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Features of seafloor hydrothermal alteration in metabasalts of mid-ocean ridge origin from the Chrystalls Beach Complex

Features of seafloor hydrothermal alteration in metabasalts of mid-ocean ridge origin from the Chrystalls Beach Complex
Features of seafloor hydrothermal alteration in metabasalts of mid-ocean ridge origin from the Chrystalls Beach Complex
The Taieri Mouth locale of the Chrystalls Beach Complex (CBC) in the South Island of New Zealand includes well preserved to strongly deformed pillow lavas and flattened veins of epidote, quartz and chlorite intercalated with basalt flows and volcanoclastic breccias. The tectonic affinity for this rare igneous portion of the predominantly sedimentary CBC has not been well established in the context of its regional metamorphic geology. New field, petrographic, geochemical and isotopic evidence suggest a mid-ocean ridge origin for the Taieri metabasalts. Further, paleo-vertical networks of epidote-quartz-chlorite veins and cross-cutting faults provide a record of seafloor fracturing and fluid-flow. Altered pillows and epidote separates have δ18O isotope values ranging from 9.3 to 13.1‰. This indicates slightly enriched δ18O fractionation resulting from seafloor weathering and low-temperature (<250°C) exchange between seawater and hydrothermal fluids in basaltic fractures. Age-corrected 87Sr/86Sr ratios between 0.704135 and 0.70624 show low temperature fluid-rock interactions where the altered pillows and veins did not succumb to major mineralogic changes or isotopic re-equilibration after formation. In contrast, compressed s-fold epidote and coarse quartz veins near metasediments are suggestive of the elevated temperatures and pressures during accretion. We differentiate between episodic seafloor venting and accretional wedge-related alteration recorded within these metabasalts.
Otago region, epidote, geochemistry, isotopic analysis, metabasalts, mid-ocean ridge processes, ophiolite, petrology, seafloor hydrothermal alteration, veins
0028-8306
Hung, Caroline
d256a592-7232-424f-bb5b-5565e5545271
Gilbert, Lisa A.
d3284232-078d-47bb-9523-d45e4dd08a0e
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Wobus, Reinhard A.
ed005160-4417-4fef-8e61-4577b573bfce
Hung, Caroline
d256a592-7232-424f-bb5b-5565e5545271
Gilbert, Lisa A.
d3284232-078d-47bb-9523-d45e4dd08a0e
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Wobus, Reinhard A.
ed005160-4417-4fef-8e61-4577b573bfce

Hung, Caroline, Gilbert, Lisa A., Teagle, Damon A.H., Craw, Dave and Wobus, Reinhard A. (2020) Features of seafloor hydrothermal alteration in metabasalts of mid-ocean ridge origin from the Chrystalls Beach Complex. New Zealand Journal of Geology and Geophysics. (doi:10.1080/00288306.2020.1803925).

Record type: Article

Abstract

The Taieri Mouth locale of the Chrystalls Beach Complex (CBC) in the South Island of New Zealand includes well preserved to strongly deformed pillow lavas and flattened veins of epidote, quartz and chlorite intercalated with basalt flows and volcanoclastic breccias. The tectonic affinity for this rare igneous portion of the predominantly sedimentary CBC has not been well established in the context of its regional metamorphic geology. New field, petrographic, geochemical and isotopic evidence suggest a mid-ocean ridge origin for the Taieri metabasalts. Further, paleo-vertical networks of epidote-quartz-chlorite veins and cross-cutting faults provide a record of seafloor fracturing and fluid-flow. Altered pillows and epidote separates have δ18O isotope values ranging from 9.3 to 13.1‰. This indicates slightly enriched δ18O fractionation resulting from seafloor weathering and low-temperature (<250°C) exchange between seawater and hydrothermal fluids in basaltic fractures. Age-corrected 87Sr/86Sr ratios between 0.704135 and 0.70624 show low temperature fluid-rock interactions where the altered pillows and veins did not succumb to major mineralogic changes or isotopic re-equilibration after formation. In contrast, compressed s-fold epidote and coarse quartz veins near metasediments are suggestive of the elevated temperatures and pressures during accretion. We differentiate between episodic seafloor venting and accretional wedge-related alteration recorded within these metabasalts.

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Accepted/In Press date: 26 July 2020
e-pub ahead of print date: 19 August 2020
Additional Information: Publisher Copyright: © 2020 The Royal Society of New Zealand.
Keywords: Otago region, epidote, geochemistry, isotopic analysis, metabasalts, mid-ocean ridge processes, ophiolite, petrology, seafloor hydrothermal alteration, veins

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Local EPrints ID: 443727
URI: http://eprints.soton.ac.uk/id/eprint/443727
ISSN: 0028-8306
PURE UUID: 31978bb6-9955-4f9d-91e4-0ce925cf4b1d
ORCID for Damon A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409

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Date deposited: 09 Sep 2020 16:35
Last modified: 17 Mar 2024 05:53

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Contributors

Author: Caroline Hung
Author: Lisa A. Gilbert
Author: Dave Craw
Author: Reinhard A. Wobus

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