Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-MP Mineralogy & Petrology

[S-MP35] Antarctica and surrounds in Supercontinent Evolution

Tue. May 22, 2018 10:45 AM - 12:15 PM 302 (3F International Conference Hall, Makuhari Messe)

convener:Tomokazu Hokada(National Institute of Polar Research), Yasuhito Osanai(Division of Evolution of Earth Environments, Faculty of Social and Cultural Studies, Kyushu University), Geoffrey Hugo Grantham (共同), Madhusoodhan Satish-Kumar(Department of Geology, Faculty of Science, Niigata University), Chairperson:Hokada Tomokazu(National Institute of Polar Research), Grantham Geoffrey(University of Johannesburg)

10:45 AM - 11:00 AM

[SMP35-06] Terminal deformation and magmatism of the Kuunga Orogeny,Dronning Maud Land, Antarctica.

*Geoffrey Hugo Grantham1, Conrad Adolf Groenewald1, Riaan Bothma2, Petrus le Roux3, Kenji Horie4 (1.Department of Geology, University of Johannesburg, Auckland Park, South Africa, 2.6 Van Broekhuizen Street Kuilsrivier 7580 South Africa, 3.Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa, 4.National Institute of Polar Research, Tachikawa, Japan.)

Keywords:Kuunga Orogeny, Gondwana , Deformation and Magmatism

Two widely distributed granitic vein types are seen in Sverdrupfjella, Western. Dronning Maud Land (WDML), in Gjelsvikjella and Central Dronning Maud Land (CDML), Antarctica. The younger generation (P2) comprise 2-mica granites and pink 2 feldspar pegmatites. The older (P1) generation comprises white biotite plagioclase rich pegmatites.

The P2 pegmatites dip mostly shallowly (~45-50o ) to N and NW and displace the older veins along planes with extensional and compressional top to the south geometries in Sverdrupfjella. Published data on these aplitic veins sindicate an age of ~480Ma. In contrast, the older P1's dip mostly ~60 o toward the S and SW with no displacements in Sverdrupfjella. Similarly oriented local shears show normal displacements to the S and SW. In Gjelsvikfjella, extensional displacements are observed. The structures are consistent with late extension toward the S and SW followed by top to the S and SE compression. In Gjelsvikfjella, these veins have meta-basic cores suggesting near synchronous emplacement. The metabasite veins are correlated with the Stabben Gabbro which has an age of ~520Ma. These veins locally have planar fabrics defined by biotite and are locally folded and boudinaged. The planar fabrics parralel their extensional geometry as well as planar fabrics in the Stabben Gabbro.

Radiogenic Sr and Nd data from the two types indicate relatively juvenile sources for the P1's, in contrast to the P1 granites which were sourced in older crust, similar to Mesoproterozoic TTG gneisses in W. Sverdrupfjella.

Radiogenic Sr/Nd data from basement gneisses hosting the veins in E and W Sverdrupfjella show differences with W Sverdrupfjella characterised by older evolved crust in contrast to the juvenile basement rocks in E. Sverdrupfjella. The two areas are separated by a major thrust fault zone coincidant with strong magnetic anomalies. Data from Gjelsvikfjella basement gneisses have juvenile Sr/Nd isotope characteristics to E. Sverdrupfjella.In contrast P2 veins intruded into juvebnile basement retain their old signature implying older basement at depth beneath the juvenile basement exposed at surface.

The data, along with recently published data from Gjelsvikfjella and Sor Rondanae are inferred to reflect the emplacement of a Kuunga Orogeny mega nappe complex with top to the S geometry at ~500Ma.