Episodicity of Mesozoic terrane accretion along the Pacific margin of Gondwana: implications for superplume–plate interactions.

A review of evidence for deformation and terrane accretion on the Late Triassic–Early Jurassic margins of Pangea and the mid-Cretaceous margins of the palaeo-Pacific ocean shows that deformation was global and synchronous with probable superplume events. Late Triassic–Early Jurassic deformation appears to be concentrated in the period 202–197 Ma and was coeval with eruption of the Central Atlantic Magmatic Province, onset of Pangaea break-up, a period of extended normal magnetic polarity and a major mass extinction event, all possible expressions of a superplume event. Mid-Cretaceous deformation occurred in two brief periods, the first from approximately 116 to 110 Ma in the west palaeo-Pacific and the second from roughly 105 to 99 Ma in the east palaeo-Pacific, with both events possibly represented in northeast Siberia. This deformation was coeval with eruption of major oceanic plateaus, core-complex formation and rifting of New Zealand from Gondwana, the Cretaceous normal polarity epoch, and a major radiation of flowering plants and several animal groups, all linked with the mid-Cretaceous superplume event. A simple unifying mechanism is presented suggesting that large continental or oceanic plates, when impacted by a superplume, tend to break-up/reorganize, associated with gravitational spreading away from a broad, thermally generated topographic high and with a resulting short-lived pulse of plate-marginal deformation and terrane accretion

The West Gondwana margin : Proterozoic to Mesozoic

The longevity and extent of the oceanic southern margin of Gondwana have made it the subject of intense study for more than 70 years. It was one of the cradles of terrane theory and remains a proving ground for theories of supercontinent amalgamation and break-up. Investigation of processes on this margin, such as accretionary orogenesis and terrane analysis, is vital to our understanding of the Proterozoic and Phanerozoic evolution of the continental crust. In this special issue of Gondwana Research, entitled “The West Gondwana Margin: Proterozoic to Mesozoic”, we have assembled 9 research papers addressing various aspects of the evolution of the West Gondwana margin, first presented at the international meeting ‘Gondwana 12 (Geological and Biological Heritage of Gondwana)’, held in Mendoza, Argentina, in November 2005. Many concern southern South America, which has a fairly continuous Proterozoic to Mesozoic geological record

Climate and geology – a Phanerozoic perspective

The Phanerozoic is comprised of over 540 million years and, with its defining accompaniment of abundant complex life, provides us with a unique perspective on the extremes of climate change. Understanding these extremes is particularly important if we are to anticipate the possible effects of global warming. The broad sweep of climate change through the Phanerozoic began with relatively cool global temperatures and recovery from late Proterozoic glaciation. This was followed by a mid-Cambrian to Ordovician episode of relatively warm global climate, after which global climate cooled, culminating in the major glaciations of the Carboniferous and Permian Periods. The Triassic and Early Jurassic were warm. The Late Jurassic–Early Cretaceous Period was cool, although without full global glaciation. Global temperatures peaked in the mid-Cretaceous. Since then, global climates have cooled, culminating in Neogene glaciation. These c. 100-million-year trends in overall climate show short intense excursions of contrasting climate, many of which have been associated with the mass extinction of life, and with major volcanic and tectonic events. This paper argues that, through the Phanerozoic, two overlapping stable climate regimes appear to have dominated: a high-CO2 (.1000 ppmv), largely warm climate regime, punctuated by many short-lived episodes of glaciation; and a low-CO2 (,1000 ppmv), largely cool regime, marked by protracted episodes of superglaciation

Relics of a complex triple junction in the Weddell Sea embayment, Antarctica

Interpretation of an airborne magnetic data compilation containing a key, new survey, together with re-tracked satellite gravity data from the WeddellSeaembayment (WSE), West Antarctica, suggests Rift–Rift–Rift triplejunction formation at the onset of Gondwana breakup in the Early Middle Jurassic. Acomplex system of northwest–southeast rifts was active contemporaneously with an east–west trending rift. This rift activity led to northward separation of the Falkland Plateau, and formation of the WeddellSea by sea floor spreading. Atypically, the Jurassic passive margin of Gondwana shows evidence for coeval extension in two directions and a large volume of interpreted magmatic material. This is consistent with initial doming above a mantle plume and we suggest that this resulted in the formation of atriplejunction. Magnetic anomalies indicate a series of faults perpendicular to igneous intrusions and extrusions with outlines that range in shape from lozenges to parallel ridges. They show remarkably good spatial correlation with free air gravity anomalies, even in areas of sea ice. We base a structural elements map and timing sequence for the events in the WSE during early Gondwana breakup on anomaly cross-cutting relationships

Small-scale convection at the interface between stratified layers of mafic and silicic magma, Campbell Ridges, NW Palmer Land, Antarctic Peninsula: Syn-magmatic way-up criteria

Experimental data suggest that some igneous mafic inclusions are formed at the interface between underlying mafic magma and more silicic magma in a reservoir by a process of gas exsolution and vesiculation. We report cm-scale plume-like structures exposed over several m2 at a candidate interface in a large composite pluton from NW Palmer Land, Antarctic Peninsula and suggest that, as well as representing ‘frozen’ mafic inclusion formation, plume-like structures of this type can be used as way-up criteria and may be of particular value in the interpretation of palaeomagnetic data

Age and tectonic significance of the Lassiter Coast Intrusive Suite, Eastern Ellsworth Land, Antarctic Peninsula

Depleted mantle model ages derived from granitoids of the Lassiter Coast Intrusive Suite, sampled over a wide geographical area in eastern Ellsworth Land, Antarctica, cluster between 1000 Ma and 1200 Ma and suggest involvement of Proterozoic crust in the petrogenesis of the suite. Ion-microprobe U–Pb zircon analyses from a small intrusion at Mount Harry, situated at the English Coast, yield a concordant age of 105.2 ± 1.1 Ma, consistent with published ages from other parts of the Lassiter Coast Intrusive Suite. Significant variation in the Sr and Nd isotope composition of the granitoids, along the extrapolation of the Eastern Palmer Land Shear Zone (a proposed terrane boundary) located close to the English Coast, is not evident. However, the isotope signature at the English Coast is more homogeneous than the Lassiter Coast; this variation may relate to geographical proximity to the Pacific margin during intrusion, may reflect subtle changes in basement with a broadly similar character across the proposed terrane boundary, or suggest that any major fault structure is located further to the north, with implications for the kinematics of regional mid-Cretaceous transpression