Evolution of the patagonian-west antarctica margin of gondwana in the palaeozoic–early mesozoic: new models constrained by zircon u-pb ages, and o and hf isotopic compositions

• Main Author: Castillo Gonzalez, Paula Alejandra
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Subjects: Antarctic; The Antarctic; Antarctic Peninsula; East Antarctica; Patagonia; West Antarctica; Pacific; Argentina; Ellsworth Mountains; Antarc*; Antarctica; Tierra del Fuego
• Online Access: http://hdl.handle.net/1885/130073; https://doi.org/10.25911/5d723d70f07af; https://openresearch-repository.anu.edu.au/bitstream/1885/130073/4/Castillo%20Gonzalez%20Thesis%202017.pdf.jpg

A number of conflicting tectonic models have been proposed to explain the geological relationships between southern South America (Patagonia) and West Antarctica within the palaeo-Pacific margin of Gondwana. Extensive fragmentation and isolation of the various tectonic blocks during Gondwana break-up have complicated interpretations and palaeogeographic reconstructions. In order to explore and test the different tectonic models, I combine zircon U-Pb, Lu-Hf and O isotopic data for samples from key locations throughout the north and south of Patagonia, the Antarctic Peninsula and the Ellsworth Mountains in West Antarctica. Zircon is a robust refractory mineral that occurs in igneous and metamorphic rocks and survives multiple sedimentary cycles with little change to its isotopic composition. It therefore preserves a perfect archive for testing tectonic correlations. Igneous rocks from the Ellsworth Mountains were dated at ca. 680 Ma, older than previously reported. These zircons indicate that rifting, which affected Mesoproterozoic crust, likely occurred in the Cryogenian and supports a connection between the Ellsworth-Whitmore Mountain block and East Antarctica before the amalgamation of Gondwana. This agrees with the break-up of Rodinia in the context of the southwest United States and East Antarctica configuration. U-Pb zircon dating and O-Hf isotopic compositions of detrital zircons from the Ellsworth Mountains also support this connection, indicating a likely East Antarctic provenance. A Cambrian magmatic event is recorded by zircon at ca. 520 Ma, also related to an extensional setting – but in this case with crustal recycling. I interpret this Cambrian magmatism as a result of a tectonic escape after a collision between the Australo-Antarctic and West Gondwana/Indo-Antarctic plates. In Tierra del Fuego, samples from drill cores indicate that Cambrian magmatism occurred between ca. 540 and 520 Ma with strong similarities to the Pampean Orogen of Argentina. Metamorphism occurred at ca. 265 Ma, when zircon ...