Age and isotopic characterisation of geological terranes in Marlborough Schist, Nelson/Marlborough, New Zealand

K-Ar and Rb-Sr ages of Marlborough Schist and Pelorus Group metasediments show coherent regional metamorphic/cooling age patterns, irrespective of their terrane protolith, in which ages are primarily inversely related to metamorphic grade and, more locally, with distance from the Picton Fault Zone. The oldest ages, from the lowest grade (prehnite-pumpellyite facies, textural grade I/IIA) Pelorus Group are mainly in the range 175-200 Ma, indicating regional metamorphism occurred at least in earliest Jurassic or latest Triassic times. Progressive cooling of Marlborough Schist resulted in a spectrum of cooling ages, mainly 110-180 Ma, which reflects slow regional uplift during the Jurassic and Early Cretaceous. Some disruption of this pattern occurred at the Picton Fault Zone where post-Early Cretaceous movement has juxtaposed high and low structural levels. Initial Sr-87/Sr-86 isotopic ratios (i) at the time of metamorphism (t), derived from Rb-Sr whole-rock isochron data, further characterise terrane protoliths identified by field, petrographic, and geochemical evidence. The (t)-(i) data largely confirm these prior regional groupings but do not entirely Confirm the terrane identifications. A less radiogenic group, (i) < 0.7055, termed Western Marlborough Schist, comprises the Pelorus Group, and schist equivalents, west of a postulated suture/terrane boundary in the schists, and is correlated with Caples Terrane rocks in Otago. "Torlesse"-type schists are more radiogenic, (i) > 0.7062, but do not match Torlesse (Rakaia) Terrane (t)-(i) data from Wellington or Otago. They correlate better with Kaimanawa Schist of the central North Island. An intermediate group, (i) = 0.7042-0.7062, is separate from the "Torlesse" group, but partly overlaps the Caples Terrane group. This correlates well with Waipapa Terrane of the central North Island and Haast Schist of uncertain terrane affinity in Otago. The combined radiogenic and intermediate groups, termed Eastern Marlborough Schist, define a lineage which thus includes Kaimanawa Schist, Pahau Subterrane rocks, and both Waipapa-type and Torlesse-type schists in Marlborough. It is possible that the Moonlight Fault Zone of Otago has a continuation in Eastern Marlborough Schist as the Picton Fault Zone.