New Age and Geochemical Data from the Southern Colville and Kermadec Ridges, SW Pacific: Insights into the recent geological history and petrogenesis of the Proto-Kermadec (Vitiaz) Arc

摘要

The intra-oceanic Kermadec arc system extends -1300 km between New Zealand and Fiji and comprises at least 30 arc front volcanoes, the Havre Trough back-arc and the remnant Colville and Kermadec Ridges. To date, most research has focussed on the Kermadec arc front volcanoes leaving the Colville and Kermadec Ridges virtually unexplored. Here, we present seven Ar-40/Ar-39 ages together with a comprehensive major and trace element and Sr-, Nd-, and Pb-isotope dataset from the Colville and Kermadec Ridges to better understand the evolution, petrogenesis and splitting of the former proto-Kermadec (Vitiaz) Arc to form these two remnant arc ridges. Our Ar-40/Ar-39 ages range from similar to 7.5-2.6 Ma, which suggests that arc volcanism at the Colville Ridge occurred continuously and longer than previously thought. Recovered Colville and Kermadec Ridge lavas range from matic picro-basalts (MgO = similar to 8 wt%) to dacites. The lavas have arc-type normalised incompatible element patterns and Sr and Pb isotopic compositions intermediate between Pacific MORB and subducted lithosphere (including sediments, altered oceanic crust and serpentinised uppermost mantle). Geochemically diverse lavas, including ocean island basalt-like and potassic lavas with high Ce/Yb, Th/Zr, intermediate Pb-206/Pb-204 and low Nd-143/Nd-144 ratios were recovered from the Oligocene South Fiji Basin (and Eocene Three Kings Ridge) located west of the Colville Ridge. If largely trench-perpendicular mantle flow was operating during the Miocene, this geochemical heterogeneity was likely preserved in the Colville and Kermadec sub arc mantle. Between 4.41 +/- 035 and 3.40 +/- 0.24 Ma some Kermadec Ridge lavas record a shift from Colville Ridge- to Kermadec arc front-like, suggesting the proto-Kermadec (Vitiaz-) arc split post 4.41 +/- 0.35 Ma. The Colville and Kermadec Ridge data therefore place new constraints on the regional tectonic evolution and highlight the complex interplay between pre-existing mantl