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

希腊安德罗斯岛高压变质作用的时间：白垩纪和始新世蓝片岩相事件的证据？

• 批准号: 428553437
• 负责人: Professor Dr. Michael Bröcker
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/428553437?language=en
• 关键词: timing; pressure; metamorphism; Andros; Island

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.

该提案寻求为实地地球化学、地质年代学和同位素地球化学研究提供资金，并试图填补在了解爱琴海中部地区构造-变质演化方面的空白。拟议的研究旨在破译白垩纪蓝片岩相变质作用的神秘的重要性，假设的Makrotantalon单元（MU）在北方安德罗斯，和独特的组合侏罗纪变蛇绿岩和HP岩石在南部安德罗斯（Cape Steno），目前被认为是基克拉迪蓝片岩单元的一部分。这一建议建议，系统地检查这些替代品的地质意义，并通过解决以下问题来澄清斯特诺角继承的地位：MU是一个构造切片的CBU与不寻常的保存前始新世蓝片岩变质？HP/LT阶段的明显白垩纪年龄是否受到外来Ar污染的强烈限制或损害？MU是否经历了不同的HP/LT变质作用？白垩纪蓝片岩相变质后是否发生始新世高压/低温事件？始新世蓝片岩的构造归属是否正确？斯特诺角蓝片岩相变质作用的年龄是多少？这套变蛇绿高压岩是CBU的一个组成部分，还是代表了一个外来的亚单元？为了回答这些问题，建议（a）使用Rb-Sr方法测定北方和安德罗斯南部的HP/LT岩石的年龄，以提供可靠的年龄限制，用于建立与CBU或希腊大陆上的Pelagonian带的相关关系，以及（B）使用整体岩石地球化学，Sr-Nd同位素特征和尖晶石化学特征，以进一步表征最近被分配到推覆叠层内不同构造位置的超镁铁岩。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。拟议研究的总体目标是进一步揭示基克拉迪地块的内部结构，并建立强大的年龄限制，以改善地质历史的解释。