Interaction of strong lower and weak middle crust during lithospheric extension in western New Zealand

Keith A. Klepeis, Daniel King, Mathew De Paoli, Geoffrey L. Clarke, George E Gehrels

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Article numberTC4017
JournalTectonics
Volume26
Issue number4
DOIs
StatePublished - Aug 2007

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New Zealand
lower crust
crusts
crust
Geochronology
interactions
Garnets
boudinage
unroofing
granulite facies
amphibolite facies
upper crust
geochronology
thinning
shear zone
magmatism
Cooling
garnet
magma
Cretaceous

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Interaction of strong lower and weak middle crust during lithospheric extension in western New Zealand. / Klepeis, Keith A.; King, Daniel; De Paoli, Mathew; Clarke, Geoffrey L.; Gehrels, George E.

In: Tectonics, Vol. 26, No. 4, TC4017, 08.2007.

Research output: Contribution to journalArticle

Klepeis, Keith A. ; King, Daniel ; De Paoli, Mathew ; Clarke, Geoffrey L. ; Gehrels, George E. / Interaction of strong lower and weak middle crust during lithospheric extension in western New Zealand. In: Tectonics. 2007 ; Vol. 26, No. 4.
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