Constraints from detrital zircon geochronology on the early deformation of the Ross orogen, Transantarctic Mountains, Antarctica

New ages of detrital zircons constrain the timing of the onset of deformation in the Ross orogen. In the Skelton Glacier area, Skelton Group was deformed before cross-cutting intrusion at 551 Ma. The youngest, significant, age-probability peaks from three samples of Skelton Group are 649 Ma, 684 Ma, and 691 Ma. The 649 Ma peak may be considered the maximum depositional age of Skelton Group, constraining the period of deformation to between 649 Ma and 551 Ma. In the upper Scott Glacier area, La Gorce Formation was deformed prior to cross-cutting intrusion at 526 Ma. The youngest, significant, age-probability peaks from two samples of La Gorce Formation are 581 Ma and 619 Ma. The 581 Ma peak may be considered the maximum depositional age of La Gorce Formation, constraining the period of deformation to between 581 Ma and 526 Ma

Geology of the Byrd Glacier Discontinuity (Ross Orogen): New survey data from the Britannia Range, Antarctica

Field activities in the Britannia Range (Transantarctic Mountains, Antarctica) highlighted new geological features around the so-called Byrd Glacier discontinuity. Recent field surveys revealed the occurrence of significant amounts of medium- to high-grade metamorphic rocks, intruded by abundant coarse-grained porphyritic granitoids. Most of the granitoids are deformed, with foliation parallel to the regional foliation in the metamorphics. Two main episodes of deformation are observed. Tight to isoclinal folds and penetrative axial plane foliation are related to the D1 phase, open folds to the D2. The main foliation (D1) trends nearly E-W in agreement with the trend in the southern portion of the Byrd Glacier. In most outcrops, granitic dykes are folded and stretched by the D2 deformation, which shows similar characteristics with the D2 deformation south of the Byrd Glacier. This suggests the occurrence in the Ross orogen of an orogen-normal structure south and north of the Byrd Glacier

Petrogenesis of the Cambrian Liv Group, a bimodal volcanic rock suite from the Ross orogen, Transantarctic Mountains

Cambrian volcanic rocks of the Liv Group, defined here as including the Wyatt, Ackerman, Taylor, Fairweather, and Leverett Formations, occur along the paleo-Pacific margin of Gondwana, in the Queen Maud Mountains, Transantarctic Mountains. The Ackerman and Wyatt Formations are dominated by massive dacite lava flows and were erupted ca. 525 Ma. The Taylor, Fairweather, and Leverett Formations form a bimodal assemblage of basalts and rhyolites and were erupted ca. 515 Ma. The dacites of the Ackerman and Wyatt Formations are the most light rare earth element (REE) and large ion lithophile element (LILE) enriched rocks (LaN/YbN = 6.6−10.2; Th/Nb = 0.9−1.8) of the Liv Group. They have the lowest ϵNdi (−1.8 to −3.1) of all the Liv Group volcanic rocks and are interpreted to be partial melts of continental crust. Sm-Nd model ages suggest that some of this crust may be as old as 1.5 Ga. The volumetrically minor basalts and basaltic andesites of the Taylor, Fairweather, and Leverett Formations are variably light REE and LILE enriched (varying from LaN/YbN = 1.5 to 6.0) and have ϵNdi between 5.7 and −1.1. The most depleted of these basalts are transitional between normal midocean ridge basalt (MORB) and enriched MORB and are interpreted as melts of asthenospheric mantle that were variably enriched in light REE and LILE by melts from lithospheric mantle and/or continental crust. The rhyolites of the Taylor, Fairweather, and Leverett Formations have LaN/YbN = 2.8−6.0, Th/Nb = 1.0−1.6, and ϵNdi between 2.1 and −2.8 and are interpreted as mixtures of fractionated mafic magma and crustal partial melt. The Liv Group rhyolites were probably generated in response to the mafic magmatism. The most likely tectonic setting for the Liv Group was in an extensional rift environment within or behind an active volcanic arc