Geochemistry of diverse lava types from the Lau Basin (South West Pacific): Implications for complex back‐arc mantle dynamics

Abstract

Lavas from back‐arc basins are generally diverse, and their geochemical compositions indicate that they received variable contributions from subduction components during petrogenesis. Obtaining comprehensive geochemistry characteristics for the entire back‐arc basin are helpful in gaining a better understanding of the complexities of back‐arc evolution. In this study, we systematically reviewed the major and trace element compositions of Lau Basin lavas. This data set covered all of the major tectonic units of the basin, for example, the Eastern Lau spreading center (ELSC), the Valu Fa ridge (VFR), the Central Lau spreading center (CLSC), the Northwestern Lau spreading center (NWLSC), the Northeastern Lau spreading center (NELSC), the Mangatolu Triple Junction (MTJ), and the Fonualei Spreading Center (FSC). The lava types from these locations are diverse, including tholeiitic basalts, alkali basalts, basaltic andesites, andesites, dacites, and rhyolites. In addition, the NELSC and FSC contain boninites. In this study, the geochemical compositions of these diverse rock types are used to investigate the spreading dynamics of the Lau Basin back‐arc. We conclude that (a) the subduction components mainly include hydrous fluids released from the subducted slab, and hydrous melt directly from the melting subducted sediment, and the influence of the subducted components on the mantle wedge and the petrogenesis of the central and southern Lau Basin lavas decreases with increasing distance from the Tonga Trench; (b) during the propagation and spreading of the Samoan mantle into the Lau Basin, lavas from the NELSC, NWLSC, MTJ, and even from the northern part of the FSC may receive variable degrees of influence from the Samoan plume; and (c) the migration of Indian MORB‐like mantle southwards into the Pacific mantle is consistent with the opening of the Lau Basin. With the gradual migration of Indian mantle into the Lau Basin, a series of spreading centers were formed, for example, in order, the NWLSC, CLSC, ELSC, and the propagating VFR.

Distinguishing Volcanic Contributions to the Overlapping Samoan and Cook-Austral Hotspot Tracks

“…In fact, it has been shown that Samoan mantle material is sampled not only by Uo Mamae, but also by Tafahi and Niuatoputapu, northern Tonga arc islands located, respectively, ~280 and ~300 km south of the trace of the Samoan hotspot track, as well as lavas in the northern Lau basin located further to the west (e.g. Wendt et al, 1997, Turner andHawkesworth, 1998;Regelous et al, 2008;Zhang et al, 2019)) (Figure 2). If Samoan-type mantle has pervaded the region beneath Papatua, which is located only ~60 km south of Tutuila Island-a Samoan hotspot volcano that has erupted EM1 rejuvenated lavas in the past 24,000 years (Reinhard et al, 2019) portion is subducting (e.g.…”

Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity

“…Sampling of the MTJ has revealed a diverse suite of lithologies, spanning the compositional range from basalt to andesite to dacite (Nilsson et al, 1989;Falloon et al, 1992;Hawkins, 1995;Langmuir et al, 2006). The NELSC has a mixed geochemical signature of OIB and N-MORB, in addition to subtle arc-like affinities (Keller et al, 2008;Zhang et al, 2018). Along the southern MTJ arm and the FRSC, IAB signatures are most abundant, with boninitic signatures in the central FRSC associated with magmas captured from the volcanic front (Escrig et al, 2012).…”

Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures using Shallow Seismicity

“…Sampling of the MTJ has revealed a diverse suite of lithologies, spanning the compositional range from basalt to andesite to dacite (Nilsson et al, 1989;Falloon et al, 1992;Hawkins, 1995;Langmuir et al, 2006). The NELSC has a mixed geochemical signature of OIB and N-MORB, in addition to subtle arc-like affinities (Keller et al, 2008;Zhang et al, 2018). Along the southern MTJ arm and the FRSC, IAB signatures are most abundant, with boninitic signatures in the central FRSC associated with magmas captured from the volcanic front (Escrig et al, 2012).…”