| 海南岛东北部木栏头变质杂岩的组成、时代及其区域大地构造意义 |
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| 引用本文： | 刘晓春,胡娟,陈龙耀,夏蒙蒙,韩建恩,胡道功.海南岛东北部木栏头变质杂岩的组成、时代及其区域大地构造意义[J].地质学报,2022,96(9):3051-3083. |
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| 作者姓名： | 刘晓春 胡娟 陈龙耀 夏蒙蒙 韩建恩 胡道功 |
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| 作者单位： | 1) 中国地质科学院地质力学研究所，北京，100081；
2) 自然资源部古地磁与古构造重建重点实验室，北京，100081 |
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| 基金项目： | 本文为国家自然科学基金项目（编号41972068）、中国地质调查局中国地质科学院基本科研业务费项目（编号DZLXJK202003）和中国地质调查局地质调查项目（编号DD20190306）资助的成果。 |
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| 摘 要： | 新的区域地质调查在海南岛东北部木栏头地区识别出一套从前未知的中级变质杂岩。木栏头变质杂岩主要沿林新—木栏头—虎威岭—赤坡—七星岭—新埠海—铺前海边沿岸呈基岩或不同尺度的无根岩块断续出露，其主体是钙硅酸盐岩和正、副片麻岩，含有少量斜长角闪岩、石英岩和大理岩，并按分布区域可进一步区分出林新片麻岩- 斜长角闪岩组合、木栏头变质火山岩- 钙硅酸盐岩组合、虎威岭- 七星岭片麻岩- 钙硅酸盐岩- 大理岩组合和新埠海- 铺前片麻岩组合等四套岩石组合。对30件变质基性岩、变质中酸性岩、变质碎屑沉积岩、钙硅酸盐岩以及花岗和伟晶岩脉等不同类型岩石的锆石U- Pb定年结果表明，木栏头变质杂岩的原岩主体是一套二叠纪火山- 沉积岩系，其内含有少量二叠纪花岗质侵入岩以及前寒武纪结晶基底的残留。前寒武纪结晶基底主要包括古元古代晚期（1670 Ma）碎屑沉积岩和中元古代早期（1460~1410 Ma）花岗质片麻岩，晚二叠世碱性花岗岩中还存在大量单一的中元古代晚期（1180 Ma）继承锆石。变质沉积岩中的早期碎屑锆石年龄峰值为2550~2490 Ma、1850~1780 Ma、1600~1560 Ma、1450 Ma和1100 Ma，表明其物源主要来自于海南岛中部的抱板群、石碌群和石灰顶组。二叠纪花岗岩的侵入时代主要为280 Ma和260 Ma，与陆缘弧前盆地环境下形成的火山- 沉积岩系的时代基本一致。这些沉积岩中的碎屑锆石除具有395~345 Ma和280~256 Ma两个年龄峰值外，部分样品还含有960~930 Ma和450~410 Ma两个重要年龄峰值，与前人在海南岛晚古生代地层中获得的年代学结果相似。木栏头变质杂岩经历了晚二叠世—中三叠世（254~235 Ma）高角闪岩相区域变质和深熔作用以及花岗和伟晶岩脉的大规模侵入，独居石U- Pb定年表明中侏罗世（159 Ma）花岗岩脉也侵入其中。结合近年发表的研究资料，我们认为海南岛应属于印支陆块的一部分，由中元古代结晶基底和早古生代盖层构成的琼南地体以及该地体演化而来的琼北构造混杂岩带两个次级构造单元组成，邦溪- 晨星构造带或昌江- 琼海断裂不能被视为华南和印支陆块间的构造边界，真正的古特提斯缝合带（即金沙江- 哀牢山- 马江缝合带的东延）应位于木栏头北部，大致相当于现今琼州海峡断裂的位置。华南和印支陆块间古特提斯洋盆的关闭始于石炭纪（340~300 Ma）洋壳的南向俯冲，形成北部的潮滩鼻榴辉岩和南部的邦溪- 晨星弧后盆地，二叠纪时期（280~255 Ma）洋盆持续俯冲形成海南岛主体大陆岛弧以及木栏头弧前盆地，而后洋盆最终关闭并进入到陆- 陆碰撞和碰撞后伸展阶段，从而形成木栏头变质杂岩以及海南岛内部其他三叠纪变质岩和同期花岗质岩石。
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| 关 键 词： | 中元古代基底 二叠纪火山- 沉积岩系 晚二叠世—中三叠世变质 海南岛 东古特提斯 |
| 收稿时间： | 2022/9/21 0:00:00 |
| 修稿时间： | 2022/9/21 0:00:00 |
The Mulantou metamorphic complex from northeastern Hainan Island, South China: compositions, ages and tectonic implications |
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| Liu Xiaochun,Hu Juan,Chen Longyao,Xia Mengmeng,Han Jianen,Hu Daogong.The Mulantou metamorphic complex from northeastern Hainan Island, South China: compositions, ages and tectonic implications[J].Acta Geologica Sinica,2022,96(9):3051-3083. |
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| Authors: | Liu Xiaochun Hu Juan Chen Longyao Xia Mengmeng Han Jianen Hu Daogong |
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| Abstract: | A suite of previously unknown medium- grade metamorphic complex, named the Mulantou metamorphic complex (MMC), was recognized in the Mulantou area on northeastern Hainan Island through a new regional geological reconnaissance. The complex crops out discontinuously along the Linxin- Mulantou- Huweiling- Chipo- Qixingling- Xinbuhai- Puqian coast, and occurs as bedrocks or rootless blocks in different sizes. The dominant components of the MMC are calc- silicate rocks and ortho- and paragneisses, with subordinate amphibolites, quartzites and marbles. Based on the regional distribution, these rocks can further be divided into four rock association, that is, the Linxin gneiss- amphibolite association, the Mulantou metavolcanic- calc- silicate rock association, the Huweiling- Qixingling gneiss- calc- silicate rock- marble association, and the Xinbuhai- Puqian gneiss association. U- Pb zircon dating for 30 different rock types, including 3 metamorphosed basic rocks, 8 metamorphosed intermediate- acid rocks, 8 metamorphosed clastic sedimentary rocks, 3 calc- silicate rocks, and 8 granite and pegmatite dykes, suggest that the protoliths of the MMC are mainly Permian volcanic- sedementary rock series, with minor Permian granitoids and Precambrian crystalline basement relics. Precambrian basement consists mainly of Late Paleoproterozoic (1670 Ma) sedimentary rocks and Early Mesoproterozoic (1460~1410 Ma) granitic gneisses. Numerous Late Mesoproterozoic inherited zircons with upper intercept age of 1180 Ma occur in Late Permian alkaline granites, which were derived from partial melting of Late Mesoproterozoic crustal materials. Earlier detrital zircons from metasedimentary rocks have age peaks at 2550~2490 Ma, 1850~1780 Ma, 1600~1560 Ma, 1450 Ma and 1100 Ma, indicating a provenance derivation from the Baoban Group, Shilu Group and Shihuiding Formation in central Hainan Island. The emplacement ages of Permian granitoids are 280 Ma and 260 Ma, in accord with the ages of volcanic- sedimentary rock series formed in a continental fore- arc basin. Except for two major younger age peaks at 395~345 Ma and 280~256 Ma for detrital zircons from metasedimentary rocks, other two important age populations peaked at 960~930 Ma and 450~410 Ma are also present in some samples. These two age populations are consistent with those obtained for detrital zircons from Late Paleozoic strata on Hainan Island. The MMC underwent upper amphibolite facies metamorphism and partial melting accompanied by widespread intrusion of granite and pegmatite dykes during the Late Permian to Middle Triassic (254~235 Ma). U- Pb monazite dating also reveals Middle Jurassic granite dykes intruding into the metamorphic rocks. Coupled with recently published data, we infer that Hainan Island belongs to part of the Indochina Block, which can be subdivided into the South Hainan terrane composed of Mesoproterozoic basement and Early Paleozoic strata and the North Hainan tectonic mélange zone that was evolved from the terrane. Consequently, the Bangxi- Chenxing tectonic belt or Changjiang- Qionghai fault cannot be regarded as a tectonic boundary between the South China and Indochina blocks. The real Paleo- Tethyan suture zone (i.e., the eastern continuation of the Jinshajiang- Ailaoshan- Song Ma suture) should be located to the north of the Mulantou area, roughly equivalent to the (Qongzhou) Strait fault. The closure of the Paleo- Tethyan ocean basin between the South China and Indochina blocks commenced in the Carboniferous (340~300 Ma). The southward subduction of oceanic crust generated the Chaotanbi eclogites in the north and the Bangxi- Chenxing back- arc basin in the south. The continuous oceanic subduction during the Permian (280~255 Ma) resulted in the formation of the Hainan continental arc and the Mulantou fore- arc basin. After that, the ocean basin was finally closed and entered into the stages of continent- continent collision and post- collisional extension, leading to the formation of the MMC and other Triassic metamorphic rocks and coeval granitoids on Hainan Island interior. |
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| Keywords: | Mesoproterozoic basement Permian volcanic- sedimentary rocks Late Permian- Middle Triassic metamorphism Hainan Island Eastern Paleo- Tethys |
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