Geology of the southern part of the Longwood complex, Southland coast and Centre Island, New Zealand

[摘要] This thesis combines the results of field work, petrographic studies and mineralogical and geochemical data from plutonic rocks of the southern part of the Longwood Complex, Southland, New Zealand.Data presented here are consistent with the Longwood Complex, part of the Brook Street Terrane, representing the remnants of the root of a volcanic arc active during Permian to Mesozoic times.The Pahia Intrusives comprise a wide range of rock types ranging from peridotite, gabbro, norite to pyroxene diorites. Primary igneous layering and mineral layering is evident, although the internal structure of the Pahia Intrusives thoughout the area is not known. Disruption of layering is common and mingling and mixing of felsic and mafic magmas is also evident. Rock compositions are compatible with cumulate formation and fractional crystallisation from a high-AI calc-alkaline to tholeiitic parent. Two-pyroxene geothermometry suggest temperatures of crystallisation between 850°C and 1030°C.The Pahia Intrusives are intruded by a series of similar but petrographically and geochemically distinct granitoid bodies, the Boat Harbour Diorite at Pahia, the Austin Quartz Monzodiorite at Wakaputa and the Oraka Diorite at Oraka. Intrusive relationships are frequently complex, a consequence of magma mixing and mingling, wall rock interaction and multiple injection of magma. Geochemical trends are consistent with crystal fractionation from a similar or related magma from which the Pahia Intrusives are derived. Enclaves occur in the granitoid rocks. The igneous textured xenoliths are indicative of mixing and mingling. Foliated xenoliths are orientated NNW-SSE in the Austin Quartz Monzodiorite which also reflects the orientation of basaltic and hornblende microdiorite dykes in the granitoid rocks. The possibility exists that the core of the Austin Quartz Monzodiorite and other granitoid rocks may be centred in the Longwood Range, north of the study area and that the quartz monzodiorite may represent a

[发布机构] University of Otago