Stable URL:http://links.jstor.org/sici?sici=0036-8075%2819750808%293%3A189%3A4201%3C419%3ACTOAEO%3E2.0.CO%3B2-NScience is currently published by American Association for the Advancement of Science.Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtainedprior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content inthe JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained athttp://www.jstor.org/journals/aaas.html.Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academicjournals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers,and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community takeadvantage of advances in technology. For more information regarding JSTOR, please contact support@jstor.org.http://www.jstor.orgFri Jan 25 16:37:09 2008

https://science.sciencemag.org/content/sci/189/4201/419.full.pdf

Cenozoic Tectonics of Asia: Effects of a Continental Collision: Features of recent continental tectonics in Asia can be interpreted as results of the India-Eurasia collision.

This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

Tectonic setting of basic volcanic rocks determined using trace element analyses

Summary Examination of more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran shows that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran. This pattern of movement avoids thickening the continental crust over much of Turkey by consuming the Eastern Mediterranean sea floor instead. The rates of relative motion of two of the small plates involved, the Aegean and the Turkish plates, are estimated, but are only within perhaps 50 per cent of the true values. These estimates are then used to reconstruct the geometry of the Mediterranean 10 million years ago. The principal difference from the present geometry is the smooth curved coast which then formed the southern coast of Yugoslavia, Greece and Turkey. This coast has since been distorted by the motion of the two small plates. Similar complications have probably been common in older mountain belts, and therefore local geological features may not have been formed by the motion between major plates. A curious feature of several of the large shocks for which fault plane solutions could be obtained for the main shock and one major aftershock was that the two often had different mechanisms.

Active tectonics of Mediterranean region

http://goldrock.persiangig.com/Document/Active%20Tectonics.pdf

Active Tectonics of the Mediterranean Region

Analysis of the sedimentary, volcanic, structural, and metamorphic chronology in mountain belts, and consideration of the implications of the new global tectonics (plate tectonics), strongly indicate that mountain belts are a consequence of plate evolution. It is proposed that mountain belts develop by the deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins. These assemblages result from the events associated with the rupture of continents and the expansion of oceans by lithosphere plate generation at oceanic ridges. The earliest assemblages thus developed are volcanic rocks and coarse clastic sediments deposited in fault-bounded troughs on a distending and segmenting continental crust, subsequently split apart and carried away from the ridge on essentially aseismic continental margins. As the continental margins move away from the ridge, nonvolcanic continental shelf and rise assemblages of orthoquartzite-carbonate, and lutite (shelf), and lutite, slump deposits, and turbidites (rise) accumulate. This kind of continental margin is transformed into an orogenic belt in one of two ways. If a trench develops near, or at, the continenal margin to consume lithosphere from the oceanic side, a mountain belt (cordilleran type) grows by dominantly thermal mechanisms related to the rise of calc-alkaline and basaltic magmas. Cordilleran-type mountain belts are characterized by paired metamorphic belts (blueschist on the oceanic side and high temperature on the continental side) and divergent thrusting and synorogenic sediment transport from the high-temperature volcanic axis. If the continental margin collides with an island arc, or with another continent, a collision-type mountain belt develops by dominantly mechanical processes. Where a continent/island arc collision occurs, the resulting mountains will be small (e.g., the Tertiary fold belt of northern New Guinea), and a new trench will develop on the oceanic side of the arc. Where a continent/continent collision occurs, the mountains will be large (e.g., the Himalayas), and the single trench zone of plate consumption is replaced by a wide zone of deformation. Collision-type mountain belts do not have paired metamorphic belts; they are characterized by a single dominant direction of thrusting and synorogenic sediment transport, away from the site of the trench over the underthrust plate. Stratigraphic sequences of mountain belts (geosynclinal sequences) match those asciated with present-day oceans, island arcs, and continental margins.

Mountain belts and the new global tectonics

The ophiolite suite is probably generated by axial plate accretion at oceanic ridges, and by diffuse slow spreading in marginal basins behind and within island arc complexes. The dunite/harzburgite component may represent the highest parts of a depleted upper mantle shell, about 16 km thick, from which a basaltic partial melt (approx. 30%) has been withdrawn to form the gabbros, dike swarms, and pillow lavas. Ophiolites have complex internal igneous, structural, and metamorphic relationships that are probably related to processes involved in their generation at ridges and in marginal basins, having no significance in terms of processes within the orogenic belt in which they are finally emplaced. Varying plate accretion rates may have a great influence on the structural and metamorphic patterns of ophiolites. The autochthonous sedimentary cap of ophiolites developed by axial accretion may, rarely, consist of continental margin non-volcanic flysch and salt, but usually comprises chert, argillite, and deep-water limestone: that of ophiolites generated in marginal basins probably consists, in addition to these facies, of andesitic flysch derived from adjacent island arcs.

Ophiolites are probably emplaced, in orogenic belts, at consuming plate margins either beneath and behind oceanic trenches (subduction zones) or by thrusting onto continental margins (obduction zones) when a continental margin meets a subduction zone. Metamorphic relationships within and around ophiolite complexes are numerous, probably reflecting processes involved in both genesis and emplacement, and may involve (1) thermal and hydrothermal alteration at the site of origin, (2) blueschist metamorphism in subduction zones, (3) regional high-temperature metamorphism in island arcs, (4) high-temperature aureoles developed around peridotites injected into oceanic crust at time of origin, into the transition region between marginal basins and island arcs or into the regionally metamorphosed assemblages of island arcs, (5) garnet-amphibolites developed along the sole thrusts of obducted peridotites, which may represent transported high-temperature arc metamorphics, oceanic crust, or metamorphic rocks generated during obduction, (6) rodingites developed during low-temperature peridotite diapirism and serpentinization on ridge flanks or during ophiolite emplacement, and (7) amphibolites and eclogites, in subduction melanges, representing transformed oceanic crust ripped up from the downgoing plate beneath trenches.

Obducted ophiolites often indicate a narrow time span between origin and emplacement, possibly due to the opening and closing of marginal basins. Evolving ridge/transform/trench and trench/trench/trench triple junctions have great significance for developing diachronous events associated with ophiolite emplacement along continental margins and island arcs.

Early Ordovician ophiolites in the Newfoundland Appalachians have complex and variable structural relationships with rocks of the Paleozoic continental margin. Immense obducted ophiolite slices carry transported garnet-amphibolites, and are believed to have developed in a marginal basin behind early Paleozoic island arcs on the northwestern (present) margin of a proto-Atlantic Ocean.

Origin and Emplacement of the Ophiolite Suite: Appalachian Ophiolites in Newfoundland

In terms of plate tectonic theory, and by analogy with modern continental margins, the Appalachian orogen evolved through a sequence of interrelated sedimentation-deformation-metamorphism patterns within a tectonic belt situated along the eastern margin of the North American continent. As exemplified by the northern part of the orogen, Appalachian stratigraphic-tectonic zones and deformation sequences are related to Late Precambrian to Ordovician expansion, followed by Ordovician through Devonian contraction, of a Proto-Atlantic ocean. This oceanic opening and closing was achieved by initial extensional necking of a single North American/African continent and by lithosphere plate accretion, followed by contractional plate loss along a trench, or complex of trenches, marginal to the drifted North American continent. A lithosphere plate model for the evolution of the orogen incorporates spatial and chronologic relations within and between bulk stratigraphic units and tectonic events. Pre-orogenic Appalachian sedimentation patterns were essentially the same as those found along modern continental margins; that is, shelf/slope/rise/abyss. Appalachian tectonic patterns are also analogous with modern tectonic patterns of continental margins, island arcs, and trenches, and involved continent-ward driven thrust sheets and ancillary exogeosynclines.

Lithosphere Plate-Continental Margin Tectonics and the Evolution of the Appalachian Orogen

The dislocation structure, recrystallization, and elongation of quartz grains in tectonites from three localities along the Moine thrust fault have been analyzed by transmission electron and optical microscopy. The dislocation density, 5×108 cm−2, and the grain size after recrystallization, 15 μ, in the basal quartzite unit at the Stack of Glencoul are independent of distance from the fault, to the maximum sampling distance of ∼100 m. The differential stress level determined from the deformation-induced microstructures is on the order of 100 MPa. The magnitude of the differential stress at the fault decreases by a factor of 2 from Knockan Crag to Loch Eriboll, a distance of 50 km. At the Stack of Glencoul, grains in the basal quartzite are progressively elongated and recrystallized approaching the fault, corresponding to a progressive increase in strain. At 100 m from the fault, the aspect ratio of relict quartz grains is ∼1:1; at 0.01 m it is 85:1. A quantitative estimate of the strain, based on the aspect ratios of the relict quartz grains, as a function of distance from the fault has been used to calculate strain rate and temperature profiles. For a creep activation energy of 0.19 MJ mol−1 the temperature decreases away from the fault with a gradient of 7.5×10−3 °C cm−1. For a differential stress of 100 MPa, a steady state thrust sheet velocity of 11 cm yr−1 would be required to produce this gradient. At 100 m from the fault, 5% of the quartzite is recrystallized from 1-mm to 15-μm grains; at 0.01 m it is 100% recrystallized to 15-μm grains. This small grain size probably favored grain boundary deformation mechanisms over grain matrix mechanisms and thus helped to concentrate the strain at the fault. Systematic changes in the elongation and recrystallization of quartz grains in Lewisian Gneiss and Moine Schist are obscured by the constraints imposed by other mineral phases. The small size of the grains after recrystallization, highly serrated grain boundaries, and large densities of free dislocations suggest that very little static recovery followed the plastic deformation event.

John M. Bird

Papers

Mountain belts and the new global tectonics

Origin and Emplacement of the Ophiolite Suite: Appalachian Ophiolites in Newfoundland

Lithosphere Plate-Continental Margin Tectonics and the Evolution of the Appalachian Orogen

Differential stress determined from deformation‐induced microstructures of the Moine Thrust Zone

Plate tectonics and geosynclines