Age and provenance of basement rocks of the Chatham Islands: an outpost of Zealandia

Rb-Sr metamorphic and U-Pb detrital zircon ages are reported for basement metasediments and cover sand-stones of the Chatham Islands. Rb-Sr metamorphic ages of the Chatham Schist are 180-198 Ma (Early Jurassic), with initial Sr-87/Sr-86 ratios 0.7075-0.7091, grouping this distinctively with Torlesse Supergroup of the Eastern Province of New Zealand. These ages impose an Early Jurassic minimum age for the sedimentary protoliths. Detrital zircons from two Chatham Schist metagreywackes have principal age peaks in the interval Late Triassic to Late Permian, and the youngest, 230-250 Ma, suggest maximum early Late Triassic to early Early Triassic ages for sedimentation. The patterns of minor, but significant, Paleozoic components and scattered Precambrian ages in these greywackes resemble those of Permian Torlesse Supergroup greywackes, but that in a greywacke from the Forty Fours islets is closer to possible latest Permian Caples Group greywackes in Otago. A Cretaceous cover sandstone from Pitt Island has a detrital zircon age pattern dominated by several Albian, 101-119 Ma, age components, reflecting contemporary volcanism, with a minor older component resembling that from a Chatham Schist source.