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Crustal temperatures within collisional orogens are anomalously high compared with temperatures at comparable depths in stable continents, which is evidence of thermal processes that are fundamental to orogenesis. These temperatures can be explained by the redistribution of crust enriched in heat-producing elements through the accretion of crust from the down-going plate to the upper plate and surface erosion. With the use of geologically reasonable rates, the model results predict high temperatures (over 600 °C) and inverted upper-plate geotherms (about 100 °C over 20 kilometers) at shallow depths (20 to 40 kilometers) by 25 to 35 million years after collision. This study emphasizes the interdependence of deformational, surficial, and thermal processes., Rocks present at the surface in many collisional orogens contain metamorphic mineral assemblages indicating high temperatures (~600 to 700 °C) at midcrustal depths (20 to 30 km) (1). In some [...]

Thought experiments imply that stratigraphic cycles controlled directly by eustasy include keep-up, catch-up, catch-down (foreshortened or truncated), and give-up variants, different patterns of thickness and facies being governed by the interplay of sedimentation rate and accommodation space. Most examples of these types are, in addition, base-cutout cycles, wherever lowstands of sea level dropped below the top of the underlying cycle. Overall thicknesses of multiple cycles at any locale are controlled ultimately by net subsidence rate. Accordingly, even keep-up and catch-up cycles can faithfully record full accommodation only where tectonic subsidence during cycle formation paced eustatic fluctuation. Paradoxically, however, only condensed cycles that fortuitously compensate for syncycle tectonic subsidence can accurately record the eustatic amplitude, as adjusted for water loading.

A methodology for assessing the seismic stability of tailings dams and possible upgrading frameworks is presented. The main seismic design factors involved in this analysis are the site-specific earthquake-induced motions and the seismic behaviour under seismic loading. Themethods of analysis in the assessment of the significance of the design seismicloading on the tailing structure are enumerated and discussed. The impact of the failure on people and the environment, cost and feasibility of upgrading works and the risk or probability of failure are the requirements in seismic upgrading.

Otoh et. al. (1990) deny evidence of a Permian-traissic orogeny in southwest Japan. However, their model suffers from the following major flaws: dating of Sanbagawa metamorphism, geological zonation, inclusion of the Yakuno complex and the Ultra-Tanba zone in the Maizuru belt, the origin of Outer belt rocks, and the reef limestone-domination of Outer zone Jurassic sediments. Their model thus ignores current evidence on Permian-early Triassic tectonometamorphism.

High-temperature creep experiments on polycrystalline perovskite ([CaTiO.sub.3]), an analog of (Mg,Fe)[SiO.sub.3] perovskite of the lower mantle, suggest that (grain size-sensitive) diffusion creep is important in the lower mantle and show that creep rate is enhanced by the transformation from the orthorhombic to the tetragonal structure. These observations suggest that grain-size reduction after a subducting slab passes through the 670-kilometer discontinuity or after a phase transformation from orthorhombic to tetragonal in perovskite will result in rheological softening in the top portions of the lower mantle., DYNAMICS OF EARTH'S INTERIOR depend critically on the plastic flow properties of its constituent materials. Plastic flow in rocks occurs either by the collective motion of atoms by dislocation glide [...]

Data from seismological observations, rock physics experiments and geodynamic modeling that offer insights into the seismic structure and dynamics of the mantle wedge are discussed. Information on the forearc and backarc of the mantle structure, temperature dependence, and melt content and flow that affect the seismic properties of rocks on the mantle wedge is also presented.

The experimental simulations of C[O.sub.2-] driven water eruptions and dynamic models of such eruptions are reviewed and a bubble plume theory is applied to the dynamics of lake eruptions. Field evidence, experimental results, and theoretical models show that lake eruptions can be violent, and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations.

The author would like to thank the discusser for his interest in the paper. The discusser provided multiple comments, and suggested that clarifications be offered in regard to three areas: [...]

Originally posted on 30 September 2013 When the IPCC policymaker summary for AR5 was released in September, it immediately began sharing the news headlines. Considering that the competing stories here [...]

We have investigated the effect that metamictization has on the weathering of zircon in detrital continental sediments and tropical soils of the Amazon basin, Brazil. The degree of radiation damage in the near-surface region of the zircon grains was determined by Raman microprobe. In each of the four series investigated (i.e., sediment, podzol, topsoil, and subsoil horizons of lateritic soil), the degree of radiation damage ranges from less than [10.sup.14] to ~3.5 x [10.sup.15] [Alpha]-decay/mg. The maximum degree of radiation damage coincides with the first percolation threshold of the metamictization process at ~3.5 x [10.sup.15] [Alpha]-decay/mg. Below this threshold, amorphous volumes in the structure of damaged zircon are not connected to each other. The ranges of U, Th, and Pb contents (in ppm) measured by proton induced X-ray emission (PIXE) microanalysis are 100 [is less than] U [is less than] 7000, 100 [is less than] Th [is less than] 18000, and 100 [is less than] Pb [is less than] 1300. Chemical ages, assessed from U, Th, and total-Pb, range between 0.15 Ga and 2.8 Ga. This range is roughly consistent with the ages reported for the Precambrian shields of the Amazon basin (0.45-3.5 Ga). Corresponding radiation doses range between [is less than] 2 x [10.sup.15] and 3 x [10.sup.16] [Alpha]-decay/mg. Comparison of calculated doses with the degree of structural damage indicates that most of the zircon grains have experienced significant annealing. However, the degree of annealing differs from one grain to another. Thus, the acute maximum limit observed for the degree of radiation damage of the whole zircon series is better explained by low-temperature alteration or weathering processes than by thermal resetting. Following this interpretation, our results provide evidence for a dramatic decrease in the chemical durability of zircon in natural weathering environments when the radiation dose exceeds 3.5 x [10.sup.15] [Alpha]-decay/mg. Below the first percolation threshold, the zircon population survives the soil formation intact, but more damaged zircons are dissolved during weathering/alteration processes.

Controversy exists over whether east-west extension in southern Tibet is related to plateau uplift or to the accommodation of plate boundary forces. Relationships between the onset of extension, plateau uplift, and the thermal state of the lithosphere are critical to this debate. We present new data on postcollisional, north-south-trending dikes in southern Tibet. Their ages range from 18.3 [+ or -] 2.7 Ma to 13.3 [+ or -] 0.8 Ma, and define the onset of regional east-west extension in southern Tibet. Dikes are compositionally indistinguishable from postcollisional lavas in southern Tibet, being either ultrapotassic, having a source in the subcontinental lithospheric mantle, or calc-alkaline with a dominantly crustal origin. The ultrapotassic dikes demonstrate that east-west extension and subcontinental lithospheric mantle-derived magmatism were temporally and spatially linked, supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning. Thus, the onset of extension by 18.3 [+ or -] 2.7 Ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces. This places a new age limitation on the attainment of high elevation in southern Tibet, with implications for models that relate Cenozoic monsoon intensification to plateau uplift. Keywords: Tibet, extension, Ar-Ar, magmatism, geodynamics.

The southeastern tip of the Peninsula de Nicoya, Costa Rica, on the Caribbean plate margin lies inboard of the rough bathymetric terrain on the subducting Cocos plate and along the landward projection of the convergence vector for the Fisher seamount group. The southern tip of the peninsula has nearly orthogonal coastlines and extensive, well-preserved, Holocene marine terraces, and is ideally situated to evaluate the spatial distribution of forearc deformation in response to seamount subduction. Two marine terraces that yielded 35 radiocarbon dates give information on the rates, style, and timing of deformation along 40 km of coastline. Ages range from 3.5 to 7.4 ka for a higher terrace and from 0.3 to 2.9 ka for a lower terrace. A maximum uplift rate is ~6.0 m/k.y, along the southeastern tip of the peninsula. Uplift rates decrease linearly to [is less than] 1.0 m/k.y, along both orthogonal coastlines and thus landward from the Middle America Trench and away from the line of subducting seamounts. The ~400 [km.sup.2] region along the tip of the peninsula can be approximated as a rotating block with an angular rotation rate of 0.02 [degrees]/k.y. about an axis with an azimuth of 80 [degrees]. Given the modern elevation and dip of the late Quaternary Cobano surface, this style of deformation is limited to a duration of 100-200 k.y. Deformation is occurring in response to seamount bypass or underplating onto the Caribbean plate margin. Keywords: Costa Rica, marine terrace, Quaternary, tectonism, seamounts.

Published age data from the Humber zone of the southern Quebec Appalachians indicate that deformation and metamorphism occurred during Middle to Late Ordovician time. This paper presents the results of a regional-scale geochronological study of 70 amphibole and mica single grains by the [sup.40]Ar/[sup.39]Ar laser step-heating method, which brings forward a more complete Middle Ordovician-Early Devonian tectonometamorphic evolution of the Quebec Appalachian Humber zone. Biotites have plateau ages varying between 420 and 411 Ma. Amphiboles are often compositionally rimmed and/or contain biotite inclusions. Their age spectra are generally disturbed, but may suggest the occurrence of two distinct events: Silurian (429-424 Ma) and Middle Ordovician (462-460 Ma). Two main groups of muscovite ages have been obtained: Middle Ordovician (469-461 Ma) and Silurian-Early Devonian (431-411 Ma), but Middle to Late Devonian (387-376 Ma) ages are also locally present. Middle Ordovician ages are interpreted to record crustal thickening by nappe emplacement during regional Taconian metamorphism. Silurian-Early Devonian ages are attributed to consequences of backthrusting and normal faulting. A statistical analysis of Silurian-Early Devonian muscovite age spectra reveals an irregular decrease in weighted apparent age maxima across the internal Humber zone. This age-decreasing trend is interpreted to result from the temporal (ca. 431-411 Ma) and possibly spatial (northwest to southeast) progression of deformation, recrystallization, and fluid circulation during tectonic exhumation of the internal Humber zone in southern Quebec. Tectonic models for the Northern Appalachian internal Humber zone should take into account the strong body of evidence for Silurian-Early Devonian hinterland-directed and extensional deformation as documented in southern Quebec. Keywords: Ar/Ar, extension tectonics, Northern Appalachians, Quebec, Silurian, Taconian orogeny.

Piezocone soundings were performed in residual silts and fine sands of the U.S. Atlantic Piedmont geologic province to investigate penetration pore-water pressures and subsequent dissipation characteristics in these 'nontextbook' geomaterials. Piedmont residuum has been formed by the in-place weathering of Paleozoic schist, gneiss, and granite. Pore-water pressures were measured at two positions: midface of the cone tip [u.sub.1] and at the shoulder or behind the tip [u.sub.2]. At the standard rate of 2 cm/s, penetration pore-water pressures on the midface element are fairly high positive values ([u.sub.1] = +600 kPa [+ or -] 200 kPa), yet readings at the shoulder element were negative ([u.sub.2] [approximately equals] -90+ kPa). At an increased penetration rate of 20 cm/s, midface and shoulder readings increased in magnitude and were positive ([u.sub.1] [approximately equals] +800 kPa and [u.sub.2] [approximately equals] +200 kPa); however, measured tip resistance [q.sub.c] exhibited an unusual decrease, per comparisons with data available in the literature. Upon halt of penetration, both [u.sub.1] and [u.sub.2] decayed quickly and reached hydrostatic values [u.sub.0] within 1-2 min.

The tectosphere, namely the portions of Earth's mantle lying below cratons, has a thermochemical structure that differs from average suboceanic mantle. The tectosphere is thought to be depleted in its basaltic components and to have an intrinsic buoyancy that balances the mass increase associated with its colder temperature relative to suboceanic mantle. Inversions of a large set of geodynamic data related to mantle convection, using tomography-based mantle flow models, indicate that the tectosphere is chemically depleted and relatively cold to 250 kilometers depth below Earth's surface. The approximate equilibrium between thermal and chemical buoyancy contributes to cratonic stability over geological time., The tectosphere refers to the mantle below continental lithosphere that is assumed to be stabilized against convective disruption by a balance between thermally generated negative buoyancy and positive chemical buoyancy [...]

Three-dimensional imaging of the Earth's interior, called seismic tomography, has achieved breakthrough advances in the last two decades, revealing fundamental geodynamical processes throughout the Earth's mantle and core. Convective circulation of the entire mantle is taking place, with subducted oceanic lithosphere sinking into the lower mantle, overcoming the resistance to penetration provided by the phase boundary near 650-km depth that separates the upper and lower mantle. The boundary layer at the base of the mantle has been revealed to have complex structure, involving local stratification, extensive structural anisotropy, and massive regions of partial melt. The Earth's high Rayleigh number convective regime now is recognized to be much more interesting and complex than suggested by textbook cartoons, and continued advances in seismic tomography, geodynamical modeling, and high-pressure--high-temperature mineral physics will be needed to fully quantify the complex dynamics of our planet's interior.

Thermobarometric and Os isotopic data for peridotite xenoliths from late Miocene and younger lavas in the Sierra Nevada reveal that the lithospheric mantle is vertically stratified: the shallowest portions ([is less than] 45 to 60 kilometers) are cold (670 ° to 740 ° C) and show evidence for heating and yield Proterozoic Os model ages, whereas the deeper portions (45 to 100 kilometers) yield Phanerozoic Os model ages and show evidence for extensive cooling from temperatures [is greater than] 1100 ° C to 750 ° C. Because a variety of isotopic evidence suggests that the Sierran batholith formed on preexisting Proterozoic lithosphere, most of the original lithospheric mantle appears to have been removed before the late Miocene, leaving only a sliver of ancient mantle beneath the crust., Lithospheric removal, in the form of detachment, foundering, or peeling away of the lithospheric mantle with or without lower crust into the convecting mantle, has been predicted by various geodynamic [...]

Fluid-inclusion studies of radiometrically dated (U/Pb, Th/Pb) calcite samples document the presence of hydrothermal fluids at ca. 251, 137, 67, and probably 39 Ma within the Tri-State Zn-Pb mining district of Missouri, Kansas, and Oklahoma. Fluid inclusions indicate minimum temperatures and equivalent salinities ranging from highs of 122 [degrees] C and 24 wt% NaCl ca. 251 Ma to lows of 52 [degrees] C and 0 wt% NaCl ca. 39 Ma. The two earliest calcites contain primary petroleum inclusious, but these are absent in samples younger than ca. 137 Ma. When combined with information on metal-rich shales, paleomagnetism, and modern groundwater flow, our results are most readily explained by periodic influxes of hydrothermal fluids of diverse compositions for [is greater than] 200 m.y. and sporadic migration of hydrocarbons for at least 100 m.y. in the southern Midcontinent. Keywords: fluid inclusions, U/Pb and Th/Pb dating, Tri-State lead-zinc ores, hydrocarbons, regional fluid flow.

Earth's magnetic field is thought to be generated by fluid motions in the iron-rich, liquid outer core. The geodynamo represents a closed system in which a homogeneous medium of rotating [...]