New isotopic constraints on age and magma genesis of an embryonic oceanic crust: The Chenaillet Ophiolite in the Western Alps
New isotopic constraints on age and magma genesis of an embryonic oceanic crust: The Chenaillet Ophiolite in the Western Alps
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对胚胎洋壳的年龄和岩浆成因的新同位素限制：西阿尔卑斯山的谢纳耶蛇绿岩
DOI：
10.1016/j.lithos.2012.12.016
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发表时间：
2013-02
期刊：
影响因子：
3.5
通讯作者：
Manatschal, Gianreto
中科院分区：
文献类型：
--
作者：
Li, Xian-Hua;Faure, Michel;Lin, Wei;Manatschal, Gianreto
Chenaillet蛇绿岩是皮埃蒙特-利古里亚洋盆保存最完好的遗迹之一，该洋盆是中大西洋的一个分支，在亚德里亚/非洲从欧洲分离期间开放。尽管在构造、岩石学、地球化学和同位素年代学等方面进行了大量的研究，但对Chenaillet蛇绿岩中各种岩浆岩的形成时间和成因仍存在争议。本文对Chenaillet蛇绿岩中的长角闪岩和钠长石岩进行了原位锆石U-Pb年龄和O-Hf同位素综合分析。结果表明，钠长岩和长英岩在~ 165 Ma同时结晶。锆石的Hf和O同位素组成均较均匀，εHf（T）=+13.5 1. 0（2SD），δ 18 O =5.4±0.4‰（2SD），表明岩浆结晶来自亏损的MORB地幔。钠长岩锆石的εHf（T）值（+13.0 ~+13.5）在误差范围内与奥长岩锆石一致，但δ 18 O值变化较大。蚀变锆石域的δ 18 O值相对较低，为4.7±0.6‰（2SD），这是由于固相线下热液蚀变所致，而蚀变最小的锆石域的δ 18 O值为5.1±0.4‰（2SD），在误差范围内无法与来自中大西洋和西南印度洋脊辉长岩、长花岗岩和斜长花岗岩的橄榄岩锆石和火成锆石区分。原位锆石O-Hf同位素数据表明，长长角闪岩和钠长岩最有可能是同生的，钠长岩是由玄武岩浆的极端分离结晶形成的。根据我们的新年龄结果和可靠文献U-Pb年龄资料的整理，东、中、西阿尔卑斯山、利古里亚和科西嘉蛇绿辉长岩的结晶时间几乎同步于158- 166 Ma，寿命短，<11百万年。皮埃蒙特-利古里亚洋域的形成，而不是一个~30m.y.寿命就像以前想的那样。Chenaillet蛇绿岩可能是一个胚胎洋壳的残余，而不是一块“成熟”的洋壳。假设贫岩浆莫尔序列的扩张速度小于3厘米/年，则皮埃蒙特-利古里亚洋底的最大宽度约为300公里。
The Chenaillet Ophiolite is one of the best-preserved remnants of the Piemont-Liguria oceanic basin, a branch of the Central Atlantic that opened during the separation of Adria/Africa from Europe. Despite numerous studies of structure, petrology, geochemistry and isotope geochronology, the timing and genesis of various magmatic rocks within the Chenaillet Ophiolite are still controversial. We provide in this study integrated in situ analyses of zircon U–Pb age and O–Hf isotopes for the troctolite and albitite within the Chenaillet Ophiolite. Our new results indicate that the troctolite and albitite crystallized synchronously at ~165Ma. Zircons from the troctolite have homogeneous Hf and O isotopic compositions, with εHf(T)=+13.5±1.0 (2SD) and δ18O=5.4±0.4‰ (2SD), indicating crystallization from magmas that were derived from a depleted, MORB-like mantle. The albitite zircons give consistent εHf(T) values (+13.0 to +13.5) within errors with those of troctolite zircons, but variable δ18O values. The altered zircon domains have relatively low δ18O values of 4.7±0.6‰ (2SD) due to subsolidus hydrothermal alteration, whilst the least-altered zircon domains give δ18Ozirvalues of 5.1±0.4‰ (2SD), indistinguishable within errors with the troctolite zircons and the igneous zircons from the Mid-Atlantic and Southwest Indian Ridges gabbros, norites, and plagiogranites of modern oceanic crust. In situ zircon O–Hf isotopic data suggest that the troctolites and albitites are most likely cogenetic, with the albitites being formed by extreme fractional crystallization from the basaltic magma. Based on our new age results and compilation of the reliable literature U–Pb age data, the ophiolitic gabbros from Eastern, Central and, Western Alps, Liguria and Corsica crystallized nearly synchronously at 158–166Ma, suggesting a short life span of <11m.y. for the formation of the Piemont-Liguria oceanic domain, rather than a ~30m.y. life span as previously thought. The Chenaillet ophiolite is likely a remnant of embryonic oceanic crust, rather than a piece of “mature” oceanic crust. Provided the spreading velocities of <3cm/yr full rate for magma-poor MOR sequences, the maximum width to the Piemont-Liguria oceanic floor would have been in the order of 300km.
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影响因子：
4.9
作者：
K. Kodama;P. Ward
通讯作者：
K. Kodama;P. Ward
DOI：
10.1016/c2009-0-07394-2
发表时间：
1979-06
期刊：
--
影响因子：
--
作者：
F. Barker
通讯作者：
F. Barker
影响因子：
3.5
作者：
D. Rubatto;D. Gebauer;M. Fanning
通讯作者：
D. Rubatto;D. Gebauer;M. Fanning
影响因子：
3.5
作者：
Li, Xian-Hua;Liu, Yu;Chamberlain, Kevin R.
通讯作者：
Chamberlain, Kevin R.
影响因子：
3.8
作者：
Li, Xian-Hua;Long, Weng-Guo;Tao, Hua
通讯作者：
Tao, Hua