Stratigraphy and petrography of some metasediments and associated intrusive rocks from central Fiordland, New Zealand

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Abstract
Some 400 km2 of high grade metasediments and intrusive rocks from central Fiordland are described in detail and petrographic descriptions given for some of the more important lithologies. Doubtful Sound and Western Manapouri Provinces are differentiated on the lithological content of each region and confirm earlier subdivisions proposed by Turner. The boundary between the provinces is tectonic, and complicated by the fact that Doubtful Sound Province is locally thrust faulted over the Western Manapouri Province. Doubtful Sound Province is subdivided into 9 formations. Deep Cove Gneiss is lithologically diverse and predominantly comprises hornblende and biotite gneisses interstratified with lesser amounts of marble and calc-gneiss. Townley Calcsilicate and Stella Psammite are characterised by thin-bedded sequences of calc-gneiss and psammite and differ mainly in respect to the relative proportions of these predominant rock types. Mackenzie Schist consists largely of pelitic and semipelitic schists and contains only minor gneiss. Mount Barber Gneiss also contains appreciable pelitic schist, but is dominated by biotite and hornblende gneisses. The metasediments have been intruded to varying degrees by Mount George Gabbro and granitic Seaforth Orthogneiss. Black Giants Anorthosite, together with the Lyvia Gneiss, an assemblage of thick-bedded hornblende and garnethornblende-biotite gneisses, comprise an alloch-thonous thrust sheet carried into the Doubtful Sound Province after the peak of metamorphism. Western Manapouri Province is subdivided into 4 informal lithological units. Of the 2 metasedimentary units, 1 consists almost entirely of plagioclasebiotite and plagioclase-hornblende-biotite gneisses with minor calc-gneiss and quartzite, whilst the other comprises psammite, minor pelite and quartzofeldspathic gneiss. These metasediments are intruded by hornblende-biotite orthogneiss which is itself intruded by massive, non-foliated leucogranite. All rocks are cut by pegmatite and acid dikerocks and the Western Manapouri Province is best described as an injection complex. Several important differences exist between the 2 provinces. Doubtful Sound Province is predominantly composed of metasediments of miogeosynclinal origin, whereas Western Manapouri Province is composed largely of metasediments of inferred eugeosynclinal provenance (greywacke, etc.). Syntectonic granitoids are common to both regions, but post-tectonic granitoids are only recognised in the Western Manapouri Province; gabbroids and their metamorphosed equivalents are restricted to the Doubtful Sound Province.

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