Late Pan-African magmatism in northeastern China: SHRIMP U-Pb zircon evidence from granitoids in the Jiamusi Massif
Late Pan-African magmatism in northeastern China: SHRIMP U-Pb zircon evidence from granitoids in the Jiamusi Massif
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DOI：
10.1016/s0301-9268(02)00217-6
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发表时间：
2003-04
影响因子：
3.8
通讯作者：
S. Wilde;S. Wilde
中科院分区：
文献类型：
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作者：
S. Wilde;S. Wilde
首次提出了中国东北部佳木斯地块晚期泛非岩浆活动的证据。最近对马山杂岩的SHRIMP锆石研究发现，该地区发生了一次重大的∼500 Ma麻粒岩相变质事件，但尚未确定较老的火成岩的年龄。对两个花岗岩类样品进行了SHRIMP锆石U-Pb分析：三道沟附近一个变形花岗岩类中的锆石具有清晰的振荡分带，其206Pb/238U加权平均年龄为523±8 Ma，相当于花岗岩原岩的年龄；佳木斯附近的一个弱变形斑岩花岗岩，其206Pb/238U的加权平均结晶年龄为515±8 Ma。此外，还对刘茅的一块变形伟晶岩进行了分析，该伟晶岩中含有震荡带状火成锆石。这些锆石富含铀，数据不一致，因此它们的解释并不模棱两可。如果以四个最老的207Pb/206Pb比值来代表锆石结晶的最小年龄，则它们的年龄为501±18 Ma。两个花岗岩样品中的几个锆石晶体在阴极发光(CL)图像中也显示出重结晶的证据，三道沟和佳木斯样品的年龄分别为505±4和497±5 Ma。这是马山杂岩南部地区麻粒岩相变质作用的时代，这些年龄仅比西伯利亚南部发现的∼490 Ma麻粒岩相变质作用略晚，可能表明它们具有共同的演化。另外，佳木斯地块中深成火成岩的存在年龄在∼515-∼525 Ma之间，与其他几个泛非晚期地体类似。特别是，∼515 Ma的花岗岩侵位和∼500 Ma的高级变质作用的时间与南澳大利亚德拉默尔造山带记录的事件相同。最近在澳大利亚东北部昆士兰州霍尔霍尔变质带中发现了∼500 Ma变质锆石，这可能预示着晚期泛非事件在澳大利亚各地的延续，支持了佳木斯地块此时位于澳大利亚北缘的观点，以及塔里木地块、北中国地块和南中国地块。
We present the first evidence of late Pan-African magmatism in the Jiamusi Massif of northeastern China. Recent SHRIMP U–Pb zircon studies of the Mashan Complex have identified a major ∼500Ma granulite facies metamorphic event in the area, but no older igneous rocks have previously been dated. Two granitoid samples have been analysed using SHRIMP U–Pb zircon techniques: a deformed granitoid from near Sandaogou contains zircons with well-defined oscillatory zoning that define a weighted mean206Pb /238U age of 523±8Ma, taken to be the age of the granite protolith; and a weakly-deformed porphyritic granite from near Jiamusi, which also contains zircons with oscillatory zoning of igneous origin, has a weighted mean206Pb /238U Ma crystallisation age of 515±8Ma. In addition, a deformed pegmatite from Liu Mao, which contains oscillatory-zoned igneous zircons, was also analysed. These zircons are rich in uranium and the data are discordant, so their interpretation is not equivocal. If the four oldest207Pb /206Pb ratios are taken to represent the minimum age of zircon crystallisation, they define an age of 501±18Ma. Several zircon crystals from both granite samples also reveal evidence of recrystallisation in cathodoluminescence (CL) images and this has been dated at 505±4 and 497±5Ma in the Sandaogou and Jiamusi samples, respectively. This is the timing of granulite facies metamorphism in the southern area of the Mashan Complex and these ages are only slightly older than the ∼490Ma granulite facies metamorphism identified in southern Siberia, possibly indicating that they had a common evolution. Alternatively, the presence of plutonic igneous rocks with ages between ∼515 and ∼525Ma in the Jiamusi Massif is comparable to several other late Pan-African terranes. In particular, the timing of granite emplacement at ∼515Ma and high-grade metamorphism at ∼500Ma is identical to events recorded in the Delamerian Orogen of South Australia. The recent discovery of ∼500Ma metamorphic zircons in the Halls Reward metamorphic belt in Queensland, NE Australia, may indicate a continuation of late Pan-African events across Australia, supporting the view that the Jiamusi Massif lay along the northern margin of Australia at this time, together with the Tarim, North China and South China blocks.