Ferrar Large Igneous Province

Ferrar Large Igneous Province. It is a major Mesozoic magmatic province, primarily composed of extensive tholeiitic basalt flows and related intrusive rocks, including the distinctive dolerite sills of the Transantarctic Mountains. Formed during the Early Jurassic, its emplacement is tightly linked to the initial rifting of the supercontinent Gondwana. The province is a key component of the much larger Karoo-Ferrar magmatic event, one of the most significant LIPs in Earth's history, and its formation coincided with a major global environmental perturbation, the Toarcian anoxic event.

Geological setting and age

The province is distributed across the former contiguous margins of East Antarctica, South Africa, and other now-dispersed Gondwana fragments. Its primary exposures are found within the Beacon Supergroup sedimentary rocks of the Transantarctic Mountains, notably in areas like the Dry Valleys and Victoria Land. Additional outcrops occur in Tasmania (the Tasmanian dolerites), the Prince Charles Mountains, and as clasts in younger strata in New Zealand. High-precision Ar-Ar and U-Pb geochronology consistently date the main pulse of magmatism to the Toarcian stage of the Early Jurassic, approximately 182 to 177 million years ago. This age is contemporaneous with the peak activity of the Karoo Large Igneous Province in southern Africa, confirming their genetic relationship as a paired LIP.

Composition and petrology

The province is remarkably homogeneous, dominated by low-Ti tholeiitic basalts and dolerites with a distinctive geochemical signature. These rocks are characterized by enriched large-ion lithophile elements, depleted high field strength elements, and initial strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) greater than 0.708, indicating significant crustal contamination of the primary magmas. The dominant intrusive rock is the massive Ferrar Dolerite, which forms extensive sills and dyke swarms. Petrogenetic models, supported by studies of xenoliths and isotope geochemistry, suggest derivation from a mantle plume-like source that interacted extensively with the ancient subcontinental lithospheric mantle and overlying Proterozoic continental crust of East Antarctica.

Emplacement and structure

Emplacement occurred through both extrusive and intrusive mechanisms over a relatively short geological interval. Extensive, laterally continuous flood basalts, such as the Kirkpatrick Basalt in Antarctica, were erupted from fissure systems. Concurrently, vast quantities of magma were injected as concordant sills into the flat-lying sedimentary strata of the Beacon Supergroup, forming the spectacular Ferrar Dolerite intrusions that can be over 1.5 kilometers thick. These sills created a laccolith-like complex, causing significant hydrothermal alteration of the host sandstones and coal measures. The magmatic system also fed regional dyke swarms, which acted as feeders for the overlying lavas.

Relationship to Gondwana breakup

The formation of this province is inextricably linked to the fragmentation of Gondwana, specifically the initial rifting between East Antarctica and the Falkland Plateau. It represents the earliest major magmatic expression of the developing Weddell Sea rift system. The linear distribution of the intrusions and lavas along the paleo-Pacific margin of Gondwana suggests magmatism was facilitated by major lithospheric lineaments, such as the proposed Explora-Andenes Escarpment. While a mantle plume (sometimes called the Karoo plume) is invoked as a primary heat source, the exact timing and causal relationship between plume impact, LIP formation, and the subsequent continental breakup recorded in the Drake Passage and Scotia Sea regions remain active topics of research.

Economic significance

While not a major source of metallic ore deposits, the province has significant geological and potential economic importance. The hydrothermal systems generated by the intruding sills locally altered host rocks, producing hornfels and, in areas like the Beardmore Glacier region, stratabound copper-silver mineralizations. The thick, resistant dolerite caps form prominent escarpments that influence glacier flow and landscape evolution in Antarctica, impacting modern ice sheet dynamics. Furthermore, the province's well-exposed sills and lavas serve as a world-class natural laboratory for studying magma transport, LIP emplacement processes, and paleoclimate change, with research supported by organizations like the British Antarctic Survey and the United States Antarctic Program.

Category:Large igneous provinces Category:Geology of Antarctica Category:Jurassic magmatism Category:Geology of Tasmania