Geology of Macquarie Island and its relationship to oceanic crust

Varne, R.; Rubenach, Michael J.

doi:10.1029/ar019p0251

Cited by 50 publications

(37 citation statements)

References 22 publications

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“…Macquarie Island (54" 15' S; 159" E) also affords an exposure of ancient oceanic crust. Field geologic, petrologic and geochemical studies of Macquarie Island by Varne, Gee & Quilty (1969) and Varne & Rubenach (1972) have revealed lithologies and a stratigraphic sequence similar to those of the Troodos ophiolite complex. In addition, studies of marine magnetic anomalies southeast of Australia have shown east-west trending anomalies as expected from seafloor spreading of the Australia-Antarctic Ridge (Weissel & Hayes 1972).…”

Section: O C E a N I C C K U S T O N M A C Q U A R I E I S L A N Dmentioning

confidence: 95%

“…Petrologic data of Varne & Rubenach (1972) indicate that pillow basalts exposed in the North Head region of Macquarie Island are relatively fresh and have not been exposed to metamorphism. Our examination of polished thin sections of eight specimens from this locality confirms this conclusion.…”

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 96%

“…Unlike the North Head locality, these rocks have experienced conditions typical of the low grades of metamorphism. Varne & Rubenach (1972) argue that this metamorphism is characteristic of the crustal accretion process at spreading oceanic ridges and is not the result of a metamorphic event associated with the tectonic uplift of Macquarie Island. Although isolated exposures and fault bounded terrain prevent unambiguous assignment to specific levels, the petrologic evidence would suggest that the North Head pillow lavas are representative of the upper (100-200-m?)…”

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 97%

“…The field geologic setting of both sampling localities is illustrated in Varne et al (1969) and Varne & Rubenach (1972). Samples were collected with a portable gasoline powered drill and were oriented by magnetic compass.…”

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 99%

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Magnetic properties of oceanic pillow basalts: evidence from Macquarie Island

Butler

Banerjee

Stout

1976

Geophysical Journal International

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A combined pdaeomagnetic, hysteresis, thermomagnetic, and electron microprobe study has been carried out on pillow basalts from Late Tertiary oceanic crust exposed on Macquarie Island. Oriented cores were collected from four sites in the North Head region where the basalts are unmetamorphosed but have suffered pervasive seafloor weathering and at four sites near Langdon Point where the pillow lavas have experienced metamorphism to the greenschist facies. Field geologic and petrologic evidence suggests that the North Head samples are representative of the weathered zone of Late Tertiary oceanic crust while the specimens from Langdon Point are representative of pillow basalts from > 5 0 0 m into the oceanic lithosphere. Geometric mean intensities of natural remanence (NRM) were 0.7 x C for North Head samples and 0.6 x 10-3C for specimens from Langdon Point. The geometric mean values of low field susceptibility (x)and Koenigsberger ratio (Q) for North Head samples (0.1 x 10-3GOe-1 and 9.8) are similar to those of DSDP basalts. The mean value of x and Q for Langdon Point samples (2.8 x 10-3G Oe-' and 0.3) is similar to those observed in metabasalt dredged from oceanic escarpments. Hysteresis, thermomagnetic and electron microprobe data indicate that the titanomaghemites in the North Head samples have suffered a high degree of low temperature oxidation. Langdon Point samples show reversible thermomagnetic curves with a magnetic Curie temperature (58OoC), indicating that metamorphism has altered the magnetic mineralogy. This metamorphism is thought to occur at or near the ridge during the seafloor spreading process. Thus, the NRM of the metamorphosed pillow basalts would still record geomagnetic reversals and contribute to magnetic lineations. The low NRM intensities are ascribed to prolonged seafloor weathering of North Head samples and to metamorphism of the basalts from Langdom Point. Since the 10-3G NRM intensities of pillow basalts are too low t o account for the 180 observed amplitude of marine magnetic anomalies, the underlying basaltic and doleritic sheeted dyke complex must also contribute to the anomalies.

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Section: O C E a N I C C K U S T O N M A C Q U A R I E I S L A N Dmentioning

confidence: 95%

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 96%

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 97%

Section: S a M P L I N G L O C A L I T I E S A N D D E S C R I P T I O Nmentioning

confidence: 99%

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Magnetic properties of oceanic pillow basalts: evidence from Macquarie Island

Butler

Banerjee

Stout

1976

Geophysical Journal International

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show abstract

“…Island in the Red Sea, St. Paul's islets in the Atlantic, and Macquarie Island in the southwestern Pacific - Bonatti et al, 1981;Dijkstra and Cawood, 2004;Melson et al, 1967;Tilley, 1947;Varne and Rubenach, 1972).…”

Section: Introductionmentioning

confidence: 99%