Sulfidation and Oxidation States of Calc-Alkaline Granitoids

钙碱性花岗岩的硫化态和氧化态

• 批准号: 0230098
• 负责人: Eric Essene
• 金额: $ 14.17万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-12-01 至 2006-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0230098&HistoricalAwards=false
• 关键词: Sulfidation; Oxidation; States; Calc; Alkaline

EsseneEAR- 0230098This work will evaluate magmatic sulfidation and oxidation states in calc-alkaline granitic rocks. These measurements will be carried out on granitoid suites from the Bingham-Park City belt of Utah, the central Chile porphyry copper belt, and the Providencia-Concepcion del Oro area in the central Sierra Madre Occidental of Mexico. Calculation of oxygen fugacity ranges over five orders of magnitude and sulfur fugacity over three orders of magnitude in different calc-alkaline granitoids. Mossbauer determination of Fe3+/Fe2+ and measurement of H2O in biotites will constrain redox reactions for biotite and provide another way to evaluate the redox state of these granitoids. In addition, systematic determinations of Ce4+/Ce3+ will be undertaken on zircons from the same suites of calc-alkaline granitoids. It is anticipated that these results will show that the granitoids possessed their unique redox signature throughout their crystallization history. The oxidation state of the magmas is most likely inherited from source regions rather than being imposed by late stage crystallization, wall-rock contamination, hydrothermal alteration or degassing history. Results of this study are expected to shed light on the source regions and evolution of calc-alkaline granitoids. Broader implications of this study relate to (1) impacts on climate by sulfur-bearing volcanic eruptions that are related to these granitoids, and (2) formation of porphyry copper ore bodies during their crystallization. The highly oxidized granitoids have sulfur mainly as sulfate, which is released in major volcanic eruptions to form sulfuric acid. These releases had a measurable impact on earth's climate during major eruptions of Mt. Pinutubo in the Philippines and El Chichon in Mexico. Porphyry copper ore deposits in the rock record are strongly correlated with emplacement of oxidized granitoids. Understanding this relationship is important for location of copper ores, most of which occur in these ore deposits.

这项工作将评估钙碱性花岗岩中岩浆的硫化和氧化状态。这些测量将在犹他州宾厄姆-帕克城带、智利中部斑岩铜矿带和墨西哥西马德雷山脉西方中部普罗维登西亚-康塞普西翁-德尔奥罗地区的花岗岩类岩套上进行。不同钙碱性花岗岩类的氧逸度在5个数量级以上，硫逸度在3个数量级以上。穆斯堡尔谱Fe 3 +/Fe 2+比值和H2O的测定将制约黑云母的氧化还原反应，为评价黑云母的氧化还原状态提供另一种途径。此外，系统的测定Ce 4 +/Ce 3+将进行锆石从同一套钙碱性花岗岩。预计这些结果将表明，花岗岩类具有其独特的氧化还原签名整个结晶历史。岩浆的氧化态很可能是从源区继承而来的，而不是由后期结晶、围岩污染、热液蚀变或脱气历史造成的。这一研究结果对钙碱性花岗岩类的源区和演化具有重要意义。这项研究的更广泛的意义涉及（1）与这些花岗岩有关的含硫火山喷发对气候的影响，以及（2）在结晶过程中形成斑岩铜矿体。高度氧化的花岗岩中的硫主要以硫酸盐的形式存在，在主要的火山爆发中释放出来形成硫酸。这些释放对地球的气候产生了可衡量的影响，在主要的火山爆发。菲律宾的Pinutubo和墨西哥的El Chichon。岩石记录中的斑岩铜矿与氧化花岗岩类侵位关系密切。了解这种关系对于铜矿的定位非常重要，大多数铜矿都出现在这些矿床中。