Geology of the Maerewhenua area, ranges west of the Maerewhenua area, or, "Wie lerne ich English in einem Jahr"

Grafe, Friedemann, 1971-

The geological mapping of the Maerewhenua area had to deal with basement rocks, an assemblage of Cretaceous-Tertiary cover rocks and a thin strata of Quaternary cover rocks. The relationships between mapped rock units bear already a lot of information about the geological history. Two unconformities and one transitional disconformity were found, and referred to two major deformation events in the geological record: 1) The Rangitata Orogeny, and 2) The Kaikura Orogeny. Furthermore, a marine transgression occurred due to subsidence starting in the early Paleocene. Polyphase deformation of schist was investigated using mesoscopic structures. The results are mostly compatible to previous work at Danseys Pass. The deformation history is characterised by at least 3 to 4 different phases. Deformation occurred under ductile conditions as well as under brittle conditions. After mostly ductile deformation during the Rangitata Orogeny, peneplanation occurred that resulted in a schist peneplain having locally significant relief. Continuos subsidence in the Eocene to Miocene caused several marine transgressions. Glauconitic sand, silt and limestone were deposited in mostly shallow marine environment. In the Oligocene tholeiitic sills intruded unconsolidated sedimentary strata. Transpression during the Kaikura Orogeny results in brittle deformation of the schist, associated basement rocks and overlying strata since the beginning of the Pliocene. Strain-estimations for the ductile deformation of the basement rocks during the Rangitata Orogeny were derived from investigation of conglomeratic schist using the Rf/<)>-Method. "Pan-cake"-like deformed quartzofeldspathic clasts were shortened about 67% along the Z-axis. In comparison with previous work NORRIS & BISHOP (1990) such value implies schist close to the boundary of TZ 2B I TZ 3A. Sampling of basement rocks and petrographical work suggest subhorizontal isograds. No significant change in metamorphic grade was revealed over more than 6 km distance. The basement rocks of Maerewhenua area is exposed in Pumpellyite-Actinolite fades. A theoretical model was given to explain vertically foliation, vertical plunging, isoclinally folded bedding and subhorizontal isograds. Similar to findings by WARD & SPORLI (1979) rotation of bedding could not have been avoid. Rotation of large blocks might still be a problem.

116 leaves : ill. (some col.), maps (some col.) ; 30 cm.

1996Grafe

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