Geochemistry and Microtextures of Vein Calcites Pervading the Izu‐Bonin Forearc and Rear Arc Crust: New Insights From IODP Expeditions 352 and 351
Open Access
- 19 February 2020
- journal article
- research article
- Published by American Geophysical Union (AGU) in Geochemistry, Geophysics, Geosystems
- Vol. 21 (2)
- https://doi.org/10.1029/2019gc008745
Abstract
International Ocean Discovery Program Expeditions 352 and 351 drilled into the Western Pacific Izu‐Bonin forearc and rear arc. The drill cores revealed that the forearc is composed of forearc basalts (FAB) and boninites, and the rear arc consists of FAB‐like rocks. These rocks are pervaded by calcite veins. Blocky vein microtextures enclosing host rock fragments dominate in all locations and suggest hydrofracturing and advective fluid flow. Significant diffusion‐fed and crystallization pressure‐driven antitaxial veining is restricted to the rear arc. The lack of faults and presence of an Eocene sedimentary cover in the rear arc facilitated antitaxial veining. Rare earth element and isotopic (δ18O, δ13C, 87Sr/86Sr, Δ47) tracers indicate varying parental fluid compositions ranging from pristine to variably modified seawater. The most pristine seawater signatures are recorded by FAB‐hosted low‐T (< 30 °C) vein calcites. Their 87Sr/86Sr ratios intersect the 87Sr/86Sr seawater curve at ~35‐33 Ma and ~22 Ma. These intersections are interpreted as precipitation ages, which concur with Pacific slab rollback. Boninite‐hosted low‐T (< 30 °C) vein calcites precipitated from seawater that was modified by fluid‐rock interactions. Mixing calculations yield a mixture of > 95 % seawater and < 5 % basaltic 87Sr/86Sr. In the rear arc, low‐T rock alteration lowered the circulating seawater in δ18O and 87Sr/86Sr. Thus, vein calcites precipitated from modified seawater with up to 20‐30 % basaltic 87Sr/86Sr at temperatures up to 74 ± 12 °C. These results show how the local geology and vein growth dynamics affect microtextures and geochemical compositions of vein precipitates.Keywords
Funding Information
- Austrian Science Fund (FWF‐P 27982‐N29)
This publication has 109 references indexed in Scilit:
- The formation of antitaxial calcite veins with well-developed fibres, Oppaminda Creek, South AustraliaJournal of Structural Geology, 2005
- Numerical simulations of polycrystal growth in veinsJournal of Structural Geology, 2005
- An expression of Philippine Sea plate rotation: the Parece Vela and Shikoku BasinsTectonophysics, 2004
- Experimental study of syntaxial vein growth during lateral fluid flow in transmitted light: first resultsJournal of Structural Geology, 2002
- A laboratory simulation of fibrous veins: some first observationsJournal of Structural Geology, 2001
- Development of crystal morphology during unitaxial growth in a progressively widening vein: II. Numerical simulations of the evolution of antitaxial fibrous veinsJournal of Structural Geology, 2001
- Development of crystal morphology during unitaxial growth in a progressively widening vein: I. The numerical modelJournal of Structural Geology, 2001
- Alteration and mineralization of an oceanic forearc and the ophiolite‐ocean crust analogyJournal of Geophysical Research, 1998
- Low limit of Mn2+-activated cathodoluminescence of calcite: state of the artSedimentary Geology, 1998
- Curved vein fibres: an alternative explanationTectonophysics, 1989