Eclogitic metagabbro from the Lanzada Window, eastern Central Alps: confirmation of subduction beneath the Malenco Unit
Eclogitic metagabbro from the Lanzada Window, eastern Central Alps: confirmation of subduction beneath the Malenco Unit
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DOI：
10.1007/s00015-014-0162-z
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发表时间：
2014-08
影响因子：
3.1
通讯作者：
G. Droop;D. Chavrit
中科院分区：
文献类型：
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作者：
G. Droop;D. Chavrit
富含绿帘石的榴辉变长岩在Malenco Val上的Lanzada窗口内形成一个小体，与位于Malenco单元下方的Lanzada - santa Anna带（LSZ）的蛇纹岩和表壳岩石相联系。常规的石榴石斜辉石和石榴石斜辉石斜辉石-辉云石测温表明，峰变质矿物组合（石榴石+辉云石+绿帘石+辉云石+钛矿+磷灰石+黄铁矿）在约2.0 GPa和525℃时达到平衡。整体成分富钙（硅灰石标准），表明岩石在高变质作用之前经历了钙交代作用。榴辉岩在LSZ内的存在加强了LSZ与含蓝片岩的Avers bendnerschiefer的相关性，并证实了Malenco单元下方曾经存在一个南倾俯冲带。
Epidote-rich eclogitic metagabbro forms a small body within the Lanzada Window, upper Val Malenco, where it is associated with serpentinites and supracrustal rocks of the Lanzada–Santa Anna Zone (LSZ), which lies structurally beneath the Malenco unit. Conventional garnet–clinopyroxene geothermometry and garnet–clinopyroxene–phengite geobarometry indicate that the peak-metamorphic mineral assemblage (garnet + omphacite + epidote + phengite + titanite + apatite + pyrite) equilibrated at ca. 2.0 GPa and 525 °C. The bulk composition is Ca-rich (wollastonite-normative), suggesting that the rock underwent Ca-metasomatism prior to high-Pmetamorphism. The presence of eclogite within the LSZ strengthens the correlation of the LSZ with the blueschist-bearing Avers Bündnerschiefer, and confirms the former existence of a southerly-dipping subduction zone beneath the Malenco unit.