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.

The present-day distributions of mylonitic belts within Yunnan and north Vietnam, along the northern boundary of early Cenozoic extruded crustal fragments around the eastern Himalayan syntaxis, collectively called the Ailao Shan–Day Nui Con Voi shear zone, cannot be traced directly into one another. There are at least three belts of mylonitic rocks, the Ailao Shan, a middle belt, and the Day Nui Con Voi, and, in Yunnan, these are separated by zones of weakly to unmetamorphosed sedimentary rocks of Triassic and possibly early Paleozoic age, narrow fault-bounded deposits of Neogene age, and young or active faults of the Red River fault zone. These three belts of mylonitic rocks are interpreted to have been originally a single through-going zone of left-lateral shear that was disrupted by younger events in an evolving shear zone. The Day Nui Con Voi belt terminates to the NW in Yunnan in a NW-plunging antiform, where it is surrounded by Triassic rocks that belong to the Yangtze platform of South China. Within Yunnan, a carapace of metasedimentary Triassic rocks locally forms the cover for the Day Nui Con Voi mylonite, but the cover is interpreted to be a tectonic cover with an original low-angle normal fault at its base. Ordovician to Triassic strata near the Vietnamese border can be inferred to be the cover of the Ailao Shan based on geological relations between the sedimentary rocks and the metamorphic and mylonitic rocks, which appear to have been joined in Mesozoic time by plutons that intruded into both sequences. The nature of the cover, whether the sedimentary rocks are the normal stratigraphic cover or a tectonic cover, is unknown. Disruption of the mylonitic belts by late Cenozoic right-lateral faulting occurred along the Red River fault zone. The preliminary tectonic conclusions suggest: (1) Triassic metamorphism, plutonism, and tectonism may have been important in the Vietnamese part of the mylonitic belts, but the extent of this event into Yunnan cannot be determined at present. (2) The early Cenozoic SE extrusion of Indochina was bounded on the NE side by a narrow mylonitic belt formed from Precambrian rocks and Paleozoic to Cenozoic igneous rocks. (3) During early Cenozoic transpressional extrusion, rocks in the evolving NE-dipping mylonitic belt were decoupled from rocks in the footwall and hanging wall by a thrust below and normal fault above. (4) While left-lateral shear was the dominant mode of deformation, upward extrusion of the ductile lower- and middle-crustal mylonitic rocks occurred early in the deformational process. (5) Decoupling of the mylonitic belt from adjacent rocks in the crust and also from rocks in the lower crust and mantle indicates that all rock units have moved relative to one another and makes determination of the magnitude of displacement difficult. (6) The Paleozoic to Triassic cover of the Ailao Shan correlates best with rocks near Erhai Lake, suggesting ~250–300 km of displacement relative to South China rocks in the hanging wall of the normal fault at the top of the mylonite belt, but they are still separated by an unknown amount of displacement from the Lanping-Simao tectonic unit farther to the SW. (7) The magnitude of displacement during disruption of the original continuous mylonite zone later in evolving transpressional left-lateral shear is limited by the broad continuity of the South China Triassic cover north of the Day Nui Con Voi and may be no more than 100 km. (8) The magnitude of late Cenozoic disruption by right-lateral brittle faults of the Red River fault zone is likewise limited by the distribution of the South China rocks and is probably ~50 km.

Recent geologic mapping has identified areas of extrusive basalts of the Middle to Late Triassic Nikolai Greenstone within the Wrangellia terrane that extend at least 80 km southwest of their previously known extent. Abundant dolerite sills of similar composition intrude Paleozoic and Mesozoic stratigraphy below the Nikolai throughout the central Talkeetna Mountains. The Talkeetna Mountains, therefore, have newly identified potential for copper, nickel, and platinum-group elements (PGEs) as disseminated, net-textured, or massive magmatic sulfide deposits hosted in mafic and ultramafic sill-form complexes related to emplacement of the Nikolai. Because of their potential high grades, similar magmatic sulfide targets have been the focus of increasing mineral exploration activity over the last decade in the Amphitheater Mountains and central Alaska Range, 100–200 km to the northeast. The Nikolai Greenstone, associated intrusions, and their metamorphosed equivalents also have potential to host stratabound disseminated “basaltic copper” deposits. Sedimentary and metasedimentary rocks overlying the Nikolai have the potential to host stratabound, disseminated, or massive “reduced-facies” type Cu-Ag deposits. Ultramafic rocks have been identified only in the extreme northeastern Talkeetna Mountains to date. However, coincident gravity and magnetic highs along the leading (northwestern) edge of and within Wrangellia in the Talkeetna and Clearwater Mountains suggest several areas that are highly prospective for ultramafic rocks related to extrusion of Nikolai lavas. In particular, the distribution, geometry, and composition of sills within the pre-Nikolai stratigraphy and the structural and tectonic controls on intrusive versus extrusive rock distribution deserve serious examination.

The Alboran Domain is constituted by the Betic-Rif orogenic system and the Alboran Sea between southwestern Europe and northwestern Africa. In this realm, the Mesozoic-Cenozoic transition represents the climax of the Alpine convergence events between Africa and Eurasia. During the rest of the Cenozoic, widespread extensional collapse and transtensional disruption occurred, which caused the generation of a wide spectrum of magmatic rocks (tholeiites, calc-alkaline to ultrapotassic series, and alkali basalts) with unusual geochemical characteristics. In the last two decades, this small spot on Earth has become a strategic site for geoscientists, inspiring more interpretations than any other comparable region of the world. The geological and volcanological complexity of the Alboran Domain has triggered a multitude of tectonomagmatic models that are often contradictory and lack the integration of all the available data. These models might be subdivided into six major groups (subduction, compression, extension, transtension, detached lithospheric roots, and mantle upwelling), plus a series of mixed scenarios. In the first section of this paper, we describe these tectonomagmatic models and then undertake a generalized review of these scenarios, in particular, the subduction schemes involving Neogene to present active subduction slabs. Then, we will suggest a tectonomagmatic model that integrates the more diagnostic geological, geophysical, and geochemical data of this domain during the Cenozoic. This unifying model involves three main stages: (1) Oligocene to early Miocene localized synorogenic extension in southern Spain involving tholeiitic dike swarms; (2) Miocene widespread postorogenic extension resulting from the convective removal of a lithospheric root, characterized by predominant calc-alkaline to ultrapotassic series (with minor tholeiitic volcanism); and (3) late Miocene to present transtension associated with a huge sinistral shear zone that spans from the Canary Islands to the North Sea which allows the extrusion of alkaline basalts.