黑龙江萝北地区黑龙江杂岩年代学研究
Geochronological study on the Heilongjiang complex at Luobei area, Heilongjiang Province
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摘要: 黑龙江杂岩主要出露在牡丹江断裂以东,并沿其呈南北向带状展布于佳木斯地块西缘。对出露于黑龙江省东部萝北地区金满屯太平沟含云母绿帘角闪岩和头道沟的混合花岗岩的锆石进行LA-ICP-MS U-Pb定年研究,获得两组较好206Pb/238U年龄数据:其加权平均年龄分别为256.0±1.0Ma(n=15, MSWD=0.89)和227.1±1.4Ma (n=11, MSWD=1.3)。含云母绿帘角闪岩和混合花岗岩显示了佳木斯地块与其西缘的洋壳俯冲过程中不同阶段或时期的产物。含云母绿帘角闪岩256.0±1Ma的年龄是其变质时代,代表了俯冲、拼贴、碰撞过程中早期的热事件;而混合花岗岩227.1±1.4Ma的年龄则代表了俯冲、拼贴、碰撞过程即将结束的热事件。结合佳木斯地块上出露的同碰撞火山弧花岗岩的形成年代,推断出佳木斯地块与其西缘的松嫩地块之间洋壳的俯冲消减作用和随之而来的陆陆碰撞作用发生在约317~220Ma之间,黑龙江杂岩主体的形成时代为海西晚期到印支期,而其蓝片岩相变质作用可能发生在256Ma之前。
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关键词:
- 黑龙江杂 /
- LA-ICP-MS锆石U-Pb定年 /
- 佳木斯地块 /
- 萝北地区
Abstract: The Heilongjian complex distributes mainly to the east of Mudanjiang fault, tending towards north-south along the western margin of Jiamusi massif. LA-ICP-MS zircon U-Pb dating of epidote amphibolite and migmatitic granite of Heilongjian complex from the Jinmantun Taipinggou and Toudaogou in Luobei area is carried out in order to determine the age and to discuss the geotectonic background and metamorphic events that the Heilongjian complex has experienced. Results show that there are two well defined group ages, i.e. weighted average 206Pb/238U ages are 256.0±1.0Ma(n=15, MSWD=0.89)and 227.1±1.4Ma (n=11, MSWD=1.3). The mica-bearing epidote amphibolite and migmatitic granite exhibited possibly two different stages of metamorphic processes during the subduction of Jiamusi massif and its western oceanic crust margin. The age of 256.1±1.4Ma from mica bearing epidote amphibolite is metamorphic age, representing a early thermal event of subduction; while migmatitic granite with 227.1±1.4Ma is late thermal event toward to the end of subduction and collision. By comparison these ages with that of collisional volcanic arc on Jiamusi massif, we suggest that the subduction and afterwards collision between the Jiamusi massif and its western Songnen block is about 220~317Ma. The Heilongjian complex mainly formed from Late Hercynian to Indo-Chinese epoch, while its blue-schist facies metamorphism that may occur before 256Ma.-
Key words:
- Heilongjian complex /
- LA-ICP-MS zircon U-Pb dating /
- Jiamusi massif /
- Luobei area
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