Abrupt spatial and geochemical changes in lamprophyre magmatism related to Gondwana fragmentation prior, during and after opening of the Tasman Sea

作者：van der Meer Quinten H A^*; Storey Michael; Scott James M; Waight Tod E

来源：Gondwana Research, 2016, 36: 142-156.

DOI：10.1016/j.gr.2016.04.004

• New Zealand
• Gondwana break-up
• Lamprophyre dike swarms
• Ar-40/Ar-39 geochronology
• Continental deformation

High-precision Ar-40/Ar-39 dating of lamprophyre dike swarms in the Western Province of New Zealand reveals that these dikes were emplaced into continental crust prior to, during and after opening of the Tasman Sea between Australia and New Zealand. Dike ages form distinct clusters concentrated in different areas. The oldest magmatism, 102-100 Ma, is concentrated in the South Westland region that represents the furthest inboard portion of New Zealand in a Gondwana setting. A later pulse of magmatism from -92 Ma to -84 Ma, concentrated in North Westland, ended when the first oceanic crust formed at the inception of opening of the Tasman Sea. Magmatic quiescence followed until -72-68 Ma, when another swarm of dikes was emplaced. The composition of the dikes reveals a dramatic change in primary melt sources while continental extension and lithospheric thinning were ongoing. The 102-100 Ma South Westland dikes represent the last mafic talc-alkaline magmatism associated with a long-lived history of the area as Gondwana's active margin. The 92-84 Ma North and 72-68 Ma Central Westland dike swarms on the other hand have strongly alkaline compositions interpreted as melts from an intraplate source. These dikes represent the oldest Western Province representatives of alkaline magmatism in the greater New Zealand region that peaked in activity during the Cenozoic and has remained active up to the present day. Cretaceous alkaline dikes were emplaced parallel to predicted normal faults associated with dextral shear along the Alpine Fault. Furthermore, they temporally correspond to polyphase Cretaceous metamorphism of the once distal Alpine Schist. Dike emplacement and distal metamorphism could have been linked by a precursor to the Alpine Fault Dike emplacement in the Western Province coupled to metamorphism of the Alpine Schist at 72-68 Ma indicates a period of possible reactivation of this proto Alpine Fault before it served as a zone of weakness during the opening of the oceanic Emerald Basin (at similar to 45 Ma) and eventually the formation of the present-day plate boundary (similar to 25 Ma-recent).

• 出版日期2016-8