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

该提案寻求为实地的地球化学、年代学和同位素地球化学研究提供资金，并试图填补对爱琴海中部地区构造变质演化的认识空白。这项拟议的研究旨在破译白垩纪蓝片岩相变质作用的神秘重要性，该变质作用被认为是安德罗斯北部的Makrotantalon单元(MU)，以及安德罗斯南部(Steno角)侏罗纪变蛇绿岩和高压岩石的独特组合，目前被认为是Cycldic蓝片岩单元的一部分。这项建议建议系统地检查这些替代方案的地质意义，并通过解决以下问题来澄清Steno角序列的状况：MU是CBU的构造切片，具有异常保存的前始新世蓝片岩变质作用吗？显然是白垩纪的HP/LT阶段受到外来Ar污染的强烈制约或损害吗？MU是否经历了不同的HP/LT变质作用？白垩纪蓝片岩相变质作用是否伴随着始新世HP/LT事件？始新世蓝片岩对MU的结构归属正确吗？斯捷诺角蓝片岩相变质作用的时代是什么？这个变蛇绿岩HP岩套是CBU不可分割的一部分，还是代表着一个奇异的亚单位？为了回答这些问题，建议(A)使用Rb-sr方法测定安德鲁斯北部和南部的HP/LT岩石的年龄，以便为建立与CBU或希腊大陆伯拉戈尼亚带的对比关系提供可靠的年龄限制，以及(B)结合块状岩石地球化学、锶-钕同位素特征和尖晶石化学应用地球化学指纹技术，进一步表征最近被指定为推覆体堆栈中不同构造位置的超镁铁质岩石。这些方面的进一步工作将有助于更好地理解变质历史和地球动力学背景。拟议研究的总体目标是进一步揭示塞克拉迪奇地块的内部结构，并为更好地解释地质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.