Ediacaran mafic magmatism recorded in Cambrian eclogites of the Ross orogen, Antarctica: Implications for the Neoproterozoic rifting episodes along the Pacific‐Gondwana margin

Abstract

We report the first finding of Ediacaran mafic magmatism in northern Victoria Land of the Ross orogen, Antarctica, based on ca. 600-590 Ma magmatic zircon cores in Cambrian eclogites. The mafic magmatism could be either linked to ca. 615-590 Ma incipient convergent margin magmatism in central segment of the Ross orogen, or ca. 600-580 Ma continental rift-related volcanism widespread in eastern Australia. The latter is preferred based on the trace-element compositions distinctive from those of arc-related basalts and the depleted mantle-like Hf isotopic compositions of zircon.Our results suggest dual rifting episodes during both the Ediacaran and Cryogenian (ca. 670-650 Ma) in the East Antarctic margin, correlative with those in eastern Australia. A spatial distribution of coeval rifting and subduction along the Ediacaran margin of East Antarctica is readily accounted for by rift inheritance; the upper-and lower-plate geometry resulting from detachment and transform faulting.

Sedimentary protolith and high-P metamorphism of oxidized manganiferous quartzite from the Lanterman Range, northern Victoria Land, Antarctica

“…The chlorite growth at the expense of garnet is also a retrograde feature, which is coeval with the relatively low-celadonite outer segment of phengite (Si = 3.14-3.27 apfu). It is noteworthy that a marginal decomposition texture of phengite into symplectites (Palmeri et al, 2003;Kim and Lee, 2023) is absent in the manganiferous quartzite sample (Fig. 4).…”

“…The grain size of phengite flakes varies largely, ranging from several hundred micrometers to 10 mm in their longest dimension. Marginal breakdown textures are negligible in phengite, in marked contrast to those observed in the surrounding garnet-phengite gneisses (Palmeri et al, 2003) and megacrystic phengite-bearing quartz veins (Kim and Lee, 2023). Secondary K-feldspar and albite form discrete bands (Fig.…”

“…506 Ma overlaps with those of the eclogite-facies peak stages recorded in the high-P rocks of the Lanterman Range, such as ca. 500 Ma of the boudin-shaped mafic eclogites (Di Vincenzo et al, 1997;Kim et al, 2019) and megacrystic phengite-bearing quartz vein (Kim and Lee, 2023) but is apparently younger than the ca. 530-515 Ma of prograde stages of the colder eclog-ites and garnet-phengite quartzofeldspathic schists/gneisses (Di Vincenzo et al, 2016) (Fig.…”

“…The authors suggested phengite breakdown into biotite-plagioclase symplectite during the amphibolite-facies retrogression. Comparable phengite decomposition textures were observed in the megacrystic phengite-bearing quartz veins that crosscut the retrogressed 2019), (5) Goodge and Dallmeyer (1996), (6) Di , and (7) Kim and Lee (2023). Boxes for (3) and ( 6) denote ranges of spot dates.…”

“…The crystallization ages of riftrelated gabbroic protoliths were estimated from the igneous cores of zircon in the colder eclogites at ca. 600-590 Ma (Kim et al, 2023). Retrograde cooling and exhumation rates under the amphibolite-facies conditions were estimated to be > 30 °C Myr −1 and 2-5 km Myr −1 , respectively (e.g., Di .…”