The timing of high-pressure metamorphism on Andros Island, Greece: evidence for both Cretaceous and Eocene blueschist-facies events?

该提案寻求资助基于野外的地球化学、地质年代学和同位素地球化学研究，并试图填补对爱琴海中部地区构造变质演化的理解空白。提出的研究旨在破译白垩纪蓝片岩相变质作用的神秘重要性，这种变质作用被假定为安德罗斯北部的Makrotantalon单元（MU），以及目前被认为是基克拉迪蓝片岩单元一部分的安德罗斯南部（Steno角）侏罗纪元蛇绿岩和HP岩石的独特组合。这一建议建议系统地检查这些备选方案的地质意义，并通过解决以下问题来澄清斯坦诺角演替的地位：MU是否是CBU的构造片，具有异常保存的前始新世蓝片岩变质作用？HP/LT阶段的明显白垩纪年龄是否受到外来氩污染的严格限制或损害？MU是否经历过不同的HP/LT变质期？白垩纪蓝片岩相变质后是否发生始新世HP/LT事件？始新世蓝片岩对MU的构造分配是否正确？斯泰诺角蓝片岩相变质作用的年代是什么时候？这个变蛇绿质HP岩套件是CBU的组成部分还是代表一个外来亚基？为了回答这些问题，我们建议(a)使用Rb-Sr方法对Andros北部和南部的HP/LT岩石进行测年，为建立与CBU或希腊大陆的Pelagonian带的相关关系提供可靠的年龄约束；(b)结合大块岩石地球化学，应用地球化学指纹。Sr-Nd同位素特征和尖晶石化学进一步表征了推覆层内不同构造位置的超基性岩石。在这些方面的进一步工作将有助于更好地了解变质历史和地球动力学背景。这项研究的首要目标是进一步揭示基克拉迪地块的内部结构，并为更好地解释地质历史建立强有力的年龄限制。

This proposal seeks funding for field-based geochemical, geochronological and isotope geochemical research and attempts to fill a gap in understanding of the tectono-metamorphic evolution of the central Aegean region. The proposed study aims at deciphering the enigmatic importance of Cretaceous blueschist-facies metamorphism that was postulated for the Makrotantalon Unit (MU) in northern Andros, and of the unique association of Jurassic meta-ophiolitic rocks and HP rocks in southern Andros (Cape Steno), currently considered to be a part of the Cycladic Blueschist Unit. This proposal suggests to systematically check the geological significance of these alternatives and to clarify the status of the Cape Steno succession by addressing the following questions: Is the MU a tectonic slice of the CBU with unusual preservation of pre-Eocene blueschist metamorphism? Is the apparently Cretaceous age for the HP/LT stage robustly constrained or compromised by extraneous Ar contamination? Did the MU experience different episodes of HP/LT metamorphism? Was Cretaceous blueschist facies metamorphism followed by an Eocene HP/LT event? Is the structural assignment of Eocene blueschists to the MU correct? What is the age of blueschist facies metamorphism at Cape Steno? Is this meta-ophiolitic HP rock suite an integral part of the CBU or representing an exotic subunit? To answer these questions, it is proposed (a) to date the HP/LT rocks from northern and southern Andros using the Rb-Sr method to provide robust age constraints for establishing a correlative relationship either to the CBU or to the Pelagonian Zone on continental Greece, and (b) to apply geochemical fingerprinting using a combination of bulk rock geochemistry, Sr–Nd isotope characteristics and spinel chemistry to further characterize ultramafic rocks that recently were assigned to different structural positions within the nappe stack. Further work on these aspects will help developing a better understanding of the metamorphic history and the geodynamic context. The overarching goal of the proposed research is to further unravel the internal architecture of the Cycladic Massif and to establish robust age constraints for an improved interpretation of the geological history.