The age and chemistry of granitic gneisses from the western H.U. Sverdrupfjella, Maud Terrane,

The age and chemistry of granitic gneisses from the western H.U. Sverdrupfjella, Maud Terrane,

western Dronning Maud Land, Antarctica .

G.H. Grantham

¹

, M.A. Elburg

¹

, H. Ueckermann

¹

, L. Iaccheri

²

, Reuben Mukwevho

¹

, N.G. Moabi

³

1

Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa.

2

WIGL, Department of Geosciences, University of the Witwatersrand, Johannesburg, South Africa.

3

Council for Geoscience, Pretoria, South Africa.

Study area is located at western end of the Kuunga Orogeny in the Maud Terrane, east of the Grunehogna Craton.

Kuunga Orogeny in Antarctica affects the area between the

Archean-age Enderby Land Craton in the east and the Grunehogna

/Kalahari Craton in the west.

Regional Setting

The Kalahari Craton in the west is overlain by the ca. 1135 Ma Ritscherflya Supergroup,

overlying the Archean

Grunehogna Craton exposed at Annandagstoppane ~ 3.3By

Study area located in the ca.

1140-1000Ma Mesoproterozoic Maud Complex/Belt.

Overlain structurally to the east by a S to SE dipping EAO

Neoproterozoic supracrustal sequence followed by

undifferentiated EAO Neo- and Mesoproterozoic rocks

eastwards.

Location of Jutulrora, Brekkerista and Roerkulten Granites in west Sverdrupfjella

Limited exposures intruded into TTG gneisses and banded supracrustal gneisses.

Brekkerista Granite

Jutulrora Granite

Roerkulten Granite

A: Outcrop extent of sheeted Roerkulten Granite – N dipping ca. 100m thick folded in N-Dipping synform. Medium grained

equigranular.

B: Jutulrora Granite – Medium grained

equigranular, south dipping sheet ca. 100m thick intruded into 1140Ma TTG gneiss

(below) and banded meta-volcano- sedimentary gneisses (above).

C: Brekkerista Granite –coarse grained rodded

augen gneiss with porphyroclastic Kfspar. Cut

by many felsic and mafic veins.

Besides quartz and feldspar

( A&B) Mineralogy Jutulrora Gt.

Hornblende, Biotite, Allanite, Titanite and Garnet.

(C&D) Mineralogy Roerkulten Gt.

Hornblende, Biotite, Allanite, and Garnet.

(E&F) Mineralogy Brekkerista Gt.

Biotite, Allanite and Titanite.

(G&H) Mineralogy dioritic vein

intruded into Brekkerista Granite

– Biotite, Hornblende, Epidote

and Titanite.

All intrusions are typically granitic in QAP and O’Connor (1965)

classification diagrams.

Plot as granite in the TAS diagram after Middlemost (1994).

Straddle the peraluminous/

metaluminous boundary.

All plot as A-type Ferroan granites in the Fe/Mg Frost&Frost (1997) classification.

Slight differences in bulk composition are evident.

All granites plot typically as A-types after Whalen et al. (1987).

Steep REE patterns with –ve Eu

anomalies. Brekkerista Granite flat HREE whereas Jutulrora and Roerkulten have depleted HREE. High REE are related to significant Allanite in the rocks.

Nb vs Ti show each granite has distinctive chemistry.

In the Pearce et al. (1984) Roerkulten Granite plots as VAG and WPG whereas Jutulrora and Brekkerista granites plot as WPG.

Zircon CL images from samples analysed by LA-ICPMS at UJ.

BK29 sampled from a dioritic vein intruding Brekkerista Granite

assumed to be ca. 520Ma. Small rounded 25 micron size zircons, some with overgrowths and one with Archaean-age xenocrystic elongate tabular grain.

BKC – this granite was thought to be Mesoproterozoic in age.

Elongate tabular grains ca. 100

micron long with oscilliatory

zoning and some overgrowths.

Zircons from Jutulrora and

Roerkulten Granites are similar with tabular equant shapes ca.

>100 micron.

Some thin metamorphic (too thin to analyse) overgrowths with many grains having

homogeneous unzoned cores.

New unexpected data results.

BKC Brekkerista Granite 2850 ± 11 Ma Archean in age – represents an Archaean basement to the Maud Terrane .

This has previously been inferred from whole rock TDm radiogenic isotope studies.

BK29 diorite vein intruding Brekkerista Granite. These veins were thought to be ca. 520 Ma based in similar veins in

eastern Sverdrupfjella.

An upper intercept age of 1119 ± 15 Ma and lower intercept age of 527 ± 230 Ma.

A concordant age of 1104 ± 8 Ma is defined by 5 grains. Data include two Archean xenocrysts from Brekkerista Granite which it intrudes.

Roerkulten and Jutulrora Granites have near identical concordant ages of 1083 ± 5 Ma and 1085 ± 5 Ma respectively with a significant number of grains.

Lower intercept ages of ~ 655 Ma are inferred to have no geological significance. Other gneisses have overgrowths of ~ 500 Ma

consistent with a Kuunga Orogeny

overprint.

εNd_1080Ma vs Sr_i1080Ma for the granites, Borgmassivet Suite, Sverdrupfjella basement, Kirwanveggan Granites and the

Archaean Annandagstoppane Granite. Granites similar to ca 1104 Ma. Borgmassivet Suite

• (C) εNdi vs Age for for the granites, Borgmassivet Suite, Sverdrupfjella basement, Kirwanveggan Granites and the >3 By Annandagstoppane Granite. Note the

similarity between the Jutulrora and Roerkulten granites and Bormassivet Suite and more juvenile than basement they intrude.

(D) εHfi vs age for the granites from Lu-Hf analyses on zircon. Data for Annandagstopane Granite from Marschall et al. (2010)

Conclusions

• Newly identified Archean-age 2850 Ma old Brekkerista Granite represents an Archean floor to 1140 Maud Terrane.

• Ca. 1080 Ma old Roerkulten and Jutulrora granites do not appear to be derived from local partial melting of TTG gneisses but have

Nd/Sr characteristics comparable to the on craton ca. 1104 Ma Borgmassivet Suite which is correlated with Mkondo LIP –

consistent with WPG, A-type signatures. No significant input of Archean crust input into Roerkylten and Jutulrora Granites

• Dioritic vein inferred to be ca. 520 Ma has age of 1104 Ma, similar

in age to TTG gneisses in the area.