| Abstrakt: |
During the late Cenozoic, the Pacific plate has been obliquely converging with the Australia plate in South Island, New Zealand. This has resulted in westward obduction of continental crust of the Pacific plate, and consequently, a major mountain range, the Southern Alps, has formed east of the Alpine fault and within the leading edge of the Pacific plate. We have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the Southern Alps, starting at the Alpine fault, to better understand the uplift age and structure of the continental collision. The results show the following: (1) Uplift was underway at 7 Ma in the south at Haast Pass and by 5 Ma in the north at Arthur's Pass. (2) Profiles of the total amount of late Cenozoic uplift show an exponential increase toward the Alpine fault. Adjacent to the Alpine fault there has been 14.5 to 21.5 km of uplift in the vicinity of Haast Pass, 14.5 to 21 km near Mt Cook, and 12.5 to 15.5 km in the Arthur's Pass transect. Adjacent to the Alpine fault in the Mount Cook region the average uplift rate from ∼5.5 Ma to ∼1 Ma was 2.3 to 2.5 mm/yr; between ∼1 Ma and the present it has averaged 6.2 mm/yr. The strongly asymmetric uplift pattern is responsible for the exposure of a 13-25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the Alpine fault known as the Alpine schists. (3) Late Cenozoic uplift of Torlesse greywackes and Alpine schists was preceeded during the Jurassic-early Cretaceous by 5-8 km of uplift. The Otago schist belt to the south was uplifted much more during this interval, and in addition, western parts of the Otago schists were uplifted 5-6 km during the late Cretaceous. (4) The fission track data do not support the notion of significant late Cenozoic shear heating about the Alpine fault, as previously suggested from spatial variations in K-Ar ages of the Otago and Alpine schists. [ABSTRACT FROM AUTHOR] |
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