Nephrite and metagabbro in the Haast Schist at Muddy Creek, northwest Otago, New Zealand

Abstract

At Muddy Creek, northwest Otago, a pod of gabbro, probably in a matrix of serpentinite, was tectonically emplaced into quartzofeldspathic sediments before the main metamorphism of the Haast Schist. Metasomatic diffusion during pumpellyite actinolite to greenschist facies metamorphism produced talc-, tremolite-, chlorite-, and muscovite-rich reaction zones at the margin of the pod. Subsequent shearing disrupted the metasomatic sequence and produced nephrite from the tremolite zone precursor.Relict magmatic hornblende and clinopyroxene from the metagabbro have compositions appropriate to a volcanic arc tectonic setting. In contrast, relict pyroxenes from four metabasaltic knockers in the Greenstone Melange have compositions indicating generation of magmas in both ocean-floor and ocean-island environments. Ultramafic and mafic rocks at Muddy Creek and in the Greenstone Melange are thought to represent fragments of the ophiolitic basement to the Haast Schist, the tectonic settings of which help constrain models for the evolution of the Rangitata Orogen.

Age determination of nephrite by in-situ SIMS U–Pb dating syngenetic titanite: A case study of the nephrite deposit from Luanchuan, Henan, China

“…Titanite is also very common in many nephrite deposits (Cooper, 1995;Ling, 2012;Liu et al, 2010;Lu, 2005;Qin, 2013;Simandl et al, 1999;Tao, 1992). Recent studies demonstrated that titanite U-Pb age determination using modern microbeam techniques (SIMS and LA-ICPMS) has great potential to provide robust constraints on the timing of highto intermediate-grade metamorphism (Li et al, 2014;Rasmussen et al, 2013;Sun et al, 2012).…”

Geochemistry and petrology of nephrite from Alamas, Xinjiang, NW China

“…Yui and Kwon (2002) reached similar conclusions according to isotopic studies. Recently, a few nephrite deposits have been documented petrologically, geochemically and isotopically (Coleman, 1966;Leaming, 1978;Tan et al, 1978;Prokhor, 1991;Cooper, 1995;Wenner, 1979;Yui et al, 1988;Yui and Kwon, 2002;Liu et al, 2010). However, most of these studies failed to provide detailed petrographic observations and geochemical data, leading to limited understanding of how dolomite-related nephrite deposits were formed.…”

Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade)

“…Composed predominantly of metamorphic mineral amphibole (tremolite-actinolite varieties) in a felted, fibrous texture, it forms very hard and highly distinctive green rocks. It has formed by metasomatic reactions between ultramafic and silica-rich basement rocks during regional metamorphism (Coleman 1966;Cooper 1976Cooper , 1995Johnston 1983), and small amounts have been found in relatively rare in situ (non-transported/in place) 'reef' outcrops mostly within, or along the margins of, ultramafic rock occurrences. Such outcrops have also been scattered by fluvial erosion so that, more commonly, pounamu is found as cobbles and pebbles in transported river (alluvial) and glacial outwash deposits, or in the active bedload of streams and rivers.…”