Fig. 4: Configuration of short-lived orogenic systems in eastern Gondwana, with compiled datasets of Ediacaran–Cambrian dates.
From: An Ediacaran orogeny in subglacial East Antarctica is uncovered by detrital garnet geochronology
a Simplified tectonic map of Australia and Antarctica in the early Permian, showing the extent of the major early Palaeozoic (Cambrian-Ordovician) orogenic systems. Ediacaran-age (~620–570 Ma) metamorphic and magmatic records from recent studies of samples from the Transantarctic mountains and clasts from Mertz Glacier dredge are as plotted43 and include (1) metamorphic garnet56, (2) metamorphic zircon50, (3) metamorphic erratic51, (4) detrital zircon52 and (5) igneous erratic44 data. The base map in a is adapted from Lawver et al.81, and the main geological units and tectonic structures30,43,83,84,85,86,87 are plotted together with the present-day coordinates of Australia and Antarctica. BG Beardmore Glacier, CTM Central Transantarctic Mountains, MG Mertz Glacier, MSZ Mertz Shear Zone, NG Nimrod Glacier, NVL Northern Victoria Land, OL Oates Land, SkG Skelton Glacier, SVL Southern Victoria Land, TA Terre Adélie, TAS Tasmania, WL Wilkes Land. b Detrital, c igneous and d metamorphic age profiles derived from previous studies along the coast of East Antarctica (between 140°E and 175°E) and the Transantarctic Mountains. Detrital ages for glaciomarine sediments in the Ross Sea are also included. References are listed in Supplementary Table 1, and the compiled ages are plotted per region in East Antarctica in Supplementary Fig. 7. The detrital garnet Lu–Hf ages (pink KDE) in (b) are from this study and were added for comparison with the existing data from other detrital minerals (KDE in full line; grains with 177Hf/176Hf < 3 and relative uncertainty on single-grain ages <20%). The dashed line KDE only includes the garnets with 177Hf/176Hf < 1.5, and illustrates the same Ediacaran peak is present when only the most precise garnet dates are plotted. Detrital garnet Lu–Hf and detrital metamorphic zircon U–Pb ages are consistently older than the igneous and unclassified detrital zircon U–Pb ages. The mica and amphibole Ar–Ar cooling ages clearly reflect the timing of Cambrian Ross Orogeny metamorphism, a phase that is distinctly younger than the Ediacaran detrital garnet and metamorphic detrital zircon peaks. The periods of alternating compression and extension43 were based on changes in syn-tectonic magma compositions and field structures. An early phase of Ediacaran thickening, as derived from the new detrital garnet ages in this study, is indicated with pink arrows. The dates for bedrock samples in c and d clearly represent Ross Orogeny metamorphism but are almost completely devoid of Ediacaran ages. Based on observations from available bedrock exposures of Ediacaran metamorphism and magmatism in (a) and palaeo ice-flow directions in Fig. 1b (and see also main text), we propose a rough estimate for the maximum extent of the crust affected by Ediacaran thickening (red area), stretching between inland George V Land and inboard the Transantarctic Mountains.
