Basement Rocks of the South-Central Ross Sea, Site 270, DSDP Leg 28

Abstract

Calcareous metamorphic rocks of a continental-type crystalline basement were recovered by drilling at Site 270 in the south-central Ross Sea. Calcareous basement gneiss is of amphibolite-facies metamorphic rank and may correlate with calcareous metasedimentary rocks of similar rank in the early Paleozoic(?) Skelton Group near McMurdo Sound. The basement rocks are overlain by 25 meters of coarse, angular, poorly sorted sedimentary breccia, the upper 3 meters of which is a deeply weathered regolith. The regolith is overlain unconformably by a thick sequence of mainly glaciomarine sediments of Oligocene and younger age.The breccia is interpreted as a probable talus or solifluction deposit derived from a nearby topographic high of basement rocks. Abundant fragments of marble and calc-silicate gneiss similar to the cored basement rocks, and numerous fragments of highly varied granitic and other metamorphic rocks in the breccia indicate that the basement terrane near Site 270 is a granitic and metamorphic complex probably similar to that of coastal parts of south Victoria Land near McMurdo Sound. Sedimentary rocks similar to those of the Devonian to Jurassic Beacon Supergroup and mafic-igneous rocks similar to those of the Jurassic Ferrar Dolerite were not observed in the breccia, suggesting that these widespread Victoria Land units do not extend to this region.

Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

“…Modeling carried out by D. Wilson, University of California, Santa Barbara. N information was obtained for the structures since sample retrieval was by drill core (Ford and Barrett, 1975;Hayes and Davey, 1975) and dredge (Luyendyk et al, 2001). DSDP 270 yielded a multicomponent AFT sample from a few grains of apatite extracted from calcsilicate gneiss (n = 16) (Fitzgerald and Baldwin, 1997).…”

Geophysical studies in the Ross Sea region

“…These uncertainties mean it is not possible to categorise basement rock type in detail on the basis of seismic velocity. For example, Barrett and Froggatt (1978) obtained a velocity of 4.5 km/s for the calcsilicate gneiss cored at DSDP site 270 (Ford and Barrett, 1975). By comparison, Houtz and Davey (1973) obtained basement seismic velocities of 5.2 and 5.3 km/s at two positions close to this site.…”

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“…The basement geology of the Central High adjacent to the Eastern Basin was penetrated at Deep Sea Drilling Project (DSDP) Site 270 and consists of high-grade Paleozoic calcareous metamorphics (Ford and Barrett, 1975) that were mylonitized during Late Cretaceous uplift (Siddoway et al, 2004). Upper Cretaceous mylonites were also recovered from the eastern part of the Eastern Basin (Luyendyk et al, 2001).…”

“…Ross Sea continental shelf sediments, including Quaternary sediments, are typically lithified muddy diamictites/mudstones (e.g., Site 270 and both ANDRILL holes) (Barrett, 1975;Passchier et al, 2011). Although drilling unconsolidated diamict is difficult and may result in poor recovery, drilling lithified glacial sediment with an indurated mud matrix is easier because it is homogeneous and cohesive.…”

“…Above 100 meters be-low seafloor (mbsf ) (Unit RSS-3), many of the units (originally classified as mudstones) are diamictites (i.e., >20% sand) that were eroded and transported by glacial ice (Barrett, 1975).…”