Drumduan Group of East Nelson, New Zealand: Plant-bearing Jurassic arc rocks metamorphosed during terrane interaction

Abstract

The Drumduan Group, consisting of the Marybank and Botanical Hill formations, forms a fault-bounded block northeast of Nelson City, and comprises bedded pyroclastic and epiclastic (including sedimentary) debris of probable terrestrial deposition. Lawsonite is widespread, but not uniformly present. Plant macrofossils, including Mataia podocarpoides, Rissikia talbragarensis, Taenioptens thamsor/lana, T sp. cf. T crassinervis, Cladophlebis sp. and Podozamites sp., in the Marybank Formation indicate aJ urassic age. The group is separated from the Brook Street Volcanics (Permian) by the Delaware Fault Zone, along which arc slivers of Wakapuaka Phyllonite (pumpellyite-actinolite facies). In the west the group shows widespread hydrothermal alteration related to the adjacent Tasman Intrusives, but the Brook Street rocks arc not similarly altered and are not metamorphosed beyond prehnite-pumpellyite facies. We infer that during the Rangitata Orogeny the Drumduan Group, the Tasman Intrusives, and the underlying basement rocks, including the Pepin Group, were underthrust below the Brook Street Volcanics along the Delaware Fault Zone. The resulting depth of burial and confining nature of the overthrust plate on one side, and the Tasman Intrusives on the other, were responsible for the development of metamorphic rocks characterised by a relatively high PIT ratio and by the crystallisation oflawsonite, locally in abundance. Fluid pressures were probably nowhere greater than lithostatic pressure. The Delaware Fault Zone appears to form a major suture between the rocks of cast and west Nelson. The Drumduan Group, the Tasman Intrusives, and the Pepin Group arc assigned to the Tuhua Orogen.

Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks

“…However, occurrences of fossils, usually acritarch and/or plant debris, have been reported in metamorphic rocks of various ages and metamorphic facies: greenschist facies conditions (e.g., Kidder and Awramik, 1990;Knoll, 1992;Molyneux, 1998;Kempe et al, 2005), amphibolite facies 0016-7037/$ -see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2010.06.011 (e.g., Franz et al, 1991;Pestal et al, 1999;Hanel et al, 1999;Squire et al, 2006;Zang, 2007), or blueschist facies (e.g., Johnston et al, 1987;Bernard et al, 2007). Altogether, these studies have shown that even high-grade metamorphic rocks may retain morphologically and geochemically recognizable traces of life (e.g., Bernard et al, 2007;Schiffbauer et al, 2007).…”

Relationships between the brook street Terrane and Median Tectonic Zone (Median Batholith): Evidence from Jurassic conglomerates

“…The two most likely sources of these clasts which are exposed in New Zealand today are the Permian Brook Street Terrane or the Jurassic Drumduan Group of the MTZ (Johnston et al 1987). Cipriano (1986) demonstrated significant differences in the petrography and geochemistry of Drumduan and Brook Street basalts.…”

“…P, Parapara Peak (Permian); K, T, location of Kirwans Dolerite (Jurassic) and Topfer Formation (Triassic); PT, location of Pourakino Trondhjemite. LB is Loch Burn Formation (Kimbrough et al 1994) and DD is Drumduan Terrace (Johnston et al 1987). …”

Age and provenance of granitoid clasts in Moeatoa Conglomerate, Kawhia Syncline, New Zealand

“…8). The Brook Street arc abuts the east side of the Median Tectonic Line and consists mainly of mafic volcanics of Permian and Jurassic age (Coombs et al 1976;Johnston et al 1987) but contains calc-alkaline granitic intrusives (Tasman and Mackay Intrusives and those of the Longwoods-Foveaux Strait area) with isotopic ages scattered within the range 250 to 130 Ma (Devereux et al, 1968;Williams and Harper, 1978). In particular, two biotite-hornblende granitoids from Foveaux Strait area have K-Ar biotite ages (214-217 Ma) and hornblende ages of 222 Ma (Devereux et al, 1968, recalculated using the constants of Steiger and Jliger, 1977) which overlap with the age of the Moeatoa dasts.…”