The onset of Pacific margin accretion in NE China: Evidence from the Heilongjiang high-pressure metamorphic belt
The onset of Pacific margin accretion in NE China: Evidence from the Heilongjiang high-pressure metamorphic belt
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DOI：
10.1016/j.tecto.2009.08.009
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发表时间：
2009-12
期刊：
影响因子：
2.9
通讯作者：
Jian‐Bo Zhou;S. Wilde;Xingzhou Zhang;Guochun Zhao;Changqing Zheng;Yuejun Wang;Xiaohui Zhang
中科院分区：
文献类型：
--
作者：
Jian‐Bo Zhou;S. Wilde;Xingzhou Zhang;Guochun Zhao;Changqing Zheng;Yuejun Wang;Xiaohui Zhang
黑龙江杂岩是一套高压变质岩系，沿着中国东北部的佳木斯-汉卡（-布热亚）和松辽-张广才地块（并向北延伸至俄罗斯远东）的缝合带。该杂岩由镁铁质-超镁铁质岩石、各种石英-超镁铁质片岩和含放射虫的石英岩（原燧石）组成。岩石变质至绿帘石-蓝片岩相，P-T条件约为T=320-450 °C和P=0.9-1.1 GPa。岩石组合和常量、微量元素组成表明，蓝片岩是OIB和E-MORB亲合的变质基性岩，最有可能形成于佳木斯地块西缘的裂谷环境中，后来经历了俯冲作用。牡丹江绿帘石-蓝片岩相变基性岩的锆石SHRIMP U-Pb ~（206）Pb/~（238）U年龄分别为213±2 Ma和224±7 Ma，而依兰200 km处的类似岩石的SHRIMP U-Pb ~（206）Pb/~（238）U年龄分别为258±2 Ma和259±4 Ma。这些数据确定了变质玄武岩的原岩年龄分别为晚三叠世和晚二叠世。这些年龄限制了黑龙江杂岩的高压变质作用的时间晚三叠世后，从以前的研究报告的氩数据相一致。4个绿帘石-蓝片岩相样品中的继承锆石组分在290-330 Ma、420-530 Ma、670-910 Ma和>1065 Ma具有明显的群体性。这样的年龄也是中亚造山带（CAOB）西部的一个特征，支持佳木斯地块最有可能是CAOB的裂谷最东段，而不是来自冈瓦纳的外来块体的观点。佳木斯-兴卡-布热亚地块与松辽地块的最终闭合发生在晚三叠世-早侏罗世，两地块因太平洋俯冲作用而增生。这表明，黑龙江杂岩记录了蒙古-华北地块向西伯利亚的北移运动正在减弱并被来自东部的太平洋增生所超越的时间，该增生自早侏罗世以来一直主导着中国东北和俄罗斯远东的构造。
The Heilongjiang Complex is a sequence of high-pressure metamorphic rocks, located along the suture zone that separates the Jiamusi–Khanka (–Bureya) and Songliao–Zhangguangcai blocks in NE China (and extending northward into Far East Russia). The complex consists of mafic–ultramafic rocks, various quartzo–feldspathic schists and radiolarian-bearing quartzite (formerly chert). The rocks were metamorphosed up to epidote–blueschist facies, with P–T conditions of approximately T=320–450 °C and P=0.9–1.1 GPa. The lithological association and major and trace element compositions indicate that the blueschists were metabasalts of OIB and E-MORB affinity, most likely generated in a rift setting at the western margin of the Jiamusi Block that later underwent subduction. Magmatic zircons extracted from two samples of epidote–blueschist facies metabasalts from Mudanjiang have SHRIMP U–Pb206Pb/238U ages of 213±2 Ma and 224±7 Ma, whereas similar rocks ∼200 km farther north at Yilan have ages of 258±2 Ma and 259±4 Ma. These data define the protolith ages of the metabasalts as Late Triassic and Late Permian, respectively. These ages limit the timing of high-pressure metamorphism in the Heilongjiang Complex to post-Late Triassic, consistent with argon data reported from previous studies. Inherited zircon components in all four epidote–blueschist facies samples show distinct populations at 290–330 Ma, 420–530 Ma, 670–910 Ma and >1065 Ma. Such ages are also a feature of the Central Asia Orogenic Belt (CAOB) to the west, supporting the view that the Jiamusi Block was most likely the rifted easternmost segment of the CAOB and not an exotic block derived from Gondwana. Final closure between the Jiamusi–Khanka–Bureya and Songliao blocks took place in the latest Triassic to Early Jurassic, with the two blocks accreted as a result of Pacific Ocean subduction. This suggests that the Heilongjiang Complex records the time when northward movement of the combined Mongolia–North China Block toward Siberia was waning and becoming surpassed by the onset of Pacific accretion from the east, which has dominated the tectonics of NE China and Far East Russia since the Early Jurassic.