RUI: Testing Models for Late Cretaceous to Cenozoic Collisional Magmatism in South-Central Alaska

阿拉斯加南部拥有经济上重要的矿藏，这些矿藏形成于大约七千万到五千万年前火山活动和岩浆侵位的独特时期。据预测，铜、锌、银、铅、金、钼和其他金属的矿床将沿着大型火成岩侵入体的边缘和沿着横切火成岩的断裂带形成，但其中许多矿床的起源尚不清楚。该项目将记录火成岩的组成，并为其起源建立模型，这将为预测阿拉斯加南部塔尔基特纳山脉北部地区矿产资源的分布提供一个系统。这一结果与美国地质调查局矿产资源计划所描述的“确保美国可靠的地质、地球化学、地球物理和矿物位置数据的可用性”的国家战略是一致的。该项目还将为本科生提供最先进的科学培训，包括国际合作。该项目的重点将放在6200万至5000万年前的火山岩和深成岩上，这些岩石是在地壳碰撞的最后阶段放置在地壳缝合带上的。初步的放射性年龄和地球化学数据表明，这些岩石不是典型的大陆边缘弧系。该项目的三年工作计划是为这些火成岩提供新的地质年代学、地球化学和野外测绘数据，以解决以下基本问题：在地壳碰撞期间和之后，岩浆的来源是什么？从地球化学上能否系统地区分与俯冲有关的弧岩与后俯冲（碰撞）火成岩？岩浆活动是否与碰撞和/或碰撞后的变形有关？这些问题将使用主要元素和微量元素化学（XRF和ICPMS方法）进行评估；全岩Nd、Sr、Pb、Hf同位素和单个锆石Hf同位素化学（全部由LA-MC-ICPMS测定）；以及40Ar/39Ar和锆石U/Pb定年，与台北国立台湾大学钟孙林博士合作。实地测绘、样本收集和数据合成将由PI和阿勒格尼学院的本科生完成。该项目的年龄、地球化学和同位素结果将通过美国国家科学基金会资助的网络数据库（NAVDAT, EarthChem）进行传播，并将为评估经济矿床的分布提供基础，并有助于建立阿拉斯加南部新生代岩浆活动的良好约束模型的长期目标。

Southern Alaska contains economically important mineral deposits that formed during unique episodes of volcanism and magma emplacement some 70 to 50 million years ago. Deposits of copper, zinc, silver, lead, gold, molybdenum and other metals are predicted to form along the margins of large igneous intrusions and along fault zones that cross-cut the igneous rocks but the origin of many of these deposits is not known. This project will document the compositions of igneous rocks and develop models for their origins which will provide a system for predicting the distribution of mineral resources in the northern Talkeetna Mountains region of southern Alaska. This outcome is consistent with a national strategy to 'ensure availability of reliable geologic, geochemical, geophysical, and mineral locality data for the United States' as described by the U.S. Geological Survey Mineral Resources Program. This project will also provide state-of-the-art scientific training for undergraduate students, including international collaboration. The focus of this project will be on 62 to 50 million year old volcanic and plutonic rocks that were emplaced in a terrane suture zone during the final stages of terrane collision. Preliminary radiometric age and geochemical data reveal that these rocks are not typical of continental margin arc systems. The three-year work plan for this project is to produce new geochronologic, geochemical, and field mapping data on these igneous rocks to address the following fundamental questions: What were the source(s) of magmas during and following terrane collision? Can subduction-related arc rocks be distinguished geochemically from post-subduction (collisional) igneous rocks in a systematic manner? Was magmatism related to collisional and/or post-collisional deformation? These questions will be evaluated using major and trace element chemistry (XRF and ICPMS methods); whole rock Nd, Sr, Pb, and Hf isotope and single zircon Hf isotope chemistry (all by LA-MC-ICPMS); and 40Ar/39Ar and zircon U/Pb dating in collaboration with Dr. Sun-Lin Chung at National Taiwan University in Taipei. Field mapping, sample collection, and data synthesis will be completed by the PI and undergraduate students from Allegheny College. The age, geochemical, and isotopic results of this project will be disseminated through NSF-funded web-based databases (NAVDAT, EarthChem) and will provide a basis for assessing the distribution of economic mineral deposits as well as contribute to the long-term goal of establishing well-constrained models for Cenozoic magmatism across southern Alaska.