| 苏鲁超高压变质带东北端多种成因类型变基性岩:来自岩石学、同位素年代学及地球化学属性的制约 |
| |
| 引用本文： | 刘利双,刘福来,王伟.苏鲁超高压变质带东北端多种成因类型变基性岩:来自岩石学、同位素年代学及地球化学属性的制约[J].岩石学报,2017,33(9):2899-2924. |
| |
| 作者姓名： | 刘利双 刘福来 王伟 |
| |
| 作者单位： | 中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037 |
| |
| 基金项目： | 本文受国家自然科学基金重点项目（41430210）、中国地质调查局地质大调查项目（DD20160121）和中国地质科学院基本科研业务费项目（YYWF201703）联合资助. |
| |
| 摘 要： | 苏鲁超高压变质带是扬子板块与华北板块在三叠纪俯冲-碰撞的产物。变基性岩是苏鲁超高压变质带内出露最广泛的岩石类型之一,研究其岩石学、年代学、地球化学属性及成因机制,对于揭示扬子板块与华北板块之间的俯冲-碰撞-折返的动力学过程具有重要的科学意义。以(退变)榴辉岩为代表的超高压变质岩石广泛出露在威海-荣成一带,少量出露在乳山地区。锆石LA-ICP-MS U-Pb定年结果显示,(退变)榴辉岩的原岩时代为792~760Ma,峰期榴辉岩相变质时代为243~226Ma,后期角闪岩相退变质时代为221~207Ma。非榴辉岩相变质的基性岩(麻粒岩和斜长角闪岩)主要出露在乳山地区,其原岩形成时代应不晚于古元古代(1939Ma),峰期麻粒岩相变质时代为1895~1870Ma,后期角闪岩相退变质时代为1848~1806Ma,与胶北地体变基性岩的原岩时代和变质时代十分相似。全岩地球化学研究结果表明,(退变)榴辉岩的原岩显示高Fe拉斑玄武岩的特点,根据其稀土和微量元素特征,可将(退变)榴辉岩进一步划分为A、B和C三组。在球粒陨石标准化稀土配分模式和原始地幔均一化蛛网图解上,A、B和C三组样品分别具有轻稀土弱亏损、轻稀土弱富集和轻稀土富集的特点。轻稀土富集或弱富集型(退变)榴辉岩的原岩地球化学性质与岛弧或大陆玄武岩相似,它们的源区可能与深部富集地幔或受流体交代的地幔楔存在密切的成因关系;而轻稀土亏损型(退变)榴辉岩的原岩可能来自于亏损地幔的部分熔融。由此可见,(退变)榴辉岩的原岩具有成因多样性的特点。乳山地区的基性麻粒岩和斜长角闪岩的原岩也具有高Fe拉斑玄武岩的地球化学属性,Al2O3与Mg O呈正相关变化,TiO_2、P_2O_5与MgO表现出一定程度的负相关性。绝大多数非榴辉岩相变质基性岩的球粒陨石标准化稀土配分模式和原始地幔均一化蛛网配分曲线具有微右倾或明显右倾的特点。上述特征表明,研究区绝大多数非榴辉岩相变质的基性岩原岩来自于富集地幔,少数来自于原始地幔或亏损地幔,并经历了斜长石和辉石的分离结晶以及不同程度的部分熔融过程。由此可见,乳山地区出露的非超高压变质基性岩的原岩具有与胶北地体(高压)基性麻粒岩相近的成因特点。岩石学、同位素年代学和地球化学特征的综合对比研究结果表明,在苏鲁超高压变质带东北端的威海-荣成-乳山地区,既存在与华北板块古老变质基底相关的变基性岩,也存在与华南板块北缘新元古代变质基底相关的超高压榴辉岩,表明三叠纪时期华北板块东南缘胶北地体的部分古老变质基底曾卷入到扬子板块与华北板块之间的俯冲-碰撞造山过程,随后与超高压岩石一起抬升折返,形成当今的构造混杂岩带。
|
| 关 键 词： | 变基性岩 锆石U-Pb年代学 地球化学 构造混杂岩 苏鲁超高压变质带 胶北地体 |
| 收稿时间： | 2017/2/21 0:00:00 |
| 修稿时间： | 2017/6/18 0:00:00 |
The polygenetic meta-mafic rocks from the northeast of Sulu ultrahigh-pressure metamorphic belt:Insight from petrology, isotope geochronology and geochemistry |
| |
| LIU LiShuang,LIU FuLai and WANG Wei.The polygenetic meta-mafic rocks from the northeast of Sulu ultrahigh-pressure metamorphic belt:Insight from petrology, isotope geochronology and geochemistry[J].Acta Petrologica Sinica,2017,33(9):2899-2924. |
| |
| Authors: | LIU LiShuang LIU FuLai and WANG Wei |
| |
| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China and Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
| |
| Abstract: | Sulu ultrahigh-pressure (UHP) metamorphic belt is a product of the subduction and collision between Yangtze Block and North China Block during Triassic. The polygenetic meta-mafic rocks and their petrogenesis is a key issue on revealing the geodynamic process of subduction-collision-exhumation between Yangtze Block and North China Block. As present study, sporadic outcrops of eclogite together with UHP country rocks are widely distributed in the Weihai-Rongcheng area, while non-UHP granulite and amphibolite outcrops are commonly identified in the Rushan area. Based on LA-ICP-MS U-Pb age data of zircons, the protolith ages of (retrograde) eclogites range from 792Ma to 760Ma, and the eclogite-facies metamorphic and subsequent retrogressive ages are constrained at 243~226Ma and 221~207Ma, respectively. In contrast, zircons from non-UHP granulites and amphibolites in the Rushan area record the Late Paleoproterozoic protolith ages (no younger than 1939Ma), whereas the granulite-facies metamorphism occurred at 1895~1870Ma with subsequent amphibolite-facies retrograde metamorphism at 1848~1806Ma. Both the protolith and metamorphic ages for the non-UHP meta-mafic rocks in the studied region are similar to those of the meta-mafic rocks within the Jiaobei terrane. Systematic analyses of whole-rock geochemistry indicate that the protolith of (retrograde) eclogites from both Weihai-Rongcheng and Rushan areas exhibit the geochemical characteristics of high-Fe tholeiite, and they can be subdivided into A, B and C three groups. In the chondrite-normalized REE patterns and the primitive mantle-normalized trace element diagrams, A, B and C groups show depleted, weak rich and rich in LREE, respectively. The protoliths of eclogites of B and C groups are similar to those of island arc basalt (IAB) or continental basalt (CB), which may be related to mantle heterogeneity or mantle wedge which were commonly influenced by enriched fluid. While the protolith of eclogites of group A may be derived from depleted lithospheric mantle. The protoliths of the non-UHP granulites and amphibolites in the Rushan area are also characterized by the high-Fe tholeiite contents and right-dipping chondrite-normalized REE patterns and the primitive mantle-normalized trace element plots. Their Al2O3, TiO2 and P2O5 contents show linearity relationships with MgO content. These non-UHP meta-mafic rocks show similar geochemical characteristics to those of the Paleoproterozoic Jiaobei terrane, and were mainly derived from the enriched mantle, which experienced subsequent fractional crystallization of plagioclase and pyroxene, as well as partial melting. A combined study of petrology, geochronology and geochemistry has revealed that the non-UHP meta-mafic rocks with affinities to the basement of both the North China Craton and the South China Craton did exist in the Sulu UHP belt. In this regards, we would have concluded that some Archean to Paleoproterozoic metamorphic rocks from the Jiaobei terrane involved into the subduction and collision process between Yangtze Block and North China Block during Triassic. Finally a possible tectonic mélange belt consisting mainly of UHP and non-UHP metamorphic rocks had been formed in the so-called Sulu UHP terrane. |
| |
| Keywords: | Ploygenetic meta-mafic rocks Zircon U-Pb dating Geochemistry Tectonic complex The Sulu UHP belt The Jiaobei terrane |
| 本文献已被 CNKI 等数据库收录！ |
| 点击此处可从《岩石学报》浏览原始摘要信息 |
| 点击此处可从《岩石学报》下载免费的PDF全文 |
|
