The University of Southampton
University of Southampton Institutional Repository
Warning ePrints Soton is experiencing an issue with some file downloads not being available. We are working hard to fix this. Please bear with us.

Evidence of porphyry copper-type hydrothermal activity from a submerged remnant back-arc volcano of the Izu-Bonin arc: implications for the volcanotectonic history of back-arc seamounts

Evidence of porphyry copper-type hydrothermal activity from a submerged remnant back-arc volcano of the Izu-Bonin arc: implications for the volcanotectonic history of back-arc seamounts
Evidence of porphyry copper-type hydrothermal activity from a submerged remnant back-arc volcano of the Izu-Bonin arc: implications for the volcanotectonic history of back-arc seamounts
The first example of a porphyry copper-type hydrothermal activity associated with the back-arc volcanism in the Izu-Bonin arc is presented. Hydrothermally-altered rocks exposed at the flat summit of the Manji Seamount show strong similarities to those associated with porphyry copper-type deposits, i.e. (1) alteration mineral assemblages corresponding to potassic and propylitic alteration zone, (2) occurrence of stockwork of quartz–magnetite veinlets, (3) copper mineralization, (4) occurrence of fluid inclusions trapping high temperature (ca. 600°C) and hyper-saline (ca. 63 wt% NaCl equivalent) fluid, (5) occurrence of acidic plutonic rocks (e.g. tonalite porphyry), which are often genetically associated with porphyry copper deposits. Volcanism of Manji Seamount occurred at around 7 Ma and shares common chemical characteristics with other back-arc seamounts in the Izu-Bonin arc, i.e. more calc-alkaline affinity, enrichment in large ion lithophile elements (LILE) and high-field strength elements (HFSE) compared to those of volcanic front. The plutonic rocks are almost contemporaneous with the volcanic rocks and are regarded as comagmatic. The age of the volcanism is within the age range of other back-arc seamounts (17–3 Ma). The porphyry copper-type hydrothermal activity is presumed to have been driven by the volcanism in the back-arc during the period between the cessation of the back-arc spreading of the Shikoku Basin and the initiation of currently active rifting. The seamount was exposed above sea level when active, but was later deeply eroded down to the interior of the volcano. Subsequent subsidence and erosion produced a wave-cut flat summit and consequently the porphyry copper system outcrops at 700 m water depth. Some characteristics of the hydrothermal activity at Manji Seamount are shared by the porphyry copper deposits in the oceanic arcs in the southwestern Pacific, e.g. petrography and chemical characteristics of related igneous rocks. However, the hydrothermal activity at Manji Seamount is located further away from the volcanic front than the deposits in the southwestern Pacific, and regional back-arc volcanism is extensive and voluminous in the Izu-Bonin arc. The porphyry copper hydrothermal system reported here is a well-preserved example associated with voluminous back-arc volcanism (i.e. arc volcanism behind the volcanic front which is not associated with back-arc rifting) in an oceanic arc setting. The discovery of porphyry copper-type hydrothermal activity associated with extensive back-arc volcanism in an intra-oceanic arc implies that back-arc regions of ancient oceanic arcs which are exposed on land might host more porphyry copper deposits.
Izu-Bonin Arc, porphyry copper, seamount, tonalite, back-arc basins, volcanism
0012-821X
381-399
Ishizuka, O.
8fe117e5-b0da-41ef-83ec-9e0bd6658747
Yuasa, M.
5a607459-19a9-42ea-b5cc-9e268eebb5a4
Uto, K.
0970f5e1-2e96-40dc-9474-c6d3ba223a7e
Ishizuka, O.
8fe117e5-b0da-41ef-83ec-9e0bd6658747
Yuasa, M.
5a607459-19a9-42ea-b5cc-9e268eebb5a4
Uto, K.
0970f5e1-2e96-40dc-9474-c6d3ba223a7e

Ishizuka, O., Yuasa, M. and Uto, K. (2002) Evidence of porphyry copper-type hydrothermal activity from a submerged remnant back-arc volcano of the Izu-Bonin arc: implications for the volcanotectonic history of back-arc seamounts. Earth and Planetary Science Letters, 198 (3/4), 381-399. (doi:10.1016/S0012-821X(02)00515-0).

Record type: Article

Abstract

The first example of a porphyry copper-type hydrothermal activity associated with the back-arc volcanism in the Izu-Bonin arc is presented. Hydrothermally-altered rocks exposed at the flat summit of the Manji Seamount show strong similarities to those associated with porphyry copper-type deposits, i.e. (1) alteration mineral assemblages corresponding to potassic and propylitic alteration zone, (2) occurrence of stockwork of quartz–magnetite veinlets, (3) copper mineralization, (4) occurrence of fluid inclusions trapping high temperature (ca. 600°C) and hyper-saline (ca. 63 wt% NaCl equivalent) fluid, (5) occurrence of acidic plutonic rocks (e.g. tonalite porphyry), which are often genetically associated with porphyry copper deposits. Volcanism of Manji Seamount occurred at around 7 Ma and shares common chemical characteristics with other back-arc seamounts in the Izu-Bonin arc, i.e. more calc-alkaline affinity, enrichment in large ion lithophile elements (LILE) and high-field strength elements (HFSE) compared to those of volcanic front. The plutonic rocks are almost contemporaneous with the volcanic rocks and are regarded as comagmatic. The age of the volcanism is within the age range of other back-arc seamounts (17–3 Ma). The porphyry copper-type hydrothermal activity is presumed to have been driven by the volcanism in the back-arc during the period between the cessation of the back-arc spreading of the Shikoku Basin and the initiation of currently active rifting. The seamount was exposed above sea level when active, but was later deeply eroded down to the interior of the volcano. Subsequent subsidence and erosion produced a wave-cut flat summit and consequently the porphyry copper system outcrops at 700 m water depth. Some characteristics of the hydrothermal activity at Manji Seamount are shared by the porphyry copper deposits in the oceanic arcs in the southwestern Pacific, e.g. petrography and chemical characteristics of related igneous rocks. However, the hydrothermal activity at Manji Seamount is located further away from the volcanic front than the deposits in the southwestern Pacific, and regional back-arc volcanism is extensive and voluminous in the Izu-Bonin arc. The porphyry copper hydrothermal system reported here is a well-preserved example associated with voluminous back-arc volcanism (i.e. arc volcanism behind the volcanic front which is not associated with back-arc rifting) in an oceanic arc setting. The discovery of porphyry copper-type hydrothermal activity associated with extensive back-arc volcanism in an intra-oceanic arc implies that back-arc regions of ancient oceanic arcs which are exposed on land might host more porphyry copper deposits.

This record has no associated files available for download.

More information

Published date: 2002
Keywords: Izu-Bonin Arc, porphyry copper, seamount, tonalite, back-arc basins, volcanism

Identifiers

Local EPrints ID: 2043
URI: http://eprints.soton.ac.uk/id/eprint/2043
ISSN: 0012-821X
PURE UUID: d82b7365-00e1-4205-ae6f-9b59bcfdc2d5

Catalogue record

Date deposited: 10 May 2004
Last modified: 09 Nov 2021 06:05

Export record

Altmetrics

Contributors

Author: O. Ishizuka
Author: M. Yuasa
Author: K. Uto

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×