Metamorphic zones, terranes, and Cenozoic faults in the Marlborough Schist, New Zealand

Abstract

The northeast-striking Picton Fault Zone is a major structural and metamorphic break that divides the Marlborough Schist into two separate blocks. The northwestern (Kaituna) block shows a regular increase in textural and metamorphic grade to the southeast from prehnitepumpellyite to greenschist facies and textural zone I to IV. The southeastern (Arapawa) block shows an irregular increase in grade to the southeast from prehnite-pumpellyite to pumpellyite-actinolite facies and textural zone I to IIB. The Kaituna block is correlated with the Caples and Torlesse Terranes and the Otago Schist of the southern South Island. The Arapawa block is correlated with the Waipapa Terrane (possibly also the Torlesse Terrane) and Kaimanawa Schist of the North Island.Isotects and the Picton Fault Zone are dextrally offset by 10-15 km across the ENE-striking Queen Charlotte Fault Zone. The latter should be included with the late Cenozoic Marlborough faults.

Age/isotopic characterisation of the Waipapa Group in Northland and Auckland, New Zealand, and implications for the status of the Waipapa Terrane

“…The rocks in the western part of this zone are often more altered and sheared, but elsewhere in New Zealand (e.g., in Otago and Marlborough Schists; Adams & Graham 1997;Adams et al 1999), K-Ar ages as young as 130 Ma are normally recorded only in tzIIIB/IV textural zones. The age transition from the Caples-type Omahuta-Puketi block (A) into true Waipapatype, Western Bay of Islands block (B) resembles the situation in eastern Marlborough, where, across the Picton Fault Zone, Haast Schist of Caples protolith passes eastwards into that of postulated Waipapa protolith (Mortimer 1993a). This transition also corresponds to a narrow zone of K-Ar ages, 90-110 Ma, significantly younger than adjacent blocks (>120Ma).…”

“…On the other hand, the Caples Group has a northern extremity in the Marlborough district, South Island, where, as the correlative Pelorus Group, it passes into greenschist facies Haast Schist. In eastern Marlborough, zones of Haast Schist of Waipapa and Caples Terrane parentage have been proposed (Mortimer 1993a;Adams et al 1999) but, because of the complex structural and metamorphic history, the Caples/Waipapa transition or boundary fault, if present, is obscured.…”

Mesozoic mesothermal quartz‐gold‐scheelite lodes, Wakamarina, Marlborough, New Zealand

“…We thus hypothesise that metamorphism in the schist belt continued at depth up to earliest Cretaceous time, when the asymmetric uplift of the Marlborough Schist block brought up the higher grade rocks that structurally lie beneath the lower grade Pelorus/Caples of the Wakamarina area (Mortimer 1993). Uplift and resultant tensional fracturing would have enabled the release of trapped fluids such as those derived from the breakdown of the hydrous mineral phases chlorite and micas during transition to higher grade metamorphic facies at depth.…”

“…It is crosscut by synmetamorphic quartz -albite -pumpellyite -sericite (illite) ± adularia veinlets. Previously described as a "meta-chert" (Mortimer 1993), Wakamarina Quartzite has oxygen isotope values (Table 1) and trace element ratios that are indicative of a sedimentary quartzite (Skinner & Brathwaite 1998). The quartzite shows calc-alkaline geochemical signatures similar to those of the enclosing schists rather than the tholeiitic signatures of the associated metabasites (Skinner & Brathwaite 1994).…”

“…1,2) on the eastern side of the Wakamarina valley (Skinner & Brathwaite 1994, 1995a) as a linear belt <2 km wide, extending northwards for some 70 km (Beck 1964). Numerous post-mineralisation, steep ENE-trending faults of the late Cenozoic Queen Charlotte Fault Zone transect the Wakamarina valley (Johnston 1993;Mortimer 1993), translating into some 15 km of total dextral separation of the Goulter Synform axis (Fig. 2).…”