Tectonic evolution of the Dunnage M¨¦lange tract and its significance to the closure of Iapetus

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• 作者：A. Zagorevski ; C.R. van Staal ; V.J. McNicoll ; L. Hartree ; N. Rogers
• 关键词：Mé ; lange development ; Syn-tectonic magma emplacement ; Magma&ndash ; mud interaction ; Forearc magmatism ; Forearc basement
• 刊名：Tectonophysics
• 出版年：2012
• 出版时间：28 September, 2012
• 年：2012
• 卷：568-569
• 期：Complete
• 页码：371-387
• 全文大小：3876 K

文摘

The Dunnage M¨¦lange comprises a chaotic, heterogeneous assemblage of unsorted blocks set in a fine-grained matrix that is situated along the main Iapetus suture zone in Newfoundland Appalachians. The origin and tectonic setting of the m¨¦lange has been controversial and it has been variously interpreted as an olistostrome and a tectonic m¨¦lange that formed in arc-trench gap or backarc settings. The m¨¦lange preserves abundant evidence of tectonic and later soft-sediment deformation, indicating that tectonic deformation is a major component in the genesis of the Dunnage M¨¦lange. The tectonic setting of the Dunnage M¨¦lange is herein investigated through the Coaker Porphyry (469 ¡À 4 Ma), a peraluminous, syn-tectonic, plutonic suite that is exclusively emplaced into the m¨¦lange. The Coaker Porphyry contains a typically peri-Gondwanan inheritance indicating derivation from the adjacent Cambro-Ordovician Victoria-Penobscot Arc and its basement. The xenoliths contained in the Coaker Porphyry are indicative of an arc origin and there is no evidence for derivation from the Iapetus Ocean lithosphere. The m¨¦lange is thus interpreted to have formed above Victoria-Penobscot arc crystalline forearc basement. The emplacement of the Coaker Porphyry coincides with regional rift-like magmatism in the adjacent Victoria Arc. We interpret the m¨¦lange formation, rift-like magmatism and generation of Coaker Porphyry to be related to a Middle Ordovician ridge-trench collision, slab window formation and inversion of the forearc strata.