Evidence of Early Cretaceous collisional-style orogenesis in northern Fiordland, New Zealand and its effects on the evolution of the lower crust

• Published in: Journal of structural geology Vol. 23; no. 4; pp. 693 - 713
• Main Authors: Daczko, Nathan R, Klepeis, Keith A, Clarke, Geoffrey L
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2001
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/S0191-8141(00)00130-9

Structural, metamorphic, and kinematic data from a well-exposed section of lower crustal rocks in northern Fiordland, New Zealand, reveal a history of intense contractional deformation and high- P metamorphism at the roots of a convergent orogen. High- P (>14 kbars) granulite facies garnet–clinopyroxene-bearing reaction zones occur adjacent to anorthositic veins within gabbroic and dioritic gneiss. These veins and reaction zones were variably deformed by two phases of high- P granulite facies deformation. Quantitative kinematic analyses, conducted using systems of rotated veins and reaction zones, indicate that the first phase produced steeply dipping shear zones within a sinistral pure-shear-dominated flow regime ( W k =0.69). This deformation occurred at conditions of P=14.0±1.3 kbars and T=676±34°C and resulted in subhorizontal, arc-parallel (NE–SW) stretching and up to 60% subhorizontal shortening in high strain zones of the lower crust at depths >45 km. The second phase of deformation occurred at P=14.1±1.2 kbars and T=674±36°C and produced vertically stacked, gently dipping ductile thrust faults that accommodated arc-normal (NW-directed) displacement. These features reflect major tectonic thickening of the crust, oblique convergence, and high- P metamorphism during the collision of the roots of a convergent orogen, represented by plutons of the Median Tectonic Zone in eastern Fiordland, with the paleo–Pacific margin of Gondwana, represented by western Fiordland. Distinctive kinematic styles suggest that this collision resulted in a partitioning of the arc-parallel (NE–SW) and arc-normal (NW–SE) components of oblique convergence onto sinistral strike-slip and ductile thrust faults, respectively, at lower crustal levels.