Emplacement, metamorphism, deformation and affiliation of mid-Cretaceous orthogneiss from the Paparoa Metamorphic Core Complex lower-plate, Charleston, New Zealand

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon dating and whole-rock geochemistry of plutonic rocks from coastal exposures of the Paparoa Metamorphic Core Complex (PMCC) lower-plate has revealed their suite affinity and magmatic and metamorphic ages. Emplacement and metamorphism of the Charleston Orthogneiss occurred at 118 + 2 Ma and 107 ±2 Ma, respectively. Metamorphism of the Charleston Orthogneiss was coeval with Buckland Granite intrusion, suggesting a link between the two. Field relations between the post-metamorphic Doctor Bay dike (DBD) and Charleston Orthogneiss indicate intrusion of the dike at 105 ±2 Ma was syn-tectonic. Deformation of the Charleston Orthogneiss occurred during mid-crustal continental extension and PMCC formation in the New Zealand region of the Pacific Gondwana margin. Fabric development in the Charleston Orthogneiss may therefore be related to mid-crustal deformation associated with extension. The Charleston Orthogneiss and DBD are assigned to the I-/ S-type Rahu Suite on the basis of their geochemistry, mid-Cretaceous ages, inherited zircon populations and inboard location. © 2011 The Royal Society of New Zealand.