New age constraints for the geodynamic evolution of the Sistan Suture Zone, eastern Iran
New age constraints for the geodynamic evolution of the Sistan Suture Zone, eastern Iran
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DOI：
10.1016/j.lithos.2013.02.012
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发表时间：
2013-06
期刊：
影响因子：
3.5
通讯作者：
M. Bröcker;G. F. Rad;R. Burgess;S. Theunissen;I. Paderin;N. Rodionov;Z. Salimi
中科院分区：
文献类型：
--
作者：
M. Bröcker;G. F. Rad;R. Burgess;S. Theunissen;I. Paderin;N. Rodionov;Z. Salimi
伊朗东部的锡斯坦缝合带沿伊朗和阿富汗边境地区延伸700多公里，是一条N-S倾向带。SSZ是阿富汗地块下方的新特提斯洋盆向东俯冲的结果，包括一个构造混杂岩，由破碎的变质蛇绿岩组成，位于低品位的超镁铁质、镁铁质和泥质片岩基质中。一些混杂岩块受到榴辉岩相、蓝片岩相和/或绿帘角闪岩相P-T条件的影响。了解这些岩石的岩石学和年代学记录对揭示SSZ的地球动力学演化具有关键作用。本研究的主要目的是评估以前公布的40Ar/39Ar年龄(约116-139 Ma)的地质意义，这些年龄没有为区域尺度上的地球动力学重建提供强有力的年龄限制。为此，在一条跨越约120公里的NNW-SSE趋势带内采集了样品，该带暴露了高压/低温岩石和绿帘角闪岩的主要产状。多点RbSr矿物等时线显示了区域一致的模式，年龄在83~87 Ma之间，代表不同变质程度和相距较远的8个样品(加权平均值为85.7±0.8 Ma)。此外，对其中五个样品进行了40Ar/39Ar测年，在大多数情况下，测年结果在分析不确定度范围内与Rbsr结果相同。其中一个样品的~(40)Ar/~(39)Ar年龄为81.3±1.3 Ma，比相应的Rbsr年龄年轻约3myr。在榴辉岩的叠加域中，对逆行绿帘石-黑云母组合测定了78.9 Ma±0.5 Ma的Rbsr年龄。两个榴辉岩和两个变质酸性岩的离子探针锆石UPB年龄加权平均206Pb/238U年龄分别为87.3±1.4 Ma、86.1±1.5 Ma、88.7±1.4 Ma和87.2±1.2 Ma。这项研究的结果并不支持以前提出的125 Ma高压/低温变质作用和角闪岩相叠置的解释，而是证明了晚白垩世俯冲带过程对SSZ地球动力学演化的重要性。
The Sistan Suture Zone (SSZ) in eastern Iran extends as a N–S trending belt over more than 700km along the border area between Iran and Afghanistan. The SSZ formed as a result of eastward-directed subduction of a Neotethyan ocean basin beneath the Afghan block and includes a tectonic mélange consisting of disrupted meta-ophiolitic rocks within a low-grade matrix of ultramafic, mafic and pelitic schists. Some mélange blocks were affected by eclogite-, blueschist- and/or epidote amphibolite-facies P–T conditions. Understanding of the petrological and geochronological record of these rocks plays a key role in unravelling the geodynamic evolution of the SSZ. The main aim of the present study was to assess the geological significance of previously published40Ar/39Ar ages (c. 116–139Ma) which have not provided robust age constraints for geodynamic reconstructions on a regional scale. For this purpose, samples were collected within a NNW–SSE trending belt spanning a distance of c. 120km that exposes the major occurrences of high-pressure/low temperature rocks and epidote amphibolites. Multi-point RbSr mineral isochrons indicate a regional consistent pattern with ages ranging between c. 83 and c. 87Ma for eight samples representing different metamorphic grade and widely separated locations (weighted mean=85.7±0.8Ma). Additional40Ar/39Ar dating for five of these samples yielded in most cases ages that are identical to the RbSr results within analytical uncertainty. For one sample the40Ar/39Ar age of 81.3±1.3Ma is about 3myr younger than the corresponding RbSr age. A still younger RbSr age of 78.9±0.5Ma was determined for a retrograde epidote-biotite assemblage in an overprinted domain of an eclogite. Ion probe UPb zircon ages for two eclogites and two meta-acidic rocks from the mélange yielded weighted mean206Pb/238U ages of 87.3±1.4Ma, 86.1±1.5Ma, 88.7±1.4Ma and 87.2±1.2Ma, respectively. The results of this study do not support previous interpretations suggesting >125Ma high-pressure/low-temperature metamorphism and amphibolite-facies overprinting, but instead document the importance of Late Cretaceous subduction zone processes for the geodynamic evolution of the SSZ.