Basalt Geochemistry and Mantle Flow During Early Backarc Basin Evolution: Havre Trough and Kermadec Arc, Southwest Pacific

Abstract

The Havre Trough (HT) backarc basin in the southwest Pacific is in the rifting stage of development. We distinguish five types of basalt there based on their amount and kind of slab component: backarc basalts (BAB) with little or no slab component, modified BAB with slight amounts, reararc (RA) with more, remnants of the preexisting arc (Colville Ridge horsts), and arc front volcanoes within the HT. Previous subarc mantle is quickly removed and replaced by more fertile mantle with less slab component. The ambient mantle is “Pacific” isotopically, and more enriched in Nb/Yb and Nd and Hf isotope ratios north of the Central Kermadec Discontinuity at 32°S than to the south. The contrast may reflect inheritance in the south of mantle that was depleted during spreading that formed the southern South Fiji Basin and a higher degree of melting because of a wetter slab‐derived flux. The slab component also differs along strike, more like a dry melt in the north and a supercritical fluid in the south. The mass fraction of slab component increases southward in the backarc as well as the arc front. RA volcanoes have the most slab component (1%–2%) and form indistinct ridges at high angles to, and <50 km behind, frontal volcanoes. Backarc basalts have less and occur throughout the basin. Slab components are distributed further into the backarc, and more irregularly, during the rifting than spreading stage of backarc basin development. The rifting stage is disorganized geochemically as well as spatially.

Petrogenesis of Havre Volcano in the Kermadec Arc: 2012 Eruption of a Chemically Homogeneous Rhyolite

“…Standards NBS-981, NBS-987, and JNdi-1 were run every five to six samples for Pb, Sr, and Nd, respectively. Nd ratios ( 143 Nd/ 144 Nd 0.513001-0.513020) relative to continental crust and instead are isotopically similar to typical mantle-derived basalts regional to Havre volcano (Figure 7; McCulloch et al, 1994;Barker et al, 2013;Timm et al, 2014;Hauff et al, 2021;Gill et al, 2021). In addition, the 2012 Havre samples, such as other Kermadec arc eruptive products (Barker et al, 2013;Timm et al, 2104), display little signs of contamination from radiogenic crust or sediment-produced melts.…”

“…The SE flank of Havre volcano merges into the Kermadec Arc ridge to the east (Wright et al, 2006), placing the volcano behind and off-axis to the west relative to the rest of the frontal volcanic arc. As most volcanoes in the Kermadec rear-arc are inactive, Havre and Giggenbach are both classified as active rear arc volcanoes (Gill et al, 2021).…”

“…Major and trace element data used in crystal fractionation models come from samples collected from the Havre Trough back-arc, Kermadec Arc Ridge, and Rear-Arc from 29 to 32 °S (Hauff et al, 2021) and reconnaissance Havre dredge samples (Wright et al, 2006). Basaltic compositions in the region show a depletion of subduction slab influence from east to west and increasing water depth (Gill et al, 2021). Basaltic samples sourced from around the Havre volcano and from the frontal and rear arc generally have a tholeiitic low to medium-K composition (Gill et al, 2021).…”

“…Basaltic compositions in the region show a depletion of subduction slab influence from east to west and increasing water depth (Gill et al, 2021). Basaltic samples sourced from around the Havre volcano and from the frontal and rear arc generally have a tholeiitic low to medium-K composition (Gill et al, 2021). Havre volcano dredge samples that pre-date the 2012 eruption are primarily dacitic to rhyolitic lava flows, a few basaltto-basaltic andesite lavas, and dacite to rhyolite pumice samples (Wright et al, 2006).…”

The Petrology and Geochemistry of a Suite of Intrusive Igneous Rocks from the Southern Kermadec Arc-Havre Trough, SW Pacific

“…The composition of the ambient mantle prior to the addition of subduction-derived components is believed to be similar to 'Pacific' MORB mantle (Gill et al, 2020, Haase et al, 2002 Haase et al, 2002). These isotopic compositions vary with latitude along the KAHT system (Gill et al, 2020, Haase et al, 2002, Timm et al, 2014. Source depletion, as traced by ratios of fluid immobile elements (e.g.…”