Large igneous provinces (LIPs) are a continuum of voluminous iron and magnesium rich rock emplacements which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts Such provinces do not originate at “normal” seafloor spreading centers We compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts Crustal thicknesses range from 20 to 40 km, and the lower crust is characterized by high (70-76 km s?1) compressional wave velocities Volumes and emplacement rates derived for the two giant oceanic plateaus, Ontong Java and Kerguelen, reveal short-lived pulses of increased global production; Ontong Java’s rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system The major part of the North Atlantic volcanic province lies offshore and demonstrates that volcanic passive margins belong in the global LIP inventory Deep crustal intrusive companions to continental flood volcanism represent volumetrically significant contributions to the crust We envision a complex mantle circulation which must account for a variety of LIP sizes, the largest originating in the lower mantle and smaller ones developing in the upper mantle This circulation coexists with convection associated with plate tectonics, a complicated thermal structure, and at least four distinct geochemical/isotopic reservoirs LIPs episodically alter ocean basin, continental margin, and continental geometries and affect the chemistry and physics of the oceans and atmosphere with enormous potential environmental impact Despite the importance of LIPs in studies of mantle dynamics and global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

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Large igneous provinces: crustal structure, dimensions, and external consequences

https://www.utdallas.edu/~rjstern/egypt/PDFs/Cenozoic%20Red%20Sea/BosworthRedSeaJAES05.pdf

The Red Sea and Gulf of Aden Basins

The concept of 'Gondwana', an ancient Southern Hemisphere supercontinent, is firmly established in geological and biogeographical models of Earth history. The term Gondwana (Gondwanaland of some authors) derives from the recognition by workers at the Indian Geological Survey in the mid- to late 19th century of a distinctive sedimentary sequence preserved in east central India. This succession, now known to range in age from Permian to Cretaceous, is lithologically and palaeontologically similar to coeval non-marine sedimentary successions developed in most of the Southern Hemisphere continents suggesting former continuity of these landmasses. Palaeomagnetic data and tectonic reconstructions suggest that the main assembly of Gondwana took place around the beginning of the Palaeozoic in near-equatorial latitudes and that the supercontinent as a whole shifted into high southern latitudes, allowing widespread glaciation by the end of the Carboniferous. From Carboniferous to Cretaceous times the southern continents had broadly similar floras but some species-level provincialism is apparent at all times. The break-up of Gondwana initiated during the Jurassic (at about 180 million years ago) and this process is continuing. The earliest rifting (crustal attenuation) within the supercontinent initiated in the west (between South America and Africa) and in general terms the rifting pattern propagated eastward with major phases of continental fragmentation in the Early Cretaceous and Late Cretaceous to Paleogene. Gondwanan floras show radical turnovers near the end of the Carboniferous, end of the Permian and the end of the Triassic that appear to be unrelated to isolation or fragmentation of the supercontinent. Throughout the late Palaeozoic and Mesozoic the high-latitude southern floras maintained a distinctly different composition to the palaeoequatorial and boreal regions even though they remained in physical connection with Laurasia for much of this time. Gondwanan floras of the Jurassic and Early Cretaceous (times immediately preceding and during break-up) were dominated by araucarian and podocarp conifers and a range of enigmatic seed-fern groups. Angiosperms became established in the region as early as the Aptian (before the final break-up events) and steadily diversified during the Cretaceous, apparently at the expense of many seed-fern groups. Hypotheses invoking vicariance or long distance dispersal to account for the biogeographic patterns evident in the floras of Southern Hemisphere continents all rely on a firm understanding of the timing and sequence of Gondwanan continental breakup. This paper aims to summarise the current understanding of the geochronological framework of Gondwanan breakup against which these biogeographic models may be tested. Most phytogeographic studies deal with the extant, angiosperm-dominated floras of these landmasses. This paper also presents an overview of pre-Cenozoic, gymnosperm-dominated, floristic provincialism in Gondwana. It documents the broad succession of pre-angiosperm floras, highlights the distinctive elements of the Early Cretaceous Gondwanan floras immediately preceding the appearance of angiosperms and suggests that latitudinal controls strongly influenced the composition of Gondwanan floras through time even in the absence of marine barriers between Gondwana and the northern continents. Go na br nd prn ti l S.ou

The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism

After thirty years of plate-tectonic theory, the reasons why supercontinents disintegrate and disperse to form smaller continental plates remain enigmatic. Possible causes range from abnormally hot mantle upwellings, or plumes, to changes in plate-boundary driving forces. The breakup of the Gondwanaland super-continent, which started about 180 million years ago, provides an excellent case history against which to test models.

The role of mantle plumes in continental breakup: case histories from Gondwanaland

Linking accretionary orogenesis with supercontinent assembly

Several late-collision and intraplate features are not entirely integrated in the classical plate tectonic model. The Pan-African orogeny (730-550 Ma) in Saharan Africa provides some insight into the contrasting behaviour of cratons and mobile belts. Simple geophysical considerations and geological observations indicate that rigidity and persistence of cratons are linked to the presence of a thick mechanical boundary layer, the upper brittle part of the continental lithospheric mantle, well attached to an ancient weakly radioactive crust. The surrounding Pan-African mobile belts, characterized by a much thinner mechanical boundary layer and more radioactive crust, were the locus of A-type granitoids, volcanism, tectonic reactivation and basin development during the Phanerozoic. During oceanic closures leading to the assembly of Gondwana, lithosphere behaviour was controlled by its mechanical boundary layer, the crust being much less rigid. We suggest that the 5000 km wide Pan-African domain of Saharan Africa, a collage of juvenile and old reactivated basement terranes, has suffered regional continental lithospheric mantle delamination during the early stages of this orogeny, as has been postulated for the more recent Himalayan orogeny in Tibet. Delamination of the continental lithospheric mantle and juxtaposition of crust against hot asthenosphere can explain many features of the late Pan-African (around 600 Ma): reactivation of old terrains, abundant late-tectonic high-K calc-alkaline granitoids, high temperature-low pressure metamorphism, important displacements along mega-shear zones and mantlederived post-tectonic granitoids linked to a rapid change in mantle source. Recycling into the asthenosphere of large amounts of continental lithospheric mantle delaminated during the Pan-African, can provide one of the reservoirs needed to explain the isotopic compositions of ocean island basalts. Lastly, the lithospheric control over the location of the alkaline rocks enjoins us to consider the thermal boundary layer (the lower ductile part of the continental lithospheric mantle) as a major mixing source zone for these rocks. Plate tectonic theory does not explain directly some intracontinental features, such as rapid uplift, widespread postcollisional crustal deformation or igneous activity far from plate boundaries (Bird 1979). The contrasting behaviour of cratons and mobile belts during and after collisions, repeated intraplate magmatism at the same place, basin development and reactivations of shear zones, also require explanation. Based on simple geophysical notions already developed in the literature, parallels drawn with Tibet and our experience in Pan-African geology and alkaline rocks, we propose a composite but coherent model which, in the plate tectonic framework, clarifies interpretations in structural geology, mantle geochemistry and global geodynamics. The Pan-African, comparable in scale to the currently active Alpine-Himalayan-Circum Pacific orogenic belt, is unique in that evidence of the end of a Wilson cycle with creation of a supercontinent, in this case Gondwana, is well preserved even if still largely undeciphered (Black 1978; Hoffman 1991). Attention will be focused on the Pan-African (750550 Ma) Trans-Saharan belt (Fig. 1) limited to the west by the West African craton stable since 2 Ga. This belt, extending from Mall to Saudi Arabia, comprises numerous accreted island arcs and related tonalite-trondhjemite-granodiorite associations, principally at both extremities. Elsewhere it is characterized by reactivated Archaean and lower Proterozoic terranes, thrusted ophiolitic sutures, abundant high-K calcalkaline granitoids, major shear zones parallel to craton margins, and widespread development of Phanerozoic anorogenic 89 alkaline magmatism. There is apparently only one solution to explain all these features: to give a major role to the continental lithospheric mantle. Continental lithospheric mantle and cratons The lithospheric mantle is the lower part of the plates which move on the convecting asthenospheric mantle. In the oceans, its lower limit is classically given by the c. 1300 °C isotherm (Kay et al. 1970), the peridotite dry solidus. However, the base of the mechanical boundary layer, the layer able to support loads of long duration (Karner et al. 1983), is much shallower and corresponds to the brittle-ductile transition in the mantle (Parsons & McKenzie 1978). The thickness of this mechanical boundary layer probably approximates to the elastic thickness, the value of which can be determined from the isostatic response of the lithosphere to loading. It is roughly equivalent to the depth of the 450 _+ 150 °C isotherm (Watts et al. 1980). The 600 °C isotherm is adopted here as corresponding to both the mechanical boundary layer and the elastic thickness (Bergman 1986; Anderson 1991). This layer is probably completely isolated from the convecting mantle and so can then acquire specific isotopic or chemical compositions (McKenzie & Bickle 1988). The thermal boundary layer constitutes a transition between the mechanical boundary layer and the asthenosphere (Fig. 2). If the conservative view that gives a small elastic strength to the continental crust is true (Grotzinger & Royden 1990), the 90 R. BLACK & J.-P. LIEGEOIS k.. / + + + + / . , : 7 ~ ,/ ~ ', ' c.,wosr "'-'"-""/-N:-:-~/ + + ÷ + + + ' . . . ; .. " & .7 ~' ' , ; ,

Magmatism and the causes of continental break-up

Mid-Cretaceous igneous rocks of central Marie Byrd Land, Antarctica record a rapid change from subduction-related to rift-related magmatism. This correlates with the final stages of subduction of the Phoenix plate and the subsequent rifting of New Zealand from West Antarctica, prior to the opening of the Southern Ocean. Rift magmatism produced diverse A-type granitoids and mafic intrusive rocks of continental flood-basalt affinity that were derived ultimately from lithospheric mantle sources. Rifting was caused by changes in plate boundary forces; however, mantle plume activity may have begun in mid-Cretaceous time, triggering melting of the lithosphere and controlling the locus of rifting.

Antarctica-New Zealand rifting and Marie Byrd Land lithospheric magmatism linked to ridge subduction and mantle plume activity

Marie Byrd Land, Antarctica, is a major part of the proto-Pacific supercontinental margin. On the basis of new geochronological and geochemical data relating to its pre-Jurassic evolution, Marie Byrd Land is subdivided into western or interior (“Ross”) and eastern or exterior (“Amundsen”) provinces, equivalent to two superterranes in New Zealand. The Ross province is characterized by Cambrian? metagraywackes and I-type orthogneiss dated at 505±5 Ma by U-Pb SHRIMP (Sensitive High Resolution Ion Microprobe). Its magmatic record consists of Devonian-Carboniferous (375±5 Ma and circa 339±6 Ma), predominantly I-type granitoids, and further minor granitic magmatism in Permo-Triassic times. This Paleozoic history is comparable to that of the Gondwana margin in northern Victoria Land, western New Zealand, and SE Australia. The Amundsen province has no observed Paleozoic graywacke succession; evidence from Rb-Sr and U-Pb SHRIMP dating supports calc-alkaline granitoid events in Ordovician/Silurian (450–420 Ma) and Permian (276±2 Ma) times. The latter may be the previously unknown source of Permian volcanic detritus in the Ellsworth and Transantarctic mountains. The Amundsen province is considered to be the equivalent of the Median Tectonic Zone of New Zealand, and arc magmatism of comparable ages is found in the Antarctic Peninsula and Thurston Island. The underlying lithosphere of the two provinces may be distinguished by Nd isotope data; granitoids and metasedimentary rocks of the Ross province have Meso-Proterozoic Nd model ages, generally 1300–1500 Ma, compared to 1000–1300 Ma for the Amundsen province. On the basis of published palaeomagnetic data, the two provinces amalgamated to form Marie Byrd Land in mid-Cretaceous times, only shortly before rifting of the New Zealand continental block away from Antarctica.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JB02605

Geochronology and geochemistry of pre-Jurassic superterranes in Marie Byrd Land, Antarctica

New Pb, Nd, and Sr isotope data are presented for geochemically similar, ∼1.1–1.2 Ga, granitoids and tonalitic‐granitic orthogneisses from Antarctica, southern Africa, and the Falkland Islands and adjoining plateau, areas originally within the supercontinents of Rodinia and Gondwana. These data support contentions for the presence of a Mesoproterozoic (∼1.2 Ga) destructive plate margin running from Namaqua‐Natal (southern Africa), through the displaced microplates of the Falkland Plateau and Falkland Islands, the Haag Nunatak crustal block (West Antarctica) and into western Dronning Maud Land (East Antarctica). The bulk of these granitoids represent juvenile Mesoproterozoic additions to the crust, except for in parts of East Antarctica (i.e., the Sverdrupfjella) where older (Paleoproterozoic or Archean) crust was involved in granitoid generation. Our isotope data permit plate reconstructions in which southern Africa, East Antarctica, and the Falkland Islands and plateau were adjacent within Rodinia.

https://www.jstor.org/stable/10.1086/516051

R.J. Pankhurst

Papers

Magmatism and the causes of continental break-up

Antarctica-New Zealand rifting and Marie Byrd Land lithospheric magmatism linked to ridge subduction and mantle plume activity

Geochronology and geochemistry of pre-Jurassic superterranes in Marie Byrd Land, Antarctica

Pb, Nd, and Sr Isotope Mapping of Grenville‐Age Crustal Provinces in Rodinia

West Antarctica in Gondwanaland: Crustal blocks, reconstruction and breakup processes