusting. The Indosinian nearly E-W-trending folds and dextral ductile shear zones are the products of N-S-striking continent-continent collision, whereas the Yanshanian NE-trending folds and top-to-SE faults are resulted from the subduction of Pacific plate underneath South China. Structural deformation, magmatism and geodynamics in Early Mesozoic are different that in Late Mesozoic, indicating that South China suffered from tectonic regime transformation in Mesozoic. Comprehensive research show that tectonic regime transformation occurred in Early Jurassic.更多还原