Jurassic formation and Eocene subduction of the Zermatt–Saas-Fee ophiolites: implications for the geodynamic evolution of the Central and Western Alps
Jurassic formation and Eocene subduction of the Zermatt–Saas-Fee ophiolites: implications for the geodynamic evolution of the Central and Western Alps
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DOI：
10.1007/s004100050421
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发表时间：
1998-08
影响因子：
3.5
通讯作者：
D. Rubatto;D. Gebauer;M. Fanning
中科院分区：
文献类型：
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作者：
D. Rubatto;D. Gebauer;M. Fanning
Zermart-Saas-Fee蛇绿岩是阿尔卑斯山脉中保存最完好的榴辉岩洋壳之一。它们形成于中生代特提斯开启期，并在阿尔卑斯山挤压过程中俯冲至高压/超高压条件。基于阴极发光的离子探针（SHRIMP）测年的不同的锆石域从变质辉长岩和海洋变质沉积物进行了约束的时间形成和俯冲的蛇绿岩，在阿尔卑斯山地球动力学的两个基本问题。蛇绿岩系的形成受到岩浆锆石域上获得的Mellichen和Allalin变辉长岩的侵入年龄（164.0 ± 2.7Ma和163.5 ± 1.8Ma）的制约。这些数据与位于Lago di Mexanana（161 ± 11 Ma）和Sparrenfusion（约100 Ma）的镁铁质岩石上的富锰变质沉积物的最大沉积年龄一致。153-154 Ma）。在Lago di Pennana的一个超高压榴辉岩和两个变质沉积物中获得了44.1± 0.7Ma的全锆石和锆石边的始新世年龄。其中一个始新世锆石含有金红石包裹体，表明在高压条件下形成。由于这些岩石的温度和压力峰值几乎一致，始新世锆石可能限制了最深俯冲的年龄。超高压变质作用的始新世年龄意味着，西太平洋板块的俯冲晚于亚得里亚海边缘（塞西亚-兰佐带），早于欧洲大陆地壳在阿普利亚之下的晚始新世俯冲。三个俯冲事件传播的时间从东南到西北的情景提出了中部和西部阿尔卑斯山的地质演化。
The Zermatt–Saas-Fee ophiolites (ZSFO) are one of the best preserved slices of eclogitic oceanic crust in the Alpine chain. They formed during the opening of the Mesozoic Tethys and underwent subduction to HP/UHPconditions during Alpine compression. A cathodoluminescence-based ion microprobe (SHRIMP) dating of different zircon domains from metagabbros and oceanic metasediments was carried out to constrain the timing of formation and subduction of this ophiolite, two fundamental questions in Alpine geodynamics. The formation of the ophiolitic sequence is constrained by the intrusion ages of the Mellichen and the Allalin metagabbros (164.0 ± 2.7 Ma and 163.5 ± 1.8 Ma) obtained on magmatic zircon domains. These data are in line with the maximum deposition age for Mn-rich metasediments which overlie the mafic rocks at Lago di Cignana (161 ± 11 Ma) and at Sparrenflue (ca. 153–154 Ma). An Eocene age of 44.1±0.7 Ma was obtained for whole zircons and zircon rims from an UHPeclogite and two metasediments at Lago di Cignana. One of the Eocene zircons contains a rutile inclusion indicating formation at HPconditions. As the temperature and pressure peak of these rocks nearly coincide, the Eocene zircons probably constrain the age for the deepest subduction of the ZSFO. This Eocene age for the UHPmetamorphism implies that the ZSFO were subducted later than the Adriatic margin (Sesia-Lanzo Zone) and before the Late Eocene subduction of the European continental crust below Apulia. A scenario with three subduction episodes propagating in time from SE to NW is proposed for the geological evolution of the Central and Western Alps.