TY - JOUR
T1 - Interaction of strong lower and weak middle crust during lithospheric extension in western New Zealand
AU - Klepeis, Keith A.
AU - King, Daniel
AU - De Paoli, Mathew
AU - Clarke, Geoffrey L.
AU - Gehrels, Georges
PY - 2007/8
Y1 - 2007/8
N2 - Exhumed sections of the middle and lower crust in western New Zealand reveal how deformation was partitioned within a thermally and rheologically evolving crustal column during Cretaceous continental extension. Structural data, P-T determinations, and U-Pb geochronology from central Fiordland and the Paparoa Range in Westland show that extension initiated in the lower crust by ∼ 114 Ma as a period of arc-related magmatism waned. Initially, deformation was localized into areas that were weakened by heat and magma. However, these hot, weak zones were ephemeral. During the perio 114-111 Ma, lower crustal fabrics record a rapid progression from magmatic flow to high-temperature deformation at the garnet-granulite facies (T > 700°C, P = 12 kbar) to cooler deformation at the upper amphibolite facies (T = 550-650°C, P = 7-9 kbar). Lower crustal cooling and compositional contrusts between mafic granulites and hydrous metasedimentary material resulted in a middle crust that was weak relative to the lower crust. Between circa 111 and circa 90 Ma, focused subhorizontal flow and vertical thinning in a weak middle crust led to the collapse of the upper crust and the unroofing of midcrustal material. During this period, arrays of conjugate-style shear zones transferred displacements vertically and horizontally through the crust, resulting in a structural style that resembles crustal-scale boudinage. The New Zealand example of continental extension shows that a weak middle crust and a relatively cool, highly viscous lower crust can result in a localized style of extension, including the formation of metamorphic core complexes that exhume the middle crust but not the lower crust.
AB - Exhumed sections of the middle and lower crust in western New Zealand reveal how deformation was partitioned within a thermally and rheologically evolving crustal column during Cretaceous continental extension. Structural data, P-T determinations, and U-Pb geochronology from central Fiordland and the Paparoa Range in Westland show that extension initiated in the lower crust by ∼ 114 Ma as a period of arc-related magmatism waned. Initially, deformation was localized into areas that were weakened by heat and magma. However, these hot, weak zones were ephemeral. During the perio 114-111 Ma, lower crustal fabrics record a rapid progression from magmatic flow to high-temperature deformation at the garnet-granulite facies (T > 700°C, P = 12 kbar) to cooler deformation at the upper amphibolite facies (T = 550-650°C, P = 7-9 kbar). Lower crustal cooling and compositional contrusts between mafic granulites and hydrous metasedimentary material resulted in a middle crust that was weak relative to the lower crust. Between circa 111 and circa 90 Ma, focused subhorizontal flow and vertical thinning in a weak middle crust led to the collapse of the upper crust and the unroofing of midcrustal material. During this period, arrays of conjugate-style shear zones transferred displacements vertically and horizontally through the crust, resulting in a structural style that resembles crustal-scale boudinage. The New Zealand example of continental extension shows that a weak middle crust and a relatively cool, highly viscous lower crust can result in a localized style of extension, including the formation of metamorphic core complexes that exhume the middle crust but not the lower crust.
UR - http://www.scopus.com/inward/record.url?scp=36249012613&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=36249012613&partnerID=8YFLogxK
U2 - 10.1029/2006TC002003
DO - 10.1029/2006TC002003
M3 - Article
AN - SCOPUS:36249012613
SN - 0278-7407
VL - 26
JO - Tectonics
JF - Tectonics
IS - 4
M1 - TC4017
ER -