Geochemistry of dike rocks in Dun Mountain Ophiolite, Nelson, New Zealand

Abstract

Basaltic dikes of the Lee River Group (Permian) at Roding River and in the Red Hills ultramafic body, both parts of the Dun Mountain Ophiolite, were analysed for major and trace elements. The dikes in the Lee River Group change into massive and pillowed lava towards the uppermost part of the sequence. The dikes in the Red Hills occur parallel to the layering of host ultramafic rocks. The Red Hills ultramafic body corresponds to the mantle-crust transition zone. The age of Red Hills dikes has been determined at c. 280 Ma. Hence, the Lee River Group and Red Hills dike complexes are about the same age. There are G96015Received 29 April 1996; accepted 24 September 1996 contrasting differences, however, between major and trace element compositions in those two dike rock groups. Lee River Group basalts show an increase in FeO*/MgO with increase in SiO 2 ; high field strength elements and REE concentrations are higher in the Lee River Group than those in the Red Hills basalts; and eNd values are +7.5 to +8.3, suggesting the source to be depleted mantle. On the other hand, Red Hills basalts do not show an increase in FeO*/ MgO with increase in SiO 2 , and are relatively enriched in large ion lithophile elements such as Ba and Sr, depleted in high field strength elements and REE, and eNd values (+6.2 and +7

Spatial delineation of the depositional footprint of the Motueka River outwelling plume in Tasman Bay, New Zealand

“…It is difficult to explain why the spatial pattern of Sr concentrations shows the opposite trend to that of Ni and Cr given that Sr is also known to be elevated in the Red Hills ultramafic rock (Sano et al 1997). Sr concentrations in sediments collected from near the Motueka River mouth were in fact the lowest of any sites measured in the present study.…”

Reassessment of the origin of the Dun Mountain Ophiolite, New Zealand: Nd‐isotopic and geochemical evolution of magma suites

“…The e Nd (T) values are similar to present-day marginal basin basalts (McCulloch et al 1980;Volpe et al 1987Volpe et al , 1988 (Fig. 2) and basalts from the Lee River Group (£Nd(T) = +7.5 to +8.3 at 280 Ma; Sano et al 1997). The stage 2 basalts have MORB-like Sr/Nd (7-10), Ti/Y (266), Zr/Y (3.2), Ti/Zr (90-100), Hf/Th (c. 12), and Ti/V (c. 30) (cf.…”

“…Moreover, the bulk of the siliceous plagiogranites are not differentiates of the isotopically distinct tholeiitic magmas that produced the ocean island basalt (OIB)-like to MORB-like basaltic lava suites also preserved in the ophiolite (indeed the lavas yield older ages; see below). Sano et al (1997) suggested that the Red Hills ultramafic body farther south in the DMOB, as well as basalt-plagiogranite dikes in the Red Hills complex, probably originated in an island arc related tectonic environment. The ophiolite stratigraphy itself, however, in no way resembles that in a normal arc, with well-defined "point source" volcanic edifices draped by substantial volcaniclastic aprons.…”

Chapter 15 Construction of a Paleozoic–Mesozoic accretionary orogen along the active continental margin of SE Gondwana (South Island, New Zealand): summary and overview

“…Supra-subduction zone ophiolites can form in both 'pre-arc' settings related to subduction initiation (prior to typical calc-alkaline arc magmatism) and also in rifted back-arc settings. Back-arc genesis has been proposed for the Dun Mountain ophiolite (Sano et al 1997;Sivell & McCulloch 2000;Jugum et al 2006) mainly on geochemical grounds. However, there is no evidence of the expected precursor volcanic arc (e.g.…”