Abstract Preserved rocks in the Jurassic Ferrar Large Igneous Province consist mainly of intrusions, and extrusive rocks, the topic of this chapter, comprise the remaining small component. They crop out in a limited number of areas in the Transantarctic Mountains and southeastern Australia. They consist of thick sequences of lavas and sporadic occurrences of volcaniclastic rocks. The latter occur mainly beneath the lavas and represent the initial eruptive activity, but also are present within the lava sequence. The majority are basaltic phreatomagmatic deposits and in at least two locations form immense phreatocauldrons filled with structureless tuff breccias and lapilli tuffs with thicknesses of as much as 400 m. Stratified sequences of tuff breccias, lapilli tuffs and tuffs are up to 200 m thick. Thin tuff beds are sparsely distributed in the lava sequences. Lava successions are mainly 400–500 m thick, and comprise individual lavas ranging from 1 to 230 m thick, although most are in the range of 10–100 m. Well-defined colonnade and entablature are seldom displayed. Lava sequences were confined topographically and locally ponded. Water played a prominent role in eruptive activity, as exhibited by phreatomagmatism, hyaloclastites, pillow lava and quenching of lavas. Vents for lavas have yet to be identified.

Abstract The Lower Jurassic Ferrar Large Igneous Province consists predominantly of intrusive rocks, which crop out over a distance of 3500 km. In comparison, extrusive rocks are more restricted geographically. Geochemically, the province is divided into the Mount Fazio Chemical Type, forming more than 99% of the exposed province, and the Scarab Peak Chemical Type, which in the Ross Sea sector is restricted to the uppermost lava. The former exhibits a range of compositions (SiO 2 = 52–59%; MgO = 9.2–2.6%; Zr = 60–175 ppm; Sr i = 0.7081–0.7138; ε Nd = −6.0 to −3.8), whereas the latter has a restricted composition (SiO 2 = c. 58%; MgO = c. 2.3%; Zr = c. 230 ppm; Sr i = 0.7090–0.7097; ε Nd = −4.4 to −4.1). Both chemical types are characterized by enriched initial isotope compositions of neodymium and strontium, low abundances of high field strength elements, and crust-like trace element patterns. The most basic rocks, olivine-bearing dolerites, indicate that these geochemical characteristics were inherited from a mantle source modified by subduction processes, possibly the incorporation of sediment. In one model, magmas were derived from a linear source having multiple sites of generation each of which evolved to yield, in sum, the province-wide coherent geochemistry. The preferred interpretation is that the remarkably coherent geochemistry and short duration of emplacement demonstrate derivation from a single source inferred to have been located in the proto-Weddell Sea region. The spatial variation in geochemical characteristics of the lavas suggests distinct magma batches erupted at the surface, whereas no clear geographical pattern is evident for intrusive rocks.

Abstract: The Ferrar Large Igneous Province forms a linear outcrop belt for 3250 km across Antarctica, which then diverges into SE Australia and New Zealand. The province comprises numerous sills, a layered mafic intrusion, remnants of extensive lava fields and minor pyroclastic deposits. High-precision zircon geochronology demonstrates a restricted emplacement duration (<0.4 myr) at c. 182.7 Ma, and geochemistry demonstrates marked coherence for most of the Ferrar province. Dyke swarms forming magma feeders have not been recognized, but locally have been inferred geophysically. The emplacement order of the various components of the magmatic system at supra-crustal levels has been inferred to be from the top-down lavas first, followed by progressively deeper emplacement of sills. This order was primarily controlled by magma density, and the emptying of large differentiated magma bodies from depth. An alternative proposal is that the magma transport paths were through sills, with magmas moving upwards to eventually reach the surface to be erupted as extrusive rocks. These two hypotheses are evaluated in terms of field relationships and geochemistry in the five regional areas where both lavas and sills crop out. Either scenario is possible in one or more instances, but neither hypothesis applies on a province-wide basis. Supplementary material: The locations of samples, and trace element data and major element analyses of samples are available at: https://doi.org/10.6084/m9.figshare.c.3819454

Abstract The development of the Transantarctic Mountains was initiated with the rifting of Rodinia and the formation of a late Neoproterozoic passive continental margin. In Cambrian time this rift setting evolved into an active margin with batholith emplacement into deformed and lightly metamorphosed upper Neoproterozoic–Cambrian strata, creating the Ross Orogen. Denudation and erosion of the Ross Orogen led to the formation of the pre-Devonian Kukri Erosion Surface on which Devonian quartzose sandstones accumulated in a continental setting. Palaeozoic magmatic arcs were intermittently active along the distal Panthalassan margin. Intra-cratonic basins developed in Permian time, one of which evolved into a foreland basin clearly related to a Permo-Triassic magmatic arc. The Palaeozoic–early Mesozoic arcs can be traced into both Australasia and South America. In Early Jurassic time the margin migrated outboard simultaneously with the advent of proximal silicic volcanism, emplacement of the Ferrar Large Igneous Province and Gondwana break-up. These events marked the onset of plate margin reorganization, and with it the early uplift of the Transantarctic Mountains. During Cretaceous and later time episodic uplift of the Transantarctic Mountains was accompanied by formation of a major crustal and lithospheric boundary marking the edge of the East Antarctic craton and the regions of crustal attenuation in the Ross (West Antarctic Rift System) and Weddell embayments.

The Permian-Triassic Transantarctic basin, which occupied the Panthalassan margin of the East Antarctic craton, including the present Transantarctic and Ellsworth Mountains, evolved above a mid-Paleozoic passive continental margin basement through the following stages: (1) Carboniferous/Permian extension, (2) late Early Permian back-arc basin, (3) Late Permian and Triassic foreland basin, and (4) Jurassic extension and tholeiitic volcanism. A mid-Paleozoic (Devonian) wedge of coastal-to-shallow marine quartzose sandstone developed on the eroded roots of the Late Cambrian-Early Ordovician Ross orogen. A lacuna in East Antarctica during the Carboniferous was followed by the inception of Gondwanan deposition in a wide Carboniferous/Permian extensional basin. Volcanic detritus at the base of the late Early Permian post-glacial marine(?) shale and sandstone sequence in the Ellsworth Mountains is the first sign of a volcanic arc and subduction along the Panthalassan margin. A similar but much thinner non-volcaniclastic sequence accumulated in the Transantarctic Mountains. The introduction of abundant volcanic detritus to the cratonic side of the basin and a 180° paleocurrent reversal in the Late Permian in the Beardmore Glacier area are the earliest indicators of tectonism along the outer margin of the basin and the inception of a foreland basin that accumulated thick Late Permian and Triassic braided stream deposits of mixed volcanic and cratonic provenance. The Permian sequences in the Ellsworth and Pensacola Mountains were folded in the Triassic. The foreland basin was succeeded in the Early Jurassic by extension and initial silicic and then tholeiitic volcanism that led to the breakup of Gondwanaland.

The upper Mesozoic to lower Cenozoic sequence in the region of James Ross Island is the only exposed marine succession of that age in Antarctica. The sequence makes up part of the fill of the James Ross Basin and includes: (1) an upper Jurassic mudstone-tuff sequence, the Nordenskjöld Formation; (2) a Lower to Upper Cretaceous conglomerate-sandstone-mudstone-tuff assemblage, the Gustav Group and equivalents; (3) an Upper Cretaceous to Paleocene poorly consolidated sand, silt, mud and tuff sequence, the Marambio Group and equivalents; and (4) an Eocene sequence of weakly consolidated, nonvolcanic fine sands and silts—the La Meseta Formation. Sedimentary facies include proximal submarine fans, shelf settings, and deltaic environments. Sea-floor anomaly data from the Pacific Ocean suggest that development of Upper Mesozoic to Cenozoic fore-arc, magmatic arc, and back-arc terrains of the Peninsula resulted from the subduction of the Phoenix Plate until the early Tertiary, and, after reorganization of spreading centers in Late Cretaceous time, subduction of the Aluk Plate. Strata in the James Ross Island region constitute the sedimentary and volcanic fill of an ensialic back-arc basin developed on the Weddell Sea flank of the Antarctic Peninsula. Broad correlations can be made between the strata and evolution of the James Ross Basin, the tectonic and magmatic history of the peninsula, and plate subduction.