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 Joining geological mapping, structural analysis, petrology and geochronology allowed the internal architecture of the Greater Himalayan Sequence (GHS) to be unraveled. Several top-to-the-south/SW tectonic–metamorphic discontinuities developed at the regional scale, dividing it into three main units exhumed progressively from the upper to the lower one, starting from c. 40 Ma and lasting for several million years. The activity of shear zones has been constrained and linked to the pressure–temperature–time–deformation ( P – T – t – D ) evolution of the deformed rocks by the use of petrochronology. Hanging wall and footwall rocks of the shear zones recorded maximum P – T conditions at different times. Above the Main Central Thrust, a cryptic tectonometamorphic discontinuity (the High Himalayan Discontinuity (HHD)) has been recognized in Central-Eastern Himalaya. The older shear zone, that was active at c. 41–28 Ma, triggered the earlier exhumation of the uppermost GHS and allowed the migration of melt, which was produced at peak metamorphic conditions and subsequently produced in abundance at the time of the activation of the HHD. Production of melt continued at low pressure, with nearly isobaric heating leading to the genesis and emplacement of andalusite- and cordierite-bearing granites. The timing of the activation of the shear zones from deeper to upper structural levels fits with an in-sequence shearing tectonic model for the exhumation of the GHS, further affected by out-of-sequence thrusts.

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 Based on present knowledge of mantle peridotites from the Ligurian Tethys ophiolites, this paper presents new ideas and a new model for passive rifting to ocean spreading in the slow–ultraslow rifting Europe–Adria realm. Relevant points include: (i) the positive feedback between deformation and melt percolation during passive magmatic rifting; (ii) the positive feedback between natural evidence and experimental data on the behaviour of the mantle lithosphere during passive rifting; (iii) the significance of hidden magmatism and the associated melt thermal advection; (iv) the role of the wedge-shaped weakened and softened axial zone; and (v) the evidence of a transition from passive to active rifting in the Ligurian Tethys. Passive rifting induced passive asthenospheric upwelling and the onset of partial melting. Fractional melts migrated through the mantle lithosphere and stagnated at shallow levels (the hidden magmatism). Melt thermal advection heated the mantle lithosphere to temperatures ( T ) of ≥1200°C and formed a wedge-shaped axial zone of rheological softened/weakened mantle peridotites that served as the future locus of continental break-up. The hotter/deeper asthenosphere ascended within this axial zone, underwent partial melting and formed aggregated mid-ocean ridge basalts (MORBs) that migrated within dunite channels to form olivine gabbro intrusions and basaltic lava flows. Rifting evolved from passive to active, and the actively upwelling asthenosphere established a ridge-type system and thermal regime.