| 超高温麻粒岩中尖晶石成分、结构特征和矿物反应的指示意义:以阿尔泰造山带超高温尖晶石-斜方辉石-石榴石麻粒岩为例 |
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| 引用本文： | 厉子龙,汪惠惠,陈汉林,肖文交,杨树锋,胡逸洲. 超高温麻粒岩中尖晶石成分、结构特征和矿物反应的指示意义:以阿尔泰造山带超高温尖晶石-斜方辉石-石榴石麻粒岩为例[J]. 地学前缘, 2010, 17(1): 74-85 |
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| 作者姓名： | 厉子龙 汪惠惠 陈汉林 肖文交 杨树锋 胡逸洲 |
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| 作者单位： | 浙江大学地球科学系,浙江,杭州,310027;中国科学院地质与地球物理研究所,北京,100029 |
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| 基金项目： | 科技部科研项目,国家自然科学基金 |
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| 摘 要： | 超高温变质作用的研究已成为世界上热门的地球科学领域之一,其中斜方辉石+夕线石+石英、假蓝宝石+石英、尖晶石+石英、大隅石+石英以及富铝斜方辉石等标型矿物组合和特征可以指示岩石经历了超高温变质作用(温度>900℃),这对查明地球深部下地壳的物质组成和构造演化具有重要意义。初次对产于世界上不同地区超高温麻粒岩尖晶石+石英共生等的标型矿物组合、不同赋存状态的尖晶石ZnO含量、XZn[Zn/(Mg+Fe2++Zn)]、XMg等进行分析和对比,认为不同地区不同赋存状态的尖晶石,其ZnO含量、XZn和XMg有所不同,但总的来说,超高温麻粒岩尖晶石中ZnO质量分数多数低于2.5%,但个别特殊的有高达近15%。尖晶石中XZn较低且尖晶石与石英共生,可以作为超高温变质的证据之一。通过对阿尔泰南缘超高温尖晶石-斜方辉石-石榴石麻粒岩中尖晶石成分及ZnO含量分析,得出与石英共生的尖晶石ZnO质量分数约为2.50%,且有与XFe成正比的变化趋势,而与钛铁矿共生的尖晶石ZnO质量分数约为1.85%,虽然两者含量稍有不同,但与世界上超高温麻粒岩中多数尖晶石ZnO含量相比都相近。结合其他特征矿物组合,可以确定该岩石中尖晶石与石英共生组合可以作为阿尔泰地区发生超高温变质作用的证据。通过对阿尔泰南缘与尖晶石-石英有关的变质反应期次划分等的初步研究,认为变质期次可划分为峰期变质和退变质两期,推测峰期的温度条件可达到1000℃,且该超高温麻粒岩可能经历了顺时针p-T演化轨迹。该超高温麻粒岩在阿尔泰造山带的出现,可能与古生代时期发生的古亚洲洋俯冲、西伯利亚板块和哈萨克斯坦—准噶尔板块碰撞造山作用过程有关。
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| 关 键 词： | 尖晶石成分 尖晶石-石英共生组合 变质矿物反应期次 超高温麻粒岩 阿尔泰造山带 |
Composition of spinels,spinel-quartz association and mineral reactions from ultrahigh-temperamre granulites:An example from spinel-orthopyroxene-garnet granulite of the South Allay orogenic belt |
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| Li Zilong,Wang Huihui,Chen Hanlin,Xiao Wenjiao,Yang Shufeng,Hu Yizhou. Composition of spinels,spinel-quartz association and mineral reactions from ultrahigh-temperamre granulites:An example from spinel-orthopyroxene-garnet granulite of the South Allay orogenic belt[J]. Earth Science Frontiers, 2010, 17(1): 74-85 |
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| Authors: | Li Zilong Wang Huihui Chen Hanlin Xiao Wenjiao Yang Shufeng Hu Yizhou |
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| Abstract: | The study of ultrahigh-temperature (UHT) metamorphism has become a key topic in the field of earth sciences recently because the occurrence of such as orthopyroxene-sillimanite-quartz,sapphirine-quartz,spinel-quartz and osumilite-quartz assemblages and high Al_2O_3-bearing orthopyroxene could indicate the ultrahigh-temperature metamorphism (＞900 ℃).We have studied the spinel+quartz associations,ZnO contents,X_(Zn)[Zn/(Mg+Fe~(2+)Zn)] and X_(Mg) of the spinels from the UHT rocks worldwide for the first time,and the study shows that the ZnO contents,X_(Zn) and X_(Mg) have some differences due to the different modes of spinels,and tectonic setting of the study areas; but ZnO contents with less than 2.5wt% from the spinels coexisting with quartz of the UHT rocks are generally common,indicating a UHT metamorphic condition.The study of ZnO contents,X_(Zn) and X_(Mg) in the spinels of the UHT granulite from the South Altay orogenic belt indicates that the ZnO contents of ca.2.50 wt% and ca.1.85 wt% from the spinels coexisting with quartz and ilmenite respectively can be obtained,and they are similar to those from the UHT rocks in the world.Combined with other specific mineral evidence,the coexisting spinel-quartz association in the UHT rock from the South Altay orogenic belt can be an evidence of the occurrence of UHT metamorphism.Based on the preliminary study of paragenesis of spinel+quartz and reactions among specific minerals,we propose that the metamorphism can be divided into two episodes:the peak metamorphism with the temperature condition of 1000 ℃ deduced and the retrograde metamorphism,and suppose a clockwise p-T path for the formation of the UHT rock from the South Altay orogenic belt.The formation of the UHT rock should be genetic link with the subduction of the Paleo-Asian Ocean and collision and orogeny of the Siberian plate and Kazakhstan-Junggar plate probably during the Paleozoic. |
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| Keywords: | spinel composition spinel-quartz paragenesis reaction episode of metamorphic minerals ultra high-temperature granulite Altay orogenic belt |
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