Geology of Conical Peak and surrounding area, Kakanui Mountains, North Otago

Martin, Gregory Mark, 1977-

Metagreywackes, argillites and a 1 00 m thick sequence of pure and impure marbles, hematitic and chloritic slates, shales and metacherts is described from an area near Conical Peak in the Kakanui Mountains, North Otago, within the Torlesse Terrane. The area extends from the Horse Range, north 9 km and from Mount Miserable, west 12 km Bands of marble, laterally continuous for up to 1 00 m, contain microscopic clasts of metavolcanics and detrital quartz in a groundmass of recrystallised calcite. Cherts are mostly recrystallised to fine quartzites. The red and green slates contain occasional recognisable volcanic sand grains leading to these beds being interpreted as metamorphosed volcaniclastic beds. Bedding indicators, where present, are subparallel to the plane of cleavage development. No facing directions are recognised. Sandstones have been metamorphosed to pumpellyite-bearing assemblages. Textural reconstitution is textural zone Ila, so the rocks can be regarded as a component of the Haast Schist. The calcareous and metavolcanic sediments are interpreted as turbidites, or debris flows sourced from a topographic high, probably a seamount. Conodont elements extracted from the marble are of late Paleozoic (probably Carboniferous) age. Similarities in content and age with the Kakahu Terrane in . Canterbury may indicate the Conical Peak marble and metavolcanic sequence may be another fragment of the Kakahu Terrane. Associated quartzofeldspathic metagreywackes and argillites are of continental provenance and have undergone pumpellyite-actinolite metamorphism to a peak of about 300°C and 3-4 kbar. Faulting through the Conical Peak area has occurred in two main phases. During Cretaceous time, northwest striking normal faults with associated northeast striking strike-slip faults offset sections of the Conical Peak marble sequence and surrounding greywacke and argillite. During Miocene time . motion on the northwest striking faults were reversed with uplift taking place on the northeastern sides. Folding as well as faulting associated with compressive Miocene tectonics has resulted in the uplift of the Horse Range along the southwest boundary of the Conical Peak area. Associated with ·folding in the Horse Range is a zone of pumpellyite-actinolite schist striking along the axis of the main Horse Range and flanked by slightly lower grade pumpellyite bearing assemblages to the northeast and southwest. Mount Miserable is composed of pumpellyite-actinolite schist, which is uplifted along a northwest striking reverse fault, relative to lower grade pumpellyite bearing schist to the southwest.

97 leaves : ill. (some col.), 2 folded maps ; 30 cm.

1999Martin

POLYGON ((170.589318331000072 -45.282807519999949,170.5854013820001 -45.282709620999981,170.580818943000054 -45.282593476999978,170.573325050000108 -45.29566351699998,170.53021357700004 -45.294275978999963,170.504651573000046 -45.247477366999931,170.504999735000069 -45.244748063999964,170.505937471000038 -45.237422094999943,170.536046020000072 -45.213865655999939,170.583484315000078 -45.215264849999983,170.606053553000038 -45.240119331999949,170.622426602000019 -45.258133569999984,170.631611411000108 -45.258565412999985,170.650767107000092 -45.259460507999961,170.650422814000081 -45.261785055999951,170.65000004400008 -45.264639130999967,170.628079809000042 -45.283793511999932,170.589318331000072 -45.282807519999949))