EAPSI: Insights into the growth of continents from an innovative method of simultaneously determining uranium-lead age, hafnium isotopes, and trace elements in zircon

大陆弧是板块构造的边界，在这里大洋板块下沉到大陆下方的地幔中。岩浆来自回收的大陆地壳、下面的地幔和下降的海洋板块，它们以大型花岗岩体的形式嵌入地壳，并在火山爆发时喷发出来。来自地幔的岩浆在上覆板块的地壳中结晶，是大陆地壳的新添加物，而来自上覆板块重熔的岩浆则是对先前存在的大陆物质的再循环和“蒸馏”。这两个过程可能都发生在大陆弧中，但每个过程的影响程度目前还存在争议。罗斯造山带是一条长约3500公里的大陆弧，大约在5亿年前活跃，它的花岗岩根暴露在南极洲。确定这些巨大的花岗质岩石是来自地幔还是来自再循环的地壳，对于大陆弧在产生大量大陆地壳中的作用具有重要意义。位于国立台湾大学的先进分析设备将用于测量矿物锆石的同位素和微量元素组成，这记录了有关矿物形成的火成岩来源的重要信息。本研究将与国立台湾大学钟孙林博士合作完成。本项目将采用铀铅年代学，结合矿物锆石的铪同位素和微量元素组成，研究罗斯造山带弧花岗岩的年龄和来源。建立了一种同时测定锆石中微量元素、U-Pb和Hf同位素的激光烧蚀电感耦合等离子体质谱方法。本研究将采用一种创新的方法来探讨大陆弧岩浆作用作为地壳生长机制的作用。​

Continental arcs are tectonic plate boundaries where an oceanic plate descends into the mantle beneath a continent. Magmas sourced from recycled continental crust, the underlying mantle, and the descending oceanic plate are emplaced in the crust as large granitic bodies and erupted at volcanoes. Magmas sourced from the mantle that crystallize in the crust of the overriding plate are new additions of continental crust, whereas magmas sourced from remelting of the overriding plate recycle and "distill" previously existing continental material. Both processes probably act in continental arcs, but the extent of each is currently debated. The granitic roots of the Ross orogen, a ~3500 km-long continental arc that was active around 500 million years ago, are exposed in Antarctica. Determining whether these huge tracts of granitic rocks were sourced from the mantle or from recycled crust has important implications for the role of continental arcs in generating large volumes of continental crust. Advanced analytical facilities housed at the National Taiwan University will be used to measure the isotope and trace element composition of the mineral zircon, which records important information about the source of the igneous rocks in which the minerals form. This research will be done in collaboration with Dr. Sun-Lin Chung at the National Taiwan University.This project will employ uranium-lead geochronology coupled with the hafnium isotope and trace element compositions of the mineral zircon to study the age and source of arc granites from the Ross orogen. A routine for the simultaneous measurement of trace elements, U-Pb, and Hf isotopes in zircons by laser-ablation inductively-coupled plasma mass spectrometry will be developed. This research will employ an innovative method to explore the role of continental arc magmatism as a mechanism of crustal growth. This NSF EAPSI award is funded in collaboration with the National Science Council of Taiwan.