MOST volcanic rocks in modern island and continental arcs are probably derived from melting of the mantle wedge, induced by hydrous fluids released during dehydration reactions in the subducted lithosphere1. Arc tholeiitic and calc-alkaline basaltic magmas are produced by partial melting of the mantle, and then evolve by crystal fractionation (with or without assimilation and magma mixing) to more silicic magmas2—basalt, andesite, dacite and rhyolite suites. Although most arc magmas are generated by these petrogenetic processes, rocks with the geochemical characteristics of melts derived directly from the subducted lithosphere are present in some modern arcs where relatively young and hot lithosphere is being subducted. These andesites, dacites and sodic rhyolites (dacites seem to be the most common products) or their intrusive equivalents (tonalites and trondhjemites) are usually not associated with parental basaltic magmas3. Here we show that the trace-element geochemistry of these magmas (termed 'adakites') is consistent with a derivation by partial melting of the subducted slab, and in particular that subducting lithosphere younger than 25 Myr seems to be required for slab melting to occur.

Derivation of some modern arc magmas by melting of young subducted lithosphere

A new tectonic model, postulating the growth of giant subduction-accretion complexes along a single magmatic arc now found contorted between Siberia and Baltica, shows that Asia grew by 5.3 million square kilometres during the Palaeozoic era. Half of this growth may have occurred by the addition of juvenile crust newly extracted from the mantle, supporting models of considerable continental growth continuing throughout the Phanerozoic eon.

Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia

Assembly, configuration, and break-up history of Rodinia: A synthesis

The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic–Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian–Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with formation of the Solonker suture. We evaluate contrasting tectonic models for the evolution of the orogenic belt. Current information provides little support for the main tenets of the one- or three-arc Kipchak model; current data suggest that an archipelago-type (Indonesian) model is more viable. Some diagnostic features of ridge–trench interaction are present in the Central Asian orogen (e.g. granites, adakites, boninites, near-trench magmatism, Alaskan-type mafic–ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, rhyolitic ash-fall tuffs). They offer a promising perspective for future investigations.

/pdf/tectonic-models-for-accretion-of-the-central-asian-orogenic-4rjcoan76s.pdf

Tectonic models for accretion of the Central Asian Orogenic Belt

We present four companion digital models of the age, age uncertainty, spreading rates, and spreading asymmetries of the world's ocean basins as geographic and Mercator grids with 2 arc min resolution. The grids include data from all the major ocean basins as well as detailed reconstructions of back-arc basins. The age, spreading rate, and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments. The age uncertainties for grid cells coinciding with marine magnetic anomaly identifications, observed or rotated to their conjugate ridge flanks, are based on the difference between gridded age and observed age. The uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities. Asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges, resulting in ridge jumps toward hot spots. We also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age-depth relationships. The new set of grids helps to investigate prominent negative depth anomalies, which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow. A combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems.

/pdf/age-spreading-rates-and-spreading-asymmetry-of-the-world-s-5bj3otyvfc.pdf

Age, spreading rates, and spreading asymmetry of the world's ocean crust

Atlas of Mesozoic and Cenozoic Plate Tectonic Reconstructions 1987 (Paleoceanographic Mapping Project)

Deconstructing Tectonics: Ten Animated Explorations

The recognition of many small terranes bordering the Early Paleozoic Iapetus Ocean has entailed the revision of previous models, that only discussed the relations between the major continents. In this paper we illustrate the development of Iapetus through 1OO Ma by means of six maps drawn by computer graphics. In addition to paleomagnetic data, we have used biogeographic affinities, sedimentary facies, tectonic events and the distribution of igneous rocks to develop our assessment of continental and terrane distributions, and the positions of arcs and trenches. The tectonic model presented here is thus much more complex than the model first postulated by Wilson (1966) invoking the presence of a "Wide ocean in the Caledonides and Northern Appalachians, or the original plate tectonic model proposed by Dewey (1969). Subsequent models for the development of Iapetus have been proposed which we have taken into account in this review.

Ordovician to Devonian Development of the Iapetus Ocean (Paleoceanographic Mapping Project Report No. 08-0185)

Paleolatitudinal distribution of lithologic indicators of climate in a paleogeographic framework

Explaining the origin of large-scale biodiversity gradients has been a key aspiration of early naturalists such as Wegener, Darwin and Humboldt; who looked at natural processes in an integrated way. Early on, these naturalists acknowledged the role of plate tectonics and climate variations in shaping modern day biodiversity patterns.&#160;As science advanced, the complexity of ecological, evolutionary, geological and climatological processes became evident while research became increasingly fragmented across different disciplines. Nevertheless, recent development in mechanistic modeling approaches now enable bringing disciplines back together, opening a new interdisciplinary scientific pathway.Here, we present GEN3SIS, the GENeral Engine for Eco-Evolutionary SImulationS. It is the first spatially explicit eco-evolutionary model that incorporates deep-time Earth history, including plate tectonics, as well as climate variations in a modular way. The modular design allows exploring the consequences of user-defined biological processes that act across &#8220;real world&#8221; spatio-temporal landscapes. Emerging from the model are specie&#8217;s ranges, alpha and beta diversity patterns, ecological traits as well as phylogenies. Subsequently, these patterns can be compared to empirical data. Furthermore, GEN3SIS allows assessing paleoclimatic and paleogeographic hypotheses by using different Earth history scenarios and comparing simulation outputs with empirical biological data.As a case study, we explore the cold-adapted plant biodiversity dynamics throughout the Earth&#8217;s Cenozoic history, based on a deep-time tectonic and climate reconstruction. The Cenozoic India-Asia collision formed the Himalayan mountain range. In this highly elevated region, the first cold niches of the Cenozoic appeared, demanding adaptation from the local living flora. We hindcast diversification of cold-adapted species with GEN3SIS, for which we use a topo-climatic reconstruction for the last 55 Myr. The model predicts the emergence of current cold-species richness patterns. Moreover, simulations indicate that cold-adapted flora emerged in the Oligocene, first in the Himalayas, followed by a spread to the Arctic. This agrees with observed low species richness and high nestedness of Arctic assemblages compared to those of the Himalayan mountain ranges. Under ongoing climate change a major loss of cold-adapted plant diversity is expected by the end of the century, particularly in lower latitude mountain ranges. Hindcasting and forecasting dynamics of cold-adapted lineages highlights the transient fate of cold organisms in a warming world.GEN3SIS is made available as an R package, which allows customizing (i) the simulated landscape including environmental variables and (ii) all the processes interacting under different spatial and temporal scales. Consequently, GEN3SIS fosters collaborations between different natural disciplines and therefore contributes to an interdisciplinary understanding of the processes that shaped Earth&#8217;s history.

Christopher R. Scotese

Papers

Atlas of Mesozoic and Cenozoic Plate Tectonic Reconstructions 1987 (Paleoceanographic Mapping Project)

Deconstructing Tectonics: Ten Animated Explorations

Ordovician to Devonian Development of the Iapetus Ocean (Paleoceanographic Mapping Project Report No. 08-0185)

Paleolatitudinal distribution of lithologic indicators of climate in a paleogeographic framework

GEN3SIS: An engine for simulating eco-evolutionary processes in the context of plate tectonics and deep-time climate variations