Premium
Three‐stage evolution of lower crustal gneiss domes at Breaksea Entrance, Fiordland, New Zealand
Author(s) -
Betka Paul M.,
Klepeis Keith A.
Publication year - 2013
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1002/tect.20068
Subject(s) - geology , metamorphism , shear zone , crust , geochemistry , gneiss , continental crust , petrology , mafic , lineation , metamorphic core complex , magmatism , continental arc , diapir , tectonics , metamorphic rock , seismology , extensional definition
New structural analyses reveal the presence of several kilometer‐scale gneiss domes and many subdomes within an exhumed section of Cretaceous lower crust in SW Fiordland. The domes are defined by complex, nearly concentric trajectories of foliations and steep high‐strain zones in migmatitic, granulite, and eclogite facies orthogneiss. Structural patterns combined with evidence of deformation that was synchronous with partial melting and high‐grade metamorphism, steep mineral lineation orientations, sense of shear indicators, and near‐isothermal decompression suggest that buoyancy‐driven diapiric flow of hot, partially molten crust aided initial dome formation. Mafic‐intermediate magmatism appears to have enhanced this process. Superimposed on all high‐grade structures are upper amphibolite facies shear zones that record a change in the style and conditions of lower crustal flow. Lineation orientations, sense of shear, evidence of cooling with decompression, and other patterns suggest that the retrograde shear zones record bulk horizontal flow and crustal thinning driven by regional tectonic forces. A preferred sequence begins with the initial emplacement of mafic‐intermediate magma into the lower crust at depths up to 70 km (D 1 ). Diapirism and initial dome formation occurred during a period of waning arc magmatism and episodic partial melting and high‐grade metamorphism (D 2 ). Following melt crystallization, dominantly horizontal flow of a cooler, strain‐hardened lower crust occurred during Late Cretaceous continental extension (D 3 ). This example highlights the interplay between mechanisms of horizontal and vertical flow at the root of a continental arc and illustrates their roles in the formation of gneiss domes.