The petrology and geochemistry of intrusions at selected nunataks in the Ahlmannryggen and Giaeverryggen, western Dronning Maud Land, Antarctica.

• Main Author: Krynauw, Johannes Reynhardt.
• Other Authors: Hunter, Donald Raymond., Wilson, Allan H.
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Geology; Stratigraphic > Precambrian; Theses > Geology; Ahlmannryggen; Annandagstoppane; Borgmassivet; Dronning Maud Land; Forstefjell; Juletoppane; Krylen; Ritscherflya; Robertskollen; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10413/11570

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986. The mid-Proterozoic Borgmassivet intrusions of western Dronning Maud Land intrude Archaean granites and a volcano-sedimentary sequence, the Ritscherflya Supergroup. They are SiO2-rich ultramafic to mafic tholeiitic rocks which occur as layered bodies of unknown dimensions and sills up to 400 m thick. This thesis records detailed field, petrographic and whole rock geochemical studies on Borgmassivet intrusions at three widely-spaced localities within an area of approximately 20 000 km in the Ahlmannryggen and Giaeverryggen. Annandagstoppane-Juletoppane-Forstefjell area: The Annandagstoppane intrusions form part of a layered body or bodies, of which only a small part is exposed. They consist of a medium-grained 'main suite ' of gabbronorites and minor anorthosites, and a Iyounger suite ' of quartz diorite pegmatites, basaltic dykes, fine- to medium-grained gabbroic sills and minor albitite veins. The main suite rocks are ortho-cumulates in which plagioclase, orthopyroxene and clinopyroxene were primocrysts which crystallized in situ. The dykes and sills show typical basaltic and doleritic textures. Geochemical evidence suggests that the main and younger suites may be consanguineous. Robertskollen-Krylen area: The layered complex at Robertskollen comprises a lower, rhythmically layered ultramafic unit, overlain by a mafic unit. Olivine, orthopyroxene and clinopyroxene are the dominant cumulus phases in the ultramafic rocks, whereas plagioclase, orthopyroxene and clinopyroxene fractionation occurred during crystallization of the mafic rocks. Metastable co-existence of quartz with olivine and anomalous incompatible trace element characteristics of the Robertskollen complex suggest contamination of the magma(s) by crustal material. The Krylen intrusions show petrographic and geochemical characteristics similar to those of the main suite at Juletoppane. A felsic dyke at Krylen may represent a rheomorphic product derived from Ritscherflya sediments. (iii) ...