Abstract
The Ross(–Delamerian) Orogeny significantly impacted the formation of the tectonic structure of the Pacific Gondwana margin during the early Paleozoic era. Northern Victoria Land (NVL) in Antarctica preserves the aspect of the Ross Orogeny that led to the union of the Wilson (WT)–Bowers (BT)–Robertson Bay Terrane. The aspect of the Ross Orogeny in the NVL is characterized by subduction of oceanic domains toward the continental margin (continental arc) and the accretion of the associated marine–continental substances from 530–480 Ma. In the Mountaineer Range in NVL, the Ross Orogeny strain zone is identified at the WT/BT boundary regions. In these areas, fold and thrust shear zones are observed and aspects of them can be seen at Mt. Murchison, the Descent Unit and the Black Spider Greenschist zone. The Dessent Unit corresponds to a tectonic slice sheared between the WT and BT. The metamorphic evolution phase of the Dessent Unit is summarized in the peak pressure (M1), peak temperature (M2) and retrograde (M3). The sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb ages of 514.6 ± 2.0 Ma and 499.2 ± 3.4 Ma obtained from the Dessent Unit amphibolite are comparable to the M1 and M2 stages, respectively. The Dessent Unit underwent intermediate pressure (P)/temperature (T)-type metamorphism characterized by 10.0–10.5 kbar/~600 °C (M1) and ~7 kbar/~700 °C (M2) followed by 4.0–4.5 kbar/~450 °C (M3). Mafic to intermediate magmatism (497–501 Ma) within the WT/BT boundary region may have given rise to the M2 stage of the Dessent Unit, and this magmatism is synchronous with the migmatization period of Mt. Murchison (498.3 ± 3.4 Ma). This indicates that a continuous process of fold-shearing–magmatic intrusion–partial melting, which is typically associated with a continental arc orogeny, occurred before and after c. 500 Ma in the Mountaineer Range. During the Ross Orogeny, the Dessent unit was initially subducted underneath the WT at depth (10.0–10.5 kbar, ~35 km) and then thrust into the shallow (~7 kbar, ~23 km), hot (≥700 °C) magmatic arc docking with the Mt. Murchison terrain, where migmatization prevailed.
Highlights
Antarctica comprises Archean to Phanerozoic (Cenozoic) lithologies, which record a dynamic history of the assembly and breakup of supercontinents [1,2,3,4,5,6]
(1) In the Mountaineer Range of Northern Victoria Land (NVL), the Ross Orogenic structures such as fold and thrust shear zones formed by dynamothermal metamorphism with regional compression are identified in the Mt
Cambrian (560–530 Ma), possibly sourced from the Mawson Craton interior and its surrounding orogenic belts (Paleoproterozoic to Mesoproterozoic ages) and Neoproterozoic rift margin hosting the early Ross orogenic products as well; this was transformed into a migmatitic gneiss (SBM173) during the main phase of the Ross Orogeny with a peak temperature stage at around 500 Ma (498.3 ± 3.4 Ma)
Summary
Antarctica comprises Archean to Phanerozoic (Cenozoic) lithologies, which record a dynamic history of the assembly and breakup of supercontinents [1,2,3,4,5,6]. The basement of East Antarctica is composed of Archean and Proterozoic rocks forming a continental shield through the amalgamation of several cratons (i.e., accretion and collision) during the Precambrian eon (Figure 1) [5,7,8,9]. The East Antarctic Shield played a significant role in its surrounding plates’ (e.g., Australian, Kalahari, Indian and Congo Cratons) arrangement and motion during the amalgamation and separation of Gondwana (Figure 1c,d) [2,4,10,11]. Minerals 2020, 10, 908 the Pacific Gondwana margin) began to increase. This increase occurred from the paleo-Pacific plate’s subduction into East Antarctica, causing the accretion of oceanic–continental domains. The subduction and accretion into the Pacific Gondwana margin, which began in the late Neoproterozoic–early
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