Metamorphic diamond from the northeastern margin of Gondwana: Paradigm shifting implications for one of Earth’s largest orogens

Abstract

We describe the first occurrence of diamond-facies ultrahigh pressure metamorphism along the Gondwana-Pacific margin of the Terra Australis Orogen. Metamorphic garnet grains from Ordovician metasediments along the Clarke River Fault in northeastern Queensland contain inclusions of diamond and quartz after coesite, as well as exsolution lamellae of rutile, apatite, amphibole, and silica. These features constrain minimum pressure-temperature conditions to >3.5 gigapascals and ~860°C, although peak pressure conditions may have exceeded 5 gigapascals. On the basis of these data, we interpret the Clarke River Fault to represent a Paleozoic suture zone and at least parts of the Terra Australis Orogen to have formed through classic Wilson cycle processes. The growth of the Terra Australis Orogen during the Paleozoic is largely attributed to accretionary style tectonics. These previously unknown findings indicate that the Terra Australis Orogen was not just a simple accretionary style orogen but rather a complex system with multiple tectonic styles operating in tandem including collisional tectonics.

Continental Deep Subduction Versus Subduction Cessation: The Fate of Collisional Orogens

“…The blue dashed line represents the depth of the phase transition from graphite to diamond, and the orange dashed line for the phase transition from coesite to stishovite. AA: Alpe Arami; AT: Altyn Tagh; Erzg: Saxonian Erzgebirge; FMC: French Massif Central; GR: Greek Rhodope; Kok: Kokchetav; Kont: Kontum; NQ: North Qaidam; QL: Qingling; TNCO: Tran‐North China orogen; WGR: Western Gneiss Region; TA: Terra Australis Orogen (Edgar et al., 2022). 1: diamond; 2: stishovite pseudomorph; 3: majorite inclusion; 4: pyroxene ± rutile ± apatite in garnet; 5: sodic amphibole exsolution in garnet; 6: aragonite and magnesite inclusions in diamond; 7: coesite exsolution lamellae in titanite; 8: FeTiO3 and chromite exsolution in olivine; 9: C2/c clinoenstatite exsolution in clinopyroxene; 10: ilmenite exsolution in olivine; 11: quartz ± rutile ± apatite exsolution in garnet; 12: phlogopite and coesite exsolution from clinopyroxene.…”

Cross‐Orogen Granite Migration as an Indicator of Slab Rollback Along Eastern Gondwana

“…The Australian Tasmanides along the eastern margin of Gondwana encompass much of the Phanerozoic and, from west to east, consist of the Delamerian, Lachlan, and New England orogens, and along strike, the equivalent Thomson and Mossman orogens in the north (Figure 1a) (P. A. Cawood, 2005; Glen, 2005). These orogens young progressively to the east and grow as a result of a combination of gradual accretion during intervals of west‐directed subduction beneath eastern Gondwana (P. A. Cawood, 2005; P. A. Cawood et al., 2009; Glen et al., 2009) but also as a result of the “quantum” addition of allochthonous island arc terranes during intervals of outboard, east‐directed subduction and orogenesis (J. C. Aitchison & Buckman, 2012; Buckman et al., 2015; Edgar et al., 2022; Zhang, Buckman, Bennett, & Nutman, 2019; Zhang, Buckman, Bennett, Nutman, & Song, 2019). However, the boundary between the Lachlan and New England orogens is covered by the Permo–Triassic Sydney Basin (Figure 1a), which masks the tectonic relationship between these two orogens (Buckman et al., 2015; Jeon et al., 2008).…”

“…Cawood, 2005;P. A. Cawood et al, 2009;Glen et al, 2009) but also as a result of the "quantum" addition of allochthonous island arc terranes during intervals of outboard, east-directed subduction and orogenesis (J. C. Aitchison & Buckman, 2012;Buckman et al, 2015;Edgar et al, 2022;Zhang, Buckman, Bennett, Nutman, & Song, 2019). However, the boundary between the Lachlan and New England orogens is covered by the Permo-Triassic Sydney Basin (Figure 1a), which masks the tectonic relationship between these two orogens (Buckman et al, 2015;Jeon et al, 2008).…”