Zircon Hf Isotopes and the Continental Evolution of Dronning Maud Land, East Antacrtica

岩石中单个矿物颗粒的地球化学研究可以用来重建地球的历史。矿物锆石（ZrSiO4）在这方面具有独特的重要性，因为它作为地质时钟的可靠性，由于它对风化、运输和温度和压力变化具有很强的持久性。锆石颗粒的铀铅（U-Pb）定年法可能是提取形成大陆地壳的地质过程时间信息的最常用方法，并已被用于约束大陆和山带随时间的演化。此外，锆石中元素铪（Hf）的同位素组成在大陆地壳是通过从下伏地幔中提取岩浆而形成的时候被用来测定。地幔和大陆地壳深处岩石的熔融作用是大陆演化的关键过程，并记录在锆石Hf同位素特征中。虽然目前锆石的U-Pb定年和Hf同位素分析方法较为完善，但我们对锆石生长及其与围岩或岩浆的元素和同位素交换的认识仍不完善。因此，这项研究的重点是揭示地球深处形成的岩石中锆石Hf同位素的演化过程。更具体地说，是将这些同位素方法应用于东南极洲Dronning Maud Land （DML）收集的岩石。在超大陆形成的过程中，淹没莫德地（DML）占据了中心位置。巨大的陆地组成了今天存在的所有大陆——5亿多年前。目前人们认为，超级大陆在地球上形成和分裂了五到六次。年代的历史。DML区域是了解最后两个超大陆形成历史的关键。合并形成这些超级大陆的大陆边界很可能隐藏在DML中。在这项研究中，将利用从DML岩石中回收的锆石颗粒的同位素组成来确定该地区广泛剖面上的这些边界。这些岩石样本是在2007年至2008年夏季在南极进行的为期两个月的探险中收集的。对不同DML地壳域的锆石进行测年和同位素分析的结果，将为了解东南极洲及其之前向非洲北部延伸的区域地质提供重要的见解。这对DML中超大陆的重建和大陆边界的确定具有重要意义。

Geochemical studies of single mineral grains in rocks can be probed to reconstruct the history of our planet. The mineral zircon (ZrSiO4) is of unique importance in that respect because of its reliability as a geologic clock due to its strong persistence against weathering, transport and changes in temperature and pressure. Uranium-Lead (U-Pb) dating of zircon grains is, perhaps, the most frequently employed method of extracting time information on geologic processes that shaped the continental crust, and has been used to constrain the evolution of continents and mountain belts through time. In addition, the isotopic composition of the element Hafnium (Hf) in zircon is used to date when the continental crust was generated by extraction of magma from the underlying mantle. Melting of rocks in the mantle and deep in the continental crust are key processes in the evolution of the continents, and they are recorded in the Hf isotopic signatures of zircon. Although the analytical procedures for U-Pb dating and Hf isotope analyses of zircon are robust now, our understanding of zircon growth and its exchange of elements and isotopes with its surrounding rock or magma are still underdeveloped. The focus of the proposed study, therefore, is to unravel the evolution of zircon Hf isotopes in rocks that were formed deep in the Earth?s crust, and more specifically, to apply these isotopic methods to rocks collected in Dronning Maud Land (DML), East Antarctica. Dronning Maud Land (DML) occupied a central location during the formation of supercontinents ? large landmasses made up of all the continents that exist today - more than 500 million years ago. It is currently thought that supercontinents were formed and dismembered five or six times throughout Earth?s history. The area of DML is key for understanding the formation history of the last two supercontinents. The boundaries of continents that were merged to form those supercontinents are most likely hidden in DML. In this study, the isotopic composition of zircon grains recovered from DML rocks will be employed to identify these boundaries across an extensive section through the area. The rock samples were collected by the investigator during a two-month expedition to Antarctica in the austral summer of 2007?2008. The results of dating and isotope analyses of zircon of the different DML crustal domains will deliver significant insight into the regional geology of East Antarctica and its previous northern extension into Africa. This has significance for the reconstruction of the supercontinents and defining the continental boundaries in DML.