Provenance history of a Late Triassic‐Jurassic Gondwana margin forearc basin, Murihiku Terrane, North Island, New Zealand: Petrographic and geochemical constraints

Abstract

The Murihiku Terrane in the North Island was a forearc basin adjacent to a volcanic arc along the eastern margin of Gondwana during the Mesozoic. The rocks that infill the basin are mainly volcaniclastic sandstones and mudstones, often turbiditic, with sparse shellbeds, rhyolitic tuffs, carbonaceous sandstones, plant beds, concretionary horizons, and rare thick granitoid-rich conglomerates. Petrographic studies of the rock fragments in the sandstones show that andesites are the dominant lithic type, but there is a wide range of other lithologies, including dacites, rhyolites, ignimbrites, granitoids, quartzofeldspathic mica schists, rare amphibolites, and reworked mudstones and sandstones. The sandstones are texturally and mineralogically immature and suggest deposition relatively close to a source of high relief, undergoing physical rather than chemical weathering in cool-to cold-temperate conditions. Geochemical analyses of 67 whole-rock volcaniclastic sandstones and siltstones indicate that they were derived from an active and dissected volcanic arc in a convergent margin setting built upon relatively thin continental crust. Modal petrographic data and whole-rock geochemistry both confirm that there were systematic variations with time in the composition of clastic material being supplied to the basin. From the Late Triassic to Middle Jurassic, there was a decrease in silicic volcanic material, plutonics, and metamorphics, and an increase in the supply of andesitic detritus. This was followed in the Late Jurassic by a broader range of volcanic detritus, varying from basaltic andesite to rhyolite, which may have been caused by progressive extension of the volcanic arc and thinning of the crust, a precursor to the breakup of Gondwana in the Early-Middle Cretaceous. Comparison with the Southland segment of the Murihiku Terrane in the South Island suggests that there were significant along-arc source variations, with relatively less silicic but greater andesitic and continental crust contributions in the North Island than in Southland. This may be analogous to the modern Taupo-Kermadec arc where there is a south-north along-arc transition from a continental to an oceanic arc.

Correlation of basement rocks from Waka Nui‐1 and Awhitu‐1, and the Jurassic regional geology of Zealandia

“…However, anhydrous 100 wt% normalised analyses match the petrography of an andesitic volcaniclastic sandstone and also lie within the field of early-Middle Jurassic sandstones from the Murihiku Terrane (Fig. 5a) (Briggs et al 2004). …”

“…The apparent absence of Wanaea species suggests an age younger than the ohineruru Formation (Heterian) of the kirikiri Group. Briggs et al (2004) showed that the Late Jurassic sandstones of the Huriwai and apotu Groups (Fig. 4) comprise silicarich and silica-poor facies that are different in composition from the early-Middle Jurassic sandstones (Fig.…”

Post-remagnetisation vertical axis rotation and tilting of the Murihiku Terrane (North Island, New Zealand)

“…Petrographic and geochemical studies of Murihiku Terrane samples show that they derived from direct volcanic eruptive materials and mainly from erosion of a volcanic arc terrane (Roser et al 2002;Briggs et al 2004). The sediments and tuff accumulated within a forearc basin probably underlain by oceanic crust (Spörli 1987;Aita and Spörli 1992).…”

“…This terrane has long been regarded as a Triassic-Jurassic forearc basin based on its simple structure, its well-bedded and fossil-rich character and its volcanic arc provenance (Briggs et al 2004).…”

Mangarara Formation: Exhumed remnants of a middle Miocene, temperate carbonate, submarine channel‐fan system on the eastern margin of Taranaki Basin, New Zealand

“…Most of this fill is offshore in the subsurface, but an exhumed window of the Neogene succession is exposed onland in eastern Taranaki Peninsula and the king Country region ( vi s e dAJ V, 23J ul y2007) ka mp et al 2004). Basement rocks are Paleozoic and Mesozoic granite and schist west of Taranaki Fault and Triassic-Jurassic sandstone and mudstone, typically greywacke and argillite, east of it (Mortimer 1995;Briggs et al 2004).…”