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The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin

Brounce, Maryjo and Kelley, Katherine A. and Stern, Robert and Martinez, Fernando and Cottrell, Elizabeth (2016) The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin. Geochemistry, Geophysics, Geosystems, 17 (10). pp. 4078-4091. ISSN 1525-2027. doi:10.1002/2016GC006457.

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In the Mariana convergent margin, large arc volcanoes disappear south of Guam even though the Pacific plate continues to subduct and instead, small cones scatter on the seafloor. These small cones could form either due to decompression melting accompanying back-arc extension or flux melting, as expected for arc volcanoes, or as a result of both processes. Here, we report the major, trace, and volatile element compositions, as well as the oxidation state of Fe, in recently dredged, fresh pillow lavas from the Fina Nagu volcanic chain, an unusual alignment of small, closely spaced submarine calderas and cones southwest of Guam. We show that Fina Nagu magmas are the consequence of mantle melting due to infiltrating aqueous fluids and sediment melts sourced from the subducting Pacific plate into a depleted mantle wedge, similar in extent of melting to accepted models for arc melts. Fina Nagu magmas are not as oxidized as magmas elsewhere along the Mariana arc, suggesting that the subduction component responsible for producing arc magmas is either different or not present in the zone of melt generation for Fina Nagu, and that amphibole or serpentine mineral destabilization reactions are key in producing oxidized arc magmas. Individual Fina Nagu volcanic structures are smaller in volume than Mariana arc volcanoes, although the estimated cumulative volume of the volcanic chain is similar to nearby submarine arc volcanoes. We conclude that melt generation under the Fina Nagu chain occurs by similar mechanisms as under Mariana arc volcanoes, but that complex lithospheric deformation in the region distributes the melts among several small edifices that get younger to the northeast.

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Additional Information:© 2016 American Geophysical Union. Received 25 MAY 2016; Accepted 27 SEP 2016; Accepted article online 29 SEP 2016; Published online 25 OCT 2016. We would like to thank Frances Jenner and two anonymous reviewers for their careful attention to our paper. We would like to thank the captain and crew aboard the Thomas G. Thompson during expedition TN273, and aboard the NOAA vessel Okeanos Explorer and ROV Deep Discoverer during expedition EX1605L1. We thank M. Lytle, B. Covellone, J. Ribeiro, W. Lieu, and E. Jordan for leadership and assistance during dredging operations for TN273. We thank A. Lanzirotti, W. Rao, and S. Wirick for assistance in beamline operations at NSLS BNL. Access to NSLS BNL was supported by the US Department of Energy under contract DE-AC02-98CH10886. We acknowledge support from NSF grant OCE-0961811 to Martinez, NSF OCE-0961559 and NSF EAR-1258940 to Kelley, NSF EAR-0841006 to Cottrell, and NSF OCE-0961352 to Stern. NSF OCE-1258771 provides curatorial support for marine geological samples at the University of Rhode Island. Supporting data are included as data tables in a supporting information file. Additional information may be obtained from the first author at
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Department of Energy (DOE)DE-AC02-98CH10886
Subject Keywords:Mariana subduction zone; arc volcano formation; oxidized basalt; back-arc spreading; hydrothermal vents
Issue or Number:10
Record Number:CaltechAUTHORS:20170103-102728976
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Official Citation:Brounce, M., K. A. Kelley, R. Stern, F. Martinez, and E. Cottrell (2016), The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin, Geochem. Geophys. Geosyst., 17, 4078–4091, doi:10.1002/2016GC006457
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73171
Deposited By: Tony Diaz
Deposited On:03 Jan 2017 19:19
Last Modified:11 Nov 2021 05:12

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