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Although the last rhyolite eruption occurred around 70 ka ago, the silicic Yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions. Geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field. We use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail. Earthquake relocations and a set of 369 well-constrained, double-couple, focal mechanism solutions were computed. Events were grouped according to location and time to investigate trends in faulting. The majority of the events have normal-faulting solutions, subordinate strike-slip kinematics, and very rarely, reverse motions. The dominant direction of extension throughout the 0.64 Ma Yellowstone caldera is nearly ENE, consistent with the perpendicular direction of alignments of volcanic vents within the caldera, but our study also reveals spatial and temporal variations. Stress-field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion. A well-resolved rotation of σ 3 was found, from NNE-SSW near the Hebgen Lake fault zone, to ENE-WSW near Norris Junction. In particular, the σ 3 direction changed throughout the years around Norris Geyser Basin, from being ENE-WSW, as calculated in the study by Waite and Smith (2004) , to NNE-SSW, while the other σ 3 directions are mostly unchanged over time. The presence of “chocolate tablet” structures, with two sets of nearly perpendicular normal faults, was identified in many stages of the deformation history both in the Norris Geyser Basin area and inside the caldera.

The continental collision between Arabia and Eurasia created large strike-slip faults in Turkey as well as mountains in the Caucasus and the volcanic plateau between them. In this study, we use regional waveforms of a new seismic array deployed between 2008 and 2012 to constrain the focal mechanisms and depths of small to moderate sized earthquakes occurring in the western part of the Central Caucasus and northeast Turkey. The distribution of aftershocks and the twelve focal mechanisms involved in the sequence of the 2009 earthquake in Racha are clearly a reactivation of a deeper segment of the 1991 M7 Racha rupture zone. The deeper segment is not well connected to the shallower decollement separating the basement and sedimentary basin. The earthquakes we determined in northeastern Turkey and southern Georgia are related to the strike-slip fault system. We further combined all of the reliably determined focal mechanisms over the last 30 years to investigate the current stress status of the crust in three areas: Racha in the western Greater Caucasus, Javakheti near the Lesser Caucasus and in Northeast Turkey. Our results show that the directions of maximum compressional stress consistently fall within − 2 to 14°N throughout the entire study region. This appears to be controlled by the continental collision. Nonetheless, the minimum compression switches from vertical (in the Greater Caucasus) to the east-west direction (in northeastern Turkey), due to the westward extrusion of the Anatolia block, which is driven partly by the Hellenic subduction. The transition of the stress field is close to the Javakheti volcanic plateau in the Lesser Caucasus, where the relative magnitude between the principal stresses appears to be strongly variable.

Analysis of seismic lines and gravity data shows the existence of Quaternary extensional depocenters beneath thick covers of < 1 Ma-old volcanic rocks in the Tromen volcanic plateau backarc region (36°40′-37°30′S). Dating and mapping of pre- and post-extensional volcanic units and structure in this area indicate that the main phase of crustal collapse developed during the 1.7-0.7 Ma time interval. However, Late Quaternary reactivations of the extensional structure show that this process is still going on, perhaps with decreasing intensity. Moreover, identification of "mechanical" rift zones and a potentially related main thermal anomaly leads to propose that an east-dipping detachment exists beneath the Late Cretaceous-Late Miocene fold and thrust belt, controlling the crustal collapse at these latitudes. The southernmost Central Andes (35°-37°30′S) have undergone a period of shallow subduction from ~ 13 to ~ 5 Ma, that led to expansion of the arc toward the foreland, generation of ductile-fragile crustal transitions, and subsequent foreland imbrications more than 550 km away from the trench. This framework shifted to a normal Andean subduction type after ~ 5 Ma, and the arc front re-established in the present western position. The consequences of this readjustment were: a) widespread volcanic eruptions of intra-plate melts in the eastern backarc (foreland plateau flows), and b) a major trough formed between the arc front and the foreland plateau basalts (Las Loicas trough). This extensional basin controlled the emplacement of crustal melts as well as primary mantle-derived products, well represented in the Tromen volcanic plateau. Fil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Bottesi, Germán. Yacimientos Petrolíferos Fiscales, Argentina; Argentina Fil: Zapata, Tomás. Yacimientos Petrolíferos Fiscales, Argentina; Argentina Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

Multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the Caribbean province. A smooth reflector B″ forms the top of widespread Cretaceous volcanic flows drilled during DSDP Leg 15 and ODP Leg 165. In addition we also show other seismic evidence of volcanism (sills and dipping horizons). The southern parts of the Venezuela and Colombia basins are underlain by rough basement that shows many characteristics of oceanic crust. Several thick volcanic plateaus separated by deep basins with thin crust comprise the Caribbean volcanic province. In the Venezuela basin only normal oceanic crust is present, but in other basins this crust is underlain by underplated volcanic material. The crust of the Venezuela basin is less than 5 km thick and was probably formed in the Pacific during the Jurassic. Refraction data indicate that a thin layer, 2V, is formed by original oceanic crust overlain by a thin volcanic layer. An intra basement reflection (sub-B″) marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material. This underplated layer forms a very thick layer, 3V, beneath the Beata and Nicaragua volcanic plateaus. The upper part of layer 3V is gabbroic and outcrops on the Beata ridge. The thickening occurs mainly in the high-velocity lower part of layer 3V and is attributed to the presence of magnesian rocks (picrites or ultramafic cumulates). A highly reflective horizon (R) is located at the top of this layer. We present a model where the Galapagos plume is 2500 km wide but has narrow heads that formed the Caribbean volcanic plateaus separated by deep basins. The Caribbean igneous province is compared to similar volcanic features in the Indian Ocean (Kerguelen plateau) and in the Western Pacific Ocean (Ontong Java plateau, Nauru and Pigafetta basins. The thick plateaus of the Caribbean province resemble the Kerguelen and Ontong Java plateaus, whereas the deep basins present some similarities with the Nauru and Pigafetta basins. The Caribbean igneous province is younger (90-75 Ma) than the Indian and Pacific plateaus (110–130 Ma); however, several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the Caribbean province could be as old as 115 Ma.

A regional analysis of the crust and upper mantle of the Colorado Plateau is presented, using existing geophysical and geological data combined with new surface wave dispersion and groundwater geothermometry data; the tectonic implications of these models are also investigated. Surface wave and seismic refraction data indicate that the crust of the interior of the Colorado Plateau is 44 + or - 3 km thick, and its crustal structure is typical of stable continental areas. Pn velocities, however, appear to be lower (7.8 km/s) than would be expected in a stable region, while silica geothermometry indicates that the average heat flow for the plateau is 55 mW per sq m (1.3 HFU).

New heat-flow measurements in the Colorado Plateau varying in depth from 400 to 1900 m suggest that the heat flux throughout the region is 1.5 HFU and greater (1 HFU = 41.8 mW/m2). Along the eastern and southern boundaries of the Plateau, near the San Juan volcanic field and the Mogollon Slope respectively, high heat flows ($2.2 HFU) are observed to intrude 50–100 km into the Plateau. It is believed that the high heat flows are associated with the sources of the volcanics in those areas. In the interior areas of the Plateau, away from the major volcanic phenomena along its boundary (e.g., the Black Mesa—Kaiparowits synclinorium, the Four Corners area, and the Piceance and Uinta basins) heat flows are generally between 1.5 and 1.8 HFU, and appear to be rather uniform over large areas. This uniform heat-flow characteristic over large areas of the interior Plateau suggests the lack of large-scale, widespread, crustal thermal sources as in the Basin and Range or along the Rio Grande rift. It is possible that lithospheric temperatures within the Colorado Plateau were once similar to lithospheric temperatures within the Stable Interior. Present heat-flow differences between the two provinces (~0.4 HFU) may define the temperature change occurring in the lithosphere of the Colorado Plateau over the past 200 m.y. This temperature change may have contributed significantly to the uplifting of the Colorado Plateau by the process of thermal expansion.

Peninsular India is characterized by some major plateau regions. These include the Deccan and Karnataka plateaus of the southern peninsular shield which together occupy an area of more than 400,000 km2 and the smaller Chotanagpur and Shillong plateaus in eastern and northeastern India, respectively. Major parts of the Deccan plateau are blanketed by basaltic lavas of the Deccan trap. The Bouguer gravity map of the region presents a number of gravity “highs” and “lows” suggestive of marked uplift and subsidence involving the crust and the seismic soundings indicate trap thickness varying from about 100 m in the eastern and southern margins of the trap territory to more than 1000 m in the western parts of Maharashtra. A major north-south fault zone has been indicated within the traps along the Bombay coast to the west of the Koyna earthquake-affected area. Marginal north-south as well as east-west faults have also been delineated by gravity and seismic surveys in the off-shore areas to the west of the Bombay coast, south of the Cambay graben and to the south of the Kathiawar peninsula. The prominent WSW-ENE trending Narmada-Son lineament to the north of the Deccan plateau comprises the Narmada-Son rift, which is characterized by basic alkaline rocks and carbonatite occurrences in its western extremity and kimberlite pipes over its eastern parts, which are of great significance in the study of plateau uplift in this region. The gravity data clearly bring out the fault system of this rift which is divided into segments. The Karnataka plateau contiguous to the Deccan plateau to its south consists mainly of Precambrian gneisses, granites and charnockites with some major plutonic masses, apparently connected to the deep-seated batholiths which are reflected in the Bouguer gravity map as strong negative anomalies. This plateau region is characterized by distinctive geomorphic features and mild seismicity. The Chotanagpur plateau also shows distinctive geomorphic features, including some prominent scarps with steep gradients and water falls. The Shillong plateau in northeast India occurs as an uplifted horst block in a zone of high seismicity astride the Himalayan range. Repeated geodetic levelling conducted during the past 70 years across this plateau indicated a total uplift of 2.5 cm during this period. The whole of peninsular India is characterized by particularly strong negative gravity anomalies, the cause of which clearly appears to be within the mantle. The plateau uplifts of peninsular India are apparently releated to thermal processes within the mantle.

The Kerguelen Plateau in the southern Indian Ocean is associated with the Broken Ridge Plateau because of their location with respect to the Southeast Indian Ridge. The Kerguelen Plateau lies south of the mid-ocean ridge and the Broken Ridge Plateau is located at a nearly equal distance to the north. Both plateaus have positive MAGSAT crustal magnetic anomalies associated with them. Comparative modeling of these anomalies places constraints on the crustal nature, the thermal structure, and the tectonic history of the plateaus. Our results support the theory that both plateaus are underlain by oceanic crust, are structurally and lithologically similar, and were formed as a single structure which has since been split by seafloor spreading. Active volcanoes on the northern part of the Kerguelen Plateau suggest that it lies on a hotspot which has raised the Curie isotherm to within the crust of the plateau, decreasing the crustal volume contributing to the magnetic anomaly and thus decreasing the amplitude of the anomaly.

Discussion sur l'article de Shurbet D. H. et Cebull S. E. paru dans Tectonophysics, NLD, 1984, 101, 159-165

Mesozoic magmatic activities in the eastern part of China were closely related to the mutual movement of the Eurasian and Kula plates. Mesozoic volcanic rocks can be divided into the southern, central and northern petrological regions. The Changzhou-Yueyang deep fault in the south and the Baodi-Changli-Jinzhou fault in the north are the main boundaries between them and extend in a roughly NEE direction. Mesozoic volcanic basins distributed in the lower reaches of the Changjiang River are located near the boundary line between the southern and central petrological regions. Based on the association of volcanic rocks they can be divided into four volcanic belts. From south to north they are as follows: (I) Guangde-Liyang-Wuxi volcanic belt; (II) Fanchang-Lishui-Zhenjiang volcanic belt; (III) Huaining-Luzong-Ningwu volcanic belt; (IV) Chuxian-Jinhu volcanic belt. These volcanic belts are nearly parallel with the Changzhou-Yueyang deep fault. Their major-element chemical variation, strontium, oxygen and sulphur isotopes and REE suggest that the dacite-rhyolitic magma in volcanic belt (I) was generated by anatexis of the lower part of the continental crust, and the andesitic magma in the volcanic belts (III) and (IV) might be generated by fusion of the upper mantle mixed with some other materials in the subducted zone under great compression, at 1200°–1250°C, with sufficient water. The “trachyandesite-latite rock series” is very different from the shoshonitic one and, it might be the product of the interaction of alkali-enriched andesitic magma with gypsum-salt beds. The volcanic rocks in belt (II) exhibit a transitional character.

Structural deformation along monoclines on the Hualapai Plateau appears to correlate with the formation of thick lacustrine limestones in deeply incised early Tertiary drainage channels. Improvements in the regional chronology and correlation of early Tertiary rocks permit the timing of regional monoclinal deformation to be better integrated with the published regional geologic syntheses for events of Laramide age. If monoclinal folding was limited to the interval between late Cretaceous and late Eocene time, the broad uplift and associated erosion of the plateau margin and adjacent regions must have begun by Paleocene time. The physiography of the Hualapai Plateau and its associated incised Tertiary drainage channels, excluding the Grand Canyon, must have developed prior to the most recent (Eocene?) episode of monocline deformation. The events recorded in the Tertiary geology along the southwest margin of the plateau demonstrate that the earliest widespread erosion was definitely pre-late Oligocene. Several small plutons of early Laramide age at or near the plateau edge have ages falling within the interval of strong regional tectonic activity adjacent to the plateau in Arizona. Since Eocene time, the Hualapai Plateau may have undergone a relatively slow geomorphic evolution by comparison with surrounding areas. This is due both to the erosional resistance of the Paleozoic rocks capping the plateau and to an Oligocene—early Miocene interval when through-flowing drainage appears to have been poorly developed. Eruption of widespread volcanic rocks across the plateau edge between late Oligocene and middle Miocene time preceded Basin and Range extensional faulting and further slowed drainage redevelopment. Except for the major younger fault scarps, the southwest margin of the plateau is still dominated by the broad physiographic features developed prior to late Oligocene time.