Rameka Creek geology : Paleozoic plutonism and structure of the Takaka Terrane


Sarll, Owen, 1974-


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This thesis reports the geology of Rameka Creek, northern Pikikiruna Range, northwest Nelson, part of the Takaka Terrane of the Western Province. The Upper Ordovician, Mount Arthur Marble, exhibits evidence for at least two, approximately coaxial, pre-late Devonian deformational phases. The timing of these deformation events is constrained by the intrusion of the Rameka Gabbro which cross-cuts F2 folds. Orientation of calc-silicate segregations (Fl) within the marble define a NE-SW trending, gently plunging, symmetrical synform with the east limb overturned relative to the west limb. Diopside-tremolite bearing segregation seams within the marble are noted, but due to a limited areal distribution, are not thought to be representative of the marble as a whole. A Paleozoic regional greenschist facies recrystallisation is favoured, with the tremolite-diopside bearing segregation seams being related to a Cretaceous, amphibolite facies thermal overprint associated with adjacent granitoid emplacement. Intruding the Mount Arthur Marble at Rameka Creek are two bodies (eastern and western) of late-Devonian hornblende-plagioclase gabbro. This rock, named the Rameka Gabbro and dated at 367 Ma by earlier workers, has been subdivided into three petrographic types on the basis of amphibole texture and petrology; (1) gabbros with interstitial amphiboles; (2) gabbros with oikocrystic amphiboles; and (3) microgabbros. Microgabbros, which outcrop exclusively in the eastern pluton, exhibit significantly different mineral chemistries compared to other types. Generally, amphibole compositions are characterised by lower Ti and Si contents , while feldspars are more sodic. Pods of Ti-rich garnet up to 1 m in diameter occur within the Rameka Gabbro. Two different types of colour zonation are present within the garnet, both of which are due to variation in Ti concentration. Study of the contact between Rameka Gabbro and Mount Arthur Marble reveals the presence of well-defined, monomineralic zones within the contact. XRF analyses of samples from within the skarn indicate that metasomatic diffusion of components across the gabbro-marble contact has occurred. Previously undocumented, stock-like bodies of granitoid rock have been mapped in the eastern part of the field area. These bodies intrude both the gabbro and marble and hence clearly post-date both units. On the basis of geographic and broad geochemical similarities, these rocks are correlated with the Caanan Granodiorite, part of the Cretaceous Separation Point batholith. Some stocks of granitoid have associated mineralised, hydrothermal quartz veins.

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


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POLYGON ((172.899711475006455 -40.939966285901228,172.962260504843499 -40.939527030575661,172.960664041409359 -40.981475234818269,172.928561664796234 -41.00195737752037,172.899617958736144 -41.001697463325236,172.899711475006455 -40.939966285901228))





Sarll, Owen, 1974-, “Rameka Creek geology : Paleozoic plutonism and structure of the Takaka Terrane,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/327.

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