Article

Structure and petrology of newly discovered volcanic centers in the northern Kermadec–southern Tofua arc, South Pacific Ocean

Journal of Geophysical Research (Impact Factor: 3.17). 01/2008; 113. DOI: 10.1029/2007JB005453

ABSTRACT The NZAPLUME III expedition of September-October 2004 to the northern
Kermadec-southern Tofua (NKST) arc, between 28°52'S and 25°07'S,
resulted in the discovery of at least seven new submarine volcanic
centers and a substantial caldera complex adjacent to the previously
known Monowai Seamount. The volcanic centers form a sublinear chain that
coincides with the Kermadec Ridge crest in the south (Hinetapeka) and
diverges ˜45 km westward of the ridge crest in the north ("V")
just to the south of where the Louisville Ridge intersects with the arc.
All of the centers contain calderas or caldera-like structures, as well
as multiple cones, domes, fissure ridges, and vent fields. All show
signs of recent eruptive and current hydrothermal activity. There are
strong structural controls on edifice location, with cones and fissure
ridges typically associated with faulting parallel to the regional
˜12° strike of the arc front. Several of the calderas are
ellipsoidal, orientated northwest-southeast in the general direction of
least compressive stress. Sampled volcanic rocks, representing the most
recently erupted lavas, are all low-K tholeiites. Two of the centers,
Gamble and Rakahore, yielded only high-silica dacite to rhyolite (69-74
wt% silica), whereas two others, Monowai and "V," yielded only basalt to
andesite (48-63 wt% silica). Mineral assemblages are
plagioclase-pyroxene dominated, with accessory Fe-Ti oxides, apatite,
olivine, and quartz/tridymite/cristobalite, typical of dry volcanic arc
systems. Hornblende occurs only in a felsitic rhyolite from Hinepuia
volcanic center, and zircon is absent. Glass contents range to 57% in
basalts-andesites (mean 20%), and 97% in andesites-rhyolites (mean 59%)
and other quench textures, including swallow-tailed, plumose, or
dendritic crystal forms and crystallites, are common. Most lavas are
highly vesicular (≤63%; mean 28%) and have low volatile contents
(mostly <2 wt%) which, together with the occurrence of tridymite or
cristobalite, indicates explosive eruption and rapid cooling. Exceptions
are rocks from "U" volcanic center, which have low vesicularity and low
glass contents across a wide compositional range, indicating effusive
eruption. Disequilibrium mineral textures, the frequent occurrence of
xenoliths and xenocrysts, and macroscopic evidence for magma mingling
indicate that many of the lavas are hybrids, having resided only a short
time in upper crustal reservoirs prior to eruption. Silicic magmas are
major components of NKST arc volcanism and caldera formation is the
dominant eruptive style. The scale of silicic magmatism is in marked
contrast to the dominant basaltic-andesitic magmatism in the southern
Kermadec arc. With evidence from other arcs, silicic magmatism is now
recognized as a major feature of intraoceanic arcs globally.

0 Bookmarks
 · 
49 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: New multibeam (swath) bathymetric sonar data acquired using an EM120 system on the RRS James Clark Ross, supplemented by sub-bottom profiling, reveals the underwater morphology of a ∼ 12,000 km2 area in the northern part of the mainly submarine South Sandwich volcanic arc. The new data extend between 55° 45′S and 57° 20′S and include Protector Shoal and the areas around Zavodovski, Visokoi and the Candlemas islands groups. Each of these areas is a discrete volcanic center. The entirely submarine Protector Shoal area, close to the northern limit of the arc, forms a 55 km long east–west-trending seamount chain that is at least partly of silicic composition. The seamounts are comparable to small subaerial stratovolcanoes in size, with volumes up to 83 km3, indicating that they are the product of multiple eruptions over extended periods. Zavodovski, Visokoi and the Candlemas island group are the summits of three 3–3.5 km high volcanic edifices. The bathymetric data show evidence for relationships between constructional volcanic features, including migrating volcanic centers, structurally controlled constructional ridges, satellite lava flows and domes, and mass wasting of the edifices. Mass wasting takes place mainly by strong erosion at sea level, and dispersal of this material along chutes, probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields. Large scale mass wasting structures include movement of unconsolidated debris in slides, slumps and debris avalanches. Volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical, being steep with abundant recent volcanism on their western flanks, and gently sloping with extinct, eroded volcanic sequences to their east. This is consistent with the calculated rate of subduction erosion of the fore-arc.
    Marine Geology. 01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Buchans Group, central Newfoundland, represents an Ordovician continental bimodal calc-alkaline arc sequence that hosts numerous volcanogenic massive sulphide (VMS) occurrences, including both in situ and mechanically transported sulphide breccia-conglomerate ore bodies. Diverse lithic clasts associated with transported deposits, include rounded granitoid clasts. Earlier workers have suggested that Buchans Group VMS-hosting felsic extrusive units, small granodiorite intrusions (e.g. Wiley’s Brook), and granitoid cobbles associated with transported ore, represent co-genetic products of the same magmatic system. The granitoid cobbles and small granodiorite intrusions are geochemically similar and closely resemble Buchans Group felsic volcanic units. U-Pb zircon age determinations show a: (i) 466.7 ± 0.5 Ma crystallization age for the WBG; (ii) 464 ± 4 Ma crystallization age for a granitoid cobble; and (iii) 466 ± 4 Ma maximum deposition age for a conglomerate-sandstone sequence associated with transported ore. Thus Buchans Group felsic plutonic rocks are within experimental error of felsic volcanism and VMS deposition. Furthermore, eNd(T) values of four granitoid cobbles (-1.95 to -4.0) overlap values obtained from Buchans Group felsic volcanic units. Our results are compatible with plutonic and volcanic rocks being related through fractional crystallization, or partial melting processes, but do not support a petrogenetic link between VMS deposition and exposed felsic plutons. Comparisons to modern arc analogues favour exhumation of plutonic rocks by extension along caldera/rift walls and/or subaerial erosion. Enigmatic rounding of Buchans granitoid clasts was likely accomplished in a subaerial or shallow marine environment, and the clasts transported into a VMS-active basin by mass flows.
    Canadian Journal of Earth Sciences 08/2013; Published on the web:http://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2013-0040?journalCode=cjes#.UkYTbe5zbZ5. · 1.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A suite of deep-sea cores were collected along transects up to 100 km across the fore-arc and back-arc regions of the predominantly submarine Kermadec arc near Raoul and Macauley islands, southwest Pacific. The cores reveal a macroscopic tephra record extending back >50 ka. This is a significant addition to the dated record of volcanism, previously restricted to fragmented late Holocene records exposed on the two islands. The 27 macroscopic tephra layers display a wide compositional diversity in glass (∼50–78 wt% SiO2). Many tephra layers comprise silicic shards with a subordinate mafic shard population. This could arise from magma mingling and may reflect mafic triggering of the silicic eruptions. Broadly, the glass compositions can be distinguished on diverging high-K and low-K trends, most likely arising from different source volcanoes. This distinction is also reflected in the tephra records exposed on Raoul (low-K) and Macauley (high-K) islands, the likely source areas. Heterogeneous tephra comprising shards of both high- and low-K affinity, silicic and mafic compositions, and more homogeneous tephra with subordinate outlier shard compositions, are best explained by post-depositional mixing of separate eruption deposits or contemporaneous eruptions. Evidently, the slow sedimentation rates of the calcareous oozes (∼101–102 mm ka−1) were insufficient to adequately separate and preserve closely spaced eruption deposits. This exemplifies the difficulty in assessing eruption frequencies and magmatic trends, and erecting a tephrostratigraphy, using geochemical fingerprinting in such environments. Despite these difficulties, the ca. 5.7 ka Sandy Bay Tephra erupted from Macauley Island can be correlated over a distance of >100 km, extending east and west of the island, showing that the mostly submerged volcanoes are capable of wide tephra dispersal. Hence there is potential for developing chronostratigraphies for the southwest Pacific beyond the region covered by the extensive rhyolite marker beds from the Taupo Volcanic Zone. Copyright © 2011 John Wiley & Sons, Ltd.
    Journal of Quaternary Science 04/2011; 26(4):422 - 432. · 2.66 Impact Factor