Crustal thickening along the West Antarctic Gondwana margin during mid-Cretaceous deformation of the Triassic intra-oceanic Dyer Arc

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• 作者：Alan P.M. Vaughan^a ; ^{a.vaughan@bas.ac.uk} ; Philip T. Leat^a ; Alison A. Dean^a ; Ian L. Millar^b
• 关键词：Antarctic Peninsula ; Palmer Land Event ; Accretion ; Terrane ; Basalt ; Mantle melting
• 刊名：Lithos
• 出版年：2012
• 期刊代码：54_00244937
• 类别：ear
• 出版时间：June, 2012
• 卷：142-143
• 期：Complete
• 页码：130-147
• 文件大小：2655 K

摘要

Subduction-related Mesozoic mafic dykes in eastern Palmer Land, Antarctic Peninsula, record the development of an intra-oceanic arc terrane, the Dyer Arc, probably of late Permian-Triassic age, represented by a tholeiitic dyke group. Arc rocks were deformed in late Triassic-early Jurassic and mid-Cretaceous times on the Gondwana margin. Eruption of syn- to post-mid-Cretaceous orogenesis magmatism is represented by a calc-alkaline group of dykes. The tholeiitic dykes intruded immature granitic crust of the Eastern Zone sub-terrane of the Central Domain, one of the magmatic terranes of the Pacific margin of Gondwana. The calc-alkaline dykes straddle the major tectonic boundary between the Central Domain and the continental margin Eastern Domain. 132 dykes were studied, 82 of which are calc-alkaline, 48 tholeiitic and two shoshonitic, across an area of approximately 4000 km². Tholeiitic dykes strike broadly NNW-SSE, transposed into parallelism with the strike of the tectonic boundary during Cretaceous orogenesis whereas calc-alkaline dykes strike tightly ESE-WNW at a high angle to the boundary. The tholeiites pre-date late Triassic deformation and metamorphism, and are interpreted as dominantly Triassic in age, whereas Ar-Ar dated calc-alkaline dykes are younger (~ 100 Ma and ~ 97 Ma) and field relations indicate that they overlap with the waning phase of the mid-Cretaceous Palmer Land Event. The tholeiites have trace element abundances similar to, but more depleted than, those of modern intra-oceanic arcs, as recorded by Zr/Hf ratios. Nb/Yb versus TiO₂*/Yb and Sm/Yb versus La/Sm plots are used to model depths of partial melting. The tholeiites were mostly generated at shallow depths corresponding to 2.5 and certainly less than 3.0 GPa in largely garnet-free mantle. The calc-alkaline magmas were generated at pressures greater than 3.0 to possibly > 3.5 GPa, in the garnet zone. The deepening of the mantle source, and onset of calc-alkaline magmatism are interpreted to have been caused by deformation of the intra-oceanic arc terrane on the Gondwana margin, and lithospheric thickening during the Palmer Land Event.