Long‐Term Geochemical and Geodynamic Segmentation of the Paleo‐Pacific Margin of Gondwana: Insight From the Antarctic and Adjacent Sectors

Abstract

Combined zircon geochemistry and geochronology of Mesozoic volcaniclastic sediments of the central Transantarctic Mountains, Antarctica, yield a comprehensive record of both the timing and geochemical evolution of the magmatic arc along the Antarctic sector of the paleo‐Pacific margin of Gondwana. Zircon age populations at 266–183 Ma, 367–328 Ma, and 550–490 Ma correspond to episodic arc activity from the Ediacaran to the Jurassic. Zircon trace element geochemistry indicates a temporal shift from granitoid‐dominated source(s) during Ediacaran to Early Ordovician times to mafic sources in the Devonian through Early Jurassic. Zircon initial εHf shifts to more radiogenic Hf isotope compositions following the Ross Orogeny and is inferred to reflect juvenile crustal growth within an extensional arc system during progressive slab rollback. These new ages and Hf isotopic record are similar to those from the Australian sector, indicating that these regions constituted an ~3,000 km laterally continuous extensional arc from at least the Carboniferous to the Permian. Conversely, the South American sector records enriched zircon Hf isotopic compositions and compressional/advancing arc tectonics during the same time period. Our new data constrain the location of this profound along‐arc geochemical and geodynamic “switch” to the vicinity of the Thurston Island block of West Antarctica.

Tracking voluminous Permian volcanism of the Choiyoi Province into central Antarctica

“…6) that is slightly younger than Permian zircon ages recorded in other regions within the proto-Weddell Sea sector discussed above as well as our data from central Antarctica (Nelson and Cottle, 2017;Elliot et al, 2017). Instead, the age of Permian-Triassic zircon from the central TAM are comparable to detrital zircon ages from Australia and New Zealand which demonstrate a broad difference in the timing of Permian arc magmatism between Australia/Zealandia and South America (see compilation in Nelson and Cottle, 2017). In summary, detrital zircon ages for Mt.…”

“…7; Nelson and Cottle, 2017). The data from central TAM, therefore, suggest zircon derived from a magmatic arc that is temporally and geochemically distinct (i.e., Marie Byrd Land, Zealandia, and Australia) from the source of central Antarctica, Paraná Basin, Patagonia, and Antarctic Peninsula (Nelson and Cottle, 2017).…”

“…Limited early to middle Permian zircon Hf isotope data exists for the central TAM but late Permian and Early Triassic Hf isotope compositions are significantly more juvenile (εHf i up to +14) and there are only a minor amount of zircon with εHf i < 0 ( Fig. 7; Nelson and Cottle, 2017). The data from central TAM, therefore, suggest zircon derived from a magmatic arc that is temporally and geochemically distinct (i.e., Marie Byrd Land, Zealandia, and Australia) from the source of central Antarctica, Paraná Basin, Patagonia, and Antarctic Peninsula (Nelson and Cottle, 2017).…”

“…Constraints on the timing and geochemistry of regional Permian volcanism in the proto-Weddell Sea segment of the paleo-Pacific margin (Fig. 1) have been greatly improved by the application of zircon geochronology and geochemistry (i.e., petrochronology) in detrital studies of volcanoclastic sediments (Canile et al, 2016;McKay et al, 2016;Nelson and Cottle, 2017;Fanning et al, 2011;Castillo et al, 2016;Kylander-Clark, 2017). In particular, detrital zircon U-Pb geochronology and Hf isotopic investigations of sedimentary rocks from the Paraná Basin and accretionary complexes of the Antarctic Peninsula and Patagonia (Fig.…”

Hf- and O-isotope data from detrital and granitoid zircons reveal characteristics of the Permian–Triassic magmatic belt along the Antarctic sector of Gondwana

“…Building on the suggestion that ε Hf and δ 18 O data can be used to interpret tectonic trends (Hawkesworth and Kemp, 2006;Kemp et al, 2007), Nelson and Cottle (2017, in their review of the Gondwana margin, interpreted ε Hf values of zircons from Triassic detrital sediments and Jurassic tuffaceous rocks to show a trend of crustal growth in an extensional tectonic regime from early Paleozoic to Permian-Triassic time, with a change to a compressional regime in the Jurassic. This proposed switch to contraction and crustal recycling in the Early Jurassic, however, is not consistent with the extensional regime documented for the Lower Jurassic Hanson Formation , unless the back-arc region was tectonically disconnected from the magmatic belt.…”