Lithological research on the Purang mantle peridotite in western Yarlung-Zangbo suture zone in Tibet.
-
摘要: 西藏雅鲁藏布江缝合带西段普兰蛇绿岩以出现面积约600余平方千米的特大型地幔橄榄岩体而引人注目。该地幔橄榄岩以方辉橄榄岩为主体,含有少量的二辉橄榄岩和纯橄榄岩,岩体中另有一些橄榄单斜辉石岩、辉长岩和辉绿岩等侵入体。地幔橄榄岩的主要造岩矿物橄榄石的Fo 90~93,其中呈包裹体的橄榄石的Fo略高,斜方辉石为顽火辉石(En 88~90),单斜辉石主要为顽透辉石和透辉石,以低铝(0.48%~3.96%)和高Mg#(91~96)为特征,铬尖晶石的Cr#值为 18~69,其中方辉橄榄岩和二辉橄榄岩中的铬尖晶石属富铝型尖晶石,而纯橄岩中为富铬型尖晶石。橄榄单斜辉石岩的橄榄石Fo值一致较低,平均为88.4,斜方辉石 En平均87,单斜辉石以透辉石为主,铬尖晶石的Cr#值为45~69。普兰地幔橄榄岩及橄榄单斜辉石岩都具有相似的稀土元素和微量元素配分模式,表现为LREE相对富集,Eu亏损不明显,微量元素中大离子亲石元素含量较低,部分样品高场强元素亏损,另一些则相对富集,显示地幔橄榄岩具有亏损地幔源区特征,但也具有俯冲带流体的交代特征,表明普兰岩体可能经历了MOR和SSZ两种构造环境,该特征与雅鲁藏布江缝合带东段的罗布莎地幔橄榄岩的特征可以对比。Abstract: The Purang ophiolite in the Yarlung-Zangbo suture zone in Tibet is characterized by containing a large mantle peridotite massif of ca. 600km2 in area. The mantle peridotite consists of dominant harzburgite, minor lherzolite and dunite, and contains some dikes or veins of olive clinopyroxenite, gabbro and diabase in the massif. The Fo values of olivine in mantle peridotite vary in the range of 90 ~ 93, and in which relatively higher Fo values of olivine are from the inclusions within other minerals in the rocks. The orthopyroxenes in the rocks are enstatite (En 88~90), and the clinopyroxenes are endiopside and diopside with low Al2O3 (0.48%~3.96%) contents and high Mg# (91~96) values. Chrome spinels have various Cr# values from 18 to 69, and in which aluminum-rich spinels are from harzburgite and lherzolite, but chromium-rich spinels from dunite. In olivine clinopyroxenites, olivines have uniformly low Fo values of around 88 and orthopyroxenes have En values around 87. Clinopyroxenes in the rocks are dominated by diopside, and chrome spinels contain both aluminum-rich and chromium-rich types with Cr# values varied in the range of 45~69. The mantle peridotite and olivine clinopyroxenite in Purang have the similar distribution patterns of rare-earth elements and trace elements, characterized by their slightly enrichment in LREE and weakly depleted in Eu, relatively lower content of large ion lithophile element (LILE), and either depleted or enriched in high filed-strength element (HFSE). These features imply a depleted mantle source, which were overlapped by fluid alteration in a subduction zone. It concludes that the Purang ophiolite formed in a MOR setting and was modified by fluids in a SSZ setting, similar to the Luobusa ophiolite in the eastern Yarlung-Zangbo suture zone.
-
Key words:
- Mantle peridotite /
- Ophiolite /
- Purang /
- Yarlung-Zangbo suture zone
-
-
[1] A甘塞尔.1983.环印度缝合带.中国地质科学院地质研究所译.特提斯构造带地质学-廿六届国际地质大会论文选译.北京:地质出版社,58-67
[2] 鲍佩声,王希斌,彭根永,陈方远.1999.中国铬铁矿床.北京:科学出版社,108-135
[3] 常承法. 1984. 雅鲁藏布江缝合带地质构造特征及其演化.见:中法喜马拉雅考察成果. 北京:地质出版社,327-340
[4] 郭铁鹰,梁定益,张宜智等. 1991. 西藏阿里地质. 武汉:中国地质大学出版社,1-464
[5] 黄圭成,莫宣学,徐德明,雷义均,李丽娟.2006.西藏西南部达巴-休古嘎布蛇绿岩带的形成与演化.华南地质与矿产,3:1-9
[6] 李建峰,夏斌,刘立文,徐力峰,何观生,王洪,张玉泉,杨之青.2008.西藏普兰地区拉昂错蛇绿岩中辉绿岩的锆石SHRIMP U-Pb年龄及其地质意义.地质通报,27(10):1739-1743
[7] 路凤香. 1988. 地幔岩岩石学. 武汉:中国地质大学出版社,114-115
[8] 邱瑞照,邓晋福,周肃,李廷栋,肖庆辉,郭铁鹰,蔡志勇,李国良,黄圭成,孟祥金. 2005.青藏高原西部蛇绿岩类型:岩石学与地球化学证据. 地学前缘,12 (2): 277-291
[9] 王希斌,鲍佩声,戎合.1995.中国蛇绿岩中变质橄榄岩的稀土元素地球化学.岩石学报,11(增刊):24-41
[10] 王希斌,鲍佩声.1996.试论中国蛇绿岩成因类型及其成矿专属性. 见:张旗主编.蛇绿岩与地球动力学研究,北京:地质出版社,69-74
[11] 韦栋梁,夏斌,周国庆,王冉.2004.西藏泽当蛇绿岩壳层火山熔岩的岩石地球化学及成因.大地构造与成矿学,28(3):270-278
[12] 韦振权,夏斌,张玉泉,王冉,杨之青,韦栋梁.2006.西藏休古嘎布蛇绿岩中辉绿岩锆石SHRIMP定年及其地质意义.大地构造与成矿学,30(1):93-97
[13] 夏斌. 1991. 西藏拉昂错蛇绿岩岩石地球化学特征及成因研究. 西藏地质,5(1):38-54
[14] 夏斌,郭令智,施央申.1998.西藏西南部蛇绿岩及其地体构造.广州:中山大学出版社,1-83
[15] 徐德明,黄圭成,黄陵勤,雷义均,李丽绢.2006.西藏西南部达巴-休古嘎布蛇绿岩带中地幔橄榄岩的成因.华南地质与矿产,3:10-18
[16] 徐德明,黄圭成,雷义均.2008.西藏西南部拉昂错地幔橄榄岩的地球化学特征及其构造意义. 岩石矿物学杂志,27(1):1-13
[17] 杨经绥,白文吉,方青松,颜秉刚,戎合,陈松永. 2004.西藏罗布莎蛇绿岩铬铁矿中发现超高压矿物柯石英.地球科学,29(6):651-660
[18] 杨经绥,史仁灯,吴才来,苏德辰,陈松永,王希斌,Joseph WOODEN.2008.北阿尔金地区米兰红柳沟蛇绿岩的岩石学特征和SHRIMP定年.岩石学报,24(7):1567-1584
[19] 张旗,周国庆. 2001. 中国蛇绿岩.北京:科学出版社,85-89
[20] 钟立峰,夏斌,崔学军,周国庆,陈根文,韦栋梁.2006.藏南罗布莎蛇绿岩壳层熔岩地球化学特征及成因.大地构造与成矿学,30 (2): 231-240
-
计量
- 文章访问数: 11550
- PDF下载数: 5955
- 施引文献: 0
下载: