The geochemistry and petrogenesis of basalts from the Taupo volcanic zone and Kermadec island arc, S.W. Pacific

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doi: 10.1016/0377-0273(93)90067-2
Authors:Gamble, J. A.; Smith, I. E. M.; McCulloch, M. T.; Graham, I. J.; Kokelaar, B. P.
Author Affiliations:Primary:
Victoria University of Wellington, Department of Geology, Wellington, New Zealand
Other:
University of Auckland, Auckland, New Zealand
Australian National University, Canberra, ACT, 2601, Australia
Institute of Geology and Nuclear Sciences, Lower Hutt, New Zealand
University of Liverpool, Liverpool, United Kingdom
Volume Title:Journal of Volcanology and Geothermal Research
Source:Journal of Volcanology and Geothermal Research, 54(3-4), p.265-290. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:1993
Note:In English. 54 refs.; illus. incl. 3 tables, sketch map
Summary:Basalts from the Taupo Volcanic Zone (TVZ), New Zealand, the Kermadec Island Arc (KA) and its back-arc basin, the Havre Trough show systematic variations in trace-element and isotope geochemistry which are attributed to differences in tectonic setting and source heterogeneity along a more or less continuous plate boundary. Basalts from the Kermadec Arc are characterised by low abundances of high field strength elements (HFSE) such as Ti, Zr, Nb, Ta and Hf and have high ratios of Ti/Zr and low ratios of Ti/Sc and Ti/V relative to typical MORB. Basalts from TVZ also show low abundances of the HFS elements relative to MORB but show lower Ti/Zr, higher Ti/V and Ti/Sc ratios and generally higher Zr abundances than KA most basalts. The Havre Trough basalt is mildly alkaline (<1% normative nepheline) like many back-arc basin basalts from the Pacific rim, contrasting with the hypersthene normative TVZ and KA rocks. It has higher Zr than most TVZ basalts and all KA basalts. Ratios such as Ti/V, Ti/Sc and Ti/Zr are within the range of TVZ and MORB basalts but distinct from KA basalts. The depleted (relative to MORB) HFSE characteristics of the KA and TVZ basalts are complemented by high abundances of large ion lithophile elements (LIL), such as Ba, Rb and K, when compared to MORB, yielding the distinctive LIL-enriched pattern of subduction related rocks on a normalised multi-element plot. In contrast, the Havre Trough basalt is MORB-like. Chondrite-normalised Rare Earth Element (REE) patterns for the TVZ basalts show a field overlapping with that defined by the southern KA (Rumble Sea Mounts), with light REE enriched patterns (Ce/Ybn=∼1.8-3) and flat heavy REE (Tb-Lu). Basalts from the northern KA are typically light REE depleted (Ce/Ybn=0.5) or slightly enriched (Ce/Ybn=1.5). The REE pattern of the Havre Trough basalt is distinctive from both the KA and TVZ fields, being richer in the heavy REE, yet similar to many basalts from back-arc basins. Sr and Nd isotopes show considerable variation from a depleted MORB-like ratio in the Havre Trough basalt (TVZ-19, 87Sr/86Sr=0.702556, εNd=+9.3) to radiogenic ratios in the Tarawera basalt (TVZ-4, 87Sr/86Sr=0.7052, εNd=+2.2) from TVZ suggestive of crustal contamination. Between these extreme values the data from the KA and TVZ define distinctive arrays trending towards the evolved andesites, rhyolites and supracrustal basement rocks of central New Zealand. This curvilinear Nd-Sr array of the TVZ data is best explained as a result of crustal contamination. At the unradiogenic-Sr end of the array, the Sr and Nd isotopic ratios of primitive TVZ basalts overlap with those from southern KA suggesting that primitive TVZ basalts were derived from sources that are isotopically similar to those from which the southern KA basalts derived. Basalts from northern KA (Herald, Raoul and Macauley Islands) are appreciably less radiogenic than those from the central part (Curtis and L'Esperance) and the southern (Rumble Seamounts) part of the arc. Using non-slab-derived HFSE ratios and abundances as a guide to relative source depletion, it is inferred that the KA source varies from strongly depleted in the north to less depleted in the TVZ in the south. The KA source has generally experienced more extensive extraction of mafic magmas and hence is impoverished in incompatible HFSE. This leads to high Ti/Zr and low (absolute) Zr, Hf, Ta and Nb abundances. The Havre Trough source is relatively fertile with regard to basalt-forming constituents but isotopically depleted because it is remote from the main fluid transfer zone of the slab-wedge interface and has not been contaminated by introduction of a (high 87Sr/86Sr) subduction component. Both the TVZ and the KA basalts show isotopic evidence for this component, which is also apparent in the LIL element abundances. The model predicts, that with increasing extraction, a relatively fertile source, such as TVZ will evolve to a more HFSE-depleted character, such as KA. The enriched LIL, depleted HFSE and isotope systematics, which are the hallmarks of subduction magmatism, reflect a combination of efficient melt extraction, mantle circulation, volume, and transfer (either fluid or melt) from slab to mantle wedge. In the TVZ, the effects of interaction with continental lithosphere bring an additional complication and we offer several models to account for this. Our preferred dynamic model allows for most efficient melt extraction beneath the volcanic front and replenishment in the back-arc together with a more distinctive slab input towards the south.
Subjects:Alkaline earth metals; Back-arc basins; Basalts; Basins; Chemical composition; Crust; Genesis; Geochemistry; Igneous rocks; Indo-Australian Plate; Island arcs; Isotopes; Lithophile elements; Metals; Mid-ocean ridge basalts; Models; Nd-144/Nd-143; Neodymium; Pacific Plate; Plate boundaries; Plate tectonics; Pollution; Rare earths; Sr-87/Sr-86; Stable isotopes; Strontium; Subduction; Trace elements; Volcanic rocks; Australasia; Havre Trough; Kermadec Islands; Kermadec Trench; New Zealand; North Island; Pacific Ocean; South Pacific; Southwest Pacific; Taupo volcanic zone; West Pacific; West Pacific Ocean Islands; Evolution; Kermadec Arc; North-central New Zealand; Rumble Seamounts
Coordinates:S392000 S380000 E1763000 E1751000
Abstract Numbers:93M/4481
Record ID:1993000246
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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