Tectonic evolution of the Mogok metamorphic belt, Burma (Myanmar) constrained by U‐Th‐Pb dating of metamorphic and magmatic rocks
Tectonic evolution of the Mogok metamorphic belt, Burma (Myanmar) constrained by U‐Th‐Pb dating of metamorphic and magmatic rocks
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DOI：
10.1029/2006tc002083
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发表时间：
2007-06
期刊：
影响因子：
4.2
通讯作者：
M. Searle;Stephen R. Noble;J. Cottle;D. Waters;A. H. G. Mitchell;Tin Hlaing;M. Horstwood
中科院分区：
文献类型：
--
作者：
M. Searle;Stephen R. Noble;J. Cottle;D. Waters;A. H. G. Mitchell;Tin Hlaing;M. Horstwood
抹谷变质带（MMB）沿着掸泰地块西缘延伸超过1500千米，从安达曼海向北延伸至东喜马拉雅构造结。先前的地质年代学研究表明，一次长期的侏罗纪 - 早白垩世与俯冲相关的事件导致了花岗闪长岩和正片麻岩的侵位（171 - 120百万年）以及一次约束较差的第三纪变质事件。基于此处所呈现的新的铀 - 铅同位素稀释热电离质谱法以及铀 - 钍 - 铅激光剥蚀 - 多接收器 - 电感耦合等离子体质谱法地质年代学研究，我们提出两次第三纪变质事件影响了缅甸的抹谷变质带。第一次是古新世事件，该事件以约59百万年时切穿后期运动的黑云母花岗岩岩脉的侵入而告终。第二次变质事件跨越始新世晚期至渐新世（至少从37百万年，可能是47百万年，到29百万年）。这导致了在夕线石级变质独居石的生长，47 - 43百万年时锆石边的生长，夕线石 + 白云母取代较老的红柱石，以及同变质熔融在45.5 ± 0.6百万年和24.5 ± 0.7百万年产生含石榴石和电气石的淡色花岗岩。这些数据表明在45 - 33百万年期间，高温夕线石 + 白云母变质作用在680°C和4.9千巴达到峰值，在29.3 ± 0.5百万年时达到约606 - 656°C和4.4 - 4.8千巴。后期变质事件比24.5 ± 0.3百万年要早，24.5 ± 0.3百万年是切穿所有早期组构的淡色花岗岩的年龄。我们的构造和地质年代学数据表明，抹谷变质带向北与西藏南部拉萨地体未出露的中地壳或下地壳岩石相连，向东与泰国西北部的高级变质核杂岩相连。
The Mogok metamorphic belt (MMB) extends for over 1500 km along the western margin of the Shan‐Thai block, from the Andaman Sea north to the eastern Himalayan syntaxis. Previous geochronology has suggested that a long‐lasting Jurassic–early Cretaceous subduction‐related event resulted in emplacement of granodiorites and orthogneisses (171–120 Ma) and a poorly constrained Tertiary metamorphic event. On the basis of new U‐Pb isotope dilution thermal ionization mass spectrometry and U‐Th‐Pb laser ablation–multicollector–inductively coupled plasma mass spectrometer geochronology presented here, we propose two Tertiary metamorphic events affected the MMB in Burma. The first was a Paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at ∼59 Ma. A second metamorphic event spanned late Eocene to Oligocene (at least from 37, possibly 47, to 29 Ma). This resulted in the growth of metamorphic monazite at sillimanite grade, growth of zircon rims at 47–43 Ma, sillimanite + muscovite replacing older andalusite, and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45.5 ± 0.6 Ma and 24.5 ± 0.7 Ma. These data imply high‐temperature sillimanite + muscovite metamorphism peaking at 680°C and 4.9 kbar between 45 and 33 Ma, to around 606–656°C and 4.4–4.8 kbar at 29.3 ± 0.5 Ma. The later metamorphic event is older than 24.5 ± 0.3 Ma, the age of leucogranites that crosscut all earlier fabrics. Our structural and geochronological data suggest that the MMB links north to the unexposed middle or lower crust rocks of the Lhasa terrane, south Tibet, and east to high‐grade metamorphic core complexes in northwest Thailand.