东南极克拉通古太古代早期的岩石:对东南极地质演化及地球早期历史的制约

Geological processes of the early earth are very attractive issues to earth scientists. However, many problems remain unresolved because limit existence of the Eoarchean to Paleoarchean geological records. Although some Early Paleoarchean geological have been reported in East Antarctica, most of them came from detrital zircons and no reliable Early Paleoarchean rocks have been indentified from East Antarctica. During former Chinese Antarctica Expeditions, some granitic rocks and quartz schists (metamorphic felsic tuff) with zircon U-Pb age at ca. 3.5 Ga have been indentified from the moraine erratic boulders in the Vestfold Hills, and provide important samples to study the early history of East Antarctica. In this research, petrology, geochemisty, zircon U-Pb geochronology, in-situ zircon Hf-O isotopes and Sr-Nd-Pb isotopes will be used to study the origin of these Early Paleoarchean rocks. Combined with present-day ice-flow directions and ice divides, the source of these rocks will also be studied. The results are not only important to understanding Early Paleoarchean evolution of the East Antarctica, but also helping in understanding the geological processes of ancient Earth.

早期地球的地质过程一直是国际地学界探索的课题，但由于从冥古宙到古太古代的地质记录不多，影响了对这一问题的认识。东南极虽然报道有古太古代早期的记录，但均来自碎屑锆石。申请人在前期的南极考察中，在西福尔丘陵东南边缘的现代冰碛物中发现了锆石U-Pb年龄为35亿年的花岗质岩石和石英片岩（原岩为火山岩），在今年的南极考察中采集到了丰富的同类砾石，为研究上述关键科学问题提供了重要的样品。本项目拟通过岩石学、岩石化学、锆石U-Pb年代学及Hf-O同位素，全岩Sr-Nd-Pb同位素等方法，研究这些岩石的成因，结合冰川运动学及冰下地貌等资料，分析其可能的来源。研究结果不但对于认识东南极冰下地质构造格架及太古宙早期地壳演化有重要意义，而且对于认识地球早期历史也有重要意义。

太古宙古老岩石（组合）记录了地球早期演化的信息。本项目对南极普里兹湾带西福尔丘陵等地区的岩石等进行了系统的岩石学及年代学研究，发现在西福尔丘陵等地区的冰碛物岩石组合复杂，发育TTG类岩石以及绿片岩等，首次确认古太古代奥长花岗岩等代表地球早期地壳的典型岩石。岩石学和Ar-Ar定年结果等表明包括古太古代花岗岩在内的各类岩石在泛非期（500-600Ma）发生绿片岩相-绿帘角闪岩相变质作用。同位素分析结果表明古太古代奥长花岗岩可能源于更老的3.6–4.1 Ga的地壳物质，揭示在东南极大陆内部可能存在更古老的地球早期陆壳成分。根据冰川流动方向可以推测其中的古太古代花岗质岩石可能来自西福尔丘陵的东南侧内陆冰盖之下，最远可能深入内陆1000公里，东南极这一古太古代古老陆块及其相关岩石的确认对认识早期太古宙的地质过程具有重要意义，相关岩石的形成和变质演化也为冈瓦纳以及罗迪尼亚古陆的重建提供了新的限定。