Thermochronology of northern Murihiku Terrane, New Zealand, derived from apatite FT analysis

Citation
Pjj. Kamp et Ij. Liddell, Thermochronology of northern Murihiku Terrane, New Zealand, derived from apatite FT analysis, J GEOL SOC, 157, 2000, pp. 345-354
Citations number
45
Categorie Soggetti
Earth Sciences
Journal title
JOURNAL OF THE GEOLOGICAL SOCIETY
ISSN journal
00167649 → ACNP
Volume
157
Year of publication
2000
Part
2
Pages
345 - 354
Database
ISI
SICI code
0016-7649(200003)157:<345:TONMTN>2.0.ZU;2-I
Abstract
Murihiku Terrane is the least deformed of a series of tectonostratigraphic terranes that have been amalgamated to form the basement underlying New Zea land. Apatite fission-track (FT) thermochronology has been applied to the y oungest beds (Late Jurassic, Hettangian-Tithonian Stages) of this terrane, located at Port Waikato in western North Island, which are broadly folded. The apatite FT ages are partially annealed, are younger than their stratigr aphic ages, and remarkably, decrease in age upsection. Interpretation and m odelling of the maximum palaeotemperatures experienced by the sample horizo ns and the timing of cooling requires a wedge of Cretaceous sedimentary roc ks to have accumulated within the axis of the major fold (Kawhia Syncline). Deposition of Murihiku Terrane sequences continued therefore into the Cret aceous and probably until c. 100 Ma. Deposition may have ended as late as 8 5 +/- 10 Ma, when cooling via denudation started. The upper parts of the fo rmer succession probably accumulated during folding. In addition, interpret ation of the FT data require a marked increase in palaeogeothermal gradient from a subnormal value of 15 degrees C km(-1) during the Late Jurassic, up to c. 30 degrees C km(-1) at 85 +/- 10 Ma. This is attributed to the termi nation of subduction along the Pacific margin of Gondwanaland, and a transi tion to a rift-transform tectonic setting in western New Zealand during Tas man Sea spreading. The latest Cretaceous-Palaeocene eastward tilting of the Murihiku basement at Port Waikato may have been accommodated on the Tarana ki Fault or another coast-parallel fault; the Waikato Fault probably acted as a transfer fault at that time accumulating a significant amount of throw .