Geology of the Grove Mountains in East Antarctica

Grove Mountains consists mainly of a series of high-grade (upper amphibolite to granulite facies) metamorphic rocks, including felsic granulite, granitic gneiss, mafic granulite lenses and charnockite, intruded by late tectonic gneissic granite and post-tectonic granodioritic veins. Geochemical analysis demonstrates that the charnockite, granitic gneiss and granite belonged to aluminous A type plutonic rocks, whereas the felsic and mafic granulite were from supracrustal materials as island-arc, oceanic island and middle oceanic ridge basalt. A few high-strained shear zones disperse in regional stable sub-horizontal foliated metamorphic rocks. Three generations of ductile deformation were identified, in which D₁ is related to the event before Pan-African age, D₂ corresponds to the regional granulite peak metamorphism, whereas D₃ reflects ductile extension in late Pan-African orogenic period. The metamorphic reactions from granitic gneiss indicate a single granulite facies event, but 3 steps from mafic granulite, with P-T condition of M1 800°C, 9.3×10⁵ Pa; M₂ 800–810°C, 6.4 × 10⁵ Pa; and M₃ 650°C have been recognized. The U-Pb age data from representative granitic gneiss indicate (529±14) Ma of peak metamorphism, (534±5) Ma of granite emplacement, and (501±7) Ma of post-tectonic granodioritic veins. All these evidences suggest that a huge Pan-African aged mobile belt exists in the East Antarctic Shield extending from Prydz Bay via Grove Mountains to the southern Prince Charles Mountains. This orogenic belt could be the final suture during the Gondwana Land assemblage.     

The distribution of tephra deposits and reconstructing the parameters of 1973 eruption on Tyatya Volcano,Kunashir I., Kuril Islands

We studied the distribution of tephra deposits discharged by the basaltic (52–54% SiO₂) explosive eruption of 1973 on Tyatya Volcano (Kunashir I., Kuril Islands). We made maps showing lines of equal tephra thickness (isopachs) and lines of maximum size of pyroclastic particles (isopleths). These data were used to find the parameters of explosive activity using the standard techniques for each of the two phases of this eruption separately. The first, phreatomagmatic, phase discharged 0.008 km³ of tephra during the generation of maars on the volcano’s northern slope. The tephra mostly consisted of fragmented host rocks with admixtures of fragments of low vesiculated juvenile basalt. The phase lasted 20 hours, the rate of pyroclastic discharge was 2 × 10⁵ kg/s; the eruptive plume reached heights of 4–6 km with wind speeds within 10 m/s. The second, magmatic, phase discharged 0.07 km³ of tephra during the generation of the Otvazhnyi scoria cone on the volcano’s southeastern slope. The tephra mostly consisted of juvenile basaltic scoria. The highly explosive Plinian part of this phase lasted 36 hours, the rate of pyroclastic discharge was 8 × 10⁵ kg/s; the eruptive plume reached heights of 6–8 km with wind speeds of 10–20 m/s. The total tephra volume discharged by the eruption was approximately 0.08 km³; the total amount of ejected pyroclastic material (including the resulting monogenic edifices) was 0.11 km³; the volume of erupted magma was 0.05 km³ (the conversion was based on 2800 kg/m³ density); the volcanic explosivity index, or VEI, was 3. The production rate of the Tyatya plumbing system is estimated as 3 × 10⁵ m³ magma per annum.     

Biostratigraphic ages of tertiary basalts on the East Greenland continental margin and their relationship to plate separation in the Northeast Atlantic

Palynological evidence indicates that the 4?5 × 10⁵ km³ pile of tholeiitic basalts on the central east Greenland coast was erupted in latest Palaeocene (late Landenian) and earliest Eocene (early Ypresian) time. Assignment of a precise numerical age of this interval is not yet possible, but it is evident that the eruptive episode was completed within about 3 m.y. The effusion rate was at least an order of magnitude faster than the current Icelandic rate. Marine horizons at the base and top of the pile show that its build-up was accompanied by concomitant crustal depression. It is argued that this major volcanic episode marks the initiation of plate separation between Greenland and northwest Europe. Implications with regard to spreading chronology and the magnetic polarity time scale are discussed.     

Influence of bedrock groundwater on streamflow characteristics in a volcanic catchment

Groundwater movements in volcanic mountains and their effects on streamflow discharge and representative elementary area (REA) have remained largely unclear. We surveyed the discharge and chemical composition of spring and stream water in two catchments: the Hontani river (NR) catchment (6.6 km²) and the Hosotani river (SR) catchment (4.0 km²) at the southern part of Daisen volcano, Japan. Daisen volcano is a young volcano (17 × 10³ years) at an early stage of erosion. Our study indicated that deep groundwater that moved through thick lava and pyroclastic flows and that could not be explained by shallow movements controlled by surface topography contributed dominantly to streamflow at larger catchment areas. At the NR catchment, the deep groundwater contribution clearly increased at a catchment boundary defined by an area of 3.0 km² and an elevation of 800 m. At the SR catchment, the contribution deep groundwater to the stream also increased suddenly at a boundary threshold of 2.0 and 700 m. Beyond these thresholds, the contributions of deep bedrock groundwater remained constant, indicating that the REA is between 2 and 3 km² at the observed area. These results indicate that the hydrological conditions of base flow were controlled mainly by the deep bedrock groundwater that moved through thick lava and pyroclastic flows in the undissected volcanic body of the upper part of the catchment. Our study demonstrates that deep and long groundwater movements via a deep bedrock layer including thick deposits of volcanic materials at the two catchments on Daisen volcano strongly determined streamflow discharge instead of the mixing of small‐scale hydrological conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Reconstruction of paleocoastlines for the northwestern South China Sea since the Last Glacial Maximum

The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal. ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only 1×10⁴ km², and thus the land-sea distribution remained nearly unchanged. Later in 15–10 cal. ka BP coastline rapidly retreated and area of land loss was up to 24×10⁴km², causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×10⁴km², and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion of about 10×10⁴km². Supported by Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences (Grant No. MSGL0711), the Guangdong Natural Science Foundation (Grant No. 04001309) and Open Fund of the Key Laboratory of Marine Geology and Environment, Chinese Academy of Sciences (Grant No. MGE2007KG04)     

The 1963–1964 eruption of Agung volcano (Bali, Indonesia)

The February 1963 to January 1964 eruption of Gunung Agung, Indonesia’s largest and most devastating eruption of the twentieth century, was a multi-phase explosive and effusive event that produced both basaltic andesite tephra and andesite lava. A rather unusual eruption sequence with an early lava flow followed by two explosive phases, and the presence of two related but distinctly different magma types, is best explained by successive magma injections and mixing in the conduit or high level magma chamber. The 7.5-km-long blocky-surfaced andesite lava flow of ～0.1?km³ volume was emplaced in the first 26?days of activity beginning on 19 February. On 17 March 1963, a major moderate intensity (～4?×?10⁷?kg?s^?1) explosive phase occurred with an ～3.5-h-long climax. This phase produced an eruption column estimated to have reached heights of 19 to 26?km above sea level and deposited a scoria lapilli to fine ash fall unit up to ～0.2?km³ (dense rock equivalent—DRE) in volume, with Plinian dispersal characteristics, and small but devastating scoria-and-ash flow deposits. On 16 May, a second intense 4-h-long explosive phase (2.3?×?10⁷?kg?s^?1) occurred that produced an ～20-km-high eruption column and deposited up to ～0.1?km³ (DRE) volume of similar ash fall and pyroclastic flow deposits, the latter of which were more widespread than in the March phase. The two magma types, porphyritic basaltic andesite and andesite, are found as distinct juvenile scoria populations. This indicates magma mixing prior to the onset of the 1963 eruption, and successive injections of the more mafic magma may have modulated the pulsatory style of the eruption sequence. Even though a total of only ～0.4?km³ (DRE volume) of lava, scoria and ash fall, and scoria-and-ash pyroclastic flow deposits were produced by the 1963 eruption, there was considerable local damage caused mainly by a combination of pyroclastic flows and lahars that formed from the flow deposits in the saturated drainages around Agung. Minor explosive activity and lahar generation by rainfall persisted into early 1964. The climactic events of 17 March and 16 May 1963 managed to inject ash and sulfur-rich gases into the tropical stratosphere.     

Sediment yield and storage variations in the Négron River catchment (south western Parisian Basin,France) during the Holocene period

In the Négron River catchment area (162 km²), surface‐sediment stores are composed of periglacial calcareous ‘grèze’ (5 × 10⁶ t) and loess (21 × 10⁶ t), and Holocene alluvium (12·6 × 10⁶ t), peat (0·6 × 10⁶ t) and colluvium (18·5 × 10⁶ t). Seventy‐five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0·6 t km^?2 a^?1) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7·0 t km^?2 a^?1 from alluvium stores and 7·6 t km^?2 a^?1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18·7 t km^?2 a^?1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub‐basin to another (3·9 to 24·5 t km^?2 a^?1) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps (‘rideaux’). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one‐third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment. Copyright © 2002 John Wiley & Sons, Ltd.     

Sediment yield estimated from reservoir siltation in the Ochil hills,Scotland

Measurements made on the floors of the temporarily-drained Glenfarg and Glenquey Reservoirs indicate that sediments with wet volumes of 63.94 × 10³ m³ and 12.64 × 10³ m³ were deposited in 56 and 73 years respectively. These figures represent 2.5 per cent and 1.1 per cent losses of original storage capacity. When corrected for water, organic, and diatom skeleton contents, and reservoir trap efficiency inorganic sediment yields of at least 31.3 tonnes km^?2 yr^?1 and of 9.0 tonnes km^?2 yr^?1 are suggested. The difference is probably related to contrasts of land use.     

Silicic magma entering a basaltic magma chamber: eruptive dynamics and magma mixing — an example from Salina (Aeolian islands,Southern Tyrrhenian Sea)

The Pollara tuff-ring resulted from two explosive eruptions whose deposits are separated by a paleosol 13 Ka old. The oldest deposits (LPP, about 0.2 km³) consist of three main fall units (A, B, C) deposited from a subplinian column whose height (7–14 km) increased with time from A to C, as a consequence of the increased magma discharge rate during the eruption (1–8x10⁶ kg/s). A highly variable juvenile population characterizes the eruption. Black, dense, highly porphyritic, mafic ejecta (SiO₂=50–55%) almost exclusively form A deposits, whereas grey, mildly vesiculated, mildly porphyritic pumice (SiO₂=56–67%) and white, highly vesiculated, nearly aphyric pumice (SiO₂=66–71%) predominate in B and C respectively. Mafic cumulates are abundant in A, while crystalline lithic ejecta first appear in B and increase upward. The LPP result from the emptying of an unusual and unstable, compositionally zoned, shallow magma chamber in which high density mafic melts capped low density salic ones. Evidence of the existence of a short crystal fractionation series is found in the mafic rocks; the andesitic pumice results from complete blending between rhyolitic and variously fractionated mafic melts (salic component up to 60 wt%), whereas bulk dacitic compositions mainly result from the presence of mafic xenocrysts within rhyolitic glasses. Viscosity and composition-mixing diagrams show that blended liquids formed when the visosities of the two end members had close values. The following model is suggested: 1. A rhyolitic magma rising through the metamorphic basement enterrd a mafic magma chamber whose souter portions were occupied by a highly viscous, mafic crystal mush. 2. Under the pressure of the rhyolitic body the nearly rigid mush was pushed upwards and mafic melts were squeezed against the walls of the chamber, beginning roof fracturing and mingling with silicic melts. 3. When the equilibrium temperature was reached between mafic and silicic melts, blended liquids rapidly formed. 4. When fractures reached the surface, the eruption began by the ejection of the mafic melts and crystal mush (A), followed by the emission of variously mingled and blended magmas (B) and ended by the ejection of nearly unmixed rhyolitic magma (C).     

The Klyuchevskoi Eruptions of 2015–2016

This paper deals with the summit eruptions of 2015–2016, as well as with the 2016 subterminal eruption of Klyuchevskoi. We estimate the dimensions of the depression that was produced by a landfall in the southeastern trough of the volcano. We estimated the volume and area of landfall deposits. The observed volumes of landfalls during the terminal eruptions of 1944?1945, 1985, and 2016 can vary within 0.006?0.140 km³. The theoretical volumes can reach 4?8 km³. We discuss the leading factors that cause landfalls on Klyuchevskoi. These include irreversible creep at depth, the influence of cracks and fissuring in the volcanic cone, as well as the constant intrusive activity of the volcano. Geodetic measurements revealed that the rates of sliding for several individual patches on the slopes varied between 6.7 cm/yr and 19.4 cm/yr. Video and photographic observations were used to estimate the thermal power of stable steam–gas and ash jets, volume of pyroclastics, and the volume of the erupted lava. The thermal power of the steam–gas jets for 2015 was approximately 122 × 10⁶ kW, that of the gas–ash jets was 5.9 × 10⁶ kW. The volume of discharged pyroclastic material was V = 0.00007 km³ for 2015 and V = 0.0003 km³ for 2016.     

The eruptive history of the Mascota volcanic field,western Mexico: Age and volume constraints on the origin of andesite among a diverse suite of lamprophyric and calc-alkaline lavas

The Mascota volcanic field is located in the Jalisco Block of western Mexico, where the Rivera Plate subducts beneath the North American Plate. It spans an area of ∼ 2000 km² and contains ∼ 87 small cones and lava flows of minette, absarokite, basic hornblende lamprophyre, basaltic andesite, and andesite. There are no contemporary dacite or rhyolite lavas. New ⁴⁰Ar/³⁹Ar ages are presented for 35 samples, which are combined with nine dates from the literature to document the eruptive history of this volcanic field. The oldest lavas (2.4 to 0.5 Ma) are found in the southern part of the field area, whereas the youngest lavas (predominantly < 0.5 Ma) are found in the northern portion. On the basis of these ages, field mapping, and the use of ortho aerial photographs and digital elevation models, it is estimated that a combined volume of 6.8 ± 3.1 km³ erupted in the last 2.4 Myr, which leads to an average eruption rate of ∼ 0.003 km³/kyr, and an average volume per eruptive unit of < 0.1 km³. The dominant lava type is andesite (2.1 ± 0.9 km³), followed by absarokite (1.6 ± 0.8 km³), basaltic andesite (1.2 ± 0.5 km³), basic hornblende lamprophyre (1.0 ± 0.4 km³), and minette (0.9 ± 0.5 km³). Thus, the medium-K andesite and basaltic andesite comprise approximately half (49%) of the erupted magma, with twice as much andesite as basaltic andesite, and they occur in close spatial and temporal association with the highly potassic, lamprophyric lavas. There is no time progression to the type of magma erupted. A wide variety of evidence indicate that the high-MgO (8–9 wt.% ) basaltic andesites (52–53% wt.% SiO₂) were formed by H₂O flux melting of the asthenopheric arc mantle wedge, whereas the mafic minettes and absarokites were formed by partial melting (induced by thermal erosion) of depleted lithospheric mantle containing phlogopite-bearing veins. There is only limited differentiation of the potassic magmas, with none more evolved than 55.4 wt.% SiO₂ and 4.4 wt.% MgO. This may be attributable to rapid crystallization of the mantle-derived melts in the deep crust, owing to their low volumes. Thus, the andesites (58–63 wt.% SiO₂) are notable for being both the most voluminous and the most evolved of all lava types in the Mascota volcanic field, which is not consistent with their extraction from extensively crystallized (60–70%), low-volume intrusions. Instead, the evidence supports the origin of the andesites by partial melting of amphibolitized, mafic lower crust, driven by the emplacement of the minettes, absarokites, and the high-Mg basaltic andesites.     

Large scale landslides triggered by Quaternary tectonics in the Acambay graben,Mexico

Detailed analysis was conducted on large‐scale gravitational‐tectonic deformations and landslides in the Acambay graben, an intra‐arc basin in the trans‐Mexican volcanic belt (TMVB). Field mapping and remote sensing revealed the slope instability of the northern graben boundary induced by the Acambay‐Tixmadejé fault. Two major landslides of 0·1 km³ and 0·05 km³ in volume were identified and their characteristics were analyzed according to the role of tectonics, mechanism of slope failure, and possible triggering factors. Quaternary faulting played a major role in increasing the local relief, and the activity of the Acambay‐Tixmadejé fault represents the main geomorphic factor conditioning the gravitational movements. Moreover, displacements along this fault generated sliding surfaces and reduced the strength of the rock mass. The two landslides are classified as large‐scale rotational slides involving volcanic rocks of late Miocene‐Pleistocene age. Since the Acambay graben is a seismogenic area with a known maximum horizontal ground acceleration of 0·5 g, a strong earthquake could be ascribed as the possible triggering mechanism of the landslides. Our work represents the first analysis of large gravitational slope movements in tectonically active regions in Mexico, a process that can be common in the intra‐arc basins of the TMVB, where active tectonic, seismicity, weak altered volcanic rocks, and heavy rains affect the slope stability. Copyright © 2010 John Wiley & Sons, Ltd.     

Exposure age and erosional history of an upland planation surface in the US Atlantic Piedmont

The upland planation surface in the Piedmont of central New Jersey consists of summit flats, as much as 130 km² in area, that truncate bedding and structure in diabase, basalt, sandstone, mudstone and gneiss. These flats define a low‐relief regional surface that corresponds in elevation to residual hills in the adjacent Coastal Plain capped by a fluvial gravel of late Miocene age. A Pliocene fluvial sand is inset 50 m below the upland features. These associations suggest a late Miocene or early Pliocene age for the surface. To assess exposure age and erosional history, a 4·4 m core of clayey diabase saprolite on a 3 km² remnant of the surface was sampled at six depths for atmospherically produced cosmogenic ¹⁰Be. The measured inventory, assuming a deposition rate of 1·3 × 10⁶ atoms cm⁻² a⁻¹, yields a minimum exposure age of 227 000 years, or, assuming continuous surface erosion, a constant erosion rate of 10 m Ma⁻¹. Because the sample site lies about 60 m above the aggradation surface of the Pliocene fluvial deposit, and itself supports a pre‐Pliocene fluvial gravel lag, this erosion rate is too high. Rather, episodic surface erosion and runoff bypassing probably have produced an inventory deficit. Reasonable estimates of surface erosion (up to 10 m) and bypassing (up to 50 per cent of total precipitation) yield exposure ages of as much as 6·4 Ma. These results indicate that (1) the surface is probably of pre‐Pleistocene age and has been modified by Pleistocene erosion, and (2) exposure ages based on ¹⁰Be inventories are highly sensitive to surface erosion and runoff bypassing. Copyright © 2000 John Wiley & Sons, Ltd.     

Study of spatial distribution of sandy desertification in North China in recent 10 years

Sandy desertification is a land degradation characterized by wind erosion, mainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regions in North China. It is one of main kinds of desertification/land degradation as well as water-soil erosion and salinization in China. Rapid and continuous spread of sandy desertification during last 50 years has created a major environmental and socio-economic problem in North China. Remote sensing monitored results in 2000 showed that the sandy desertified land area has been 38.57 × 10⁴ km². The area of potential to slightly sandy desertified land is 13.93 × 10⁴ km², moderately land 9.977 ×10⁴ km², severely land 7.909 × 10⁴ k² and very severely land 6.756 × 10⁴ km². Sandy desertification mainly occurs in the semi-arid mixed farming-grazing zone and its northern rangeland zone, semi-arid dryland rainfed cropping zone and arid oasis-desert margin zone. The average annually developmental rate of sandy desertified land increased from 2,100 km² · a^-1 in 1976–1988 to 3,600 km² · a^-1 in 1988–2000. The basic status of sandy desertification in North China is “overall deterioration, while local rehabilitation”. Already achieved rehabilitation results and monitoring assessment show that about 60% of desertified land in North China can be restored under the conditions of rational land-use ways and intensity.

     

Changes in magma composition at Arenal volcano,Costa Rica, 1968–1985: Real-time monitoring of open-system differentiation

Arenal volcano in Costa Rica has been erupting nearly continuously, but at a diminishing rate, since 1968, producing approximately 0.35 km³ of lavas and tephras that have shown consistent variations in chemistry and mineralogy. From the beginning of the eruption in July 1968 to early 1970 (stage 1, vol.=0.12 km³) tephras and lavas became richer in Ca, Mg, Ni, Cr, Fe, Ti, V, and Sc and poorer in Al₂O₃ and SiO₂. Concentrations of incompatible trace elements (including Sr) decreased by 5%–20%. Phenocryst contents increased 20–50 vol%. During stage 2 (1970–1973, vol. = 0.13 km³) concentrations of compatible trace elements rose, and concentrations of incompatible trace elements either remained constant or also rose. Al₂O₃ contents decreased by 1 wt%. Phenocryst content increased slightly, principally due to increased orthopyroxene. During stage 3 (mid-1974 to the present, vol.= 0.10 km³) concentrations of SiO₂ increased by 1 wt%, compatible trace elements decreased slightly, and incompatible trace element concentrations increased by 5% to 10%. Although crystals increased in size during stage 3, their overall abundance stayed roughly constant.Our modeling suggests that early stage-1 magmas were produced by boundary layer fractionation under high-p H₂O conditions of an unseen basaltic andesitic magma that intruded into the Arenal system after approximately 500 B.P. Changes in composition during stage 2 resulted from mixing of this more mafic original magma with new magma that had a similar SiO₂ content, but higher compatible and incompatible element concentrations. The changes during stage 3 resulted from continued influx of the same magma plus crystal removal.We conclude that the eruption proceeded in the following way. Before 1968 zoned stage-1 magma resided in the deep crust below Arenal. A new magma intruded into this chamber in July 1968 causing ejection of the stage-1 magmas. The intruding magma mixed with mafic portions of the original chamber producing the mixed lavas of stage 2. Continued mixing plus crystal fractionation along the chamber and conduit walls produced stage-3 lavas. The time scales of crustal level magmatic processes at Arenal range 10⁰–10³ years, which are 3–6 orders of magnitude shorter than those of larger, more silicic systems.     

Features and trends of the environmental change in the arid areas in Central Asia

RS-monitoring index systems of ecological environment changes at a large scale, based on empirical data and trends in environmental change in Central Asia, are developed using NOAA and MODIS data. Moreover, with the help of mathematical statistics and GIS spatial analysis, the degrees, hazards and distribution extent of various possible ecological problems are discussed, environmental changes in Central Asia in 1990 and 2005 are separately evaluated, and dynamic changes in the environment in Central Asia over a 15-year period are analyzed. The results reveal that during the 15-year period from 1990 to 2005, areas of degenerated vegetation in Kazakhstan, Uzbekistan, Turkmenistan, Kirghizstan and Tadzhikistan were enlarged by 0.069×10⁵ km², 0.081×10⁵ km², 0.296×10⁵ km², 0.022×10⁵ km² and 0.112×10⁵ km², respectively. The ecological environment in Central Asia was in the state of significant degeneration and even deterioration. This study proves that NOAA and MODIS data can be used to successfully monitor the environment and provide useful results.     

The Monte Guardia eruption (Lipari,Aeolian Islands): an example of a reversely zoned magma mixing sequence

The Monte Guardia rhyolitic eruption (~22 ka, Lipari, Aeolian Islands, Italy) produced a sequence of pyroclastic deposits followed by the emplacement of lava domes. The total volume of dense magma erupted was nearly 0.5 km³. The juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence (mafic magmatic enclaves, streaky pumices, mineral disequilibria and heterogeneous glass composition). Petrographic, mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre-eruptive chemico-physical magmatic conditions. The results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member. A denser, mixed magma was first erupted, followed by a larger volume of an unmixed, lighter rhyolitic one. This compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber. The Monte Guardia rhyolitic magma, stored below 200 MPa, was volatile-rich and fluid-saturated, or very close to this, despite its relatively low explosivity. In contrast to previous interpretations, there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input. The entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence: (1) the occurrence of thermal instabilities in a density stratified, salic to mafic magma chamber and (2) the intrusion of rising rhyolite into a shallower mafic sill/dike.     

Geochemistry and Ar/Ar geochronology of Miocene volcanic rocks from the Karaburun Peninsula: Implications for amphibole-bearing lithospheric mantle source,Western Anatolia

New geochemical and ⁴⁰Ar/³⁹Ar age data are presented from the Neogene volcanic units of the Karaburun Peninsula, the westernmost part of Western Anatolia. The volcanic rocks in the region are associated with Neogene lacustrine deposition and are characterized by (1) olivine-bearing basaltic-andesites to shoshonites (Karaburun volcanics), high-K calc-alkaline andesites, dacites and latites (Yaylaköy, Arma?anda? and Kocada? volcanics) of ~ 16–18 Ma, and (2) mildly-alkaline basalts (Ovac?k basalt) and rhyolites (Urla volcanics) of ~ 11–12 Ma. The first group of rocks is enriched in LILE and LREE with respect to the HREE and HFSE on N-MORB-normalised REE and multi-element spider diagrams. They are comparable geochemically with volcanic rocks in the surrounding regions such as Chios Island and other localities in Western Anatolia. The Ovac?k basalt is geochemically similar to the first stage early–middle Miocene volcanic rocks but differs from NW Anatolian late Miocene alkali basalts.     

The large fissure eruption in the region of Plosky Tolbachik volcano in Kamchatka, 1975–1976

The paper describes the course of the Large Tolbachik fissure eruption taking place in Kamchatka from July 6, 1975 to December 10, 1976. The eruption zone extended for 30 km. The formation of monogenic scoria cones nearly 300 m high, lava tubes and basalt sheets up to 80 m thick and more than 40 km² in area and subsidence of the Plosky Tolbachik summit caldera to a depth of more than 400 m were observed during the eruption. The volume of eruption products amounted to more than 2 km³. It was the largest basalt eruption which has taken place in the Kurile-Kamchatka volcanic belt in historic time.     

Paleomagnetism of some mafic intrusions in the South Carolina Piedmont. I. Magnetic systems with single characteristic directions

Four mafic and two dioritic igneous bodies intruding along the flanks of the Charlotte belt, within the King's Mountain belt and near the Slate-Kiokee-Charlotte belt boundaries in the South Carolina Piedmont, were studied paleomagnetically. The results suggest that these mafic rocks with a single characteristic magnetization are broadly contemporaneous. A mean paleomagnetic pole position of 38.9°N 120.8°E has been calculated for the six bodies. This pole position falls near the 300 Ma old point of Irving's apparent polar wander path (APWP) for North America. The α95 circle of confidence (10.2°) includes points on the APWP between 250–360 Ma. Anomalously old KAr apparent ages, greater than one billion years, are suggestive of excess ⁴⁰Ar contamination for the mafic Buffalo pluton, whereas apparent ages in the range of 360–395 Ma old are interpreted as a maximum age for the other bodies, due to the possibility of small amounts of excess ⁴⁰Ar being present. A 10° westerly tilt correction suggested by Dooley and Smith for early Mesozoic diabase brings the mafic pole position of this study to more nearly coincide with the 350 Ma virtual geomagnetic position of Irving's curve, but the test is inconclusive, awaiting better definition of radiometric ages. The simplest interpretation of the data is that the mafic pole position reflects the direction of the geomagnetic field in late Devonian Carboniferous times. The similarity of this pole position with the points on the APWP for North America provides little evidence for displaced terrains and, with the precision of this pole position, horizontal displacements on the order of that suggested by the Consortium for Continental Reflection Profile (COCORP) results, or by subsequent studies, are not detectable. This and other pole positions from granitic rocks in the southern Appalachian orogen suggest that if displaced terrains exist, the evidence must be found in older rocks, or in other geologic belts.