Abstract
Based on the published data of pillow lava-hosted mineralized veins, this study compares post-magmatic fracturing, fluid flow, and secondary mineralization processes in the Troodos and Izu–Bonin supra-subduction zone (SSZ) and discusses the crucial factors for the development of distinct vein types. Thin section and cathodoluminescence petrography, Raman spectroscopy, fluid inclusion microthermometry, and trace element and isotope (87Sr/86Sr, δ18O, δ13C, Δ47) geochemistry indicate that most veins consist of calcite that precipitated from pristine to slightly modified seawater at temperatures < 50 °C. In response to the mode of fracturing, fluid supply, and mineral growth dynamics, calcites developed distinct blocky (precipitation into fluid-filled fractures), syntaxial (crack and sealing), and antitaxial (diffusion-fed displacive growth) vein microtextures with vein type-specific geochemical signatures. Blocky veins predominate in all study areas, whereas syntaxial veins represent subordinate structures. Antitaxial veins occur in all study areas but are particularly abundant in the Izu–Bonin rear arc where the local geological setting was conducive of antitaxial veining. The temporal framework of major calcite veining coincides with the onset of extensional faulting in the respective areas and points to a tectonic control on veining. Thus, major calcite veining in the Troodos SSZ began contemporaneously with volcanic activity and extensional faulting and completed within ~ 10–20 Myr. This enabled deep seawater downflow and hydrothermal fluid upflow. In the Izu–Bonin forearc, reliable ages of vein calcites point to vein formation > 15 Myr after subduction initiation. Therefore, high-T mineralization (calcite, quartz, analcime) up to 230 °C is restricted to the Troodos SSZ.
Highlights
Rocks and geological structures exposed in ophiolites and drill cores recovered during the International Ocean Discovery Program (IODP) and its predecessors provide insights into the tectono-magmatic evolution and architecture of the oceanic crust (Dilek et al 2000)
International Journal of Earth Sciences (2021) 110:627–649 hydraulic seal for the oceanic basement (e.g., Anderson and Hobart 1976; Spinelli et al 2004; Coogan and Gillis 2018). These post-magmatic processes are the subject of this paper in which we compare published data of mineralized veins from the Late Cretaceous Troodos ophiolite (Cyprus) and the Early Eocene Western Pacific Izu–Bonin forearc and rear arc (Alt et al 1998; Gillis et al 2015; Quandt et al 2018, 2019, 2020a; Weinzierl et al 2018; Coogan et al 2019). This data set comprises (1) petrographic observations based on thin section and cathodoluminescence (CL) microscopy, (2) mineralogical determinations concluded from Raman spectroscopy, (3) mineral formation temperatures derived from δ18O, clumped isotope (Δ47), and fluid inclusion thermometry, (4) parental fluid compositions inferred from rare earth element and yttrium (REE + Y) and isotope (87Sr/86Sr, δ18O, δ13C, Δ47) geochemistry, (5) and relative ages of vein calcite precipitation deduced from 87Sr/86Sr stratigraphy
CL microscopy reveals that most vein calcites show simple growth zonations that are characterized by non-luminescent cores and luminescent grain boundaries (Quandt et al 2018, 2020a)
Summary
Rocks and geological structures exposed in ophiolites and drill cores recovered during the International Ocean Discovery Program (IODP) and its predecessors provide insights into the tectono-magmatic evolution and architecture of the oceanic crust (Dilek et al 2000). These post-magmatic processes are the subject of this paper in which we compare published data of mineralized veins from the Late Cretaceous Troodos ophiolite (Cyprus) and the Early Eocene Western Pacific Izu–Bonin forearc and rear arc (Alt et al 1998; Gillis et al 2015; Quandt et al 2018, 2019, 2020a; Weinzierl et al 2018; Coogan et al 2019) This data set comprises (1) petrographic observations based on thin section and cathodoluminescence (CL) microscopy, (2) mineralogical determinations concluded from Raman spectroscopy, (3) mineral formation temperatures derived from δ18O, clumped isotope (Δ47), and fluid inclusion thermometry, (4) parental fluid compositions inferred from rare earth element and yttrium (REE + Y) and isotope (87Sr/86Sr, δ18O, δ13C, Δ47) geochemistry, (5) and relative ages of vein calcite precipitation deduced from 87Sr/86Sr stratigraphy. This comparative study provides a robust basis to test if specific vein types show distinct geochemical signatures and contributes to the understanding of vein formation within the volcanic units of the oceanic crust in general
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