Geodynamic evolution of Proterozoic supracrustal rocks from the northern Shackleton Range, East Antarctica

该项目的前期工作(Schmädicke&Will，2006)导致识别出来自沙克尔顿山脉北部的超镁铁质岩石的高温高压变质作用(约710-810℃，20-23kbar)。这一发现是沙克尔顿山脉榴辉岩相变质作用的第一个证据，据我们所知，也是第一个在普遍认为的泛非造山带中描述榴辉岩相超镁铁岩的证据。这些超镁铁质岩石的岩石学最好的解释是它们标志着北部沙克尔顿山脉内的缝合带，这可能追踪到东西冈瓦那之间的汇合点。到目前为止，在这个假定的缝合带上还没有发现真正年轻的新元古代地壳的证据。因此，导致冈瓦那超大陆合并的地球动力学过程仍然具有高度的投机性。沙克尔顿山脉据称蛇绿质镁铁质岩石(Talarico等人，1999年)提供的Sm-ND同位素数据并不是决定性的，因为它们给出了不切实际的新元古代或更老的元古界到太古代的模式年龄。为了对前寒武纪末期超大陆形成这一基本问题作出贡献，我们打算重点研究从以前对沙克尔顿山脉的考察中获得的精选表壳和基底岩石的同位素和地球化学技术。这项工作将以目前正在进行的关于这些岩石的PT演化的变质研究为基础。总的目标是更好地评估沙克尔顿山脉的构造演化，即区分中元古代和新元古代的地壳形成事件，并限制各种镁铁质原岩的源区年龄和表壳围岩的来源。为此，计划利用Sm-ND石榴石、U-Pb单颗锆石和独居石以及Ar-Ar角闪石逐步定年的方法进行全岩Sm-ND、Rb-Sr和Pb全岩同位素分析、Hf锆石原位分析和年代学研究。

Preliminary work to this project (Schmädicke & Will, 2006) led to the recognition of high-temperature and high-pressure metamorphism (c. 710-810 °C, 20-23 kbar) of ultramafic rocks from the northern Shackleton Range. This finding is the first evidence of eclogite-facies metamorphism in the Shackleton Range and, to our knowledge, the first description of eclogite-facies ultramafic rocks in a generally perceived Pan-African orogen. The petrology of these ultramafic rocks is best explained by them marking a suture zone within the northern Shackleton Range, which possibly traces the convergence site between East- and West-Gondwana. To date, no evidence of truly juvenile Neoproterozoic crust has been found along this postulated suture zone. Thus the geodynamic processes that led to the amalgamation of the Gondwana supercontinent remain highly speculative. Available Sm-Nd isotope data from allegedly ophiolitic mafic rocks of the Shackleton Range (Talarico et al., 1999) are not conclusive, because they yield either unrealistic young or older Proterozoic to Archean model ages. To contribute to the fundamental question of supercontinent formation towards the end of the Precambrian, we intend to focus on isotopic and geochemical techniques on selected supracrustal and basement rocks, available from a previous expedition to the Shackleton Range. This work will follow, and will be based upon, currently on-going metamorphic studies on the PT evolution of these rocks. The overall goal is to better assess the tectonic evolution of the Shackleton Range, i.e. to distinguish between Meso- and Neoproterozoic crust-forming events and to constrain both the age of the source for the various mafic protoliths and the provenance of the supracrustal country rocks. To this effect, it is planned to carry out Sm-Nd, Rb-Sr and Pb whole rock isotope analyses, Hf zircon in-situ analyses, and geochronological studies by means of Sm-Nd garnet, U-Pb single zircon and/or monazite as well as stepwise Ar-Ar hornblende dating.