| 榍石：U－Pb定年及变质P－T－t轨迹的建立 |
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| 引用本文： | 向华,张利,钟增球,周汉文,曾雯.榍石：U－Pb定年及变质P－T－t轨迹的建立[J].地球科学进展,2007,23(12):1258-1267. |
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| 作者姓名： | 向华 张利 钟增球 周汉文 曾雯 |
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| 作者单位： | 1. 中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学学院,湖北,武汉,430074;西北大学大陆动力学国家重点实验室,陕西,西安,710069
2. 中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学学院,湖北,武汉,430074 |
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| 基金项目： | 国家重点基础研究发展计划(973计划)
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西北大学大陆动力学国家重点实验室开放课题基金
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浙江省国土资源厅地质勘查资金项目
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中国地质大学校科研和教改项目 |
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| 摘 要： | 榍石在各类岩石中普遍存在，其稳定性受全岩成分、氧逸度和水活度以及温度和压力等因素影响。它在岩浆岩中主要存在于高Ca/Al比值的岩石中，在变质岩中常见于绿片岩相、蓝片岩相和角闪岩相岩石，在钙质变质岩中其稳定范围可达榴辉岩相或高压麻粒岩相。一般榍石结构中U含量较高，且具有高达高角闪岩相上限的U Pb同位素体系封闭温度，是理想的U-Pb定年矿物。由于榍石的组成元素均为岩石中的主要元素，很容易与其它矿物、熔体及流体发生反应，所以榍石的U-Pb年龄记录的更可能是结晶年龄，而不是简单的扩散重置年龄；也因为它容易反应，变质榍石复杂的U Pb体系可能记录了岩石的整个变质历史信息。通过与榍石平衡共生的矿物组合或利用榍石Zr温压计可确定岩石的P T条件，结合相关的榍石年龄信息即可建立变质过程的P T t轨迹。利用SHRIMP、LA MC ICP MS以及LA ICP MS方法可对不均一榍石颗粒内部进行原位微区分析得到有意义的U Pb年龄；利用榍石中Zr含量对温度，尤其是对压力比较敏感，可建立榍石Zr含量温压计。
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| 关 键 词： | 榍石 变质反应 UPb定年 榍石温压计 PTt轨迹 |
| 文章编号： | 1001-8166（2007）12-1258-10 |
| 收稿时间： | 2007-08-04 |
| 修稿时间： | 2007-10-15 |
Titanite: U-Pb Dating and Applications on Defining P-T-t Path of Metamorphic Rocks |
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| XIANG Hua,ZHANG Li,ZHONG Zeng-qiu,ZHOU Han-wen,ZENG Wen.Titanite: U-Pb Dating and Applications on Defining P-T-t Path of Metamorphic Rocks[J].Advance in Earth Sciences,2007,23(12):1258-1267. |
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| Authors: | XIANG Hua ZHANG Li ZHONG Zeng-qiu ZHOU Han-wen ZENG Wen |
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| Institution: | 1.State Key Laboratory of Geological Processes and Mineral Resources,Faculty of Earth Sciences,China University of Geosciences ,Wuhan 430074,China;2.State Key Laboratory of Continental Dynamics,Northwest University ,Xi'an 710069,China |
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| Abstract: | The stability of titanite is controlled by pressure, temperature, compositions of the bulk rock and the coexisting fluid, activity of H2O, fugacity of O2. Titanite is a common accessory mineral in a large range of rocks. It is widespread in magmatic rocks with high Ca/Al ratio. It appears in different metamorphic rocks ranging from greenschist facies, blueschist facies and amphibolite facies. Its stability may extend into eclogite facies and high pressure granulite facies in calcic rocks. Because of its high U in its structure and high closure temperature (upper limit of amphibolite faces), titanite is an ideal U Pb dating mineral. In contrast to zircon, titanite (composed mainly of Ca and Ti) is quite reactive in most rocks contain Ca and Ti at different conditions. Therefore, its U Pb ages are likely to yield the age of metamorphic crystallization rather than resetting by simple diffusion, such that metamorphic titanite may preserve complicated U Pb system that contains information of the whole metamorphic history of the rock, which can be revealed by in situ U Pb dating, e.g., SHRIMP, LA MC ICP MS and LA ICP MS. Importantly, Zr concentration in titanite is sensitive to temperature and pressure, and accordingly Zr concentration in titanite is a good thermobarometer. Both mineral assemblages in equilibrium with titanite and titanite Zr thermobarometer can be used to determine pressure and temperature. Consequently, P T t paths of metamorphism can be defined in combination with U Pb titanite ages. |
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| Keywords: | Titanite Metamorphic reaction U-Pb dating Titanite thermobarometer P-T-t path |
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