土耳其南部蛇绿岩和变质底板对新特提斯洋俯冲起始的构造学、年代学和地球化学制约

In the studies of Tethyan orogenic belt, some hot topics are when and how subduction initiation of Neo-Tethyan ocean occurred and what type of mineralization is associated. This project is designed to investigate the ophiolites and metamorphic soles in southern Turkey in terms of petrology, tectonics and geochemistry. We aim to constrain subduction initiation of the Neo-Tethyan ocean from three aspects. 1) Timing of subduction initiation will be constrained by precise dating on metamorphic sole rocks and mafic rocks in ophiolites; The dynamic mechanism of subduction initiation will be revealed by investigations on the contact relation between metamorphic sole and ophiolites, deformation and metamorphic characteristics and P-T-t trajectory of metamorphic sole. 2) We will conduct field survey, geochronological and geochemical analyses on the multiple mafic dikes in the ophiolites (Pozantı-Karsantı and Kızıldaǧ ophiolites in particular) to clarify magmatic activities in ophiolites from formation, emplacement to post-emplacement of the ophiolites. These data will be used to further constrain the relationship of the magmatism and subduction event, and the formation, subduction and closure of the Neo-Tethyan ocean. 3) We plan to investigate the distribution of chromite deposits in the ophiolites in south Turkey and focus on the deposits in the Pozantı-Karsantı and Kızıldaǧ ophiolites. Petrology, mineralogy and non-traditional stable isotope analyses will be conducted on these chromite deoposits to trace characteristics and nature of their parental magmas. The links between mineralization process and Neo-Tethyan ocean subduction will be discussed.

新特提斯洋俯冲起始是如何及何时发生的及其产生了何种资源效应，是特提斯构造域研究中的重要科学问题。本项目拟以土耳其南部蛇绿岩和变质底板为研究对象，开展岩石、构造和地球化学多学科研究，从三方面对新特提斯洋俯冲起始进行制约。1)对蛇绿岩中基性岩和变质底板的精确定年进行年代学约束，以变质底板与蛇绿岩的接触关系、变质变形特征和P-T-t轨迹理解俯冲起始的动力学过程；2）以Pozantı-Karsantı和Kızıldaǧ蛇绿岩中的多期基性岩脉为剖析对象，进行野外产状、年代学和地球化学分析，厘清蛇绿岩形成-演化-侵位-侵位后的岩浆活动及其与俯冲过程的对应关系，刻画新特提斯洋的形成-俯冲-消减过程；3）查明铬铁矿床的分布规律，重点对Pozantı-Karsantı和Kızıldaǧ中的铬铁矿进行岩石矿物学和稳定同位素分析，揭示其母岩浆性质和成分变化及其与俯冲起始事件的联系。

新特提斯洋俯冲起始是如何及何时发生的及其产生了何种资源效应，是特提斯构造域研究中的重要科学问题。本项目拟以土耳其南部蛇绿岩和变质底板为研究对象，开展岩石、构造和地球化学多学科研究，从三方面对新特提斯洋俯冲起始进行制约。对土耳其多个蛇绿岩及其变质底板开展了构造学和年代学剖析，获得了基性岩和变质底板岩石的高精度SIMS U-Pb定年结果，二者均形成于90Ma左右，限定了新特提斯洋俯冲起始时间。对变质底板岩石和不同类型基性岩进行了地球化学分析，揭示了变质底板岩石的原岩性质和变质特征，以及基性岩随时间的成分变化，提出俯冲开始之后，随着俯冲物质的不断加入，岩浆类型有一快速转变的过程，即蛇绿岩记录的岩浆事件与俯冲过程的对应关系，并指出这是一个先挤压后伸展的诱发俯冲起始过程。对铬铁矿床的系统研究，揭示其母岩浆富Ca的特征，发现了异常的Fe和Cr同位素分馏和流体活动的矿物学记录，提出了“选择性蚀变”的概念，揭示了“水”在铬铁岩中的存在形式、来源、命运及其元素交换的介质作用，建立了蛇绿岩中铬铁矿床形成的熔流体不混溶模型。发现了与高Al型和高Cr型铬铁矿共生的过渡型铬铁矿，对多个蛇绿岩中各个岩石单元的矿物元素和同位素分析，并与不同构造背景的蛇绿岩进行对比，提出大洋初始俯冲的三个阶段（大洋板块下沉-软流圈上涌、大洋板片物质加入并与地幔熔体混合、板片熔流体进入到地幔楔导致其进一步熔融）分别对应高Al型、过渡型和高Cr型铬铁矿的形成过程和矿物成分变化特征。