The oldest rocks of Antarctica (Enderby Land)

Sobotovich, E. V.; Kamenev, Ve.N.; Kornanstyy, A.A.; Rudnik, V.A.

doi:10.1080/00206817609471218

Cited by 35 publications

(9 citation statements)

References 3 publications

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“…These rocks, for which an age of ca. 4000Ma had earlier been postulated by Sobotovitch, Kamenev, Komaristyy & Rudnik (1976), have a similar crustal history to that of the Napiercomplex to the E. Isotopic data from the Black et al (1983) study did not support an age as old as 4000Ma, but nevertheless demonstrated that Fyfe Hills rocks had an early Archaean origin.…”

Section: Introductionmentioning

confidence: 80%

Geochronology and geological evolution of metamorphic rocks in the Field Islands area, East Antarctica

Black

James

Harley

1983

Journal Metamorphic Geology

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Detailed geochronological, structural and petrological studies reveal that the geological evolution of the Field Islands area, East Antarctica, was substantially similar to that of the adjacent Archaean Napier Complex, though with notable differences in late and post Archaean times. These differences reflect the area's proximity to the Proterozoic Rayner Complex and consequent vulnerability to tectonic process involved in the formation of the latter. Distinctive structural features of the Field Islands are ( I ) consistent development of a discordant, pervasive S, axial-plane foliation; (2) re-orientation of S, axial planes to approximate to the subsequent E-W tectonic trend of the nearby Rayner Complex; (3) selective retrogression by a post-D, static thermal overprint; and (4) relatively common development of retrogressive, E-Wtrending, mylonitic shear zones.Peak metamorphic conditions in excess of 800°C at 900 100 MPa (9 kbar) were attained at one locality following, but probably close to the time of D, folding. D, took place in late Archaean times when metamorphic temperatures were about 650°C and pressures were about 600 MPa (6 kbar). Later, temperatures of 600 f 50°C and pressures of 700MPa (7kbar) were attained in an amphibolite-facies event, presumably associated with the widespread granulite to amphibolite-facies metamorphism and intense deformation involved in the formation of the Rayner Complex a t about 1100 Ma. The area was subsequently subjected to near-isothermal uplift.Rb-Sr isotopic data indicate that the pervasive D, fabric developed at about 240&2500Ma, and this age can be further refined to 2456': Ma by concordant zircon analyses from a syn-D, c) 1983 Blackwell Scientific Pubhcdtions 02634929/83/1200-0277 $02.00 pegmatite. All zircons were affected by only minor (<7-10%) Pb loss and/or new zircon growth during the Rayner event at about 1100 Ma. Thus the 45&8SOpg/g U concentrations of these zircons were too low to cause sufficient lattice damage over the 1350 Ma (from 2450 Ma) for excessive Pb to be lost during the 1100 Ma event. The emplacement of pegmatite a t 522 f 10 Ma substantially changed the Rb-Sr systematics of the only analysed rock that developed a penetrative fabric during the I100 Ma event. Monazite in this pegmatite contains an inherited Pb component, which probably resides in small opaque inclusions.A good correlation is found between Rb-Sr total-rock ages and rock fabric. U-Pb zircon intercepts with concordia also mostly correspond to known events. However, in one example a near perfect alignment of zircon analyses, probably developed by mixing of unrelated components, produced concordia intercepts that appear to have no direct geochronological significance.

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Section: Introductionmentioning

confidence: 80%

Geochronology and geological evolution of metamorphic rocks in the Field Islands area, East Antarctica

Black

James

Harley

1983

Journal Metamorphic Geology

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“…Reports of Pb-Pb ages ofc. 4000 Ma for orthogneisses from the Fyfe Hills (Ravich et al 1975, Sobotovich et al 1976 generated intense interest in the age of the Napier Complex, and appeared to be supported by initial ion-microprobe studies (Lovering 1979(Lovering ,1980. SHRIMP U-Pbzirconanalyses (Black et al 1986a) produced a similar age of 3927510 Ma for orthogneissfromMount Sones, but Rb-Sr and conventional U-Pb zircon studies (Black et al 1986b) showed that felsic magmatism also occurred at considerably younger times.…”

Section: Introductionmentioning

confidence: 98%

A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies

1997

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The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c. 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was caused by volume diffusion at these abnormally high regional crustal temperatures.

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“…Particularly distinctive of the Napier Complex is the occurrence of: (1)multiple generations of mafic dykes, including unmetamorphosed Amundsen dykes; (2) a sequence consisting of units of massive 'orthogneiss' interlayered with supracrustal successions metamorphosed in the granulite facies; and (3) sapphirine--quartz gneisses in unusually magnesian metapelitic compositions. The recognition of supracrustal gneisses at Fyfe Hills negates arguments that this sequence derives from a (metasomatically altered) intermediate intrusive complex (Sobotovich et al, 1976;Kamenev, 1982); and casts doubt on the validity of the Tula/Raggatt series subdivision of the Napier Complex (Grikurov et ai., 1976) in the Fyfe Hills region. The occurrence of calcareous metasediments at Fyfe Hills is unusual, as these rock types are rare in the Napier Complex (the only previous record of calc-silicates is from Forefinger Point (E.S.…”

Section: Discussionmentioning

confidence: 99%

“…(3) The predominance of supracrustal rocks at Fyfe Hills suggests that the Tula and Raggatt series subdivision of the Napier Complex, as originally defined by Grikurov et al (1976), and as applied to the Fyfe Hills region by Sobotovich et al (1976), is inadequate. Detailed investigations of contact relationships between dominantly metasedimentary and dominantly metaigneous sequences are required elsewhere in the Napier Complex before the significance of this subdivision can be properly evaluated.…”

Section: Discussionmentioning

confidence: 99%

“…This research is based on field work during the 1979/80 ANARE expedition to Enderby Land as part of a research program complementing regional based tectonic and geochronologic investigations by other Australian geologists (e.g., Black et al, 1983a,b). The Fyfe Hills gneisses comprise both metasedimentary and meta-igneous rocks (Sobotovich et al, 1976;Kamenev, 1982;DePaolo et al, 1982, Black et al, 1983a. As with many Archaean gneissic terrains (cf.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The origin of Archaean gneisses in the Fyfe Hills Region, Enderby Land; field occurrence, petrography and geochemistry

Sandiford¹,

Wilson²

1986

Precambrian Research

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The oldest rocks of Antarctica (Enderby Land)

Cited by 35 publications

References 3 publications

Geochronology and geological evolution of metamorphic rocks in the Field Islands area, East Antarctica

Geochronology and geological evolution of metamorphic rocks in the Field Islands area, East Antarctica

A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies

The origin of Archaean gneisses in the Fyfe Hills Region, Enderby Land; field occurrence, petrography and geochemistry

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