Shallow magma diversions during explosive diatreme-forming eruptions.

PubMed

Le Corvec, Nicolas; Muirhead, James D; White, James D L

2018-04-13

The diversion of magma is an important mechanism that may lead to the relocation of a volcanic vent. Magma diversion is known to occur during explosive volcanic eruptions generating subterranean excavation and remobilization of country and volcanic rocks. However, feedbacks between explosive crater formation and intrusion processes have not been considered previously, despite their importance for understanding evolving hazards during volcanic eruptions. Here, we apply numerical modeling to test the impacts of excavation and subsequent infilling of diatreme structures on stress states and intrusion geometries during the formation of maar-diatreme complexes. Explosive excavation and infilling of diatremes affects local stress states which inhibits magma ascent and drives lateral diversion at various depths, which are expected to promote intra-diatreme explosions, host rock mixing, and vent migration. Our models demonstrate novel mechanisms explaining the generation of saucer-shaped sills, linked with magma diversion and enhanced intra-diatreme explosive fragmentation during maar-diatreme volcanism. Similar mechanisms will occur at other volcanic vents producing crater-forming eruptions.

Magma intrusion beneath long valley caldera confirmed by temporal changes in gravity

PubMed

Battaglia; Roberts; Segall

1999-09-24

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 +/- 6 microgals (1 microgal = 10(-8) meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 +/- 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 10(3) to 4.1 x 10(3) kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.

Magma intrusion beneath Long Valley caldera confirmed by temporal changes in gravity

USGS Publications Warehouse

Battaglia, Maurizio; Roberts, C.; Segall, P.

1999-01-01

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 ?? 6 microgals (1 microgal = 10-8 meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 ?? 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 103 to 4.1 x 103 kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.

Coupling fluid dynamics and host-rock deformation associated with magma intrusion in the crust: Insights from analogue experiments

NASA Astrophysics Data System (ADS)

Kavanagh, J. L.; Dennis, D. J.

2014-12-01

Models of magma ascent in the crust tend to either consider the dynamics of fluid flow within intrusions or the associated host-rock deformation. However, these processes are coupled in nature, and so to develop a more complete understanding of magma ascent dynamics in the crust both need to be taken into account. We present a series of gelatine analogue experiments that use both Particle Image Velocimentry (PIV) and Digital Image Correlation (DIC) techniques to characterise the dynamics of fluid flow within intrusions and to quantify the associated deformation of the intruded media. Experiments are prepared by filling a 40x40x30 cm3 clear-Perspex tank with a low-concentration gelatine mixture (2-5 wt%) scaled to be of comparable stiffness to crustal strata. Fluorescent seeding particles are added to the gelatine mixture during its preparation and to the magma analogue prior to injection. Two Dantec CCD cameras are positioned outside the tank and a vertical high-power laser sheet positioned along the centre line is triggered to illuminate the seeding particles with short intense pulses. Dyed water (the magma analogue) injected into the solid gelatine from below causes a vertically propagating penny-shaped crack (dike) to form. Incremental and cumulative displacement vectors are calculated by cross-correlation between successive images at a defined time interval. Spatial derivatives map the fluid flow within the intrusion and associated strain and stress evolution of the host, both during dike propagation and on to eruption. As the gelatine deforms elastically at the experimental conditions, strain calculations correlate with stress. Models which couple fluid dynamics and host deformation make an important step towards improving our understanding of the dynamics of magma transport through the crust and to help constrain the tendency for eruption.

Analogue modelling on the interaction between shallow magma intrusion and a strike-slip fault: Application on the Middle Triassic Monzoni Intrusive Complex (Dolomites, Italy)

NASA Astrophysics Data System (ADS)

Michail, Maria; Coltorti, Massimo; Gianolla, Piero; Riva, Alberto; Rosenau, Matthias; Bonadiman, Costanza; Galland, Olivier; Guldstrand, Frank; Thordén Haug, Øystein; Rudolf, Michael; Schmiedel, Tobias

2017-04-01

The southwestern part of the Dolomites in Northern Italy has undergone a short-lived Ladinian (Middle Triassic) tectono-magmatic event, forming a series of significant magmatic features. These intrusive bodies deformed and metamorphosed the Permo-Triassic carbonate sedimentary framework. In this study we focus on the tectono-magmatic evolution of the shallow shoshonitic Monzoni Intrusive Complex of this Ladinian event (ca 237 Ma), covering an area of 20 km^2. This NW-SE elongated intrusive structure (5 km length) shows an orogenic magmatic affinity which is in contrast to the tectonic regime at the time of intrusion. Strain analysis shows anorogenic transtensional displacement in accordance with the ENE-WSW extensional pattern in the central Dolomites during the Ladinian. Field interpretations led to a detailed description of the regional stratigraphic sequence and the structural features of the study area. However, the geodynamic context of this magmatism and the influence of the inherited strike-slip fault on the intrusion, are still in question. To better understand the specific natural prototype and the general mechanisms of magma emplacement in tectonically active areas, we performed analogue experiments defined by, but not limited to, first order field observations. We have conducted a systematic series of experiments in different tectonic regimes (static conditions, strike-slip, transtension). We varied the ratio of viscous to brittle stresses between magma and country rock, by injecting Newtonian fluids both of high and low viscosity (i.e. silicone oil/vegetable oil) into granular materials of varying cohesion (sand, silica flour, glass beads). The evolving surface and side view of the experiments were monitored by photogrammetric techniques for strain analyses and topographic evolution. In our case, the combination of the results from field and analogue experiments brings new insights regarding the tectonic regime, the geometry of the intrusive body, and

Multiple magma emplacement and its effect on the superficial deformation: hints from analogue models

NASA Astrophysics Data System (ADS)

Montanari, Domenico; Bonini, Marco; Corti, Giacomo; del Ventisette, Chiara

2017-04-01

To test the effect exerted by multiple magma emplacement on the deformation pattern, we have run analogue models with synchronous, as well as diachronous magma injection from different, aligned inlets. The distance between injection points, as well as the activation in time of injection points was varied for each model. Our model results show how the position and activation in time of injection points (which reproduce multiple magma batches in nature) strongly influence model evolution. In the case of synchronous injection at different inlets, the intrusions and associated surface deformation were elongated. Forced folds and annular bounding reverse faults were quite elliptical, and with the main axis of the elongated dome trending sub-parallel to the direction of the magma input points. Model results also indicate that the injection from multiple aligned sources could reproduce the same features of systems associated with planar feeder dikes, thereby suggesting that caution should be taken when trying to infer the feeding areas on the basis of the deformation features observed at the surface or in seismic profiles. Diachronous injection from different injection points showed that the deformation observed at surface does not necessarily reflect the location and/or geometry of their feeders. Most notably, these experiments suggest that coeval magma injection from different sources favor the lateral migration of magma rather than the vertical growth, promoting the development of laterally interconnected intrusions. Recently, some authors (Magee et al., 2014, 2016; Schofield et al., 2015) have suggested that, based on seismic reflection data analysis, interconnected sills and inclined sheets can facilitate the transport of magma over great vertical distances and laterally for large distances. Intrusions and volcanoes fed by sill complexes may thus be laterally offset significantly from the melt source. Our model results strongly support these findings, by reproducing

Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

2018-05-01

-ocean-ridge-basalt mantle and enriched-mantle I components. The Permian mafic-ultramafic intrusions in North Xinjiang were formed from tholeiitic basaltic magmas derived from decompression partial melting of the metasomatized mantle in a post-collision extensional tectonic setting. The tholeiitic basaltic magmas are equivalent to the voluminous underplated basaltic magmas that formed during vertical crustal growth of the Central Asian Orogenic Belt in the later Paleozoic.

The Dovyren Intrusive Complex (Southern Siberia, Russia): Insights into dynamics of an open magma chamber with implications for parental magma origin, composition, and Cu-Ni-PGE fertility

NASA Astrophysics Data System (ADS)

Ariskin, Alexey; Danyushevsky, Leonid; Nikolaev, Georgy; Kislov, Evgeny; Fiorentini, Marco; McNeill, Andrew; Kostitsyn, Yuri; Goemann, Karsten; Feig, Sandrin T.; Malyshev, Alexey

2018-03-01

The Dovyren Intrusive Complex (DIC, Northern Baikal region, 728 Ma) includes the layered dunite-troctolite-gabbronorite Yoko-Dovyren massif (YDM), associated mafic-ultramafic sills, and dykes of olivine-rich to olivine-free gabbronorite. Major rock types of the DIC are presented, including a diversity of olivine orthocumulates to olivine-plagioclase and gabbroic adcumulates, carbonate-contaminated ultramafics and Cu-Ni-PGE mineralisation. Detailed comparisons of complete cross-sections of the YDM in its centre and at the NE and SW margins demonstrate differences in the cumulate succession, mineral chemistry, and geochemical structure that likely reflect variations in parental magma compositions. Combining petrochemical reconstructions for most primitive rocks and calculations using the COMAGMAT-5 model, it is shown that the central and peripheral parts of the intrusion formed by olivine-laden parental magmas ranged in their temperatures by 100 °C, approximately from 1290 °C ( 11 wt% MgO, olivine Fo88) to 1190 °C ( 8 wt% MgO, olivine Fo86). Thermodynamic modelling suggests that the most primitive high-Mg magma was S-undersaturated, whereas its derivatives became S-saturated at T < 1240-1200 °C. These estimates are consistent with geological observations that mostly sulphide-poor mineralisation occurs in the centre of the intrusion, whereas Cu-Ni sulphide ores (locally net-textured) occur in its NE and SW parts, as well as in the underlying peridotite sills. The primitive S-undersaturated olivine cumulates became sulphide-saturated at a post-cumulus stage. As a result, Ni-rich immiscible sulphides formed within and migrated through the early olivine-rich cumulate piles to generate poorly-mineralised plagiodunite. In the troctolite and gabbroic parts of the Dovyren chamber, sulphide immiscibility likely occurred at lower temperatures, producing Cu-rich sulphide precursors, which gave rise to the 'platinum group mineral' (PGM-containing) troctolite and low

Eddy Flow during Magma Emplacement: The Basemelt Sill, Antarctica

NASA Astrophysics Data System (ADS)

Petford, N.; Mirhadizadeh, S.

2014-12-01

The McMurdo Dry Valleys magmatic system, Antarctica, forms part of the Ferrar dolerite Large Igneous Province. Comprising a vertical stack of interconnected sills, the complex provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested magma slurry1. Image-based numerical modelling where the intrusion geometry defines its own unique finite element mesh allows simulations of the flow regime to be made that incorporate realistic magma particle size and flow geometries obtained directly from field measurements. One testable outcome relates to the origin of rhythmic layering where analytical results imply the sheared suspension intersects the phase space for particle Reynolds and Peclet number flow characteristic of macroscopic structures formation2. Another relates to potentially novel crystal-liquid segregation due to the formation of eddies locally at undulating contacts at the floor and roof of the intrusion. The eddies are transient and mechanical in origin, unrelated to well-known fluid dynamical effects around obstacles where flow is turbulent. Numerical particle tracing reveals that these low Re number eddies can both trap (remove) and eject particles back into the magma at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and magma chemistry that may otherwise not occur where the contact between magma and country rock is linear. Simulations indicate that eddy formation is best developed where magma viscosity is in the range 1-102 Pa s. Higher viscosities (> 103 Pa s) tend to dampen the effect implying eddy development is most likely a transient feature. However, it is nice to think that something as simple as a bumpy contact could impart physical and by implication chemical diversity in igneous rocks. 1Marsh, D.B. (2004), A

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 2: Predicted emplacement processes and observations)

NASA Astrophysics Data System (ADS)

Head, James W.; Wilson, Lionel

2017-02-01

We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike intrusions, and effusive and explosive eruptions. We make predictions about the intrusion and eruption processes and compare these with the range of observed styles of mare volcanism, and related features and deposits. Density contrasts between the bulk mantle and regions with a greater abundance of heat sources will cause larger heated regions to rise as buoyant melt-rich diapirs that generate partial melts that can undergo collection into magma source regions; diapirs rise to the base of the anorthositic crustal density trap (when the crust is thicker than the elastic lithosphere) or, later in history, to the base of the lithospheric rheological trap (when the thickening lithosphere exceeds the thickness of the crust). Residual diapiric buoyancy, and continued production and arrival of diapiric material, enhances melt volume and overpressurizes the source regions, producing sufficient stress to cause brittle deformation of the elastic part of the overlying lithosphere; a magma-filled crack initiates and propagates toward the surface as a convex upward, blade-shaped dike. The volume of magma released in a single event is likely to lie in the range 102 km3 to 103 km3, corresponding to dikes with widths of 40-100 m and both vertical and horizontal extents of 60-100 km, favoring eruption on the lunar nearside. Shallower magma sources produce dikes that are continuous from the source region to the surface, but deeper sources will propagate dikes that detach from the source region and ascend as discrete penny-shaped structures. As the Moon cools with time, the lithosphere thickens, source regions become less abundant, and rheological traps become increasingly deep; the state of stress in the lithosphere becomes increasingly contractional

Time dependent model of magma intrusion in and around Miyake and Kozu Islands, Central Japan in June August, 2000

NASA Astrophysics Data System (ADS)

Murase, Masayuki; Irwan, Meilano; Kariya, Shinichi; Tabei, Takao; Okuda, Takashi; Miyajima, Rikio; Oikawa, Jun; Watanabe, Hidefumi; Kato, Teruyuki; Nakao, Shigeru; Ukawa, Motoo; Fujita, Eisuke; Okayama, Muneo; Kimata, Fumiaki; Fujii, Naoyuki

2006-02-01

A time-dependent model of magma intrusion is presented for the Miyake-Kozu Island area in central Japan based on global positioning system (GPS) measurements at 28 sites recorded between June 27 and August 27, 2000. A model derived from a precise hypocenter distribution map indicates the presence of three dikes between Miyake and Kozu Islands. Other dike intrusion models, including a dike with aseismic creep and a dike associated with a deep deflation source are also discussed. The optimal parameters for each model are estimated using a genetic algorithm (GA) approach. Using Akaike's information criteria (AIC), the three-dike model is shown to provide the best solution for the observed deformation. Volume changes in spherical inflation and deflation sources, as well as three dikes, are calculated for seven discretized periods after GA optimization of the dike geometry. The optimization suggests a concentration of dike expansion near Miyake Island in the period from June 27 to July 1 associated with large deflation at a depth of about 7 km below Miyake volcano, indicating magma supply from depth below Miyake Island. In the period from July 9 to August 10, a huge dike intrusion near Kozu Island is inferred, accompanied by expansion of the lower parts of a central dike, suggesting magma supply from depth in the region between Miyake and Kozu Islands.

Nonexplosive and explosive magma/wet-sediment interaction during emplacement of Eocene intrusions into Cretaceous to Eocene strata, Trans-Pecos igneous province, West Texas

USGS Publications Warehouse

Befus, K.S.; Hanson, R.E.; Miggins, D.P.; Breyer, J.A.; Busbey, A.B.

2009-01-01

Eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified, Upper Cretaceous (Maastrichtian) to Eocene fluvial strata in part of the Trans-Pecos igneous province in West Texas produced an array of features recording both nonexplosive and explosive magma/wet-sediment interaction. Intrusive complexes with 40Ar/39Ar dates of ~ 47-46??Ma consist of coherent basalt, peperite, and disrupted sediment. Two of the complexes cutting Cretaceous strata contain masses of conglomerate derived from Eocene fluvial deposits that, at the onset of intrusive activity, would have been > 400-500??m above the present level of exposure. These intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the Trans-Pecos province. Disrupted Cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions. Eocene conglomerate slumped downward from higher levels during vent excavation. Coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate, within disrupted Cretaceous strata in the conduit walls, and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism. A younger series of intrusions with 40Ar/39Ar dates of ~ 42??Ma underwent nonexplosive interaction with Upper Cretaceous to Paleocene mud and sand. Dikes and sills show fluidal, billowed, quenched margins against the host strata, recording development of surface instabilities between magma and groundwater-rich sediment. Accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment. More intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite, but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions. This work suggests that

Time-resolved seismic tomography detects magma intrusions at Mount Etna.

PubMed

Patanè, D; Barberi, G; Cocina, O; De Gori, P; Chiarabba, C

2006-08-11

The continuous volcanic and seismic activity at Mount Etna makes this volcano an important laboratory for seismological and geophysical studies. We used repeated three-dimensional tomography to detect variations in elastic parameters during different volcanic cycles, before and during the October 2002-January 2003 flank eruption. Well-defined anomalous low P- to S-wave velocity ratio volumes were revealed. Absent during the pre-eruptive period, the anomalies trace the intrusion of volatile-rich (>/=4 weight percent) basaltic magma, most of which rose up only a few months before the onset of eruption. The observed time changes of velocity anomalies suggest that four-dimensional tomography provides a basis for more efficient volcano monitoring and short- and midterm eruption forecasting of explosive activity.

Lunar floor-fractured craters: Modes of dike and sill emplacement and implications of gas production and intrusion cooling on surface morphology and structure

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2018-05-01

Lunar floor-fractured craters (FFCs) represent the surface manifestation of a class of shallow crustal intrusions in which magma-filled cracks (dikes) rising to the surface from great depth encounter contrasts in host rock lithology (breccia lens, rigid solidified melt sheet) and intrude laterally to form a sill, laccolith or bysmalith, thereby uplifting and deforming the crater floor. Recent developments in the knowledge of lunar crustal thickness and density structure have enabled important revisions to models of the generation, ascent and eruption of magma, and new knowledge about the presence and behavior of magmatic volatiles has provided additional perspectives on shallow intrusion processes in FFCs. We use these new data to assess the processes that occur during dike and sill emplacement with particular emphasis on tracking the fate and migration of volatiles and their relation to candidate venting processes. FFCs result when dikes are capable of intruding close to the surface, but fail to erupt because of the substructure of their host impact craters, and instead intrude laterally after encountering a boundary where an increase in ductility (base of breccia lens) or rigidity (base of solidified melt sheet) occurs. Magma in dikes approaching the lunar surface experiences increasingly lower overburden pressures: this enhances CO gas formation and brings the magma into the realm of the low pressure release of H2O and sulfur compounds, both factors adding volatiles to those already collected in the rising low-pressure part of the dike tip. High magma rise velocity is driven by the positive buoyancy of the magma in the part of the dike remaining in the mantle. The dike tip overshoots the interface and the consequent excess pressure at the interface drives the horizontal flow of magma to form the intrusion and raise the crater floor. If sill intrusion were controlled by the physical properties at the base of the melt sheet, dikes would be required to approach to

Crustal Strain Patterns in Magmatic and Amagmatic Early Stage Rifts: Border Faults, Magma Intrusion, and Volatiles

NASA Astrophysics Data System (ADS)

Ebinger, C. J.; Keir, D.; Roecker, S. W.; Tiberi, C.; Aman, M.; Weinstein, A.; Lambert, C.; Drooff, C.; Oliva, S. J. C.; Peterson, K.; Bourke, J. R.; Rodzianko, A.; Gallacher, R. J.; Lavayssiere, A.; Shillington, D. J.; Khalfan, M.; Mulibo, G. D.; Ferdinand-Wambura, R.; Palardy, A.; Albaric, J.; Gautier, S.; Muirhead, J.; Lee, H.

2015-12-01

Rift initiation in thick, strong continental lithosphere challenges current models of continental lithospheric deformation, in part owing to gaps in our knowledge of strain patterns in the lower crust. New geophysical, geochemical, and structural data sets from youthful magmatic (Magadi-Natron, Kivu), weakly magmatic (Malawi, Manyara), and amagmatic (Tanganyika) sectors of the cratonic East African rift system provide new insights into the distribution of brittle strain, magma intrusion and storage, and time-averaged deformation. We compare and contrast time-space relations, seismogenic layer thickness variations, and fault kinematics using earthquakes recorded on local arrays and teleseisms in sectors of the Western and Eastern rifts, including the Natron-Manyara basins that developed in Archaean lithosphere. Lower crustal seismicity occurs in both the Western and Eastern rifts, including sectors on and off craton, and those with and without central rift volcanoes. In amagmatic sectors, lower crustal strain is accommodated by slip along relatively steep border faults, with oblique-slip faults linking opposing border faults that penetrate to different crustal levels. In magmatic sectors, seismicity spans surface to lower crust beneath both border faults and eruptive centers, with earthquake swarms around magma bodies. Our focal mechanisms and Global CMTs from a 2007 fault-dike episode show a local rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with time-averaged strain recorded in vent and eruptive chain alignments. These patterns suggest that strain localization via widespread magma intrusion can occur during the first 5 My of rifting in originally thick lithosphere. Lower crustal seismicity in magmatic sectors may be caused by high gas pressures and volatile migration from active metasomatism and magma degassing, consistent with high CO2 flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and

Disequilibrium growth of olivine in mafic magmas revealed by phosphorus zoning patterns of olivine from mafic-ultramafic intrusions

NASA Astrophysics Data System (ADS)

Xing, Chang-Ming; Wang, Christina Yan; Tan, Wei

2017-12-01

Olivine from mafic-ultramafic intrusions rarely displays growth zoning in major and some minor elements, such as Fe, Mg and Ni, due to fast diffusion of these elements at high temperatures. These elements in olivine are thus not useful in deciphering magma chamber processes, such as magma convection, multiple injection and mixing. High-resolution X-ray elemental intensity mapping reveals distinct P zoning patterns of olivine from two mafic-ultramafic intrusions in SW China. Polyhedral olivine grains from lherzolite and dunite of the Abulangdang intrusion show P-rich dendrites similar to those observed in volcanic rocks. Rounded olivine grains from net-textured Fe-Ti oxide ores of the Baima layered intrusion have irregular P-rich patches/bands crosscut and interlocked by P-poor olivine domains. P-rich patches/bands contain 250 to 612 ppm P, much higher than P-poor olivine domains with 123 to 230 ppm P. In electron backscattered diffraction (EBSD) maps, P-rich patches/bands within a single olivine grain have the same crystallographic orientation, indicating that they were remnants of the same crystal. Thus, both P-rich patches/bands and P-poor olivine domains in the same grain show a disequilibrium texture and clearly record two-stage growth. The P-rich patches/bands are likely the remnants of a polyhedral olivine crystal that formed in the first stage, whereas the P-poor olivine domains containing rounded Ti-rich magnetite and Fe-rich melt inclusions may have formed from an Fe-rich ambient melt in the second stage. The complex P zoning of olivine can be attributed to the dissolution of early polyhedral olivine and re-precipitation from the Fe-rich ambient melt. The early polyhedral olivine was in chemical disequilibrium with the ambient melt that may have been developed by silicate liquid immiscibility in a crystal mush. Our study implies that olivine crystals in igneous cumulates with an equilibrium appearance may have experienced disequilibrium growth processes

Intrusion of Magmatic Bodies Into the Continental Crust: 3-D Numerical Models

NASA Astrophysics Data System (ADS)

Gorczyk, Weronika; Vogt, Katharina

2018-03-01

Magma intrusion is a major material transfer process in the Earth's continental crust. Yet the mechanical behavior of the intruding magma and its host are a matter of debate. In this study we present a series of numerical thermomechanical simulations on magma emplacement in 3-D. Our results demonstrate the response of the continental crust to magma intrusion. We observe change in intrusion geometries between dikes, cone sheets, sills, plutons, ponds, funnels, finger-shaped and stock-like intrusions, and injection time. The rheology and temperature of the host are the main controlling factors in the transition between these different modes of intrusion. Viscous deformation in the warm and deep crust favors host rock displacement and plutons at the crust-mantle boundary forming deep-seated plutons or magma ponds in the lower to middle crust. Brittle deformation in the cool and shallow crust induces cone-shaped fractures in the host rock and enables emplacement of finger- or stock-like intrusions at shallow or intermediate depth. Here the passage of magmatic and hydrothermal fluids from the intrusion through the fracture pattern may result in the formation of ore deposits. A combination of viscous and brittle deformation forms funnel-shaped intrusions in the middle crust. Intrusion of low-density magma may more over result in T-shaped intrusions in cross section with magma sheets at the surface.

Coronae as a result of giant magma intrusions in the lithosphere of Venus: insights from laboratory experiments

NASA Astrophysics Data System (ADS)

Galland, Olivier; Polteau, Stephane; Werner, Stephanie C.

2013-04-01

Coronae on the surface of Venus are unique volcano-tectonic structures in the solar systems. Their circular morphology is associated with various topographic signatures, from bell-shape domes, flat-topped plateaus, to uplifted rings surrounding a subsided centre similar to caldera. Their extensive size and associated lava flows erupting from their periphery, indicate that they result from deep processes in the Venus mantle. Understanding their origin is thus essential for unraveling the dynamics of Venus through time. There are several scenarios explaining the formation of coronae, the most popular being the interaction between an upwelling mantle plume and the lithosphere, creating dynamic topography. In this contribution, we propose that coronae can result from the emplacement of giant magma intrusions below the Venus' lithosphere, on the basis of laboratory experiments. The experimental apparatus consists of a square box filled with compacted fine-grained silica flour (model crust), in which a low viscosity vegetable oil (model magma) is injected at constant flow rate. The initial conditions are such that magma initially flows horizontally, forming a sill-like body, to simulate magmatic underplating. During the experiments, oil injection triggers deformation of the model surface, which is monitored periodically using a moiré projection device, producing time series topographic maps of the model surface. Our results show that the surface evolution of the models follows three stages: (1) initial bell-shaped doming occurs above the injection inlet, producing radial open fractures at the model surfaces; (2) the bell-shape dome evolves to a flat-topped plateau, at the rim of which the oil erupts; (3) after the injection stops, the centre of the plateau subsides, and a positive topographic ring surrounding a depression, like a caldera, remains. The collapse of the plateau also generates concentric extensional fractures at the rims of the caldera. After the dynamic

Time Dependent Model of Magma Intrusion in and around Miyake and Kozu Islands, Central Japan in June-August, 2000

NASA Astrophysics Data System (ADS)

Murase, M.; Irwan, M.; Kariya, S.; Tabei, T.; Okuda, T.; Miyajima, R.; Kimata, F.; Fujii, N.

2004-12-01

We discuss a time dependent model of magma intrusion in and around Miyake and Kozu Islands, Central Japan from GPS measurements at 28 sites in Miyake Island, Kozu Island and their surrounding islands in the period from June 27 to August 27, 2000. A dike complex model of three sheets is assumed between Miyake and Kozu Islands, suggested from the precise hypocenter distribution map (Sakai et al., 2003). Other dike intrusion models, a dike with an aseismic creep model (Nishimura et al.,2001; Furuya et al.,2003) and a dike with a deep deflation source model (Yamaoka et al., submitted) , are also discussed. Akaike's Information Criteria (AIC) value of optimal parameters of a dike complex model indicates lower than that of other two models. After fixing the geometry of three dikes using a genetic algorithm (GA), the amounts of dike openings of top, inside, and bottom of each dike are estimated by GA for seven time periods. In the period from June 27 to July 8, dike opening is concentrated in the dike near Miyake Island, and a large deflation is also estimated at a depth of 5 km of Miyake Volcano. It suggests that magma is supplied from the depths of Miyake Island. In next period until August 10, a huge dike intrusion is characterized in the dike near Kozu Island and the lower parts of dike in central and near Miyake Island. This suggests that magma is supplied from depth between Miyake and Kozu Islands. In the period of August 10 to 27, a huge deflation is estimated at a depth of 10 km under Miyake Volcano, and dike opening is limited

Hindered settling and the formation of layered intrusions

NASA Astrophysics Data System (ADS)

Bons, Paul D.; Baur, Albrecht; Elburg, Marlina A.; Lindhuber, Matthias J.; Marks, Michael A. W.; Soesoo, Alvar; van Milligen, Boudewijn P.; Walte, Nicolas P.

2015-04-01

Layered intrusions are characterized by (often repetitive) layering on a range of scales. Many explanations for the formation of such layering have been proposed over the past decades. We investigated the formation of "mats" by hindered crystal settling, a model that was first suggested by Lauder (1964). The interaction of sinking and rising crystals leads to the amplification of perturbations in crystal density within a magma chamber, a process similar to the formation of traffic jams in dense traffic (Bons et al., 2015). Once these "crystal traffic jams" form they constitute a barrier for further settling of crystals. Between these barriers, the magma evolves in a semi-closed system in which stratification may develop by gravitational sorting. Barriers, and therefore layers, form sequentially during inward cooling of the magma chamber. Barring later equilibration, mineralogical and geochemical trends within the layers are repetitive, but with variations due to the random process of initial perturbation formation. Layers can form in the transition between two end-member regimes: (1) in a fast cooling and/or viscous magma crystals cannot sink or float a significant distance and minerals are distributed homogeneously throughout the chamber; (2) in a slow cooling and/or low-viscosity magma crystals can quickly settle at the top and bottom of the chamber and crystals concentrations are never high enough to form "traffic jams". As a result, heavy and light minerals get fully separated in the chamber. Between these two end members, crystals can sink and float a significant distance, but not the whole height of the magma chamber before entrapment in "traffic jams". We illustrate the development of layers with numerical models and compare the results with the layered nepheline syenites (kakortokites) of the Ilímaussaq intrusion in SW Greenland. References: Bons, P.D., Baur, A., Elburg, M.A., Lindhuber, M.J., Marks, M.A.W., Soesoo, A., van Milligen, B.P., Walte, N.P. 2015

Hazard Models From Periodic Dike Intrusions at Kı¯lauea Volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Montgomery-Brown, E. K.; Miklius, A.

2016-12-01

The persistence and regular recurrence intervals of dike intrusions in the East Rift Zone (ERZ) of Kı¯lauea Volcano lead to the possibility of constructing a time-dependent intrusion hazard model. Dike intrusions are commonly observed in Kı¯lauea Volcano's ERZ and can occur repeatedly in regions that correlate with seismic segments (sections of rift seismicity with persistent definitive lateral boundaries) proposed by Wright and Klein (USGS PP1806, 2014). Five such ERZ intrusions have occurred since 1983 with inferred locations downrift of the bend in Kı¯lauea's ERZ, with the first (1983) being the start of the ongoing ERZ eruption. The ERZ intrusions occur on one of two segments that are spatially coincident with seismic segments: Makaopuhi (1993 and 2007) and Nāpau (1983, 1997, and 2011). During each intrusion, the amount of inferred dike opening was between 2 and 3 meters. The times between ERZ intrusions for same-segment pairs are all close to 14 years: 14.07 (1983-1997), 14.09 (1997-2011), and 13.95 (1993-2007) years, with the Nāpau segment becoming active about 3.5 years after the Makaopuhi segment in each case. Four additional upper ERZ intrusions are also considered here. Dikes in the upper ERZ have much smaller opening ( 10 cm), and have shorter recurrence intervals of 8 years with more variability. The amount of modeled dike opening during each of these events roughly corresponds to the amount of seaward south flank motion and deep rift opening accumulated in the time between events. Additionally, the recurrence interval of 14 years appears to be unaffected by the magma surge of 2003-2007, suggesting that flank motion, rather than magma supply, could be a controlling factor in the timing and periodicity of intrusions. Flank control over the timing of magma intrusions runs counter to the historical research suggesting that dike intrusions at Kı¯lauea are driven by magma overpressure. This relatively free sliding may have resulted from decreased

Linking magma transport structures at Kīlauea volcano

USGS Publications Warehouse

Wech, Aaron G.; Thelen, Weston A.

2015-01-01

Identifying magma pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period events (LPs) dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending magma. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008-2014. We find the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader-band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the MFZ. We propose the overlying MFZ promotes lateral magma transport, linking this deep intrusion with Kīlauea’s shallow magma plumbing.

The Sonju Lake layered intrusion, northeast Minnesota: Internal structure and emplacement history inferred from magnetic fabrics

USGS Publications Warehouse

Maes, S.M.; Tikoff, B.; Ferre, E.C.; Brown, P.E.; Miller, J.D.

2007-01-01

The Sonju Lake intrusion (SLI), in northeastern Minnesota, is a layered mafic complex of Keweenawan age (1096.1 ?? 0.8 Ma) related to the Midcontinent rift. The cumulate paragenesis of the intrusion is recognized as broadly similar to the Skaergaard intrusion, a classic example of closed-system differentiation of a tholeiitic mafic magma. The SLI represents nearly closed-system differentiation through bottom-up fractional crystallization. Geochemical studies have identified the presence of a stratabound, 50-100 m thick zone anomalously enriched in Au + PGE. Similar to the PGE reefs of the Skaergaard intrusion, this PGE-enriched zone is hosted within oxide gabbro cumulates, about two-third of the way up from the base of the intrusion. We present a petrofabric study using the anisotropy of magnetic susceptibility (AMS) to investigate the emplacement and flow patterns within the Sonju Lake intrusion. Petrographic and electron microprobe studies, combined with AMS and hysteresis measurements indicate the primary source of the magnetic signal is pseudo-single domain (PSD) magnetite or titanomagnetite. Low field AMS was measured at 32 sites within the Sonju Lake intrusion, which provided information about primary igneous fabrics. The magnetic fabrics in the layered series of the Sonju Lake intrusion are consistent with sub-horizontal to inclined emplacement of the intrusion and show evidence that the cumulate layers were deposited in a dynamic environment. Well-aligned magnetic lineations, consistently plunging shallowly toward the southwest, indicate the source of the magma is a vertical sill-like feeder, presumably located beneath the Finland granite. The Finland granite acted as a density trap for the Sonju Lake magmas, forcing lateral flow of magma to the northeast. The strongly oblate magnetic shape fabrics indicate the shallowly dipping planar fabrics were enhanced by compaction of the crystal mush. ?? 2007 Elsevier B.V. All rights reserved.

Mafic intrusion remobilising silicic magma under El Hierro, Canary Islands

NASA Astrophysics Data System (ADS)

Sigmarsson, O.; Laporte, D.; Marti, J.; Devouard, B.; Cluzel, N.

2012-04-01

elevated incompatible element concentrations and primitive mantle normalised spectra characteristic for the Canary Island basanites (e.g. La is of 100 times higher concentration than primitive mantle with important LREE enrichments). In contrast, the trace element composition of the alkali rhyolite shows surprisingly low concentrations for all elements except the most incompatible ones (such as Rb, Ba, K and Th). All other measured incompatible LILE, HFSE and REE have significantly lower concentration than the basanitic counterpart. This differences increase with the atomic number of the REE reaching maximum for the MREE and thus forming an intriguing U-shaped rhyolite spectra. Furthermore, unusual U-depletion is observed in the rhyolite. Other negative spikes, such as those for Sr and P, are readily accounted for by the removal of plagioclase and apatite during magma evolution from a basanite to a more evolved melt. The results obtained so far suggest an intrusion of gas-rich basanitic melt at the base of an evolved intrusion remobilising a stagnant phonolitic melt present as late differentiate in the crust. Interaction with old oceanic crust and the volcanic edifice can be quantified and shown to have modified the phonolite melt composition and produced the alkali rhyolitic composition of the white floating pumice. Extensive gas exsolution shortly before the melt-glass transition explains the foam texture and the low volatile concentrations in the quenched alkali rhyolite.

Failed magmatic eruptions: Late-stage cessation of magma ascent

USGS Publications Warehouse

Moran, S.C.; Newhall, C.; Roman, D.C.

2011-01-01

When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which magma reaches but does not pass the "shallow intrusion" stage, i. e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.

Intrusive rocks of the Wadi Hamad Area, North Eastern Desert, Egypt: Change of magma composition with maturity of Neoproterozoic continental island arc and the role of collisional plutonism in the differentiation of arc crust

NASA Astrophysics Data System (ADS)

Basta, Fawzy F.; Maurice, Ayman E.; Bakhit, Bottros R.; Azer, Mokhles K.; El-Sobky, Atef F.

2017-09-01

The igneous rocks of the Wadi Hamad area are exposed in the northernmost segment of the Arabian-Nubian Shield (ANS). These rocks represent part of crustal section of Neoproterozoic continental island arc which is intruded by late to post-collisional alkali feldspar granites. The subduction-related intrusives comprise earlier gabbro-diorites and later granodiorites-granites. Subduction setting of these intrusives is indicated by medium- to high-K calc-alkaline affinity, Ta-Nb troughs on the spider diagrams and pyroxene and biotite compositions similar to those crystallized from arc magmas. The collisional alkali feldspar granites have high-K highly fractionated calc-alkaline nature and their spider diagrams almost devoid of Ta-Nb troughs. The earlier subduction gabbro-diorites have lower alkalis, LREE, Nb, Zr and Hf values compared with the later subduction granodiorites-granites, which display more LILE-enriched spider diagrams with shallower Ta-Nb troughs, reflecting variation of magma composition with arc evolution. The later subduction granitoids were generated by lower degree of partial melting of mantle wedge and contain higher arc crustal component compared with the earlier subduction gabbro-diorites. The highly silicic alkali feldspar granites represent extensively evolved melts derived from partial melting of intermediate arc crustal sources during the collisional stage. Re-melting of arc crustal sources during the collisional stage results in geochemical differentiation of the continental arc crust and the silicic collisional plutonism drives the composition of its upper part towards that of mature continental crust.

Rapid laccolith intrusion driven by explosive volcanic eruption

NASA Astrophysics Data System (ADS)

Castro, Jonathan M.; Cordonnier, Benoit; Schipper, C. Ian; Tuffen, Hugh; Baumann, Tobias S.; Feisel, Yves

2016-11-01

Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ~0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ~20-200 m and overpressures (~1-10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards.

Rapid laccolith intrusion driven by explosive volcanic eruption.

PubMed

Castro, Jonathan M; Cordonnier, Benoit; Schipper, C Ian; Tuffen, Hugh; Baumann, Tobias S; Feisel, Yves

2016-11-23

Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km 3 . Deformation and conduit flow models indicate laccolith depths of only ∼20-200 m and overpressures (∼1-10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards.

Estimating the magma supply rate at Kilauea volcano, Hawaii

NASA Astrophysics Data System (ADS)

Wright, T. L.; Klein, F. W.

2006-12-01

A frequent question is whether the magma supply rate to Kilauea is constant. Before seaward spreading of the south flank of Kilauea was demonstrated by the slip on a basal decollement that accompanied the M7.2 1975 south flank earthquake, the magma supply rate was equated to the identical eruption rates for three long-lived eruptions (3). Later, a continuous tilt record at Kilauea's summit was used to derive the volume of magma transported during deflations associated with rift eruptions (2), concluding that over a 30-year period about 38% of Kilauea's magma supply was left underground, but agreeing with the equivalency of overall magma supply and sustained eruption rates. Recent modeling of geodetic data gathered during Kilauea's current eruption (1) estimated a supply rate to accommodate spreading at 1.5 times the eruption rate. We approach the problem of magma supply, making two assumptions: 1. Eruption rates are controlled by the capacity of the underground transport paths to deliver magma to the surface. 2. Spreading of Kilauea's south flank is magma-driven and all space created during spreading is filled with new magma. On these premises, and in consideration of the physical properties of magma, eruption rates would have to be less than the supply rate; equivalence would imply a rigid edifice in which an open channel could deliver magma as if it were water. We are working to establish a third indicator of magma supply, the occurrence of seismic swarms in the stressed south flank. Many such swarms have been previously identified in association with documented eruptions and intrusions, but other swarms occur independently and may be associated with passive intrusion filling the room created during spreading. We contrast the seismic and geodetic data gathered during Kilauea's two longest monitored eruptions, Mauna Ulu (1969-1974) and Pu'u `O'o-Kupaianaha (1983-ongoing). For episodic high-fountaining episodes we calculate eruption efficiency as the ratio of

Uplift and magma intrusion at Long Valley caldera from InSAR and gravity measurements

USGS Publications Warehouse

Tizzani, Pietro; Battaglia, Maurizio; Zeni, Giovanni; Atzori, Simone; Berardino, Paolo; Lanari, Riccardo

2009-01-01

The Long Valley caldera (California) formed ~760,000 yr ago following the massive eruption of the Bishop Tuff. Postcaldera volcanism in the Long Valley volcanic field includes lava domes as young as 650 yr. The recent geological unrest is characterized by uplift of the resurgent dome in the central section of the caldera (75 cm in the past 33 yr) and earthquake activity followed by periods of relative quiescence. Since the spring of 1998, the caldera has been in a state of low activity. The cause of unrest is still debated, and hypotheses range from hybrid sources (e.g., magma with a high percentage of volatiles) to hydrothermal fluid intrusion. Here, we present observations of surface deformation in the Long Valley region based on differential synthetic aperture radar interferometry (InSAR), leveling, global positioning system (GPS), two-color electronic distance meter (EDM), and microgravity data. Thanks to the joint application of InSAR and microgravity data, we are able to unambiguously determine that magma is the cause of unrest.

Magmatic intrusions in the lunar crust

NASA Astrophysics Data System (ADS)

Michaut, C.; Thorey, C.

2015-10-01

The lunar highlands are very old, with ages covering a timespan between 4.5 to 4.2 Gyr, and probably formed by flotation of light plagioclase minerals on top of the lunar magma ocean. The lunar crust provides thus an invaluable evidence of the geological and magmatic processes occurring in the first times of the terrestrial planets history. According to the last estimates from the GRAIL mission, the lunar primary crust is particularly light and relatively thick [1] This low-density crust acted as a barrier for the dense primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basin: at least part of the crust must have been removed for the magma to reach the surface. However, the trajectory of the magma from the mantle to the surface is unknown. Using a model of magma emplacement below an elastic overlying layer with a flexural wavelength Λ, we characterize the surface deformations induced by the presence of shallow magmatic intrusions. We demonstrate that, depending on its size, the intrusion can show two different shapes: a bell shape when its radius is smaller than 4 times Λ or a flat top with small bended edges if its radius is larger than 4 times Λ[2]. These characteristic shapes for the intrusion result in characteristic deformations at the surface that also depend on the topography of the layer overlying the intrusion [3].Using this model we provide evidence of the presence of intrusions within the crust of the Moon as surface deformations in the form of low-slope lunar domes and floor-fractured craters. All these geological features have morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. Further more,at floor-fractured craters, the deformation is contained within the crater interior, suggesting that the overpressure at the origin of magma ascent and intrusion was less than the pressure due to the weight of the crust removed by

In situ strontium and sulfur isotope investigation of the Ni-Cu-(PGE) sulfide ore-bearing Kevitsa intrusion, northern Finland

NASA Astrophysics Data System (ADS)

Luolavirta, Kirsi; Hanski, Eero; Maier, Wolfgang; Lahaye, Yann; O'Brien, Hugh; Santaguida, Frank

2018-01-01

The 2.06-Ga Kevitsa mafic-ultramafic intrusion in northern Finland hosts a large disseminated Ni-Cu-PGE deposit. The deposit occurs in the ultramafic olivine-pyroxene cumulates and shows a range in Ni tenors varying from 4-7 wt% (regular ore) to > 10 wt% (Ni-PGE ore). There are also a metal-poor sulfide mineralization (false ore) and contact mineralization that are uneconomic (Ni tenor < 4 wt%). The obtained 87Sr/86Sr(i) values of the Kevitsa ultramafic cumulates are highly radiogenic (> 0.7045) in comparison to the estimated depleted mantle Sr isotope ratio of 0.702 at 2.06 Ga. The sulfur δ 34S values are generally higher than + 2‰, which together with the Sr isotope data imply involvement of crustal material in the genesis of the Kevitsa intrusion and its ores. The 87Sr/86Sr(i) values obtained from the ore-bearing domain of the intrusion show stratigraphic variation and exceed 0.7050, with the maximum value reaching up to 0.7109. In contrast, in rocks around the ore domain, the initial Sr isotope compositions remain more or less constant (0.7047-0.7060) throughout the intrusive stratigraphy. The isotope data suggest that the ore-bearing domain of the intrusion represents a dynamic site with multiple injections of variably contaminated magma, whereas the surrounding part of the intrusion experienced a less vigorous emplacement history. No correlation is observed between the strontium and sulfur isotope compositions. This is explained by bulk assimilation of the silicate magma in a deeper staging magma chamber and variable assimilation of sulfur during magma transport into the Kevitsa magma chamber. The low level of metals in false ore and the Ni-depleted nature of its olivine suggest that some sulfides may have precipitated and deposited in the feeder conduit during the initial stage of magma emplacement. Cannibalization of early-formed sulfides by later magma injections may have been important in the formation of the economic ore deposit.

Timing of magmatism following initial convergence at a passive margin, southwestern U.S. Cordillera, and ages of lower crustal magma sources

USGS Publications Warehouse

Barth, A.P.; Wooden, J.L.

2006-01-01

Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali-calcic Fe- and Sr-enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal-miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo-Triassic intrusion ages, and a prolonged postemplacement thermal history within the long-lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc. ?? 2006 by The University of Chicago. All rights reserved.

Rapid laccolith intrusion driven by explosive volcanic eruption

PubMed Central

Castro, Jonathan M.; Cordonnier, Benoit; Schipper, C. Ian; Tuffen, Hugh; Baumann, Tobias S.; Feisel, Yves

2016-01-01

Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ∼20–200 m and overpressures (∼1–10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards. PMID:27876800

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

USGS Publications Warehouse

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-01-01

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

PubMed Central

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-01-01

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

PubMed

Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-08-25

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

Noble gas systematics of the Skaergaard intrusion

NASA Astrophysics Data System (ADS)

Horton, F.; Farley, K. A.; Taylor, H. P.

2017-12-01

The noble gas isotopic compositions of olivines from the Skaergaard layered mafic intrusion in Greenland reveal that magmas readily exchange noble gases with their environment after emplacement. Although Skaergaard magmas are thought to have derived from the upper mantle, all of the olivine separates we analyzed have 3He/4He ratios less than that of the upper mantle ( 8 Ra, where Ra = 3He/4He of the atmosphere, 1.39 x 10-6). This suggests that crustal and/or atmospheric noble gases have contaminated all Skaergaard magmas to some extent. We obtained the highest 3He/4He ratios ( 2 Ra) from olivines found in the lowermost exposed layers of the intrusion away from the margins. Excess radiogenic 4He (indicated by Ra<1) along the margin of the intrusion indicates that noble gases from the Archean host-rock were incorporated into the cooling magma chamber, probably via magmatic assimilation. Noble gases in olivines from the upper portions of the intrusion have atmospheric isotopic compositions, but higher relative helium abundances than the atmosphere. We suggest that post-crystallization hydrothermal circulation introduced atmosphere-derived noble gases into uppermost layers of the intrusion. Such high temperature exchanges of volatiles between plutons and their immediate surroundings may help explain why so few mantle-derived rocks retain mantle-like noble gas signatures.

Successive reactive liquid flow episodes in a layered intrusion (Unit 9, Rum Eastern Layered Intrusion, Scotland)

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Blundy, Jon; Holness, Marian

2014-05-01

moving upwards and laterally through the cumulate pile. The Rum layered intrusion is an open intrusive complex, composed of individual partially molten zones, evolving independently. The Rum layered intrusion offers a direct overview of processes taking place in shallow intra-plate and ridge magma chambers. Intrusion of hot magma into a pre-existing cumulate pile results in the modification both the incoming liquid and the host-rock cumulates. Our study highlights the necessity of considering this type of process when modelling the geochemistry of lavas erupted from magma chambers subject to repeated replenishment.

Rocks Whose Compositions are Determined by Flow Differentiation of Olivine- and Sulfide Droplet-Laden Magma: the Jinchuan Story

NASA Astrophysics Data System (ADS)

Li, C.; Ripley, E. M.; de Waal, S. A.; Xu, Z.

2002-12-01

The Jinchuan intrusion in western China is an elongated, deeply-dipping dyke-like body of dominantly olivine-rich ultramafic rocks of high magnesium basaltic magma. It hosts the second largest Ni-Cu sulfide deposit in the world. More than 500 million tones of sulfide ore grading 1.2 percent Ni and 0.7 percent Cu occur mostly as next-textured and disseminated sulfide (pyrrhotite, pentlendite and chalcopyrite) with cumulus olivine in about half of the rocks of the intrusion. Based on different petrological zonations, the Jinchuan intrusion is further divided into three segments: eastern, central and western segments. The central segment is characterized by concentric enrichments of cumulus olivine and sulfide, whereas the eastern and western segments are characterized by the increase of both cumulus olivine and sulfide toward the footwall. The forsterite contents of fresh olivine from different segments are similar and vary between 82 and 86 mole percent. The small range of olivine compositional variation corresponds to less than 6 percent of fractional crystallization. Mass balance calculations based on sulfide solubility in basaltic magma indicate that the volume of the parental magma of the sulfide is many times larger than that which is currently represented in the intrusion. Large amounts of cumulus olivine (more than 40 weight percent) in the marginal samples and high concentrations of sulfide in the intrusion are consistent with an interpretation that the Jinchuan intrusion was formed by olivine- and sulfide droplet-laden magma ascending through a subvertical conduit to a higher level. Differentiation processes of the olivine- and sulfide droplet-laden magma varied in different parts of the conduit. Sub-vertical flow differentiation controlled the central segment of the conduit, resulting in further enrichment of olivine crystals and sulfide droplets in the conduit center. In contrast, sub-lateral flow and gravitational differentiation dominated in the eastern

Petrogenesis of the Pd-rich intrusion at Salt Chuck, Prince of Wales island: an early Paleozoic Alaskan-type ultramafic body

USGS Publications Warehouse

Loney, R.A.; Himmelberg, G.R.

1992-01-01

The early Paleozoic Salt Chuck intrusion has petrographic and chemical characteristics that are similar to those of Cretaceous Alaskan-type ultramafic-mafic bodies. The intrusion is markedly discordant to the structure of the early Paleozoic Descon Formation, in which it has produced a rather indistinct contact aureole a few meters wide. Mineral assemblages, sequence of crystallization, and mineral chemistry suggest that the intrusion crystallized under low pressures (~2 kbar) with oxidation conditions near those of the NNO buffer, from a hydrous, silica-saturated, orthopyroxene-normative parental magma. The Salt Chuck deposit was probably formed by a two-stage process: 1) a stage of magmatic crystallization in which the sulfides and PGE accumulated in a disseminated manner in cumulus deposits, possibly largely in the gabbro, and 2) a later magmatic-hydrothermal stage during which the sulfides and PGE were remobilized and concentrated in veins and fracture-fillings. In this model, the source of the sulfides and PGE was the magma that produced the Salt Chuck intrusion. -from Authors

Lifetime and size of shallow magma bodies controlled by crustal-scale magmatism

NASA Astrophysics Data System (ADS)

Karakas, Ozge; Degruyter, Wim; Bachmann, Olivier; Dufek, Josef

2017-06-01

Magmatic processes on Earth govern the mass, energy and chemical transfer between the mantle, crust and atmosphere. To understand magma storage conditions in the crust that ultimately control volcanic activity and growth of continents, an evaluation of the mass and heat budget of the entire crustal column during magmatic episodes is essential. Here we use a numerical model to constrain the physical conditions under which both lower and upper crustal magma bodies form. We find that over long durations of intrusions (greater than 105 to 106 yr), extensive lower crustal mush zones develop, which modify the thermal budget of the upper crust and reduce the flux of magma required to sustain upper crustal magma reservoirs. Our results reconcile physical models of magma reservoir construction and field-based estimates of intrusion rates in numerous volcanic and plutonic localities. Young igneous provinces (less than a few hundred thousand years old) are unlikely to support large upper crustal reservoirs, whereas longer-lived systems (active for longer than 1 million years) can accumulate magma and build reservoirs capable of producing super-eruptions, even with intrusion rates smaller than 10-3 to 10-2 km3 yr-1. Hence, total duration of magmatism should be combined with the magma intrusion rates to assess the capability of volcanic systems to form the largest explosive eruptions on Earth.

Seismic signature of active intrusions in mountain chains.

PubMed

Di Luccio, Francesca; Chiodini, Giovanni; Caliro, Stefano; Cardellini, Carlo; Convertito, Vincenzo; Pino, Nicola Alessandro; Tolomei, Cristiano; Ventura, Guido

2018-01-01

Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals. We analyze an anomalously deep seismic sequence (maximum magnitude 5) characterized by low-frequency bursts of earthquakes that occurred in 2013 in the Apennine chain in Italy. We provide seismic evidences of fluid involvement in the earthquake nucleation process and identify a thermal anomaly in aquifers where CO 2 of magmatic origin dissolves. We show that the intrusion of dike-like bodies in mountain chains may trigger earthquakes with magnitudes that may be relevant to seismic hazard assessment. These findings provide a new perspective on the emplacement mechanisms of intrusive bodies and the interpretation of the seismicity in mountain chains.

Seismic signature of active intrusions in mountain chains

PubMed Central

Di Luccio, Francesca; Chiodini, Giovanni; Caliro, Stefano; Cardellini, Carlo; Convertito, Vincenzo; Pino, Nicola Alessandro; Tolomei, Cristiano; Ventura, Guido

2018-01-01

Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals. We analyze an anomalously deep seismic sequence (maximum magnitude 5) characterized by low-frequency bursts of earthquakes that occurred in 2013 in the Apennine chain in Italy. We provide seismic evidences of fluid involvement in the earthquake nucleation process and identify a thermal anomaly in aquifers where CO2 of magmatic origin dissolves. We show that the intrusion of dike-like bodies in mountain chains may trigger earthquakes with magnitudes that may be relevant to seismic hazard assessment. These findings provide a new perspective on the emplacement mechanisms of intrusive bodies and the interpretation of the seismicity in mountain chains. PMID:29326978

Using magma flow indicators to infer flow dynamics in sills

NASA Astrophysics Data System (ADS)

Hoyer, Lauren; Watkeys, Michael K.

2017-03-01

Fabrics from Anisotropy of Magnetic Susceptibility (AMS) analyses and Shape Preferred Orientation (SPO) of plagioclase are compared with field structures (such as bridge structures, intrusive steps and magma lobes) formed during magma intrusion in Jurassic sills. This is to constrain magma flow directions in the sills of the Karoo Igneous Province along the KwaZulu-Natal North Coast and to show how accurately certain structures predict a magma flow sense, thus improving the understanding of the Karoo sub-volcanic dynamics. The AMS fabrics are derived from magnetite grains and are well constrained, however the SPO results are commonly steeply inclined, poorly constrained and differ to the AMS fabrics. Both techniques resulted in asymmetrical fabrics. Successful relationships were established between the AMS fabric and the long axes of the magma flow indicators, implying adequate magma flow prediction. However, where numerous sill segments merge, either in the form of magma lobes or bridge structures, the coalescence process creates a new fabric between the segments preserving late-stage magma migration between the merged segments, overprinting the initial magma flow direction.

The Torres del Paine intrusion as a model for a shallow magma chamber

NASA Astrophysics Data System (ADS)

Baumgartner, Lukas; Bodner, Robert; Leuthold, Julien; Muntener, Othmar; Putlitz, Benita; Vennemann, Torsten

2014-05-01

The shallow magmatic Torres del Paine Intrusive Complex (TPIC) belongs to a series of sub-volcanic and plutonic igneous bodies in Southern Chile and Argentina. This trench-parallel belt is located in a transitional position between the Patagonia Batholith in the West, and the alkaline Cenozoic plateau lavas in the East. While volumetrically small amounts of magmatism started around 28 my ago in the Torres del Paine area, and a second period occurred between 17-16 Ma, it peaked with the TPIC 12.59-12.43 Ma ago. The spectacular cliffs of the Torres del Paine National park provide a unique opportunity to study the evolution of a very shallow magma chamber and the interaction with its host rocks. Intrusion depth can be estimated based on contact metamorphic assemblages and granite solidus thermobarometry to 750±250 bars, corresponding to an intrusion depth of ca. 3km, ca. 500m above the base of the intrusion. Hornblende thermobarometry in mafic rocks agrees well with these estimates (Leuthold et al., 2014). The TPIC is composed of a granitic laccolith emplaced over 90ka (Michel et al., 2008) in 3 major, several 100m thick sheets, forming an overall thickness of nearly 2 km. Contacts are sharp between sheets, with the oldest sheet on the top and the youngest on the bottom (Michel et al., 2008). The granitic laccolith is under-plated by a ca. 400m thick mafic laccolith, built up over ca. 50ka (Leuthold et al. 2012), constructed from the bottom up. Granitic and mafic sheets are themselves composed of multiple metric to decametric pulses, mostly with ductile contacts between them, resulting in outcrop patterns resembling braided stream sediments. The contact of the TPIC with the Cretaceous flysch sediments document intrusion mechanism. Pre-existing sub-horizontal fold axes are rotated in the roof of the TPIC, clearly demonstrating ballooning of the roof; no ballooning was observed in the footwall of the intrusion. Extension during ballooning of the roof is indicated by

Emplacement of the early Miocene Pinto Peak intrusion, Southwest Utah, USA

NASA Astrophysics Data System (ADS)

Petronis, Michael S.; O'Driscoll, Brian

2013-12-01

In this contribution, we report rock magnetic, petrographic, and anisotropy of magnetic susceptibility (AMS) data from the Pinto Peak intrusion, all of which bear on volcanic construction. Rock magnetic data indicate that the dominant magnetic mineral phase is low-Ti titanomagnetite of multidomain grain size, the composition of which varies spatially across the intrusion. The intrusion is a porphyritic andesite dominated by Ca-rich plagioclase (>60%) as well as biotite, amphibole, olivine, and opaque minerals. Reflected light petrography reveals mostly euhedral-subhedral (titano)magnetite crystals that often form clustered glomerocrysts and stringers of equant crystals, without exhibiting a consistent mineral alignment fabric. Moderate-to-shallow plunging prolate magnetic susceptibility ellipsoids dominate the northern part of the intrusion while steeply dipping/plunging magnetic susceptibility ellipsoids are generally restricted to the southern part of the intrusion. The vent facies rocks yield moderate-to-steep oblate susceptibility ellipsoids. We interpret the flow pattern in the north to reflect subhorizontal flow of magma, filling a tabular sheet-like body associated with propagation of the intrusion to the north. We argue that the southern part of the intrusion represents the ascent site of the magma rising to shallow crustal levels along a steep feeder system. The oblate magnetic fabrics in the vent area plausibly represent flattening against the conduit walls as evidenced by a weak planar flow foliation observed in the vent conduit rocks. On reaching shallow crustal levels, the magma deformed and uplifted the roof rocks leading to gravitational instability. As the slide mass released from the roof, an explosive eruption ensued resulting in the emplacement of the Rocks of Paradise tuff and associated effusive lava flows. Following eruption, magma pressure decreased and the magma drained northward forming the northern intrusive phase.

A refined model for Kilauea's magma plumbing system

NASA Astrophysics Data System (ADS)

Poland, M. P.; Miklius, A.; Montgomery-Brown, E. D.

2011-12-01

Studies of the magma plumbing system of Kilauea have benefitted from the volcano's frequent eruptive activity, ease of access, and particularly the century-long observational record made possible by the Hawaiian Volcano Observatory. The explosion of geophysical data, especially seismic and geodetic, collected since the first model of Kilauea's magmatic system was published in 1960 allows for a detailed characterization of Kilauea's magma storage areas and transport pathways. Using geological, geochemical, and geophysical observations, we propose a detailed model of Kilauea's magma plumbing that we hope will provide a refined framework for studies of Kilauea's eruptive and intrusive activity. Kilauea's summit region is underlain by two persistently active, hydraulically linked magma storage areas. The larger reservoir is centered at ~3 km depth beneath the south caldera and is connected to Kilauea's two rift zones, which radiate from the summit to the east and southwest. All magma that enters the Kilauea edifice passes through this primary storage area before intrusion or eruption. During periods of increased magma storage at the summit, as was the case during 2003-2007, uplift may occur above temporary magma storage volumes, for instance, at the intersection of the summit and east rift zone at ~3 km depth, and within the southwest rift zone at ~2 km depth. The east rift zone is the longer and more active of Kilauea's two rift zones and apparently receives more magma from the summit. Small, isolated pods of magma exist within both rift zones, as indicated by deformation measurements, seismicity, petrologic data, and geothermal drilling results. These magma bodies are probably relicts of past intrusions and eruptions and can be highly differentiated. Within the deeper part of the rift zones, between about 3 km and 9 km depth, magma accumulation is hypothesized based on surface deformation indicative of deep rift opening. There is no direct evidence for magma within

Geochemistry and field geology of shoshonitic magmas in the Late Cretaceous foreland fold and thrust belt of southwestern Montana: Results from the North Doherty Mountain Intrusive Complex

NASA Astrophysics Data System (ADS)

Beranek, L. P.; Burton, B. R.; Ihinger, P. D.

2002-12-01

The North Doherty Mountain Intrusive Complex (NDMIC) is one of several satellite plutons related to the areally extensive Boulder batholith of southwestern Montana. The Boulder batholith comprises multiple plutons and intrusive phases, and the magmatism has long been thought to be the result of subduction due to its calc-alkaline granodioritic composition. The batholith is situated in the Helena salient, which differs from other parts of the North American Cordilleran foreland because there, magmatism spatially and temporally overlaps with deformation in the foreland fold and thrust belt. The North Doherty Mountain Intrusive Complex (NDMIC) is one of several satellite plutons related to the Boulder batholith and represents an ideal microcosm of the batholith for petrogenetic and structural studies because it exposes both mafic and felsic units and was emplaced in the limb of a major thrust related fold. We present new geologic mapping and detailed trace element geochemical analyses to show that the entire mafic-to-felsic suite of rocks in the NDMIC are cogenetic and shoshonitic in character. Shoshonites are unusual magmas that are distinguished by their high concentrations of K, Rb, Sr, Ba, Zr, and Th contents, and are thought to represent partial melting at great depths within the mantle wedge above a subducting slab. The presence of shoshonitic magma in the Cordilleran foreland fold and thrust belt provides important clues into the nature of the formation of this unusual magma type and can provide insights into our understanding of magmatism in foreland structural settings.

Magma volumes and storage in the middle crust

NASA Astrophysics Data System (ADS)

Memeti, V.; Barnes, C. G.; Paterson, S. R.

2015-12-01

Quantifying magma volumes in magma plumbing systems is mostly done through geophysical means or based on volcanic eruptions. Detailed studies of plutons, however, are useful in revealing depths and evolving volumes of stored magmas over variable lifetimes of magma systems. Knowledge of the location, volume, and longevity of stored magma is critical for understanding where in the crust magmas attain their chemical signature, how these systems physically behave and how source, storage levels, and volcanoes are connected. Detailed field mapping, combined with single mineral geochemistry and geochronology of plutons, allow estimates of size and longevity of melt-interconnected magma batches that existed during the construction of magma storage sites. The Tuolumne intrusive complex (TIC) recorded a 10 myr magmatic history. Detailed maps of the major units in different parts of the TIC indicate overall smaller scale (cm- to <1 km) compositional variation in the oldest, outer Kuna Crest unit and mainly larger scale (>10 km) changes in the younger Half Dome and Cathedral Peak units. Mineral-scale trace element data from hornblende of granodiorites to gabbros from the Kuna Crest lobe show distinct hornblende compositions and zoning patterns. Mixed hornblende populations occur only at the transition to the main TIC. This compositional heterogeneity in the first 1-2 myr points to low volume magmatism resulting in smaller, discrete and not chemically interacting magma bodies. Trace element and Sr- and Pb-isotope data from growth zones of K-feldspar phenocrysts from the two younger granodiorites indicate complex mineral zoning, but general isotopic overlap, suggesting in-situ, inter-unit mixing and fractionation. This is supported by hybrid zones between units, mixing of zircon, hornblende, and K-feldspar populations and late leucogranites. Thus, magma body sizes increased later resulting in overall more homogeneous, but complexly mixing magma mushes that fractionated locally.

Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

USGS Publications Warehouse

Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

2011-01-01

The type examples for the class of deposits termed intrusion-related gold systems occur in the Tombstone-Tungsten belt of Alaska and Yukon, on the eastern side of the Tintina gold province. In this part of the northern Cordillera, extensive mid-Cretaceous postcollisional plutonism took place following the accretion of exotic terranes to the continental margin. The most cratonward of the resulting plutonic belts comprises small isolated intrusive centers, with compositionally diverse, dominantly potassic rocks, as exemplified at Scheelite Dome, located in central Yukon. Similar to other spatially and temporally related intrusive centers, the Scheelite Dome intrusions are genetically associated with intrusion-related gold deposits. Intrusions have exceptional variability, ranging from volumetrically dominant clinopyroxene-bearing monzogranites, to calc-alkaline minettes and spessartites, with an intervening range of intermediate to felsic stocks and dikes, including leucominettes, quartz monzonites, quartz monzodiorites, and granodiorites. All rock types are potassic, are strongly enriched in LILEs and LREEs, and feature high LILE/HFSE ratios. Clinopyroxene is common to all rock types and ranges from salite in felsic rocks to high Mg augite and Cr-rich diopside in lamprophyres. Less common, calcic amphibole ranges from actinolitic hornblende to pargasite. The rocks have strongly radiogenic Sr (initial 87Sr/86Sr from 0.711-0.714) and Pb isotope ratios (206Pb/204Pb from 19.2-19.7), and negative initial εNd values (-8.06 to -11.26). Whole-rock major and trace element, radiogenic isotope, and mineralogical data suggest that the felsic to intermediate rocks were derived from mafic potassic magmas sourced from the lithospheric mantle via fractional crystallization and minor assimilation of metasedimentary crust. Mainly unmodified minettes and spessartites represent the most primitive and final phases emplaced. Metasomatic enrichments in the underlying lithospheric mantle

Compaction and Crystallisation in Magma Chambers: Towards a Model of the Skaergaard Intrusion

NASA Astrophysics Data System (ADS)

McKenzie, D. P.

2010-12-01

The equations governing the conservation of mass, momentum and energy are first simplified by using the extended Boussinesq approximation, and then solved numerically to study the time dependent behaviour of a compacting solidifying layer at the base of a magma chamber when variations in the horizontal plane can be neglected. The most important result is that the concept of a trapped liquid fraction, which has been widely used to model the bulk composition of layered intrusions, is a useful concept to describe the steady state behaviour of compacting layers. The result is at first sight surprising, because there is relative movement between the melt and crystals during compaction, and the system is therefore open. The reason why it is correct is because both the melt and the crystals are moving downwards in a frame fixed to the upper surface of the compacting layer. Since the mass of all elements must be conserved, what goes into the top of the layer as melt and solid must come out of its bottom as a solid when the behaviour is not time dependent. However, when time dependent behaviour occurs the concept of a trapped liquid fraction ceases to be useful. The governing equations are then used to model the concentration of phosphorous in the lower part of the Skaergaard intrusion, where it behaves incompatibly. The observed behaviour requires the viscosity of the solid part of the compacting layer to have a viscosity of about 10^18 Pa s.

Sill intrusion in volcanic calderas: implications for vent opening probability

NASA Astrophysics Data System (ADS)

Giudicepietro, Flora; Macedonio, Giovanni; Martini, Marcello; D'Auria, Luca

2017-04-01

Calderas show peculiar behaviors with remarkable dynamic processes, which do not often culminate in eruptions. Observations and studies conducted in recent decades have shown that the most common cause of unrest in the calderas is due to magma intrusion; in particular, the intrusion of sills at shallow depths. Monogenic cones, with large areal dispersion, are quite common in the calderas, suggesting that the susceptibility analysis based on geological features, is not strictly suitable for estimating the vent opening probability in calderas. In general, the opening of a new eruptive vent can be regarded as a rock failure process. The stress field in the rocks that surrounds and tops the magmatic reservoirs plays an important role in causing the rock failure and creating the path that magma can follow towards the surface. In this conceptual framework, we approach the problem of getting clues about the probability of vent opening in volcanic calderas through the study of the stress field produced by the intrusion of magma, in particular, by the intrusion of a sill. We simulate the intrusion of a sill free to expand radially, with shape and dimensions which vary with time. The intrusion process is controlled by the elastic response of the rock plate above the sill, which bends because of the intrusion, and by gravity, that drives the magma towards the zones where the thickness of the sill is smaller. We calculated the stress field in the plate rock above the sill. We found that at the bottom of the rock plate above the sill the maximum intensity of tensile stress is concentrated at the front of the sill and spreads radially with it, over time. For this reason, we think that the front of the spreading sill is prone to open for eruptive vents. Even in the central area of the sill the intensity of stress is relatively high, but at the base of the rock plate stress is compressive. Under isothermal conditions, the stress soon reaches its maximum value (time interval

Episodic intrusion, internal differentiation, and hydrothermal alteration of the miocene tatoosh intrusive suite south of Mount Rainier, Washington

USGS Publications Warehouse

du Bray, E.A.; Bacon, C.R.; John, D.A.; Wooden, J.L.; Mazdab, F.K.

2011-01-01

The Miocene Tatoosh intrusive suite south of Mount Rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral Cascades arc magmatism. Tatoosh intrusive suite plutons have individually diagnostic characteristics, including texture, mineralogy, and geochemistry, and apparently lack internal contacts. New ion-microprobe U-Pb zircon ages indicate crystallization of the Stevens pluton ca. 19.2 Ma, Reflection-Pyramid pluton ca. 18.5 Ma, and Nisqually pluton ca. 17.5 Ma. The Stevens pluton includes rare, statistically distinct ca. 20.1 Ma zircon antecrysts. Wide-ranging zircon rare earth element (REE), Hf, U, and Th concentrations suggest late crystallization from variably evolved residual liquids. Zircon Eu/Eu*-Hf covariation is distinct for each of the Reflection-Pyramid, Nisqually, and Stevens plutons. Although most Tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration, and sparse mineralized veins cut some of these rocks, significant base or precious metal mineralization is absent. At the time of shallow emplacement, each of these magma bodies was largely homogeneous in bulk composition and petrographic features, but, prior to final solidification, each of the Tatoosh intrusive suite plutons developed internal compositional variation. Geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt, possibly represented by late aplite dikes or erupted as rhyolite, from crystal-rich magma. Crystal-rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth. Assembled by episodic intrusion, the Tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes. ?? 2011 Geological Society of America.

Syn-emplacement fracturing in the Sandfell laccolith, eastern Iceland – implications for rhyolite intrusion growth and volcanic hazards

NASA Astrophysics Data System (ADS)

Mattsson, Tobias; Burchardt, Steffi; Almqvist, Bjarne S. G.; Ronchin, Erika

2018-02-01

Felsic magma commonly pools within shallow mushroom-shaped magmatic intrusions, so-called laccoliths or cryptodomes, which can cause both explosive eruptions and collapse of the volcanic edifice. Deformation during laccolith emplacement is primarily considered to occur in the host rock. However, shallowly emplaced laccoliths (cryptodomes) show extensive internal deformation. While deformation of magma in volcanic conduits is an important process for regulating eruptive behavior, the effects of magma deformation on intrusion emplacement remain largely unexplored. In this study, we investigate the emplacement of the 0.57 km3 rhyolitic Sandfell laccolith, Iceland, which formed at a depth of 500 m in a single intrusive event. By combining field measurements, 3D modeling, anisotropy of magnetic susceptibility, microstructural analysis, and FEM modeling we examine deformation in the magma to constrain its influence on intrusion emplacement. Concentric flow bands and S-C fabrics reveal contact-parallel magma flow during the initial stages of laccolith inflation. The magma flow fabric is overprinted by strain-localization bands and more than one third of the volume of the Sandfell laccolith display concentric intensely fractured layers. A dominantly oblate magmatic fabric in the fractured areas and conjugate geometry of strain-localization bands, and fractures in the fracture layers demonstrate that the magma was deformed by intrusive stresses. This implies that a large volume of magma became viscously stalled and was unable to flow during intrusion. Fine-grained groundmass and vesicle-poor rock adjacent to the fracture layers point to that the interaction between the strain-localization bands and the flow bands at sub-solidus state caused the brittle-failure and led to decompression degassing and crystallization and rapid viscosity increase in the magma. The extent of syn-emplacement fracturing in the Sandfell laccolith further shows that strain-induced degassing limited

Magnetic fabric constraints of the emplacement of igneous intrusions

NASA Astrophysics Data System (ADS)

Maes, Stephanie M.

Fabric analysis is critical to evaluating the history, kinematics, and dynamics of geological deformation. This is particularly true of igneous intrusions, where the development of fabric is used to constrain magmatic flow and emplacement mechanisms. Fabric analysis was applied to three mafic intrusions, with different tectonic and petrogenetic histories, to study emplacement and magma flow: the Insizwa sill (Mesozoic Karoo Large Igneous Province, South Africa), Sonju Lake intrusion (Proterozoic Midcontinent Rift, Minnesota, USA), and Palisades sill (Mesozoic rift basin, New Jersey, USA). Multiple fabric analysis techniques were used to define the fabric in each intrusive body. Using digital image analysis techniques on multiple thin sections, the three-dimensional shape-preferred orientation (SPO) of populations of mineral phases were calculated. Low-field anisotropy of magnetic susceptibility (AMS) measurements were used as a proxy for the mineral fabric of the ferromagnetic phases (e.g., magnetite). In addition, a new technique---high-field AMS---was used to isolate the paramagnetic component of the fabric (e.g., silicate fabric). Each fabric analysis technique was then compared to observable field fabrics as a framework for interpretation. In the Insizwa sill, magnetic properties were used to corroborate vertical petrologic zonation and distinguish sub-units within lithologically defined units. Abrupt variation in magnetic properties provides evidence supporting the formation of the Insizwa sill by separate magma intrusions. Low-field AMS fabrics in the Sonju Lake intrusion exhibit consistent SW-plunging lineations and SW-dipping foliations. These fabric orientations provide evidence that the cumulate layers in the intrusion were deposited in a dynamic environment, and indicate magma flowed from southwest to northeast, parallel to the pre-existing rift structures. In the Palisades sill, the magnetite SPO and low-field AMS lineation have developed orthogonal to

Formation of tectonic peperites from alkaline magmas intruded into wet sediments in the Beiya area, western Yunnan, China

USGS Publications Warehouse

Xu, Xing-Wang; Cai, Xin-Ping; Zhong, Jia-You; Song, Bao-Chang; Peters, Stephen G.

2007-01-01

Tertiary (3.78 Ma to 3.65 Ma) biotite-K-feldspar porphyritic bodies intrude Tertiary, poorly consolidated lacustrine sedimentary rocks in the Beiya mineral district in southwestern China. The intrusives are characterized by a microcrystalline and vitreous-cryptocrystalline groundmass, by replacement of some tabular K-feldspar phenocrysts with microcrystalline chlorite and calcite, and by Fe-rich rings surrounding biotite phenocrysts. Peculiar structures, such as contemporary contact faults and slickensides, ductile shear zones and flow folds, foliation and lineations, tension fractures, and banded and boudin peperites, are developed along the contact zones of the intrusives. These features are related to the forceful intrusion of the alkaline magmas into the wet Tertiary sediments. The partially consolidated magmas were deformed and flattened by continued forceful magma intrusion that produced boudinaged and banded peperites. These peperites characterized by containing oriented deformation fabrics are classified as tectonic peperites as a new type of peperite, and formation of these tectonic peperites was related to fracturing of magmas caused by forceful intrusion and shear deformation and to contemporary migration and injection of fluidized sediments along fractures that dismembered the porphyritic magma. Emplacement of the magma into the wet sediments in the Beiya area is interpreted to be related to a large pressure difference rather than to the buoyancy force.

Magma traps and driving pressure: consequences for pluton shape and emplacement in an extensional regime

NASA Astrophysics Data System (ADS)

Hogan, John P.; Price, Jonathan D.; Gilbert, M. Charles

1998-09-01

The level of emplacement and final form of felsic and mafic igneous rocks of the Wichita Mountains Igneous Province, southwestern Oklahoma, U.S.A. are discussed in light of magma driving pressure, lithostatic load, and crustal magma traps. Deposition of voluminous A-type rhyolites upon an eroded gabbroic substrate formed a subhorizontal strength anisotropy that acted as a crustal magma trap for subsequent rising felsic and mafic magma. Intruded along this crustal magma trap are the A-type sheet granites (length/thickness 100:1) of the Wichita Granite Group, of which the Mount Scott Granite sheet is typical, and smaller plutons of biotite bearing Roosevelt Gabbro. In marked contrast to the subhorizontal granite sheets, the gabbro plutons form more equant stocks with flat roofs and steep side walls. Late Diabase dikes cross-cut all other units, but accompanying basaltic flows are extremely rare in the volcanic pile. Based on magmastatic calculations, we draw the following conclusions concerning the level of emplacement and the shape of these intrusions. (1) Magma can rise to a depth at which the magma driving pressure becomes negligible. Magma that maintains a positive driving pressure at the surface has the potential to erupt. (2) Magma ascent may be arrested at a deeper level in the crust by a subhorizontal strength anisotropy (i.e. crustal magma trap) if the magma driving pressure is greater than or equal to the lithostatic load at the depth of the subhorizontal strength anisotropy. (3) Subhorizontal sheet-intrusions form along crustal magma traps when the magma driving pressure greatly exceeds the lithostatic load. Under such conditions, the magma driving pressure is sufficent to lift the overburden to create the necessary space for the intrusion. (4) Thicker steep-sided stocks or batholiths, with flat roofs, form at crustal magma traps when the magma driving pressure approximates that of the lithostatic load. Under these conditions, the necessary space for the

Isotopic variation in the Tuolumne Intrusive Suite, central Sierra Nevada, California

USGS Publications Warehouse

Kistler, R.W.; Chappell, B.W.; Peck, D.L.; Bateman, P.C.

1986-01-01

Granitoid rocks of the compositionally zoned Late Cretaceous Toulumne Intrusive Suite in the central Sierra Nevada, California, have initial87Sr/86Sr values (Sri) and143Nd/144Nd values (Ndi) that vary from 0.7057 to 0.7067 and from 0.51239 to 0.51211 respectively. The observed variation of both Sri and Ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons. The largest variation in chemistry, Ndi, and Sri is present in the outer-most equigranular units of the Tuolumne Intrusive Suite. Sri varies positively with SiO2, Na2O, K2O, and Rb concentrations, and negatively with Ndi, Al2O3, Fe2O3, MgO, FeO, CaO, MnO, P2O5, TiO2, and Sr concentrations. This covariation of Sri, Ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent SiO2 of 48.0 and 73.3 respectively. Isotopic characteristic of the mafic magma are Sri=0.7047, Ndi=0.51269 and ??18O=6.0, and of the felsic magma are Sri=0.7068, Ndi=0.51212 and ??18O=8.9. The rocks sampled contain from 50 to 80% of the felsic component. An aplite in the outer equigranular unit of the Tuolumne Intrusive Suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above. Siliceous magmas derived from the lower crust, having a maximum of 15 percent mantle-derived mafic component, are represented by the inner prophyritic units of the Tuolumne Intrusive Suite. ?? 1986 Springer-Verlag.

Incremental growth of an upper crustal, A-type pluton, Argentina: Evidence of a re-used magma pathway

NASA Astrophysics Data System (ADS)

Alasino, Pablo H.; Larrovere, Mariano A.; Rocher, Sebastián; Dahlquist, Juan A.; Basei, Miguel A. S.; Memeti, Valbone; Paterson, Scott; Galindo, Carmen; Macchioli Grande, Marcos; da Costa Campos Neto, Mario

2017-07-01

Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (< 2 kbar). One of these, the San Blas intrusive complex formed over millions of years (≤ 2-3 m.y.) through three periods of magma additions that are characterized by variations in magma sources and emplacement style. The main units, mostly felsic granitoids, have U-Pb zircon crystallization ages within the error range. From older to younger (based on cross-cutting relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNdt = - 5.8 and εHft in zircon = - 2.9 to - 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNdt = + 0.6 to - 4.8 and εHft in zircon = + 3 to - 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include

The 2001 Mt. Etna eruption: new constraints on the intrusive mechanism from ground deformation data

NASA Astrophysics Data System (ADS)

Palano, Mimmo; González, Pablo J.

2013-04-01

The occurrence of seismic swarms beneath the SW flank of Mt. Etna, often observed just a few months before an eruption, has been considered as the fragile response to a magma intrusion (Bonanno et al., 2011 and reference therein). These intrusions and/or pressurization of deep magmatic bodies, have been able to significantly affect the seismic pattern within the volcano edifice, leading to a changes in the local stress field. For example, during the months preceding the 1991-1993 Mt. Etna eruption, shallow intense seismic swarms (4-6 km deep) occurring in the SW flank (e.g. Cocina et al., 1998), related to the magma intrusion before the eruption onset, were observed contemporaneously with a rotation of stress field of about 90°. A similar scenario was observed during January 1998, when a magma recharging phases induced a local rotation of stress tensor, forcing a buried fault zone located beneath the SW flank of Mt. Etna to slip as a right-lateral strike-slip fault (Bonanno et al., 2011). This fault system was forced to slip again, during late April 2001 (more than 200 events in less than 5 days; maximum Magnitude = 3.6) by the pressurization of the magmatic bodies feeding the July-August 2001 Mt. Etna eruption. Here we analyzed in detail the July-August 2001 Mt. Etna eruption as well as the dynamics preceding this event, by using a large dataset of geodetic data (GPS and synthetic aperture radar interferometry) collected between July 2000 and August 2001. References Cocina, O., Neri, G., Privitera, E. and Spampinato S., 1998. Seismogenic stress field beneath Mt. Etna South Italy and possible relationships with volcano-tectonic features. J. Volcanol. Geotherm. Res., 83, 335-348. Bonanno A., Palano M., Privitera E., Gresta S., Puglisi G., 2011. Magma intrusion mechanisms and redistribution of seismogenic stress at Mt. Etna volcano (1997-1998). Terra Nova, 23, 339-348, doi: 10.1111/j.1365-3121.2011.01019.x, 2011.

Magma replenishment and volcanic unrest inferred from the analysis of VT micro-seismicity and seismic velocity changes at Piton de la Fournaise Volcano

NASA Astrophysics Data System (ADS)

Brenguier, F.; Rivemale, E.; Clarke, D. S.; Schmid, A.; Got, J.; Battaglia, J.; Taisne, B.; Staudacher, T.; Peltier, A.; Shapiro, N. M.; Tait, S.; Ferrazzini, V.; Di Muro, A.

2011-12-01

allow magma to reach the edifice summit. Moreover, we have identified transient seismic velocity changes lasting a few weeks that could be associated with unreported lateral magma intrusions not leading to eruptions. The clustering of pre-eruptive micro-seismicity between mid 1999-2003 shows that seismic events repeat over successive seismic swarms and suggests that the magma pathway is spatially separated from the seismic faults. Also, the inversion for focal mechanisms shows dominant sub-horizontal P-axes indicating that part of the pre-eruptive micro-seismicity is due to the horizontal compressive stress induced by magma injection. Finally, the analysis of long-term GPS data recorded on the edifice flank shows a constant lateral displacement rate of 3.5 cm/year. More work will be needed in order to infer the possible mutual interactions between magma unrest and transport and the large-scale deformation of the edifice flank.

Role of the source to building lateral separation distance in petroleum vapor intrusion.

PubMed

Verginelli, Iason; Capobianco, Oriana; Baciocchi, Renato

2016-06-01

The adoption of source to building separation distances to screen sites that need further field investigation is becoming a common practice for the evaluation of the vapor intrusion pathway at sites contaminated by petroleum hydrocarbons. Namely, for the source to building vertical distance, the screening criteria for petroleum vapor intrusion have been deeply investigated in the recent literature and fully addressed in the recent guidelines issued by ITRC and U.S.EPA. Conversely, due to the lack of field and modeling studies, the source to building lateral distance received relatively low attention. To address this issue, in this work we present a steady-state vapor intrusion analytical model incorporating a piecewise first-order aerobic biodegradation limited by oxygen availability that accounts for lateral source to building separation. The developed model can be used to evaluate the role and relevance of lateral vapor attenuation as well as to provide a site-specific assessment of the lateral screening distances needed to attenuate vapor concentrations to risk-based values. The simulation outcomes showed to be consistent with field data and 3-D numerical modeling results reported in previous studies and, for shallow sources, with the screening criteria recommended by U.S.EPA for the vertical separation distance. Indeed, although petroleum vapors can cover maximum lateral distances up to 25-30m, as highlighted by the comparison of model outputs with field evidences of vapor migration in the subsurface, simulation results by this new model indicated that, regardless of the source concentration and depth, 6m and 7m lateral distances are sufficient to attenuate petroleum vapors below risk-based values for groundwater and soil sources, respectively. However, for deep sources (>5m) and for low to moderate source concentrations (benzene concentrations lower than 5mg/L in groundwater and 0.5mg/kg in soil) the above criteria were found extremely conservative as the

Magma transport and storage at Kilauea volcano, Hawaii II: 1952-2008

NASA Astrophysics Data System (ADS)

Klein, F.; Wright, T. L.

2011-12-01

We trace the evolution of Kilauea between the Halemaumau eruptions of 1952 and 2008. The magma supply path from the mantle is defined by the distribution of earthquakes deeper than 20 km. We compared the accumulated moment release from deep magma supply, south flank and rift zone earthquakes. We identified every intrusion and eruption in time plots of summit tilt and seismic activity in all regions, and plotted the earthquake distribution for ~ 1 week covering the period prior to, during and following the event. The establishment and continued growth of modern seismic and geodetic networks allow us to define three types of intrusions. 'Normal' intrusions occur with or without eruption and are accompanied by sharp tilt deflation at Kilauea's summit. 'Inflationary' intrusions occur during periods of summit inflation accompanied by rift earthquake swarms in the near-summit parts of both rift zones. 'Slow' intrusions are defined by isolated swarms of south flank earthquakes distributed perpendicular to the rift zones. Magnitudes of inflation and deflation shown by the daily tilt record at Kilauea's summit are converted to volume using a factor determined by previous workers. Magma supply rates are determined by summation of the volumes in cubic kilometers of (1) net summit inflation (2) sharp summit deflation accompanying rift activity and (3) summit and long continuous rift eruptions, divided by the elapsed time in years. Eruption efficiency is calculated by comparing the volumes of rift eruption and summit deflation. In this study we have reached the following conclusions: 1) Magma supply rates have increased from the pre-1952 value of 0.062 km3/yr to 0.1 km3/yr during the Mauna Ulu eruption of 1969-74 to 0.2 km3/yr during much of the eruption that began in 1983. 2) Eruption efficiencies show cyclic increases with increased activity, culminating in an efficiency averaging 100% during episodes of high fountaining in the period 1983-86. 3) Some south flank earthquake

Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

USGS Publications Warehouse

Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

2010-01-01

Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

Shallow magma diversions during explosive maar-diatreme eruptions in mafic volcanic fields

NASA Astrophysics Data System (ADS)

Le Corvec, N.; Muirhead, J.; White, J. D. L.

2017-12-01

Maar-diatremes are inverted conical structures formed by subterranean excavation and remobilization of country rocks during explosive volcanism and common in mafic volcanic fields. We focus on impacts of excavation and filling of maar-diatremes on the local state of stress, and its subsequent influence on underlying feeder dikes, which are critical for understanding the development of intrusive networks that feed surface eruptions. We address this issue using finite element models in COMSOL Multiphysics®. Inverted conical structures of varying sizes are excavated in a gravitationally loaded elastic half-space, and then progressively filled with volcaniclastic material, resulting in changes in the orientations and magnitudes of stresses generated within surrounding rocks and within the filling portion of the maar-diatreme. Our results show that rapid unloading during maar-diatreme excavation generates a horizontal compressive stress state beneath diatremes. These stresses allow magma to divert laterally as saucer-shaped sills and circumferential dikes at varying depths in the shallow feeder system, and produce intrusion geometries consistent with both field observations from exhumed volcanic fields and conceptual models of diatreme growth. Stresses generated in these models also provide an explanation for the evolving locations of fragmentation zones over the course of diatreme's filling. In particular, results from this study suggest that: (1) extensional stresses at the base of the diatreme fill favor magma ascent in the lower half of the structure, and possibly promote volatile exsolution and magma fragmentation; and (2) increased filling of diatremes creates a shallow compressive stress state that can inhibit magma ascent to the surface, promoting widespread intra-diatreme explosions, efficient mixing of host rock, and upward widening of the diatreme structure.

Oxygen regime of Siberian alkaline-ultramafic magmas

NASA Astrophysics Data System (ADS)

Ryabchikov, Igor; Kogarko, Liya

2017-04-01

Regimes of S2 and O2 are decisive factors controlling behavior of chalcophile and siderophile elements in magmatic processes. These parameters play important role during magmagenesis and in the course of crystallization and fluid mass transfer in magma chamber. Alkaline-ultramafic magmatism in Maymecha-Kotuy Province (Polar Siberia) is represented by giant intrusive complexes as well as by volcanics and dyke rocks, which include a well-known variety - meimechites. The latter are considered primary magmas of alkaline-ultramafic plutons in the region like for instance Guli intrusive complex. Sulfur content in primitive magmas estimated from the analyses of melt inclusions in olivine megacrysts from meimechites is close to 0.1 %. fO2 values calculated using olivine+clinopyroxene+spinel and spinel+melt oxygen barometers (1, 2) are 2-3 log units above QFM buffer. The relatively high oxygen potential at the early magmatic stage of alkaline-ultramafic Guli pluton provide predominance of sulfates among other forms of sulfur in the melt. This leads to the almost complete absence of sulfides in highly magnesian rocks. The oxidizing conditions exert important effect on behavior of many ore metals. At the stage of magma generation absence of sulfides in mantle materialresults in the presence of siderophile elements in metallic form and saturation of primary magmas in respect of metallic phases at an early stage of injection of the melt into the magma chamber. Later, under favorable circumstances during magma crystallization nuggets of precious metals may be formed. During further evolution of magmatic system fO2 and activity of oxidized sulfur decrease due to intensive crystallization of magnetite during the formation of koswites, then oxygen fugacity becomes even lower as a result serpentinization at a postmagmatic stage. These serpentization processes are caused by the displacement of reactions in the aqueous phase due to cooling towards the formation of methane and other

Layered intrusion formation by top down thermal migration zone refining (Invited)

NASA Astrophysics Data System (ADS)

Lundstrom, C.

2009-12-01

The formation of layered mafic intrusions by crystallization from cooling magmas represents the textbook example of igneous differentiation, often attributed to fractional crystallization through gravitational settling. Yet in detail, such interpretations have significant problems such that it remains unclear how these important features form. Put in the Earth perspective that no km scale blob of >50% melt has ever been imaged geophysically and that geochronological studies repeatedly indicate age inconsistencies with “big tank” magma chambers, it may be questioned if km scale magma chambers have ever existed. I will present the case for forming layered intrusions by a top down process whereby arriving basaltic magma reaches a permeability barrier, begins to underplate and forms the intrusion incrementally by sill injection with the body growing downward at ~1 mm/yr rate or less. A temperature gradient zone occurs in the overlying previously emplaced sills, leading to chemical components migrating by diffusion. As long as the rate of diffusion can keep up with rate of sill addition, the body will differentiate along a path similar to a liquid line of descent. In this talk, I will integrate data from 3 areas: 1) laboratory experiments examining the behavior of partially molten silicates in a temperature gradient (thermal migration); 2) numerical modeling of the moving temperature gradient zone process using IRIDIUM (Boudreau, 2003); 3) measurements of Fe isotope ratios and geochronology from the Sonju Lake Intrusion in the Duluth Complex. This model provides the ability to form km scale intrusions by a seismically invisible means, can explain million year offsets in chronology, and has implications for reef development and PGE concentration. Most importantly, this model of top down layered intrusion formation, following a similar recent proposal for granitoid formation (Lundstrom, 2009), represents a testable hypothesis: because temperature gradient driven

Magma intrusion and accumulation in the southern Altiplano: Structural observations from the PLUTONS project

NASA Astrophysics Data System (ADS)

West, M. E.; Christensen, D. H.; Pritchard, M. E.; Del Potro, R.; Gottsmann, J.; Unsworth, M.; Minaya, E.; Sunagua, M.; McNutt, S. R.; Yu, Q.; Farrell, A. K.

2012-12-01

The PLUTONS project is attempting to capture the process of magma intrusion and pluton formation, in situ, through multi-disciplinary study of known magmatic inflation centers. With support from the NSF Continental Dynamics program, and a sister project in the UK funded by NERC, two such centers are receiving focused study. Uturuncu volcano in the Altiplano of southern Bolivia is being investigated with combined seismics, magnetotellurics, geodesy, microgravity, geomorphology, petrology, geochemistry, historical studies and modeling. 350 km to the south, comparable investigations are targeting the Lastarria-Cordon del Azufre complex. Field studies are ongoing into 2013. In this presentation we highlight results from Uturuncu that bear on the crustal magmatic process. Seismic tomography, gravity and magnetotellurics indicate a complex structure in the upper 20 km with some evidence for partial melt. Seismic receiver functions indicate a layer of very low velocities across the region at 15-25 km depth that is almost certainly melt-rich. High conductivities corroborate the interpretation of a partial melt component to this layer. In addition to the throughgoing melt layer, seismic velocities and attenuation indicate shallow features above the melt body extending upward toward the surface. It is not clear whether these features are associated with recent uplift or are remnants from a previous period of activity. Uturuncu is seismically active with hundreds of locatable earthquakes each year. Seismic lineations and swarm behavior suggest that the seismicity reflects regional stress patterns. While there is little evidence that these earthquakes are the direct result of magmatic intrusion, the resulting high heat flow may be hastening existing strains.

Dynamic model of intrusion of magma and/or magmatic fluids in the large-scale deformation source of the Campi Flegrei caldera (Italy).

NASA Astrophysics Data System (ADS)

Crescentini, Luca; Amoruso, Antonella; Luongo, Annamaria

2015-04-01

The Campi Flegrei (CF) caldera is located in a densely populated area close to Naples (Southern Italy). It is renowned as a site of continual slow vertical movements. After the last eruption in 1538, the caldera generally subsided until 1969 when minor uplift occurred. In the early 1970s this uplift became significant (~1.5 m max). A further large uplift episode occurred from 1982 to 1984 (~1.8 m max), and subsequently smaller uplift episodes have occurred since then. Amoruso et al. (2014a,b) have recently shown that the CF surface deformation field from 1980 to 2013 can be decomposed into two stationary parts. Large-scale deformation can be explained by a quasi-horizontal source, oriented NW to SE and mathematically represented by a pressurized finite triaxial ellipsoid (PTE) ~4 km deep, possibly related to the injection of magma and/or magmatic fluids from a deeper magma chamber into a sill, or pressurization of interconnected (micro)cavities. Residual deformation not accounted for by PTE is confined to the Solfatara fumarolic area and can be mathematically explained by a small (point) pressurized oblate spheroid (PS) ~2 km below the Solfatara fumarolic field, that has been equated with a poroelastic response of the substratum to pore pressure increases near the injection point of hot magmatic fluids into the hydrothermal system. A satisfying feature of this double source model is that the geometric source parameters of each are constant over the period 1980-2013 with the exception of volume changes (potencies). Several papers have ascribed CF deformation to the injection of magmatic fluids at the base of the hydrothermal system. All models predict complex spatial and temporal evolution of the deformation pattern and consequently contrast with the observed deformation pattern stationarity. Also recently proposed dynamic models of sill intrusion in a shallow volcanic environment do not satisfy the observed CF deformation pattern stationarity. We have developed an

Aftershock decay, productivity, and stress rates in Hawaii: Indicators of temperature and stress from magma sources

USGS Publications Warehouse

Klein, Fred W.; Wright, Tom; Nakata, Jennifer

2006-01-01

We examined dozens of aftershock sequences in Hawaii in terms of Gutenberg-Richter and modified Omori law parameters. We studied p, the rate of aftershock decay; Ap, the aftershock productivity, defined as the observed divided by the expected number of aftershocks; and c, the time delay when aftershock rates begin to fall. We found that for earthquakes shallower than 20 km, p values >1.2 are near active magma centers. We associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs. Deep earthquakes near Kilauea's inferred magma transport path show a range of p values, suggesting the absence of a large, deep magma reservoir. Aftershock productivity is >4.0 for flank earthquakes known to be triggered by intrusions but is normal (0.25 to 4.0) for isolated main shocks. We infer that continuing, post-main shock stress from the intrusion adds to the main shock's stress step and causes higher Ap. High Ap in other zones suggests less obvious intrusions and pulsing magma pressure near Kilauea's feeding conduit. We calculate stress rates and stress rate changes from pre-main shock and aftershock rates. Stress rate increased after many intrusions but decreased after large M7–8 earthquakes. Stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers. We found sequences triggered by intrusions tend to have high Ap, high (>0.10 day) c values, a stress rate increase, and sometimes a peak in aftershock rate hours after the main shock. We interpret these values as indicating continuing intrusive stress after the main shock.

Geophysical observations of Kilauea Volcano, Hawaii, 2. Constraints on the magma supply during November 1975-September 1977

USGS Publications Warehouse

Dzurisin, D.; Anderson, L.A.; Eaton, G.P.; Koyanagi, R.Y.; Lipman, P.W.; Lockwood, J.P.; Okamura, R.T.; Puniwai, G.S.; Sako, M.K.; Yamashita, K.M.

1980-01-01

Following a 22-month hiatus in eruptive activity, Kilauea volcano extruded roughly 35 ?? 106 m3 of tholeiitic basalt from vents along its middle east rift zone during 13 September-1 October, 1977. The lengthy prelude to this eruption began with a magnitude 7.2 earthquake on 29 November, 1975, and included rapid summit deflation episodes in June, July, and August 1976 and February 1977. Synthesis of seismic, geodetic, gravimetric, and electrical self-potential observations suggests the following model for this atypical Kilauea eruptive cycle. Rapid summit deflation initiated by the November 1975 earthquake reflected substantial migration of magma from beneath the summit region of Kilauea into the east and southwest rift zones. Simultaneous leveling and microgravity observations suggest that 40-90 ?? 106 m3 of void space was created within the summit magma chamber as a result of the earthquake. If this volume was filled by magma from depth before the east rift zone intrusive event of June 1976, the average rate of supply was 6-13 ?? 106 m3/month, a rate that is consistent with the value of 9 ?? 106 m3/month suggested from observations of long-duration Kilauea eruptions. Essentially zero net vertical change was recorded at the summit during the 15-month period beginning with the June 1976 intrusion and ending with the September 1977 eruption. This fact suggests that most magma supplied from depth during this interval was eventually delivered to the east rift zone, at least in part during four rapid summit deflation episodes. Microearthquake epicenters migrated downrift to the middle east rift zone for the first time during the later stages of the February 1977 intrusion, an occurrence presumably reflecting movement of magma into the eventual eruptive zone. This observation was confirmed by tilt surveys in May 1977 that revealed a major inflation center roughly 30 km east of the summit in an area of anomalous steaming and forest kill first noted in March 1976. ?? 1980.

The petrogenesis of late Neoproterozoic mafic dyke-like intrusion in south Sinai, Egypt

NASA Astrophysics Data System (ADS)

Azer, M. K.; Abu El-Ela, F. F.; Ren, M.

2012-08-01

New field, petrographical and geochemical studies are presented here for the late Neoproterozoic Rimm intrusion (˜15 km long) exposed in the southern Sinai Peninsula, Egypt in the northernmost Arabian-Nubian Shield (ANS). Field relations indicate that the Rimm intrusion is younger than the surrounding metamorphic rocks and calc-alkaline syn-tectonic granodiorite and it was not affected by regional metamorphism. The anorogenic peralkaline granite of Gebel Serbal crosscuts the Rimm intrusion. The Rimm intrusion is made up of several consanguineous rock types with gradational contacts. It is composed chiefly of pyroxene-hornblende gabbro, hornblende gabbro and minor quartz diorite. The chemical composition of the mafic minerals indicated that the studied rocks derived from calc-alkaline mafic magma. Geochemically, the studied rocks are characterized by enrichment in LILE relative to HFSE and LREE relative to HREE [(Ce/Yb)N = 4.50-6.36]. Quartz diorite display slightly concave HREE pattern and slightly negative Eu-anomaly [(Eu/Eu*)n = 0.91] which may be the result of fractionation of amphibole and plagioclase from the source melt, respectively. The Rimm intrusion evolved from mafic mantle magma into different type rocks by fractional crystallization with minor crustal contamination. The initial magma corresponds to pyroxene-hornblende gabbro and the crystallization of hornblende was caused by slight H2O increase in magma after crystallization of near-liquidus clinopyroxene and Ca-rich plagioclase. Amphiboles geobarometer indicate that the gabbroic rocks of the Rimm intrusion crystallized at pressures between 4.8 and 6.4 Kb, while quartz diorite crystallized at 1.3-2.1 Kb. Crystallization temperatures range between 800 and 926 °C for the gabbros and between 667 and 784 °C for the quartz diorite. The Rimm intrusion represents a post-orogenic phase formed during the crustal thinning and extension of the Arabian-Nubian Shield.

Aligning petrology with geophysics: the Father's Day intrusion and eruption, Kīlauea Volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

2016-12-01

of magma decompression prior to eruption. These are compared to timescales of lateral dike intrusion measured using tilt, GPS and seismology to refine our understanding of horizontal and vertical magma flow in dikes between the summit reservoir and ERZ.

Cup-shaped Intrusions, Morphology and Emplacement Mechanism Investigate Through Analogue Modelling

NASA Astrophysics Data System (ADS)

Mathieu, L.; van Wyk de Vries, B.

2007-12-01

We investigate the morphology of large-scale shallow-depth magma intrusions and sub-volcanic complexes with analogue models. Intrusions of analogue magma are done in a granular material that can contain a ductile layer. The model surface is flat to model the formation of plutonic intrusions and it is overlain by a cone when modelling late sub-volcanic complexes. For flat-top models, we obtain cup-shaped intrusions fed by dykes. Cup-shaped intrusions are inverted-cone like bodies. They are different from saucer-shaped intrusions as they possess neither a well developed sill-base, nor an outer rim. However, like saucers, cups are shallow depth intrusions that dome the country rocks. They initiate from an advancing dyke and first develop an inverted-cone like morphology. Then, the central thickness increases and thrusts form at the edge of the domed country rocks. At this stage, the intrusions progressively involve toward a lopolith shape. By using analogue magma of various viscosities we have been able to constrain key relationships: higher intrusion viscosity causes deeper initiation and the deeper they initiate, the larger is the intrusion diameter. A natural example of such intrusion might by the circles of volcanoes like the Azufre-Lastaria (Peru) that might be overlain be a large-scale cup-shaped intrusion. When adding a cone at the surface of the model and, sometimes, a thin ductile layer in the substratum, the morphology of cup-shaped intrusions vary. Note that the ductile layer of our models is not thick enough to induce the gravitational spreading of the cone. Generally, cup-shaped intrusions are asymmetric in cross section and elliptical in plan view. Their formation creates extension structures in the cone (croissant-shaped rift, straight rift or normal fault) and thrusts in some sectors below the cone. Both types of structures are bordered by strike-slip faults. Cups and saucers share many similarities, but differ probably in the fact that saucers are

Intrusion Triggering of Explosive Eruptions: Lessons Learned from EYJAFJALLAJÖKULL 2010 Eruptions and Crustal Deformation Studies

NASA Astrophysics Data System (ADS)

Sigmundsson, F.; Hreinsdottir, S.; Hooper, A. J.; Arnadottir, T.; Pedersen, R.; Roberts, M. J.; Oskarsson, N.; Auriac, A.; Decriem, J.; Einarsson, P.; Geirsson, H.; Hensch, M.; Ofeigsson, B. G.; Sturkell, E. C.; Sveinbjornsson, H.; Feigl, K.

2010-12-01

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic. This eruption was preceded by an effusive flank eruption of olivine basalt from 20 March - 12 April 2010. Geodetic and seismic observations revealed the growth of an intrusive complex in the roots of the volcano during three months prior to eruptions. After initial horizontal growth, modelling indicates both horizontal and sub-vertical growth in three weeks prior the first eruption. The behaviour is attributed to subsurface variations in crustal stress and strength originating from complicated volcano foundations. A low-density layer may capture magma allowing pressure to build before an intrusion can ascend towards higher levels. The intrusive complex was formed by olivine basalt as erupted on the volcano flank 20 March - 12 April; the intrusive growth halted at the onset of this eruption. Deformation associated with the eruption onset was minor as the dike had reached close to the surface in the days before. Isolated eruptive vents opening on long-dormant volcanoes may represent magma leaking upwards from extensive pre-eruptive intrusions formed at depth. A deflation source activated during the summit eruption of trachyandesite is distinct from, and adjacent to, all documented sources of inflation in the volcano roots. Olivine basalt magma which recharged the volcano appears to have triggered the summit eruption, although the exact mode of triggering is uncertain. Scenarios include stress triggering or propagation of olivine basalt into more evolved magma. The trachyandesite includes crystals that can be remnants of minor recent intrusion of olivine basalt

Field and Experimental Constraints on the Dynamics of Replenished Silicic Magma Chambers

NASA Astrophysics Data System (ADS)

Bain, A. A.; Jellinek, M.

2008-12-01

The underlying causes of catastrophic caldera-forming volcanic eruptions remain poorly understood. However, the occurrence of magma mixing within bimodal systems has become increasingly linked with such eruptions. In particular, buoyancy effects related to unstable density contrasts arising as a result of silicic- basaltic magma interactions may play an important role in the growth, differentiation and catastrophic eruption of silicic magma chambers. Evidence of such magmatic interactions can be found in layered intrusions from the Coastal Maine Magmatic Province (USA), where well-exposed cross-sections reveal hundreds of laterally-extensive basaltic sheets, apparently injected as intrusive lava flows onto the growing floors of silicic magma chambers. Interfaces between mafic and silicic layers are commonly sharply defined and exhibit deformation parallel to the inferred direction of palaeo-gravity. Our field observations suggest that the cooling, settling and buckling of gravitationally-unstable mafic replenishments may have driven large-scale (basalt layer depth) and small- scale (crystal diameter) upwelling and/or overturning of underlying buoyant silicic cumulate material. In order to characterize the full range of buoyancy effects, we carried out extensive spectral analysis of high- resolution digital field measurements from the Pleasant Bay and Mount Desert Island intrusions. In many cases, Rayleigh-Taylor theory and the longest measured wavelength of deformation indicate that a large and potentially-quantifiable fraction of the original, pre-replenishment silicic cumulate thickness may be missing, implying that vertical mass transfer has occurred. In addition, the shortest wavelengths of deformation are generally consistent with observed length-scales of crystals and clumps of crystals at these localities. With the aim of understanding the initial conditions that gave rise to these field observations, we conduct a series of laboratory experiments in which we

The Role of Magma During Continent-Ocean Transition

NASA Astrophysics Data System (ADS)

Bastow, Ian; Keir, Derek; Rooney, Tyrone; Kendall, J.-Michael

2010-05-01

Passive margins worldwide are often considered magmatic because they are characterised by thick sequences of extrusive and intrusive igneous rocks emplaced around the time of continental breakup. Despite the global abundance of such margins, however, it is difficult to discriminate between different models of both extension and melt generation, since most ruptured during Gondwana breakup >100Ma and the continent-ocean transition (COT) is now hidden by thick, basaltic seaward dipping reflectors (SDRs). These margins are no longer tectonically active so the roles of faulting, stretching and magma intrusion in accommodating extension, and timing of SDRs emplacement during rift evolution have to be inferred from rifting models or from the geological record preserved at the fully developed passive margin. Similarly mantle processes during COT development have long since ceased, so whether breakup was characterized by broad thermal upwelling, small-scale convection or a fertile geoscientific mantle remains ambiguous. The East African rift in Ethiopia offers a unique opportunity to address all these problems because south-to-north it exposes subaerially the transition from continental rifting and incipient sea-floor spreading within a young flood basalt province. Here we present a suite of geophysical and geochemical observations from Ethiopia that document the significance of magma intrusion and extrusion as rifting evolves from an initially broad zone of stretching and faulting to a narrower axial graben in which magma injection dominates strain.

Stress barriers controlling lateral migration of magma revealed by seismic tomography.

PubMed

Martí, J; Villaseñor, A; Geyer, A; López, C; Tryggvason, A

2017-01-13

Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011-2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt.

Stress barriers controlling lateral migration of magma revealed by seismic tomography

NASA Astrophysics Data System (ADS)

Martí, J.; Villaseñor, A.; Geyer, A.; López, C.; Tryggvason, A.

2017-01-01

Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011-2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt.

Stress barriers controlling lateral migration of magma revealed by seismic tomography

PubMed Central

Martí, J.; Villaseñor, A.; Geyer, A.; López, C.; Tryggvason, A.

2017-01-01

Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011–2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt. PMID:28084436

Volcanic tremor and frequency gliding during dike intrusions at Kı¯lauea—A tale of three eruptions

NASA Astrophysics Data System (ADS)

Unglert, K.; Jellinek, A. M.

2015-02-01

To characterize syneruptive/intrusive deviations from background volcanic tremor at Kı¯lauea, Hawai`i, we analyze the spatial and temporal properties of broadband tremor during dike intrusions into the East Rift Zone (ERZ) in 2007 and 2011, as well as during explosive eruptive activity at Kı¯lauea's summit in 2008. Background tremor was similar for each event, and the 2008 explosions did not affect its properties. In contrast, the intrusions were accompanied by departures from this background in the form of two phases of seismicity that were separated in space and time. In both 2007 and 2011, Phase I was characterized by a quick succession of discrete events, which were most intense at the onset of intrusion near the presumed locations of the dikes intruding into the ERZ. Phase II, marked by continuous broadband tremor around the summit, followed 10-14 h later. In 2007, Phase II tremor was accompanied by a monotonic downward shift (glide) of spectral peaks between ˜0.6 and 1.5 Hz over at least 15 h. During Phase II in 2011, a gradual upward and subsequent symmetric downward glide between ˜0.6 and 6.6 Hz occurred over 5-10 h, respectively. The spectra during both phases differed from the background and 2008, as well as from each other, indicating different physical mechanisms. Phase I in 2007 and 2011 is probably related to the mechanics of dike intrusion. Phase II tremor may be characteristic for evolving magma-bubble dynamics related to the geometry of the plumbing system and the style of magma flow.

Differentiation and magma mixing on Kilauea's east rift zone: A further look at the eruptions of 1955 and 1960. Part II. The 1960 lavas

USGS Publications Warehouse

Wright, T.L.; Helz, R.T.

1996-01-01

New and detailed petrographic observations, mineral compositional data, and whole-rock vs glass compositional trends document magma mixing in lavas erupted from Kilauea's lower east rift zone in 1960. Evidence includes the occurrence of heterogeneous phenocryst assemblages, including resorbed and reversely zoned minerals in the lavas inferred to be hybrids. Calculations suggest that this mixing, which is shown to have taken place within magma reservoirs recharged at the end of the 1955 eruption, involved introduction of four different magmas. These magmas originated beneath Kilauea's summit and moved into the rift reservoirs beginning 10 days after the eruption began. We used microprobe analyses of glass to calculate temperatures of liquids erupted in 1955 and 1960. We then used the calculated proportions of stored and recharge components to estimate the temperature of the recharge components, and found those temperatures to be consistent with the temperature of the same magmas as they appeared at Kilauea's summit. Our studies reinforce conclusions reached in previous studies of Kilauea's magmatic plumbing. We infer that magma enters shallow storage beneath Kilauea's summit and also moves laterally into the fluid core of the East rift zone. During this process, if magmas of distinctive chemistry are present, they retain their chemical identity and the amount of cooling is comparable for magma transported either upward or laterally to eruption sites. Intrusions within a few kilometers of the surface cool and crystallize to produce fractionated magma. Magma mixing occurs both within bodies of previously fractionated magma and when new magma intersects a preexisting reservoir. Magma is otherwise prevented from mixing, either by wall-rock septa or by differing thermal and density characteristics of the successive magma batches.

Time, space, and composition relations among northern Nevada intrusive rocks and their metallogenic implications

USGS Publications Warehouse

duBray, E.A.

2007-01-01

Importantly, modal composition, age, and geochemical characteristics of intrusions associated with large mineral deposits along the trends, are indistinguishable from non-mineralized intrusions in northern Nevada and thus do not identify intrusions associated with significant deposits. Moreover, intrusion age and composition show little correlation with mineral-deposit type, abundance, and size. Given the lack of diagnostic characteristics for intrusions associated with deposits, it is uncertain whether age, modal composition, and geochemical data can identify intrusions associated with mineral deposits. These findings suggest that associations between northern Nevada intrusions and mineral deposits reflect superimposition of many geologic factors, none of which was solely responsible for mineral-deposit formation. These factors might include intrusion size, efficiency of fluid and metal extraction from magma, prevailing redox and sulfidation conditions, or derivation of metals and ligands from host rocks and groundwater. The abundance and diversity of mineral deposits in northern Nevada may partly reflect geochemical inheritance, for example, along the mineral trends rather than the influence of petrologically unique magma or associated fluids.

Infiltration metasomatism within the Rum layered intrusion (Scotland)

NASA Astrophysics Data System (ADS)

Leuthold, J.; Blundy, J.; Holness, M.

2012-04-01

The well studied Rum Isle layered intrusion was built up by emplacement of a series of 15 macro-rhythmic units. Magma intruded 60.53±0.08 Ma (Hamilton et al., 1998), at a pressure <0.5 kbar (Holness, 1999). Units are composed of feldspathic peridotite at the base, overlain by troctolite and gabbro. Layering is induced by fractional crystallization from picritic magma (Upton et al., 2002; Holness et al., 2007). Rum magma liquid line of descent is complicated by reactive melt percolation within crystal mushes, either originating from continuous compaction of the cumulate pile or from a newly injected reactive picritic magma. The studied Unit 9 sequence is well known for the injection of a picritic sill within the layered intrusion. Clinopyroxene textures are very diverse above the Unit 9 intrusive picritic sill. (1) Late-stage interstitial crystals occur in the basal intrusive peridotite, corresponding to the picritic sill. The Cr2O3 content varies from 1.2 to 0.6 wt% along core to rim profiles. (2) Within the overlying troctolite, poikilitic crystals (up to 2 cm in diameter) enclose randomly oriented plagioclase and olivine, wrapped by a foliated troctolitic assemblage. Within the first 3 meters, the Cr2O3 composition of the few clinopyroxene crystals is very similar to the underlying peridotite one, but it then drops to lower concentration (0.5 to 0 wt%). The plagioclase-clinopyroxene-plagioclase median dihedral angle also decreases from ~90° to ~80° (Sides, 2008). The Cr2O3 content increases progressively towards the troctolite-gabbro wavy horizon. Gabbroic enclaves occur within the troctolite. (3) Cumulus clinopyroxene grains occur in the summit gabbro. Their Cr2O3 content regularly decreases from 1.2-0.8 to 0.7-0.3 across the gabbro pile. Cr-spinel crystals are rare. Median plagioclase-clinopyroxene-plagioclase dihedral angles evolve from ~85° to ~95°. We propose that troctolites, that contain gabbroic enclaves, result from clinopyroxene primocryst

[The spectrum studies of structure characteristics in magma contact metamorphic coal].

PubMed

Wu, Dun; Sun, Ruo-Yu; Liu, Gui-Jian; Yuan, Zi-Jiao

2013-10-01

The structural parameters evolution of coal due to the influence of intrusions of hot magma was investigated and analyzed. X-ray diffraction and laser confocal microscope Raman spectroscopy were used to test and analyze 4 coal samples undergoing varying contact-metamorphism by igneous magmas in borehole No. 13-4 of Zhuji coal mine, Huainan coalfield. The result showed that coal XRD spectrum showed higher background intensity, with the 26 degrees and 42 degrees nearby apparent graphite diffraction peak. Two significant vibration peaks of coal Raman spectra were observed in the 1 000-2 000 cm(-1) frequency range: broad "D" peak at 1 328-1 369 cm(-1) and sharp "G" peak at 1 564-1 599 cm(-1). With the influence of magma intrusion, the relationship between coal structural parameters and coal ranks was excellent.

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow.

PubMed

Gudmundsson, Magnús T; Jónsdóttir, Kristín; Hooper, Andrew; Holohan, Eoghan P; Halldórsson, Sæmundur A; Ófeigsson, Benedikt G; Cesca, Simone; Vogfjörd, Kristín S; Sigmundsson, Freysteinn; Högnadóttir, Thórdís; Einarsson, Páll; Sigmarsson, Olgeir; Jarosch, Alexander H; Jónasson, Kristján; Magnússon, Eyjólfur; Hreinsdóttir, Sigrún; Bagnardi, Marco; Parks, Michelle M; Hjörleifsdóttir, Vala; Pálsson, Finnur; Walter, Thomas R; Schöpfer, Martin P J; Heimann, Sebastian; Reynolds, Hannah I; Dumont, Stéphanie; Bali, Eniko; Gudfinnsson, Gudmundur H; Dahm, Torsten; Roberts, Matthew J; Hensch, Martin; Belart, Joaquín M C; Spaans, Karsten; Jakobsson, Sigurdur; Gudmundsson, Gunnar B; Fridriksdóttir, Hildur M; Drouin, Vincent; Dürig, Tobias; Aðalgeirsdóttir, Guðfinna; Riishuus, Morten S; Pedersen, Gro B M; van Boeckel, Tayo; Oddsson, Björn; Pfeffer, Melissa A; Barsotti, Sara; Bergsson, Baldur; Donovan, Amy; Burton, Mike R; Aiuppa, Alessandro

2016-07-15

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption. We use multiparameter geophysical and geochemical data to show that the 110-square-kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, near-exponential decline of both collapse rate and the intensity of the 180-day-long eruption. Copyright © 2016, American Association for the Advancement of Science.

Linking magnetic fabric and cumulate texture in layered mafic-ultramafic intrusions (Invited)

NASA Astrophysics Data System (ADS)

O Driscoll, B.; Stevenson, C.; Magee, C.

2013-12-01

Research on the magnetic fabrics of igneous rocks, pioneered by Balsley and Buddington[1] and Khan[2], has greatly contributed to our understanding of magma dynamics in lava flows, sheet intrusions and plutons over the past five decades. However, considerably few magnetic fabric studies have focused on layered mafic-ultramafic intrusions, particularly ';lopolithic' intrusions, despite the fact that such rocks may preserve a large range of small-scale kinematic structures potentially related to important magma chamber processes. This may be partly due to the fact that mafic-ultramafic cumulates commonly exhibit visible planar fabrics (mineral lamination), as well as compositional layering, in contrast to the frequent absence of such features in granite bodies or fine-grained mafic lava flows. Indeed, debates in the 1970s and 1980s on the development of layering and mineral fabrics in mafic-ultramafic intrusions, focused around the crystal settling versus in situ crystallisation paradigms, are classic in the subject of igneous petrology. Central to these debates is the notion that a wide range of magma chamber processes occur in layered mafic-ultramafic intrusions that are not frequently considered to occur in their relatively viscous granitic counterparts; in essence, the latter have historically been viewed as much more likely to ';freeze-in' a primary magma flow fabric whilst mafic-ultramafic intrusions are subjected to a more protracted solidification history. This wide array of potential initial sources for layering and mineral fabrics in layered mafic-ultramafic intrusions, together with the possible modification of textures at the postcumulus stage, demands a cautious application of any fabric analysis and presents a problem well-suited to interrogation by the AMS technique. The purpose of this contribution is to provide specific context on the application of AMS to elucidating the formation of cumulates in layered mafic-ultramafic intrusions. Examples of AMS

Ultrabasic breccias in layered intrusions - The Rhum complex

NASA Technical Reports Server (NTRS)

Donaldson, C. H.

1975-01-01

Two breccias in the southwest part of the ultrabasic Rhum complex are considered. Aspects of field relations are discussed along with questions regarding the petrography of the matrix. Attention is given to textures and chemical mineralogy, the mechanism of brecciation, matrix magmas, and the possible implications of the findings. It is concluded that the Harris Bay and Ard Mheall ultrabasic breccias formed by brecciation due to the intrusion of feldspathic peridotite magmas.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2017-02-01

zones deeper within the mantle. Thus magma accumulations at the base of the crust would have been able to intrude dikes part-way through the crust, but not able to feed eruptions to the surface; in order to be erupted, magma must have been extracted from deeper mantle sources, consistent with petrologic evidence. Buoyant dikes growing upward from deep mantle sources of partial melt can disconnect from their source regions and travel through the mantle as isolated bodies of melt that encounter and penetrate the crust-mantle density boundary. They adjust their lengths and internal pressure excesses so that the stress intensity at the lower tip is zero. The potential total vertical extent of the resulting melt body depends on the vertical extent of the source region from which it grew. For small source extents, the upper tip of the resulting dike crossing the crust-mantle boundary cannot reach the surface anywhere on the Moon and therefore can only form a dike intrusion; for larger source extents, the dike can reach the surface and erupt on the nearside but still cannot reach the surface on the farside; for even larger source extents, eruptions could occur on both the nearside and the farside. The paucity of farside eruptions therefore implies a restricted range of vertical extents of partial melt source region sizes, between ∼16 and ∼36 km. When eruptions can occur, the available pressure in excess of what is needed to support a static magma column to the surface gives the pressure gradient driving magma flow. The resulting typical turbulent magma rise speeds are ∼10 to a few tens of m s-1, dike widths are of order 100 m, and eruption rates from 1 to 10 km long fissure vents are of order 105 to 106 m3 s-1. Volume fluxes in lunar eruptions derived from lava flow thicknesses and surface slopes or rille lengths and depths are found to be of order 105 to 106 m3 s-1 for volume-limited lava flows and >104 to 105 m3 s-1 for sinuous rilles, with dikes widths of ∼50 m. The

Conduit magma convection of a rhyolitic magma: Constraints from cosmic-ray muon radiography of Iwodake, Satsuma-Iwojima volcano, Japan

NASA Astrophysics Data System (ADS)

Shinohara, Hiroshi; Tanaka, Hiroyuki K. M.

2012-10-01

Quantitative re-evaluation of the muon radiography data obtained by Tanaka et al. (2009) was conducted to constrain conduit magma convection at the Iwodake rhyolitic cone of Satsuma-Iwojima volcano, Japan. Re-evaluation of the measurement error considering topography and fake muon counts confirms the existence of a low-density body of 300 m in diameter and with 0.9-1.0 g cm-3 at depths of 135-190 m from the summit crater floor. The low-density material is interpreted as rhyolitic magma with 60% vesicularity on average, and existence of this unstable highly vesiculated magma at shallow depth without any recent eruptive or intrusive activity is considered as evidence of conduit magma convection. The structure of the convecting magma column top was modeled based on density calculations of vesiculated ascending and outgassed descending magmas, compared with the observed density anomaly. The existence of the low-density anomaly was confirmed by comparison with published gravity measurements, and the predicted degassing at the shallow magma conduit top agrees with observed heat discharge anomaly distribution localized at the summit area. This study confirms that high viscosity of silicic magmas can be compensated by a large size conduit to cause the conduit magma convection phenomena. The rare occurrence of conduit magma convection in a rhyolitic magma system at Iwodake is suggested to be due to its specific magma features of low H2O content and high temperature.

Depositional features and stratigraphic sections in granitic plutons: implications for the emplacement and crystallization of granitic magma

NASA Astrophysics Data System (ADS)

Wiebe, R. A.; Collins, W. J.

1998-09-01

Many granitic plutons contain sheet-like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature, more mafic magma during crystallization of the granitic plutons. Small-scale structures associated with these bodies (e.g. load-cast and compaction features, silicic pipes extending from granitic layers into adjacent gabbroic sheets) indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber (on granitic crystal mush and beneath crystal-poor magma) while the mafic magma was incompletely crystallized. These structures indicate 'way up', typically toward the interior of the intrusions, and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition. Hence, these plutons preserve a stratigraphic history of events involved in the construction (filling, replenishment) and crystallization of the magma chamber. The distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions, which usually preserve mutual intrusive contacts and 'dike-sill' relations of different magma types. The considerable thickness of material that can be interpreted as depositional, and the evidence for replenishment, suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton. Thus, magma chambers may be constructed much more slowly than presently envisaged. The present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber (along with the underlying solidified granite and country rock) sank during continuing episodes of magma chamber replenishment. These internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber.

Concomitant skarn and syenitic magma evolution at the margins of the Zippa Mountain pluton

NASA Astrophysics Data System (ADS)

Coulson, I. M.; Westphal, M.; Anderson, R. G.; Kyser, T. K.

2007-07-01

Zippa Mountain pluton is a Mesozoic concentrically-zoned intrusion, located within the Canadian Cordillera of British Columbia. An extensive phase of K-feldspar bearing syenite grades towards its margins to mela-syenite and clinopyroxenite. This simple pattern of petrological zonation is overprinted by localised occurrences of silica-undersaturated, peralkaline rock types. High-purity wollastonite skarns occur within and peripheral to the intrusion and result from extensive interaction between intrusion-related fluids and Permian limestone/marble, at shallow crustal levels. Field, chemical and isotopic studies provide insights into interaction between a parental syenitic magma and these country rocks. To achieve this, petrological studies of four of the skarn bodies present have been combined with chemical and isotopic data from the pluton, and from drill core through the skarn into the pluton, to reconstruct the stages in the development of wollastonite skarn and progressive magma-country rock interaction. Derivation of peralkaline compositions from the syenitic magma requires either a loss of Si and Al, or addition of Na and/or K. Our studies preclude the addition of alkali elements but highlight extensive Si-infiltration into the limestone, while the conversion of marble to grossular-andradite skarn, indicates Al-infiltration. Fluid egress resulted in de-silicification/de-alumination of the Zippa Mountain magmas, and increased peralkalinity; wollastonite and garnet-bearing skarn formed as a by-product. Hence, the development of peralkaline rock compositions at Zippa Mountain required a parental syenitic magma, and reaction and/or interaction with calcareous country rocks.

Numerical modeling of magma-tectonic interactions at Pacaya Volcano, Guatemala

NASA Astrophysics Data System (ADS)

Wauthier, C.

2017-12-01

Pacaya Volcano is composed of several volcanic cones located along the southern rim of the Amatitlan caldera, approximately 25 km south of Guatemala City. It is a basaltic volcano located in the Central American Volcanic Arc. The shallow magma plumbing system at Pacaya likely includes at least three magma reservoirs: a very shallow ( 0.2-0.4 km depth) reservoir located below and possibly within the MacKenney cone, a 4 km deep reservoir located northwest of the summit, and a shallow dike-like conduit below the summit which fed the recent flank eruptions. Pacaya's western flank is slipping in a stick-slip fashion, and the instability seems associated with larger volume eruptions. Flank instability phases indeed occurred in 2010 and 2014 in coincidence with major intrusive and eruptive phases, suggesting a positive feedback between the flank motion and major intrusions. Simple analytical models are insufficient to fit the geodetic observations and model the flank processes and their mechanical interactions with the magmatic system. Here, numerical modeling approaches are used to characterize the 2014 flank deformation episode and magma-tectonic interactions.

Evidence for magma convection to shallow depths during quiescent degassing of Mt. Etna

NASA Astrophysics Data System (ADS)

La Spina, Alessandro; Mike, Burton; Giovanni, Salerno Giuseppe

2015-04-01

degassing relative to HCl indicates a process of deep intrusion, in which magma rather than ascending to the shallow (~3 km depth) conduit is stored at depth where it may later erupt. On the contrary, reduced HCl degassing indicates a reduction in magma supply to the uppermost 500m of the magmatic system, which may occur during a shallow intrusion. Over the investigated period we observed both these processes, but overall the system remained very close to bulk degassing, suggesting that such intrusions are temporary deviations from a system which can efficiently degas essentially all the magma that enters the uppermost 4-5km of the feeding system.

Wall Rock Assimilation and Magma Migration in the Sierra Nevada Batholith: A Study of the Courtright Intrusive Zone, Central California

NASA Astrophysics Data System (ADS)

Torrez, G.; Putirka, K. D.

2010-12-01

The Sierra Nevada Batholith is composed of various plutons that interact with each other, and with pre- and syn-batholith metamorphic rocks. In the central part of the Sierra Nevada Batholith, at Courtright Reservoir in California, the younger Mt. Givens Pluton (87-93 Ma; McNulty et al., 2000) intrudes the Dinkey pluton (103 Ma; Bateman et al., 1964), and metasediments (a metamorphic screen) that, in places, separate the two plutons. This Courtright Reservoir Intrusive zone, as termed by Bateman et al. (1964), provides an ideal setting to examine the dynamics of intrusion and assimilation. Whole rock major and trace element compositions of the plutons, their mafic enclaves, and the metasediments, show that all such samples, from both plutons, fall on a single mixing trend. We thus infer that magmas parental to both plutons were roughly similar in composition, and assimilated significant amounts of the same, or very similar metasedimentary wall rocks. We also examined changes in whole rock compositions within the Mt. Givens pluton, as a function of distance from the two rock units with which it is now in contact (the metasediments, and the Dinkey Creek). In the vicinity of the contact between are an abundance of enclaves that are rounded, and appear to have been transported in vertical pipes. Whole rock analysis of the host granitoid material that surrounds these enclaves is clearly more mafic than the granitoid magmas from interior parts of the pluton. These whole rock compositions indicate that the pluton becomes more homogenous moving away from the contact, with a compositional decay occurring over a span of about 50-100 m. There are at least two possible interpretations. The compositional decay may represent a diffusive exchange of mass between an early crystallizing marginal phase of the pluton and the pluton interior. Another (not mutually incompatible) possibility is that the mafic margins represent pipes or tubes (Paterson, 2010), related to some convective

Petrogenesis of Mount Rainier andesite: magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades

USGS Publications Warehouse

Sisson, Thomas W.; Salters, V.J.M.; Larson, P.B.

2013-01-01

The dominant cause of magmatic evolution at Mount Rainier, however, is inferred to be a version of in situ crystallization-differentiation and mixing (Langmuir, 1989) wherein small magma batches stall as crustal intrusions and solidify extensively, yielding silicic residual liquids with trace element concentrations influenced by accessory mineral saturation. Subsequent magmas ascending through the intrusive plexus entrain and mix with the residual liquids and low-degree re-melts of those antecedent intrusions, producing hybrid andesites and dacites. Mount St. Helens volcanic rocks have geochemical similarities to those at Mount Rainier, and may also result from in situ differentiation and mixing due to low and intermittent long-term magma supply, accompanied by modest crustal assimilation. Andesites and dacites of Mount Adams isotopically overlap the least contaminated Mount Rainier magmas and derive from similar parental magma types, but have trace element variations more consistent with progressive crystallization-differentiation, probably due to higher magma fluxes leading to slower crystallization of large magma batches, allowing time for progressive separation of minerals from melt. Mount Adams also sits atop the southern projection of a regional anticlinorium, so Eocene sediments are absent, or are at shallow crustal levels, and so are cold and difficult to assimilate. Differences between southwest Washington stratovolcanoes highlight some ways that crustal geology and magma flux are primary factors in andesite generation.

Slab break-off and the formation of Permian mafic-ultramafic intrusions in southern margin of Central Asian Orogenic Belt, Xinjiang, NW China

NASA Astrophysics Data System (ADS)

Song, Xie-Yan; Xie, Wei; Deng, Yu-Feng; Crawford, Anthony J.; Zheng, Wen-Qin; Zhou, Guo-Fu; Deng, Gang; Cheng, Song-Lin; Li, Jun

2011-11-01

The Baishiquan and Pobei Early Permian mafic-ultramafic intrusions were emplaced into Proterozoic metamorphic rocks in the Central Tianshan and the Beishan Fold Belt, northern Xinjiang, NW China. The Baishiquan intrusion comprises mainly gabbro, and mela-gabbro sills occurring within and along the margins of the gabbro body. In the Pobei intrusion, two distinct gabbroic packages, a lower gabbro and the main gabbro, are intruded and overlain by small cumulate wehrlite bodies. Both intrusions are characterized by enrichments of large ion lithophile elements and Th and U relative to the high field strength elements, and show strong negative Nb and Ta anomalies and positive K and Pb anomalies, leading to higher Th/Yb and Nb/Yb than in mid-ocean ridge basalt and ocean island basalt. These features are comparable with subduction-related mafic rocks and post-collisional magmas. Geological and geochemical considerations indicate that the parental magmas of the two intrusions were derived from decompression melting of ascending asthenosphere and reacted with overlying subduction-modified lithospheric mantle. We believe that these parental magmas were generated by post-collisional extension along the Chinese Tianshan, perhaps triggered by slab break-off or delamination of thickened lithosphere. Relatively lower (143Nd/144Nd)i and higher (87Sr/86Sr)i than other Permian mafic-ultramafic intrusions in the eastern Chinese Tianshan indicate that the parental magmas of these two intrusions experienced significant contamination by old crustal rocks.

Impact of chemical lateral boundary conditions in a regional air quality forecast model on surface ozone predictions during stratospheric intrusions

NASA Astrophysics Data System (ADS)

Pendlebury, Diane; Gravel, Sylvie; Moran, Michael D.; Lupu, Alexandru

2018-02-01

A regional air quality forecast model, GEM-MACH, is used to examine the conditions under which a limited-area air quality model can accurately forecast near-surface ozone concentrations during stratospheric intrusions. Periods in 2010 and 2014 with known stratospheric intrusions over North America were modelled using four different ozone lateral boundary conditions obtained from a seasonal climatology, a dynamically-interpolated monthly climatology, global air quality forecasts, and global air quality reanalyses. It is shown that the mean bias and correlation in surface ozone over the course of a season can be improved by using time-varying ozone lateral boundary conditions, particularly through the correct assignment of stratospheric vs. tropospheric ozone along the western lateral boundary (for North America). Part of the improvement in surface ozone forecasts results from improvements in the characterization of near-surface ozone along the lateral boundaries that then directly impact surface locations near the boundaries. However, there is an additional benefit from the correct characterization of the location of the tropopause along the western lateral boundary such that the model can correctly simulate stratospheric intrusions and their associated exchange of ozone from stratosphere to troposphere. Over a three-month period in spring 2010, the mean bias was seen to improve by as much as 5 ppbv and the correlation by 0.1 depending on location, and on the form of the chemical lateral boundary condition.

Relating stress models of magma emplacement to volcano-tectonic earthquakes

NASA Astrophysics Data System (ADS)

Vargas-Bracamontes, D.; Neuberg, J.

2007-12-01

Among the various types of seismic signals linked to volcanic processes, volcano-tectonic earthquakes are probably the earliest precursors of volcanic eruptions. Understanding their relationship with magma emplacement can provide insight into the mechanisms of magma transport at depth and assist in the ultimate goal of forecasting eruptions. Volcano-tectonic events have been observed to occur on faults that experience increases in Coulomb stress changes as the result of magma intrusions. To simulate stress changes associated with magmatic injections, we test different models of volcanic sources in an elastic half-space. For each source model, we look at several aspects that influence the stress conditions of the magmatic system such as the regional tectonic setting, the effect of varying the elastic parameters of the media, the evolution of the magma with time, as well as the volume and rheology of the ascending magma.

Direct Observation of Rhyolite Magma by Drilling: The Proposed Krafla Magma Drilling Project

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Sigmundsson, F.; Papale, P.; Markusson, S.; Loughlin, S.

2014-12-01

Remarkably, drilling in Landsvirkjun Co.'s geothermal field in Krafla Caldera, Iceland has encountered rhyolite magma or hypersolidus rhyolite at 2.1-2.5 km depth in 3 wells distributed over 3.5 km2, including Iceland Deep Drilling Program's IDDP-1 (Mortensen, 2012). Krafla's most recent rifting and eruption (basalt) episode was 1975-1984; deformation since that time has been simple decay. Apparently rhyolite magma was either emplaced during that episode without itself erupting or quietly evolved in situ within 2-3 decades. Analysis of drill cuttings containing quenched melt from IDDP-1 yielded unprecedented petrologic data (Zierenberg et al, 2012). But interpreting active processes of heat and mass transfer requires knowing spatial variations in physical and chemical characteristics at the margin of the magma body, and that requires retrieving core - a not-inconceivable task. Core quenched in situ in melt up to 1150oC was recovered from Kilauea Iki lava lake, Hawaii by the Magma Energy Project >30 years ago. The site from which IDDP-1 was drilled, and perhaps IDDP-1 itself, may be available to attempt the first-ever coring of rhyolite magma, now proposed as the Krafla Magma Drilling Project (KMDP). KMDP would also include geophysical and geochemical experiments to measure the response of the magma/hydrothermal system to fluid injection and flow tests. Fundamental results will reveal the behavior of magma in the upper crust and coupling between magma and the hydrothermal system. Extreme, sustained thermal power output during flow tests of IDDP-1 suggests operation of a Kilauea-Iki-like freeze-fracture-flow boundary propagating into the magma and mining its latent heat of crystallization (Carrigan et al, EGU, 2014). Such an ultra-hot Enhanced Geothermal System (EGS) might be developable beneath this and other magma-heated conventional hydrothermal systems. Additionally, intra-caldera intrusions like Krafla's are believed to produce the unrest that is so troubling in

Carbon dioxide in magmas and implications for hydrothermal systems

USGS Publications Warehouse

Lowenstern, J. B.

2001-01-01

This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems

Forecasting magma-chamber rupture at Santorini volcano, Greece.

PubMed

Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

2015-10-28

How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

Forecasting magma-chamber rupture at Santorini volcano, Greece

PubMed Central

Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

2015-01-01

How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011–2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

Magma transport and storage at Kilauea volcano, Hawaii I: 1790-1952

NASA Astrophysics Data System (ADS)

Wright, T. L.; Klein, F.

2011-12-01

We trace the evolution of Kilauea from the time of the first oral records of an explosive eruption in 1790 to the long eruption in Halemaumau crater in 1952. The establishment of modern seismic and geodetic networks in the early 1960s showed that eruptions and intrusions were fed from two magma sources beneath the summit at depths of 2-6 and ~1 km respectively (sources 1 and 2), and that seaward spreading of the south flank took place on a decollement at 10-12 km depth at the base of the Kilauea edifice. A third diffuse, pressure-transmitting magma system (source 3) between the shallow East rift zone and the decollement was also identified. We test the null hypothesis that the volcano has behaved similarly throughout its lifetime, and conclude that the null hypothesis is not met for the period preceding the 1952 summit eruption because of changes in magma supply rate and differences in ground deformation patterns. The western missionaries arriving at Kilauea in 1823 were confronted with a caldera-wide lava lake. Filling rates determined by visual observation correspond to magma supply rates that averaged more than 0.3 km3/yr prior to 1840 and declined to 1894, when lava disappeared altogether at Halemaumau crater. The Hawaiian Volcano Observatory (HVO) was established by Thomas A. Jaggar in 1912 adjacent to the Volcano House Hotel on the rim of Kilauea. Instrumental observation at HVO began using a seismometer that doubled as a tiltmeter. A 1912-1924 magma supply rate of 0.024 km3/yr agreed with the rate of filling of Kilauea caldera from 1840-1894. 1924 was a critical year. An intrusion that moved down Kilauea's East rift zone beginning in February culminated beneath the lower East rift zone in April. In May, explosive eruptions accompanied a dramatic draining of Halemaumau. Triangulation results between 1912 and 1921 showed uplift extending far beyond Kilauea caldera and an equally large regional subsidence occurred between 1921 and 1927. HVO tilt narrows the

Geophysical Evidence for Magma Intrusion across the Non-Transform Offset between the Famous and North Famous segments of The Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Giusti, M.; Dziak, R. P.; Maia, M.; Perrot, J.; Sukhovich, A.

2017-12-01

In August of 2010 an unusually large earthquake sequence of >700 events occurred at the Famous and North Famous segments (36.5-37°N) of the Mid-Atlantic Ridge (MAR), recorded by an array of five hydrophones moored on the MAR flanks. The swarm extended spatially >70 km across the two segments. The non-transform offset (NTO) separating the two segements, which is thought to act as strucutural barrier, did not appear to impede or block the earthquake's spatial distribution. Broadband acoustic energy (1-30 Hz) was also observed and accompanied the onset of the swarm, lasting >20 hours. A total of 18 earthquakes from the swarm were detected teleseismically, four had Centroid-Moment Tensor (CMT) solutions derived. The CMT solutions indicated three normal faulting events, and one non-double couple (explosion) event. The spatio-temporal distribution of the seismicity and broadband energy show evidence of two magma dike intrusions at the North Famous segment, with one intrusion crossing the NTO. This is the first evidence for an intrusion event detected on the MAR south of the Azores since the 2001 Lucky Strike intrusion. Gravimetric data were required to identify whether or not the Famous area is indeed comprised of two segments down to the level of the upper mantle. A high resolution gravity anomaly map of the two segments has been realized, based on a two-dimensional polygons model (Chapman, 1979) and will be compared to gravimetric data originated from SUDACORES experiment (1998, Atalante ship, IFREMER research team). Combined with the earthquake observations, this gravity anomaly map should provide a better understanding the geodynamic processes of this non-transform offset and of the deep magmatic system driving the August 2010 swarm.

Hydrous parental magmas of Early to Middle Permian gabbroic intrusions in western Inner Mongolia, North China: New constraints on deep-Earth fluid cycling in the Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Pang, Chong-Jin; Wang, Xuan-Ce; Xu, Bei; Luo, Zhi-Wen; Liu, Yi-Zhi

2017-08-01

The role of fluids in the formation of the Permian-aged Xigedan and Mandula gabbroic intrusions in western Inner Mongolia was significant to the evolution of the Xing'an Mongolia Orogenic Belt (XMOB), and the active northern margin of the North China Craton (NCC). Secondary Ion Mass Spectroscopy (SIMS) U-Pb zircon geochronology establishes that the Xigedan gabbroic intrusion in the northern NCC was emplaced at 266 Ma, and is therefore slightly younger than the ca 280 Ma Mandula gabbroic intrusion in the XMOB. Along with their felsic counterparts, the mafic igneous intrusions record extensive bimodal magmatism along the northern NCC and in the XMOB during the Early to Middle Permian. The Mandula gabbroic rocks have low initial 87Sr/86Sr ratios (0.7040-0.7043) and positive εNd(t) (+6.2 to +7.3) and εHf(t) values (+13.4 to +14.5), resembling to those of contemporaneous Mandula basalts. These features, together with the presence of amphibole and the enrichment of large ion lithophile elements (LILE, e.g., Rb, Ba, U and Sr) and depletion of Nb-Ta suggest that the parental magmas of the Mandula mafic igneous rocks were derived from a depleted mantle source metasomatized by water-rich fluids. In contrast, the Xigedan gabbroic rocks are characterised by high 87Sr/86Sr ratios (0.7078-0.7080) and zircon δ18O values (5.84-6.61‰), but low εNd(t) (-9.3 to -10.2) and εHf(t) values (-8.76 to -8.54), indicative of a long-term enriched subcontinental lithosphere mantle source that was metasomatized by recycled, high δ18O crustal materials prior to partial melting. The high water contents (4.6-6.9 wt%) and arc-like geochemical signature (enrichment of fluid-mobile elements and depletion of Nb-Ta) of the parental magmas of the Xigedan gabbroic rocks further establish the existence of a mantle hydration event caused by fluid/melts released from hydrated recycled oceanic crust. Incompatible element modelling shows that 5-10% partial melting of an enriched mantle source by

Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry

NASA Astrophysics Data System (ADS)

Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.

2015-12-01

Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at <900°C are dominated by early crystallization of hornblende and apatite, and late crystallization (~<780°C) of titanite

Understanding the mechanical coupling between magma emplacement and the resulting deformation: the example of saucer-shaped sills

NASA Astrophysics Data System (ADS)

Galland, O.; Neumann, E. R.; Planke, S.

2009-12-01

The mechanical coupling between magma intrusions and the surrounding rocks plays a major role in the emplacement of volcanic plumbing systems. The deformation associated with magma emplacement has been widely studied, such as caldera inflation/deflation, volcano deformation during dike intrusion, and doming above laccoliths. However, the feedback processes, i.e. the effect of deformation resulting from intruding magma on the propagation of the intrusion itself, have rarely been studied. Saucer-shaped sills are adequate geological objects to understand such processes. Indeed, observation show that saucer-shaped sills are often associated with dome-like structures affecting the overlying sediments. In addition, there is a clear geometrical relation between the sills and the domes: the dome diameters are almost identical to those of saucers, and the tips of the inclined sheets of saucers are superimposed on the edges of the domes. In this presentation, we report on experimental investigations of the emplacement mechanisms of saucer-shaped sills and associated deformation. The model materials were (1) cohesive fine-grained silica flour, representing brittle crust, and (2) molten low-viscosity oil, representing magma. A weak layer located at the top of the injection inlet simulates strata. The main variable parameter is injection depth. During experiments, the surface of the model is digitalized through a structured light technique based on the moiré projection principle. Such a tool provides topographic maps of the surface of the model and allows a periodic (every 1.5 s) monitoring of the model topography. When the model magma starts intruding, a symmetrical dome rises above the inlet. Subsequently, the dome inflates and widens, and then evolves to a plateau-like feature, with nearly flat upper surface and steep sides. At the end of the experiments, the intruding liquid erupts at the edge of the plateau. The intrusions formed in the experiments are saucer-shaped sills

Factors controlling the structures of magma chambers in basaltic volcanoes

NASA Technical Reports Server (NTRS)

Wilson, L.; Head, James W.

1991-01-01

The depths, vertical extents, and lateral extents of magma chambers and their formation are discussed. The depth to the center of a magma chamber is most probably determined by the density structure of the lithosphere; this process is explained. It is commonly assumed that magma chambers grow until the stress on the roof, floor, and side-wall boundaries exceed the strength of the wall rocks. Attempts to grow further lead to dike propagation events which reduce the stresses below the critical values of rock failure. The tensile or compressive failure of the walls is discussed with respect to magma migration. The later growth of magma chambers is accomplished by lateral dike injection into the country rocks. The factors controlling the patterns of growth and cooling of such dikes are briefly mentioned.

Fate of a perched crystal layer in a magma ocean

NASA Technical Reports Server (NTRS)

Morse, S. A.

1992-01-01

The pressure gradients and liquid compressibilities of deep magma oceans should sustain the internal flotation of native crystals owing to a density crossover between crystal and liquid. Olivine at upper mantle depths near 250 km is considered. The behavior of a perched crystal layer is part of the general question concerning the fate of any transient crystal carried away from a cooling surface, whether this be a planetary surface or the roof of an intrusive magma body. For magma bodies thicker than a few hundred meters at modest crustal depths, the major cooling surface is the roof even when most solidification occurs at the floor. Importation of cool surroundings must also be invoked for the generation of a perched crystal layer in a magma ocean, but in this case the perched layer is deeply embedded in the hot part of the magma body, and far away from any cooling surface. Other aspects of this study are presented.

Characteristics and Significance of Magma Emplacement Horizons, Black Sturgeon Sill, Nipigon, Ontario

NASA Astrophysics Data System (ADS)

Zieg, M. J.; Hone, S. V.

2017-12-01

Spatial scales strongly control the timescales of processes in igneous intrusions, particularly through the thermal evolution of the magma, which in turn governs the evolution of crystallinity, viscosity, and other important physical and chemical properties of the system. In this study, we have collected a highly detailed data set comprising geochemical (bulk rock composition), textural (size and alignment of plagioclase crystals), and mineralogical (modal abundance) profiles through the central portion of the 250 m thick Black Sturgeon diabase sill. In this data, we have identified characteristic signals in texture (soft and somewhat diffuse chills), composition (reversals in differentiation trends), and mineralogy (olivine accumulations), all coinciding and recurring at roughly 10 meter intervals. Based on these signatures, we are able to map out multiple zones representing discrete pulses of magma that were emplaced sequentially as the intrusion was inflated. Simple thermal calculations suggest that each 10 meters of new crystallization would require repose times on the order of 10-100 years. To build up 250 meters of magma at this rate would only require approximately 250-2500 years, significantly less than the thermal lifetime of the entire sill. The soft chills we observe in the Black Sturgeon sill are therefore consistent with a system that remained warm throughout the emplacement process. Successive pulses were injected into partially crystalline mush, rather than pure liquid (which would result in hybridization) or solid (which would produce sharp hard chills). Episodic emplacement is by now widely recognized as a fundamental process in the formation of large felsic magma chambers; our results suggest that this also may be an important consideration in understanding the evolution of smaller mafic intrusions.

Geochemistry and tectonic implications of the Early Carboniferous Keketuobie intrusion in the West Junggar foldbelt, NW China

NASA Astrophysics Data System (ADS)

Deng, Yu-Feng; Yuan, Feng; Zhou, Taofa; Hollings, Pete; Zhang, Dayu

2018-06-01

The Keketuobie intrusion is situated in the northern part of the West Junggar foldbelt at the southern margin of the Central Asian Orogeic Belt. The intrusion consists of medium- to coarse-grained gabbro, fine-grained gabbro and diorite. Igneous zircons from the medium- to coarse-grained gabbro yielded a LA-ICP-MS U-Pb age of 320.8 ± 5.7 Ma, indicating that the intrusion was emplaced in the Early Carboniferous. The intrusive contact between the medium- to coarse-grained gabbro and the fine-grained gabbro indicates they formed from distinct magma pulses. Magnetite crystals from the fine-grained gabbro have lower V2O3 but higher TiO2 and Al2O3 contents than those of the medium- to coarse-grained gabbro, suggesting that the fine-grained gabbro crystallized in a relatively higher fO2 and temperature magma than the medium- to coarse-grained gabbro. The Keketuobie intrusive rocks are characterized by enriched large ion lithophile elements and depleted high field strength elements relative to N-MORB with restricted (87Sr/86Sr)t ratios (0.70370-0.70400) and εNd(t) values (+5.85 to +6.97). The petrography and geochemistry are comparable to those of subduction-related volcanic rocks. The trace elements and isotopic compositions of the mafic intrusive rocks suggest that the primary magmas were derived from mixing of metasomatized lithospheric mantle and depleted asthenospheric melts, perhaps triggered by slab break-off. The Keketuobie intrusion is younger than adjacent ophiolite sequences, island arc volcanic rocks and porphyry deposits, but predates the post-collisional A-type granites and bimodal volcanic rocks in the district, suggesting that the Keketuobie intrusion likely formed in a syn-collisional setting.

Fault-Magma Interactions during Early Continental Rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa

NASA Astrophysics Data System (ADS)

Weinstein, A.; Oliva, S. J.; Ebinger, C.; Aman, M.; Lambert, C.; Roecker, S. W.; Tiberi, C.; Muirhead, J.

2017-12-01

Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2D studies. We analyze seismicity data from a 13-month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3D velocity model reveal lower crustal earthquakes along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 66 earthquakes, and a longer time period of relocated earthquakes from global arrays reveal an along-axis stress rotation of 50 o ( N150 oE) in the magmatically active zone. Using Kostrov summation of local and teleseismic mechanisms, we find opening directions of N122ºE and N92ºE north and south of the magmatically active zone. The stress rotation facilitates strain transfer from border fault systems, the locus of early stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Earthquakes are largely driven by stress state around inflating magma bodies, and more dike intrusions with surface faulting, eruptions, and earthquakes are expected.

Oblique rift opening revealed by reoccurring magma injection in central Iceland.

PubMed

Ruch, Joël; Wang, Teng; Xu, Wenbin; Hensch, Martin; Jónsson, Sigurjón

2016-08-05

Extension deficit builds up over centuries at divergent plate boundaries and is recurrently removed during rifting events, accompanied by magma intrusions and transient metre-scale deformation. However, information on transient near-field deformation has rarely been captured, hindering progress in understanding rifting mechanisms and evolution. Here we show new evidence of oblique rift opening during a rifting event influenced by pre-existing fractures and two centuries of extension deficit accumulation. This event originated from the Bárðarbunga caldera and led to the largest basaltic eruption in Iceland in >200 years. The results show that the opening was initially accompanied by left-lateral shear that ceased with increasing opening. Our results imply that pre-existing fractures play a key role in controlling oblique rift opening at divergent plate boundaries.

Magma Intrusion at Mount St. Helens, Washington, from Temporal Gravity Variations

NASA Astrophysics Data System (ADS)

Battaglia, Maurizio; Lisowski, Mike; Dzursin, Dan; Poland, Mike; Schilling, Steve; Diefenbach, Angie; Wynn, Jeff

2017-04-01

Mount St. Helens is a stratovolcano in the Pacific Northwest region of the United States, best known for its explosive eruption in May 1980 - deadliest and most economically destructive volcanic event in US history. Volcanic activity renewed in September 2004 with a dome forming eruption that lasted until 2008. This eruption was surprising because the preceding four years had seen the fewest earthquakes and no significant deformation since the 1980-86 eruption ended. After the dome forming eruption ended in July 2008, the volcano seismic activity and deformation went back to background values. Time-dependent gravimetric measurements can detect subsurface processes long before magma flow leads to earthquakes or other eruption precursors. A high-precision gravity monitoring network (referenced to a base station 36 km NW of the volcano) was set up at Mount St Helens in 2010. Measurements were made at 12 sites on the volcano (at altitudes between 1200 and 2350 m a.s.l.) and 4 sites far afield during the summers of 2010, 2012, and 2014. The repeated gravity measurements revealed an increase in gravity between 2010 and 2014. Positive residual gravity anomalies remained after accounting for changes in surface height, in the Crater Glacier, and in the shallow hydrothermal aquifer. The pattern of residual gravity changes, with a maximum of 57±12 μGal from 2010 to 2014, is radially symmetric and centered on the 2004-08 lava dome. Inversion of the residual gravity signal points to a source 2.5-4 km beneath the crater floor (i.e., in the magma conduit that fed eruptions in 1980-86 and 2004-08). We attribute the gravity increase to re-inflation of the magma plumbing system following the 2004-8 eruption. Recent seismic activity (e.g., the seismic swarm of March 2016) has been interpreted as a response to the slow recharging of the volcano magma chamber.

Petrogenesis and metallogenesis of the Wajilitag and Puchang Fe-Ti oxide-rich intrusive complexes, northwestern Tarim Large Igneous Province

NASA Astrophysics Data System (ADS)

Zhang, Dongyang; Zhang, Zhaochong; Huang, He; Cheng, Zhiguo; Charlier, Bernard

2018-04-01

liquidus earlier in the crystallization sequence, especially relative to the crystallization of plagioclase. This is attributed to the relatively high TFeO, TiO2 and initial H2O contents of the parental magma. In combination with definitive field and petrological evidence, the enrichment of highly incompatible elements (e.g., Zr, Hf, Nb and Ta) and the depletion of rare earth elements in the Fe-Ti oxide ores is consistent with the plausible interpretation that the ores could be formed by fractional crystallization and crystal accumulation of the Fe-Ti oxide crystals from the ferrobasaltic parental magmas. A considerable amount of the Fe-Ti oxides in the Puchang has transported and sunk from higher up in the chamber to the underlying unconsolidated silicate crystal pile. The highly dense Fe-Ti oxide crystal slurries further tended to effective accumulate Fe-Ti oxides to form high-grade Fe-Ti oxide ore bodies, and subsequent rapid collapse and intrusive into lower lithologies within the complex under a H2O-rich environment during the late-stage of magmatic differentiation. The development of massive Fe-Ti oxide ores in the case of the Puchang, could plausibly result from a combination of the protracted differentiation history of a Fe highly enriched parental magma and the later addition of external H2O from the country rocks (e.g., carbonates) to the slowly cooling magma chamber.

Modeling the three-dimensional structure of macroscopic magma transport systems: Application to Kilauea volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryan, M.P.; Koyanagi, R.Y.; Fiske, R.S.

1981-08-10

We report the results of modeling the three-dimensional internal structure of Kilauea's magmatic passageways. The approach uses a clear plexiglass model containing equally-spaced levels upon which well-located seismic hypocenters are plotted. Application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures. Four magma transport and storage structures produce have been identified within and beneath Kilauea: (1) Primary conduit. The conduit transporting magma into Kilauea's summit storage reservoir rises from the model base (14.6 km) to 6.5 km depth level. It ismore » a zone of intense fracturing and inferred intrusion, whose horizontal sections are elliptical in planform. Over its height, the average major axis of component horizontal section is 3.3 km, with an average minor axis of 1.7 km. This yields an aspect ratio of xi = 0.52. At the 14.6 km level, the strike of the major axis is N67 /sup 0/E. During passage from the upper mantle through the oceanic crust, this axis rotates in a right-handed sense, until the strike is N41 /sup 0/W at the 6.5 km level. (2) Magma chamber complex floor. The interval from 6.5 to 5.7 km, immediately over the primary conduit, is aseismic. This suggests differentially high fluid-to-rock ratios, and relatively weak pathways for further vertical transport into higher levels of the storage complex, as well as lateral leakage eastward into the Mauna Ulu staging area: for later vertical ascent beneath the upper east rift zone. Seismicity within the immediately subjacent rocks that form the top of the primary conduit (at 6.5 km) suggests that this inferred magma-rich horizon forms the effective floor of the summit storage complex. (3) Magma chamber crown. Intense seismicity over the 1.1--1.9 km depth interval defines an elliptical region in plan view.« less

On the Principles of Building a Layered Intrusion

NASA Astrophysics Data System (ADS)

Marsh, B. D.

2009-12-01

An accurate and realistic understanding of all magmatic processes involves knowing the combined physical and chemical fundamentals governing the overall process. Magmatic processes involve such a vast array of sub-processes (e.g., heat and mass transfer, crystal growth, slurry transport and sorting, annealing, resorbtion, etc.) that rarely is there any single feature or measurement that can be safely inverted to solve the problem. And each event as in the formation of an intrusion must at some level for heuristic purposes be defined as an isolated event. This is commonly done without much forethought, as is the absolutely critical assumption of the initial conditions defining the beginning of the event. Almost without exception, it is the initial conditions that determine the outcome of the entire process in all physical and biological systems. Automobile factories produce motorized vehicles not water melons or chimpanzees. Nucleosynthesis of H and He always gives the same set of elements. The initial conditions of the magma giving rise to the end product for mafic layered systems are especially difficult to discern and must be bounded by observing simpler, real time magmatic and volcanic processes. Initial conditions come from posing a series of questions: What was the style and duration of filling? What was the rate of influx and final volume of each delivery of magma? What was the compositional variation and phenocryst content of the individual magmatic deliveries? If phenocrysts are present, were they sorted prior to injection during ascension? What was the original and ongoing shape of the magmatic reservoir? A failure to appreciate or answer such basic questions leads to vastly untenable evolutionary scenarios. Unrealistic initial conditions necessarily lead to unrealistic magmatic scenarios. There are certain safe starting points. Eruptive and emplacement fluxes are limited. The larger an intrusion is the longer it took to build and the longer to build the

Magma mixing in granitic rocks of the central Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Reid, John B.; Evans, Owen C.; Fates, Dailey G.

1983-12-01

The El Capitan alaskite exposed in the North American Wall, Yosemite National Park, was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite. Comparisons of petrographic and compositional data for these dikes and alaskite with published data for Sierra Nevada plutons lead us to suggest that mafic magmas were important in the generation of the Sierra Nevada batholith. Specifically, we conclude that: (1) intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite (rhyolitic) magmas; (2) interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements; (3) most mafic inclusions in Sierra Nevada plutons represent chilled pillows of mafic magmas, related by fractional crystallization and granitoid assimilation, that dissolve into their felsic host and contaminate it to intermediate (granodioritic) compositions; (4) vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton's domed ceiling causing the zoning (mafic margins-to-felsic core) that these plutons exhibit.

Magma Reservoirs Feeding Giant Radiating Dike Swarms: Insights from Venus

NASA Technical Reports Server (NTRS)

Grosfils, E. B.; Ernst, R. E.

2003-01-01

Evidence of lateral dike propagation from shallow magma reservoirs is quite common on the terrestrial planets, and examination of the giant radiating dike swarm population on Venus continues to provide new insight into the way these complex magmatic systems form and evolve. For example, it is becoming clear that many swarms are an amalgamation of multiple discrete phases of dike intrusion. This is not surprising in and of itself, as on Earth there is clear evidence that formation of both magma reservoirs and individual giant radiating dikes often involves periodic magma injection. Similarly, giant radiating swarms on Earth can contain temporally discrete subswarms defined on the basis of geometry, crosscutting relationships, and geochemical or paleomagnetic signatures. The Venus data are important, however, because erosion, sedimentation, plate tectonic disruption, etc. on Earth have destroyed most giant radiating dike swarm's source regions, and thus we remain uncertain about the geometry and temporal evolution of the magma sources from which the dikes are fed. Are the reservoirs which feed the dikes large or small, and what are the implications for how the dikes themselves form? Does each subswarm originate from a single, periodically reactivated reservoir, or do subswarms emerge from multiple discrete geographic foci? If the latter, are these discrete foci located at the margins of a single large magma body, or do multiple smaller reservoirs define the character of the magmatic center as a whole? Similarly, does the locus of magmatic activity change with time, or are all the foci active simultaneously? Careful study of giant radiating dike swarms on Venus is yielding the data necessary to address these questions and constrain future modeling efforts. Here, using giant radiating dike swarms from the Nemesis Tessera (V14) and Carson (V43) quadrangles as examples, we illustrate some of the dike swarm focal region diversity observed on Venus and briefly explore some

Pressurized magma reservoir within the east rift zone of Kīlauea Volcano, Hawai`i: Evidence for relaxed stress changes from the 1975 Kalapana earthquake

NASA Astrophysics Data System (ADS)

Baker, Scott; Amelung, Falk

2015-03-01

We use 2000-2012 InSAR data from multiple satellites to investigate magma storage in Kīlauea's east rift zone (ERZ). The study period includes a surge in magma supply rate and intrusion-eruptions in 2007 and 2011. The Kupaianaha area inflated by ~5 cm prior to the 2007 intrusion and the Nāpau Crater area by ~10 cm following the 2011 intrusion. For the Nāpau Crater area, elastic modeling suggests an inflation source at 5 ± 2 km depth or more below sea level. The reservoir is located in the deeper section of the rift zone for which secular magma intrusion was inferred for the period following the 1975 Mw7.7 décollement earthquake. Reservoir pressurization suggests that in this section of the ERZ, extensional stress changes due to the earthquake have largely been compensated for and that this section is approaching its pre-1975 state. Reservoir pressurization also puts the molten core model into question for this section of Kīlauea's rift zone.

Whole-rock and mineral compositional constraints on the magmatic evolution of the Ni-Cu-(PGE) sulfide ore-bearing Kevitsa intrusion, northern Finland

NASA Astrophysics Data System (ADS)

Luolavirta, Kirsi; Hanski, Eero; Maier, Wolfgang; Santaguida, Frank

2018-01-01

The 2.06 Ga mafic-ultramafic Kevitsa intrusion is located in the Central Lapland greenstone belt. The lower ultramafic part of the intrusion hosts a large disseminated Ni-Cu-(PGE) sulfide deposit with Ni tenors ranging widely from < 4 wt% (uneconomic false ore and contact mineralization) to 4-7 wt% (regular ore) and up to 40 wt% (Ni-PGE ore). The stratigraphy of the ultramafic cumulates is divided into the basal pyroxenite-gabbro (Basal series), olivine pyroxenite (OLPX), pyroxenite, and plagioclase-bearing (ol) websterite (pOLWB), of which the latter occurs together with minor microgabbros in the ore-bearing domain of the intrusion. Around the ore domain, the ultramafic cumulate succession records a simple lithological stratigraphy and modest and predictable variations in whole-rock and mineral compositions. The ore-bearing domain, in contrast, is characterized by a complex internal architecture, variations in whole-rock and mineral compositions, and the presence of numerous inclusions and xenoliths. The OLPXs are mainly composed of cumulus olivine (Fo77-89) and clinopyroxene (Mg#81-92) with variable amounts of oikocrystic orthopyroxene (Mg#79-84). They comprise the bulk of the ultramafic cumulates and are the dominant host rocks to the sulfide ore. The host rocks to the regular and false ore type are mineralogically and compositionally similar (Fo 80-83, mostly) and show mildly LREE-enriched REE patterns (CeN/YbN 2), characteristic for the bulk of the Kevitsa ultramafic cumulates. The abundance of orthopyroxene and magnetite is lowest in the host rocks to the Ni-PGE ore type, being in line with the mineral compositions of the silicates, which are the most primitive in the intrusion. However, it contrasts with the LREE-enriched nature of the ore type (CeN/YbN 7), indicating significant involvement of crustal material in the magma. The contrasting intrusive stratigraphy in the different parts of the intrusion likely reflects different emplacement histories. It is

Variations of trace element concentration of magnetite and ilmenite from the Taihe layered intrusion, Emeishan large igneous province, SW China: Implications for magmatic fractionation and origin of Fe-Ti-V oxide ore deposits

NASA Astrophysics Data System (ADS)

She, Yu-Wei; Song, Xie-Yan; Yu, Song-Yue; He, Hai-Long

2015-12-01

In situ LA-ICP-MS trace elemental analysis has been applied to magnetite and ilmenite of the Taihe layered intrusion, Emeishan large igneous province, SW China, in order to understand better fractionation processes of magma and origin of Fe-Ti-V oxide ore deposits. The periodic reversals in Mg, Ti, Mn in magnetite and Mg, Sc in ilmenite are found in the Middle Zone of the intrusion and agree with fractionation trends as recorded by olivine (Fo), plagioclase (An) and clinopyroxene (Mg#) compositions. These suggest the Taihe intrusion formed from open magma chamber processes in a magma conduit with multiple replenishments of more primitive magmas. The V and Cr of magnetite are well correlated with V and Cr of clinopyroxene indicating that they became liquidus phases almost simultaneously at an early stage of magma evolution. Ilmenite from the Middle and Upper Zones shows variable Cr, Ni, V, Mg, Nb, Ta and Sc contents indicating that ilmenite at some stratigraphic levels crystallized slightly earlier than magnetite and clinopyroxene. The early crystallization of magnetite and ilmenite is the result of the high FeOt and TiO2 contents in the parental magma. The ilmenite crystallization before magnetite in the Middle and Upper Zones can be attributed to higher TiO2 content of the magma due to the remelting of pre-existing ilmenite in a middle-level magma chamber. Compared to the coeval high-Ti basalts, the relatively low Zr, Hf, Nb and Ta contents in both magnetite and ilmenite throughout the Taihe intrusion indicate that they crystallized from Fe-Ti-(P)-rich silicate magmas. Positive correlations of Ti with Mg, Mn, Sc and Zr of magnetite, and Zr with Sc, Hf and Nb of ilmenite also suggest that magnetite and ilmenite crystallized continuously from the homogeneous silicate magma rather than an immiscible Fe-rich melt. Therefore, frequent replenishments of Fe-Ti-(P)-rich silicate magma and gravitational sorting and settling are crucial for the formation the massive and

Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

NASA Astrophysics Data System (ADS)

Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

2013-12-01

The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible

Mush Column Magma Chambers

NASA Astrophysics Data System (ADS)

Marsh, B. D.

2002-12-01

Magma chambers are a necessary concept in understanding the chemical and physical evolution of magma. The concept may well be similar to a transfer function in circuit or time series analysis. It does what needs to be done to transform source magma into eruptible magma. In gravity and geodetic interpretations the causative body is (usually of necessity) geometrically simple and of limited vertical extent; it is clearly difficult to `see' through the uppermost manifestation of the concentrated magma. The presence of plutons in the upper crust has reinforced the view that magma chambers are large pots of magma, but as in the physical representation of a transfer function, actual magma chambers are clearly distinct from virtual magma chambers. Two key features to understanding magmatic systems are that they are vertically integrated over large distances (e.g., 30-100 km), and that all local magmatic processes are controlled by solidification fronts. Heat transfer considerations show that any viable volcanic system must be supported by a vertically extensive plumbing system. Field and geophysical studies point to a common theme of an interconnected stack of sill-like structures extending to great depth. This is a magmatic Mush Column. The large-scale (10s of km) structure resembles the vertical structure inferred at large volcanic centers like Hawaii (e.g., Ryan et al.), and the fine scale (10s to 100s of m) structure is exemplified by ophiolites and deeply eroded sill complexes like the Ferrar dolerites of the McMurdo Dry Valleys, Antarctica. The local length scales of the sill reservoirs and interconnecting conduits produce a rich spectrum of crystallization environments with distinct solidification time scales. Extensive horizontal and vertical mushy walls provide conditions conducive to specific processes of differentiation from solidification front instability to sidewall porous flow and wall rock slumping. The size, strength, and time series of eruptive behavior

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode.

PubMed

Wright, Tim J; Ebinger, Cindy; Biggs, Juliet; Ayele, Atalay; Yirgu, Gezahegn; Keir, Derek; Stork, Anna

2006-07-20

Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the approximately 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of approximately 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975-84) Krafla events in Iceland, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia-Arabia plate boundary.

The genesis of the newly discovered giant Wuben magmatic Fe-Ti oxide deposit in the Emeishan Large Igneous Province: a product of the late-stage redistribution and sorting of crystal slurries

NASA Astrophysics Data System (ADS)

Bai, Zhong-Jie; Zhong, Hong; Zhu, Wei-Guang; Hu, Wen-Jun; Chen, Cai-Jie

2018-04-01

A giant Fe-Ti oxide deposit hosted by the Wuben mafic intrusion has recently been discovered in the Pan-Xi area of the Emeishan Large Igneous Province (ELIP). The evolved compositions of the gangue minerals within the Fe-Ti oxide ores indicate that they formed during later stages of magma differentiation than those within the neighboring Panzhihua intrusion or other ore-bearing intrusions in this area. The rocks from the Wuben intrusion and MZb of the Panzhihua intrusion contain compositionally similar silicate minerals and have similar titanomagnetite/ilmenite ratios, suggesting that the former is related to and probably connected to the latter by subsurface magmatic conduits. This indicates that unconsolidated minerals that formed in the MZb flowed as crystal slurries into the Wuben magma chamber during the later stages of evolution of the parental magma. The later secondary enrichment of Fe-Ti oxides by mechanical redistribution and the sorting of crystals as a result of density and size differences generated the Wuben massive Fe-Ti oxide bodies. The ilmenite was commonly saturated in the magma at late stage of differentiation in the ELIP, thereby the associated deposit contains much higher contents of ilmenite. This indicates that future exploration for Fe-Ti oxide mineralization in the ELIP should not merely focus on the lower parts of large layered intrusions but should also include nearby relatively small intrusions or even the upper parts of large intrusions, especially as ilmenite-enriched Fe-Ti oxide deposits may have greater economic value than ilmenite-poor deposits.

From a long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)

NASA Astrophysics Data System (ADS)

Buret, Yannick; von Quadt, Albrecht; Heinrich, Christoph; Selby, David; Wälle, Markus; Peytcheva, Irena

2016-09-01

The formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system, which provides the source of porphyry magmas, as well as metal and sulphur-charged mineralising fluids. Reading the geochemical record of this large magmatic source region, as well as constraining the time-scales for creating a much smaller porphyry copper deposit, are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits. This study focuses on the Bajo de la Alumbrera porphyry copper deposit in Northwest Argentina. The deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections. To constrain the duration of ore formation, we dated zircons from four porphyry intrusions, including pre-, syn- and post-mineralisation porphyries based on intersection relations between successive intrusion and vein generations, using high precision CA-ID-TIMS. Based on the youngest assemblages of zircon grains, which overlap within analytical error, all four intrusions were emplaced within 29 ka, which places an upper limit on the total duration of hydrothermal mineralisation. Re/Os dating of hydrothermal molybdenite fully overlaps with this high-precision age bracket. However, all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the ∼200 ka preceding the emplacement of the porphyries. Zircon trace element variations, Ti-in-zircon temperatures, and Hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history, and that the four intrusions were derived from the same upper-crustal magma chamber. Trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation. However, zircon

Thermally-assisted Magma Emplacement Explains Restless Calderas

NASA Astrophysics Data System (ADS)

Amoruso, A.; Crescentini, L.; D'Antonio, M.; Acocella, V.

2017-12-01

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei, Italy, which is the best-known, yet most dangerous calderas, lying to the west of Naples and restless since the 1950s at least.Our elaboration of the geodetic data indicates that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust.Our thermal models show that the repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth 3 ka before the last eruption and, in turn, contributed to maintain the thermal anomaly itself. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks.Available information at other calderas highlights similarities to Campi Flegrei, in the pattern and cause of unrest. All monitored restless calderas have either geodetically (Yellowstone, Aira Iwo-Jima, Askja, Fernandina and, partly, Long Valley) or geophysically (Rabaul, Okmok) detected sill-like intrusions inducing repeated unrest. Some calderas (Yellowstone, Long Valley) also show stable deformation pattern, where inflation insists on and mimics the resurgence uplift. The common existence of sill-like sources, also responsible for stable deformation patterns, in restless calderas suggests close similarities to Campi Flegrei. This suggests a wider applicability of our model of thermally-assisted sill emplacement, to be tested by future studies to better understand not only the dynamics of restless

Evidence for crustal recycling during the Archean: The parental magmas of the stillwater complex

NASA Technical Reports Server (NTRS)

Mccallum, I. S.

1988-01-01

The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area.

Dynamics of the 2014-15 Bardarbunga-Holuhraun magma propagation

NASA Astrophysics Data System (ADS)

Caudron, C.; White, R. S.; Rivalta, E.

2016-12-01

The 2014-15 Holuhraun eruption was the largest eruption in Europe since 1784. During the two weeks preceding the eruption, the magma migrated from the south, around Bardarbunga volcano, to the north. This 48 km-long segmented propagation triggered, at a variable rate, more than 30,000 micro-earthquakes, and eventually discharged huge amount of lava and sulphur dioxide. A network comprising more than 70 seismometers captured the melt intrusion with an unprecedented resolution, providing scientists with a wealth of data to better understand volcano shallow magma storage and transport. This unique dataset first serves as a calibration of the seismic amplitude ratio methodology (Taisne et al., 2011), specifically designed to track the micro seismicity associated with magma migration, and better assess its limitations. The technique remarkably tracks magma propagations, even in the absence of earthquakes located using traditional techniques (based on P and S wave arrivals). This finding is in agreement with Bakker et al. (2016) who experimentally showed that the seismicity remain significant as long as magma movement continues. It also highlights intriguing systematic retreats of the seismicity to the back of each active segment. The seismic energy persists at this location for several hours (up to 80 hours), before surging again forward. This peculiar behaviour was also, although less clearly, observed during the Afar (Ethiopia) and Krafla (Iceland) intrusions. The shape of a dyke is controlled by the topographic and flow gradients. After calculating and low-passing the topographic gradient, the most intense migrations occur where the gradient is lower. Following advances at the tip of the dyke, the seismic activity retreats, the active seismic area becomes wider and correlates with larger modelled dyke openings (up to 6 m). Since the flow gradient in these settings is mostly determined by the difference in pressure between the head and the tail of the dyke, the active

Petrogenesis of Cretaceous volcanic-intrusive complex from the giant Yanbei tin deposit, South China: Implication for multiple magma sources, tin mineralization, and geodynamic setting

NASA Astrophysics Data System (ADS)

Li, Qian; Zhao, Kui-Dong; Lai, Pan-Chen; Jiang, Shao-Yong; Chen, Wei

2018-01-01

The giant Yanbei tin ore deposit is the largest porphyry-type tin deposit in South China. The orebodies are hosted by the granite porphyry in the central part of the Yanbei volcanic basin in southern Jiangxi Province. The Yanbei volcanic-intrusive complex mainly consists of dacitic-rhyolitic volcanic rocks, granite, granite porphyry and diabase dikes. In previous papers, the granite porphyry was considered as subvolcanic rocks, which came from the same single magma chamber with the volcanic rocks. In this study, zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemical and Sr-Nd isotopic compositions of different magmatic units in the Yanbei complex are reported. Geochronologic results show that various magmatic units have different formation ages. The dacite yielded a zircon U-Pb age of 143 ± 1 Ma, and the granite porphyry has the emplacement age of 138 ± 1 Ma. Diabase dikes which represented the final stage of magmatism, yielded a zircon U-Pb age of 128 ± 1 Ma. Distinctive whole rock Sr-Nd and zircon Hf isotopic compositions suggest that these magmatic units were derived from different magma sources. The volcanic rocks were mainly derived from the partial melting of Paleoproterozoic metasedimentary rocks without additions of mantle-derived magma. The granite porphyry has an A-type geochemical affinity, and was derived from remelting of Paleo-Mesoproterozoic crustal source with involvement of a subordinate mantle-derived magma. The granite porphyry is also a typical stanniferous granite with high F (4070-6090 ppm) and Sn (7-39 ppm) contents. It underwent strongly crystal fractionation of plagioclase, K-feldspar, and accessory minerals (like apatite, Fe-Ti oxides), which may contribute to the tin mineralization. The diabase was derived by partial melting of enriched lithospheric mantle which had been metasomatised by slab-derived fluids. The change of magmatic sources reflected an increasing extensional tectonic environment, perhaps induced by slab

Regional and temporal variability of melts during a Cordilleran magma pulse: Age and chemical evolution of the jurassic arc, eastern mojave desert, California

USGS Publications Warehouse

Barth, A.P.; Wooden, J.L.; Miller, David; Howard, Keith A.; Fox, Lydia; Schermer, Elizabeth R.; Jacobson, C.E.

2017-01-01

Intrusive rock sequences in the central and eastern Mojave Desert segment of the Jurassic Cordilleran arc of the western United States record regional and temporal variations in magmas generated during the second prominent pulse of Mesozoic continental arc magmatism. U/Pb zircon ages provide temporal control for describing variations in rock and zircon geochemistry that reflect differences in magma source components. These source signatures are discernible through mixing and fractionation processes associated with magma ascent and emplacement. The oldest well-dated Jurassic rocks defining initiation of the Jurassic pulse are a 183 Ma monzodiorite and a 181 Ma ignimbrite. Early to Middle Jurassic intrusive rocks comprising the main stage of magmatism include two high-K calc-alkalic groups: to the north, the deformed 183–172 Ma Fort Irwin sequence and contemporaneous rocks in the Granite and Clipper Mountains, and to the south, the 167–164 Ma Bullion sequence. A Late Jurassic suite of shoshonitic, alkali-calcic intrusive rocks, the Bristol Mountains sequence, ranges in age from 164 to 161 Ma and was emplaced as the pulse began to wane. Whole-rock and zircon trace-element geochemistry defines a compositionally coherent Jurassic arc with regional and secular variations in melt compositions. The arc evolved through the magma pulse by progressively greater input of old cratonic crust and lithospheric mantle into the arc magma system, synchronous with progressive regional crustal thickening.

A hybrid composite dike suite from the northern Arabian Nubian Shield, southwest Jordan: Implications for magma mixing and partial melting of granite by mafic magma

NASA Astrophysics Data System (ADS)

Jarrar, Ghaleb H.; Yaseen, Najel; Theye, Thomas

2013-03-01

The Arabian Nubian Shield is an exemplary juvenile continental crust of Neoproterozoic age (1000-542 Ma). The post-collisional rift-related stage (~ 610 to 542 Ma) of its formation is characterized among others by the intrusion of several generations of simple and composite dikes. This study documents a suite of hybrid composite dikes and a natural example of partial melting of granite by a mafic magma from the northernmost extremity of Arabian Nubian Shield in southwest Jordan. The petrogenesis of this suite is discussed on the basis of field, petrographic, geochemical, and Rb/Sr isotopic data. These dikes give spectacular examples of the interaction between basaltic magma and the granitic basement. This interaction ranges from brecciation, partial melting of the host alkali feldspar granite to complete assimilation of the granitic material. Field structures range from intrusive breccia (angular partially melted granitic fragments in a mafic groundmass) to the formation of hybrid composite dikes that are up to 14 m in thickness. The rims of these dikes are trachyandesite (latite) with alkali feldspar ovoids (up to 1 cm in diameter); while the central cores are trachydacite to dacite and again with alkali feldspar ovoids and xenoliths from the dike rims. The granitic xenoliths in the intrusive breccia have been subjected to at least 33% partial melting. A seven-point Rb/Sr isochron from one of these composite dikes yields an age of 561 ± 33 Ma and an initial 87Sr/86Sr ratio of 0.70326 ± 0.0003 (2σ) and MSWD of 0.62. Geochemical modeling using major, trace, rare earth elements and isotopes suggests the generation of the hybrid composite dike suite through the assimilation of 30% to 60% granitic crustal material by a basaltic magma, while the latter was undergoing fractional crystallization at different levels in the continental crust.

Temporal Evolution of Surface Deformation and Magma Sources at Pacaya Volcano, Guatemala Revealed by InSAR

NASA Astrophysics Data System (ADS)

Wnuk, K.; Wauthier, C.

2016-12-01

Pacaya Volcano, Guatemala is a persistently active volcano whose western flank is unstable. Despite continuous activity since 1961, a lack of high temporal resolution geodetic surveying has prevented detailed modeling of Pacaya's underlying magmatic plumbing system. A new, temporally dense dataset of Interferometric Synthetic Aperture Radar (InSAR) RADARSAT-2 images, spanning December 2012 to March 2014, shows magmatic deformation before and during major eruptions in January and March 2014. Inverse modeling of InSAR surface displacements suggest that three magma bodies are responsible for observed deformation: (1) a 3.7 km deep spherical reservoir located northwest of the summit, (2) a 0.4 km deep spherical source located directly west of the summit, and (3) a shallow dike below the summit that provides the primary transport pathway for erupted materials. Periods of heightened activity are brought on by magma pulses at depth, which result in rapid inflation of the edifice. We observe an intrusion cycle at Pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion. Intrusion volumes are proportional to reservoir volume loss, and do not always result in an eruption. Periods of increased activity culminate with larger dike fed eruptions. Large eruptions are followed by inter eruptive periods marked by a decrease in crater explosions and a lack of deformation. A full understanding of magmatic processes at Pacaya is required to assess potential impacts on other aspects of the volcano such as the unstable western flank. Co-eruptive flank motion appears to have initiated a new stage of volcanic rifting at Pacaya defined by repeated NW-SE dike intrusions. This creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induces flank motion

Syntectic Reactions involving Limestones and Limestone-Derived Carbonatitic Melts in the Generation of some Peralkalic Magmas: Reflections on Reginald Daly's Insights 100 Years Later

NASA Astrophysics Data System (ADS)

Lentz, D.

2017-12-01

The theoretical analysis of how sedimentary limestones and marbles could melt as a result of infiltrative contact metasomatism associated with silicate magmas, enables reconsideration of the limestone syntectic (assimilation) hypothesis for the origin of some peralkalic rocks. Reginald Daly's syntectic model published in detail in early 1918 fell out of favor because experimental evidence from the early 1960's suggested; 1) that limestone assimilation would increase P(CO2) and cause solidification of the silicate intrusion, 2) that there is a thermal barrier between silica-saturated and undersaturated magmas that would inhibit extensive desilication of the magma, and 3) the endothermic decarbonation reactions would require heat via magmatic crystallization of near-solidus magmas. However, these concerns were not as critical for high-T mafic melts relative to more low-T silicic melts, although most subsequent researchers dismissed syntexis as isotopic arguments also seemed robust. However, skarn-related limestone melts can interact much more easily with silicate magma, resulting in calc-silicate-forming (endoskarn-like) limestone syntectic (desilication - calcification-magnesification processes) decarbonation reactions with compositional evolution into the silica-undersaturated field. If mafic in composition originally when syntectically modified, then the CO2-bearing derivative peralkalic melt may subsequently react with the dominant volume magma or fractionate separately into a more evolved composition. As well, an increase in P(CO2) within the modified silicate fraction coupled with compositional evolution to more silica-undersaturated compositions enhances the stability of the immiscible, extremely low viscosity carbonate melt fraction. In addition, dynamic interaction of these co-existing immiscible melts (analogous to the current hypothesis) would partition elements, as well as isotopic signatures, such that they would be virtually unrecognizable as having a

Intrusive hyaloclastite and peperitic breccias associated to sill and cryptodome emplacement on an Early Paleocene polymagmatic compound cone-dome volcanic complex from El Guanaco mine, Northern Chile

NASA Astrophysics Data System (ADS)

Páez, G. N.; Permuy Vidal, C.; Galina, M.; López, L.; Jovic, S. M.; Guido, D. M.

2018-04-01

This work explores the textural characteristics, morphology and facies architecture of well-preserved Paleocene hyaloclastic and peperitic breccias associated with subvolcanic intrusions at El Guanaco gold mine (Northern Chile). The El Guanaco mine volcanic sequence is part of a polymagmatic compound cone-dome volcanic complex grouping several dacitic domes and maar-diatremes, and subordinated subvolcanic intrusions of basaltic, andesitic and dacitic compositions. The Soledad-Peñafiel Fault System is a first order regional structure controlling the location and style of the volcanism in the region. Three different intrusive bodies (Basaltic sills, Dacitic cryptodomes and Andesitic cryptodomes) were found to intrude into a wet and poorly consolidated pyroclastic sequence representing the upper portions of a maar-diatreme. Consequently, extensive quench fragmentation and fluidization along their contacts occurred, leading to the formation of widespread breccia bodies enclosing a coherent nucleus. Differences in matrix composition allows to define two main breccias types: 1) poorly-sorted monomictic breccias (intrusive hyaloclastites) and 2) poorly-sorted tuff-matrix breccias (peperites). The observed facies architecture is interpreted as the result of the interplay of several factors, including: 1) magma viscosity, 2) the geometry of the intrusives, and 3) variations on the consolidation degree of the host rocks. Additionally, the overall geometry of each intrusive is interpreted to be controlled by the effective viscosity of the magmas along with the available magma volume at the time of the intrusions. The presence of three compositionally different subvolcanic bodies with intrusive hyaloclastite and peperite envelopes indicate, not only that all these intrusions occurred in a short period of time (probably less than 2-3 Ma), but also that the volcaniciclastic pile suffer little or none compaction nor consolidation during that time. The presence of three

Magma reservoir subsidence mechanics: Theoretical summary and application to Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Ryan, Michael P.; Blevins, James Y. K.; Okamura, Arnold T.; Koyanagi, Robert Y.

1983-05-01

An analytic model has been developed for the prediction of the three-dimensional deformation field generated by the withdrawal of magma from a sill-like storage compartment during an intrusion or eruption cycle. The model is based on the work of Berry and Sales (1961, 1962) and predicts the vertical displacement components over the areal plane. Model parameters are the depth of burial h, the intrusion half width a, the intrusion half length b, the thickness of the magmatic interior at the moment of melt withdrawal tm, and the planform aspect ratio ξ = a/b. The products of the model include areal deformation maps. Systematic variation in model parameters within the context of Kilauea Volcano, Hawaii, have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth. Moreover, the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns. The model has been applied to Kilauea Volcano for three periods of pronounced summit subsidence: (1) 1921-1927 (bracketing the steamblast eruptive phases of 1924); (2) June 1972 to December 1972, and (3) December 1972 to May 1973. Application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps: (1) the vertical displacement maxima; (2) the vertical displacement gradients over the areal plane, (3) the lateral extent of the deformation field, (4) the aspect ratio of the subsidence pattern, and (5) the strike of the major axis of the deformation field. The constrained geometries and volumes of the inferred collapsed storage cavities for each period are (1) 1921-1927: depth ≅ 3 km, a ≅ 1500 m, b ≅ 4500 m, tm ≅ 20 m, V 540×106 m3, (2) June 1972 to December 1972: depth ≅ 3.3 km, a ≅ 600 m, b ≅ 2000 m, tm ≅ 1 m, V ≅ 4.8×106 m3, and (3) December 1972 to May 1973: depth ≅ 2.2 km, a ≅ 500

Magma supply, storage, and transport at shield-stage Hawaiian volcanoes: Chapter 5 in Characteristics of Hawaiian volcanoes

USGS Publications Warehouse

Poland, Michael P.; Miklius, Asta; Montgomery-Brown, Emily K.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

2014-01-01

Magma supply to Hawaiian volcanoes has varied over millions of years but is presently at a high level. Supply to Kīlauea’s shallow magmatic system averages about 0.1 km3/yr and fluctuates on timescales of months to years due to changes in pressure within the summit reservoir system, as well as in the volume of melt supplied by the source hot spot. Magma plumbing systems beneath Kīlauea and Mauna Loa are complex and are best constrained at Kīlauea. Multiple regions of magma storage characterize Kīlauea’s summit, and two pairs of rift zones, one providing a shallow magma pathway and the other forming a structural boundary within the volcano, radiate from the summit to carry magma to intrusion/eruption sites located nearby or tens of kilometers from the caldera. Whether or not magma is present within the deep rift zone, which extends beneath the structural rift zones at ~3-km depth to the base of the volcano at ~9-km depth, remains an open question, but we suggest that most magma entering Kīlauea must pass through the summit reservoir system before entering the rift zones. Mauna Loa’s summit magma storage system includes at least two interconnected reservoirs, with one centered beneath the south margin of the caldera and the other elongated along the axis of the caldera. Transport of magma within shield-stage Hawaiian volcanoes occurs through dikes that can evolve into long-lived pipe-like pathways. The ratio of eruptive to noneruptive dikes is large in Hawai‘i, compared to other basaltic volcanoes (in Iceland, for example), because Hawaiian dikes tend to be intruded with high driving pressures. Passive dike intrusions also occur, motivated at Kīlauea by rift opening in response to seaward slip of the volcano’s south flank.

Repeated magmatic intrusions at El Hierro Island following the 2011-2012 submarine eruption

NASA Astrophysics Data System (ADS)

Benito-Saz, Maria A.; Parks, Michelle M.; Sigmundsson, Freysteinn; Hooper, Andrew; García-Cañada, Laura

2017-09-01

After more than 200 years of quiescence, in July 2011 an intense seismic swarm was detected beneath the center of El Hierro Island (Canary Islands), culminating on 10 October 2011 in a submarine eruption, 2 km off the southern coast. Although the eruption officially ended on 5 March 2012, magmatic activity continued in the area. From June 2012 to March 2014, six earthquake swarms, indicative of magmatic intrusions, were detected underneath the island. We have studied these post-eruption intrusive events using GPS and InSAR techniques to characterize the ground surface deformation produced by each of these intrusions, and to determine the optimal source parameters (geometry, location, depth, volume change). Source inversions provide insight into the depth of the intrusions ( 11-16 km) and the volume change associated with each of them (between 0.02 and 0.13 km3). During this period, > 20 cm of uplift was detected in the central-western part of the island, corresponding to approximately 0.32-0.38 km3 of magma intruded beneath the volcano. We suggest that these intrusions result from deep magma migrating from the mantle, trapped at the mantle/lower crust discontinuity in the form of sill-like bodies. This study, using joint inversion of GPS and InSAR data in a post-eruption period, provides important insight into the characteristics of the magmatic plumbing system of El Hierro, an oceanic intraplate volcanic island.

Drilling Magma for Science, Volcano Monitoring, and Energy

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Lavallée, Y.; Blankenship, D.

2017-12-01

Magma chambers are central to understanding magma evolution, formation of continental crust, volcanism, and renewal of hydrothermal systems. Information from geology, petrology, laboratory experiments, and geophysical imagery has led to little consensus except a trend to see magma systems as being crystal-dominant (mush) rather than melt dominant. At high melt viscosities, crystal-liquid fractionation may be achieved by separation of melt from mush rather than crystals from liquid suspension. That the dominant volume has properties more akin to solid than liquid might explain the difficulty in detecting magma geophysically. Recently, geothermal drilling has intersected silicic magma at the following depths and SiO2 contents are: Puna, Hawaii, 2.5 km, 67 wt%; Menengai, Kenya 2.1 km, 67 wt%; Krafla, Iceland, 2.1 km, 75 wt%. Some similarities are: 1) Drillers encountered a "soft", sticky formation; 2) Cuttings or chips of clear quenched glass were recovered; 3) The source of the glass flowed up the well; 4) Transition from solid rock to recovering crystal-poor glass occurred in tens of meters, apparently without an intervening mush zone. Near-liquidus magma at the roof despite rapid heat loss there presents a paradox that may be explained by very recent intrusion of magma, rise of liquidus magma to the roof replacing partially crystallized magma, or extremely skewed representation of melt over mush in cuttings (Carrigan et al, this session). The latter is known to occur by filter pressing of ooze into lava lake coreholes (Helz, this session), but cannot be verified in actual magma without coring. Coring to reveal gradients in phase composition and proportions is required for testing any magma chamber model. Success in drilling into and controlling magma at all three locations, in coring lava lakes to over 1100 C, and in numerical modeling of coring at Krafla conditions (Su, this session) show this to be feasible. Other unprecedented experiments are using the known

Rapid thermal rejuvenation of high-crystallinity magma linked to porphyry copper deposit formation; evidence from the Koloula Porphyry Prospect, Solomon Islands

NASA Astrophysics Data System (ADS)

Tapster, S.; Condon, D. J.; Naden, J.; Noble, S. R.; Petterson, M. G.; Roberts, N. M. W.; Saunders, A. D.; Smith, D. J.

2016-05-01

Magmas containing the components needed to form porphyry copper deposits are relatively common within arcs, yet mineralising events are uncommon within the long-lived magmatic systems that host them. Understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models. We have constrained the tempo of pre- and syn-mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world's youngest exposed plutonic-porphyry systems, the Inamumu Zoned Pluton, Koloula Porphyry Prospect, Solomon Islands. High precision ID-TIMS U-Pb dates of texturally and chemically characterised zircons indicate pluton emplacement over <150 kyr was superseded after ca. 50 kyr by two discrete episodes of mineralising porphyritic melt emplacement. Their associated hydrothermal systems initiated within ca. 30 kyrs of each other. Zircon populations within evolved intrusions contain resorbed cores that were recycled from the deeper magmatic system, yet their youngest dates are statistically indistinguishable from those yielded by crystals lacking resorption. Comparisons of Ti-in-zircon proxy temperatures, modelled zircon saturation temperatures and temperature-crystallinity relationships suggest that prior to being heated and emplaced within the shallow level pluton, magmas were stored at depth in a high-crystallinity (>50% crystals) state, past the point of rheological lock-up. We estimate that thermal rejuvenation of the deeper high-crystallinity magma and generation of a mobile melt fraction may have occurred ≤10 kyr before its transport and emplacement within the porphyry environment. The underlying pluton likely cooled and returned to high-crystallinity states prior to subsequent remobilisation-emplacement events. Titanium-in-zircon geothermometry and whole-rock geochemistry suggest pre-mineralisation intrusions were remobilised by mixing of a silicic magma with a

Long-period seismicity reveals magma pathways above a laterally propagating dyke during the 2014-15 Bárðarbunga rifting event, Iceland

NASA Astrophysics Data System (ADS)

Woods, Jennifer; Donaldson, Clare; White, Robert S.; Caudron, Corentin; Brandsdóttir, Bryndís; Hudson, Thomas S.; Ágústsdóttir, Thorbjörg

2018-05-01

The 2014-15 Bárðarbunga-Holuhraun rifting event comprised the best-monitored dyke intrusion to date and the largest eruption in Iceland in 230 years. A huge variety of seismicity was produced, including over 30,000 volcano-tectonic earthquakes (VTs) associated with the dyke propagation at ∼6 km depth below sea level, and large-magnitude earthquakes accompanying the collapse of Bárðarbunga caldera. We here study the long-period seismicity associated with the rifting event. We systematically detect and locate both long-period events (LPs) and tremor during the dyke propagation phase and the first week of the eruption. We identify clusters of highly similar, repetitive LPs, which have a peak frequency of ∼1 Hz and clear P and S phases followed by a long-duration coda. The source mechanisms are remarkably consistent between clusters and also fundamentally different to those of the VTs. We accurately locate LP clusters near each of three ice cauldrons (depressions formed by basal melting) that were observed on the surface of Dyngjujökull glacier above the path of the dyke. Most events are in the vicinity of the northernmost cauldron, at shallower depth than the VTs associated with lateral dyke propagation. At the two northerly cauldrons, periods of shallow seismic tremor following the clusters of LPs are also observed. Given that the LPs occur at ∼4 km depth and in swarms during times of dyke-stalling, we infer that they result from excitation of magmatic fluid-filled cavities and indicate magma ascent. We suggest that the tremor is the climax of the vertical melt movement, arising from either rapid, repeated excitation of the same LP cavities, or sub-glacial eruption processes. This long-period seismicity therefore represents magma pathways between the depth of the dyke-VT earthquakes and the surface. Notably, we do not detect tremor associated with each cauldron, despite melt reaching the base of the overlying ice cap, a concern for hazard monitoring.

Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes.

PubMed

Passarelli, L; Rivalta, E; Shuler, A

2014-01-28

As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process.

Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes

PubMed Central

L., Passarelli; E., Rivalta; A., Shuler

2014-01-01

As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process. PMID:24469260

Ephemeral magma chambers in the Trinity peridotite, northern California

NASA Astrophysics Data System (ADS)

Cannat, Mathilde; Lécuyer, Christophe

1991-02-01

The Trinity Massif comprises the major lithologies of an ophiolite, as defined at the 1972 Penrose conference. Previous studies have shown, however, that it differs from the Semail (Oman) or Table Mountain (Newfoundland) ophiolitic massifs, particularly because its crustal section is thin, and because its mantle section has vertical plastic flow planes. These features have led to an interpretation of the Trinity Massif as a fragment of slow-spreading oceanic lithosphere (Le Sueur et al., 1984; Boudier and Nicolas, 1985). In this paper, we show that the Trinity gabbros occur in discontinuous, kilometre-sized pockets, intrusive into the mantle peridotites. The internal stratigraphy and the petrological characteristics of these gabbros suggest that they formed in short-lived magma chambers. These ephemeral magma chambers developed after the end of the plastic deformation in the surrounding mantle, when it had cooled down to lithospheric temperatures. We discuss the possibility that these small and ephemeral magma chambers formed at a slow-spreading oceanic ridge.

Highly differentiated magmas linked with polymetallic mineralization: A case study from the Cuihongshan granitic intrusions, Lesser Xing'an Range, NE China

NASA Astrophysics Data System (ADS)

Fei, Xianghui; Zhang, Zhaochong; Cheng, Zhiguo; Santosh, M.; Jin, Ziliang; Wen, Bingbing; Li, Zixi; Xu, Lijuan

2018-03-01

The genetic link between granitoids and polymetallic skarn mineralization has remained equivocal. The Cuihongshan skarn-porphyry W-Mo-Pb-Zn-(Fe-Cu) deposit in the eastern part of the Central Asian Orogenic Belt provides a unique example to address this issue. The major rock types in the mine area are Early Paleozoic intrusions composed of biotite syenogranite and biotite porphyritic granite and Early Mesozoic intrusions represented by porphyritic quartz monzonite, biotite monzogranite, and porphyritic granite. The diagnostic mineralogical and geochemical features indicate that the rocks belong to A2-type granites. The Early Paleozoic suite shows zircon U-Pb ages of 501 Ma, and εHf(t) values of - 4.4 to + 2.7 and + 2.4 to + 7.6, respectively. In combination with their coherent geochemical trends, these rocks are inferred to be products of in-situ differentiation. Although the Mesozoic suite shows crystallization ages of 194-196 Ma, εHf(t) values are in the range of - 2.5 to + 7.5 for the porphyritic quartz monzonite, the - 1.8 to + 4.5 values for the monzogranite and the + 2.3 to + 8.0 range for the porphyritic granite. The porphyritic quartz monzonite displays distinct mineral assemblage and shows significant compositional gap with the other two lithofacies. In contrast, the monzogranite and porphyritic granite have similar geochemical features, and are thus inferred to be co-magmatic. Considering the high SiO2 contents, variable εHf(t) (- 4.4 to + 8.0) and εNd(t) values (- 8.4 to + 0.28) for the two suites, we infer that both episodes of granitoid magmatism resulted from partial melting of crustal materials with a mixed source containing varying proportions of juvenile and Precambrian crustal components. The Early Mesozoic porphyritic granite shows a highly evolved F-rich geochemical affinity, and experienced magma-fluid interaction. Cassiterite from the calcic skarn and the magnesian skarn that coexists with magnetite orebodies shows a mean U-Pb age of 195

Igneous intrusion models for floor fracturing in lunar craters

NASA Technical Reports Server (NTRS)

Wichman, R. W.; Schultz, P. H.

1991-01-01

Lunar floor-fractured craters are primarily located near the maria and frequently contain ponded mare units and dark mantling deposits. Fracturing is confined to the crater interior, often producing a moat-like feature near the floor edge, and crater depth is commonly reduced by uplift of the crater floor. Although viscous relaxation of crater topography can produce such uplift, the close association of modification with surface volcanism supports a model linking floor fracture to crater-centered igneous intrusions. The consequences of two intrusion models for the lunar interior are quantitatively explored. The first model is based on terrestrial laccoliths and describes a shallow intrusion beneath the crater. The second model is based on cone sheet complexes where surface deformation results from a deeper magma chamber. Both models, their fit to observed crater modifications and possible implications for local volcanism are described.

Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California

USGS Publications Warehouse

Underwood, S.J.; Feeley, T.C.; Clynne, M.A.

2012-01-01

Hydrogen isotope ratio, water content and Fe3 +/Fe2 + in coexisting amphibole and biotite phenocrysts in volcanic rocks can provide insight into shallow pre- and syn-eruptive magmatic processes such as vesiculation, and lava drainback with mixing into less devolatilized magma that erupts later in a volcanic sequence. We studied four ~ 35 ka and younger eruption sequences (i.e. Kings Creek, Lassen Peak, Chaos Crags, and 1915) at the Lassen Volcanic Center (LVC), California, where intrusion of crystal-rich silicic magma mushes by mafic magmas is inferred from the varying abundances of mafic magmatic inclusions (MMIs) in the silicic volcanic rocks. Types and relative proportions of reacted and unreacted hydrous phenocryst populations are evaluated with accompanying chemical and H isotope changes. Biotite phenocrysts were more susceptible to rehydration in older vesicular glassy volcanic rocks than coexisting amphibole phenocrysts. Biotite and magnesiohornblende phenocrysts toward the core of the Lassen Peak dome are extensively dehydroxylated and reacted from prolonged exposure to high temperature, low pressure, and higher fO2 conditions from post-emplacement cooling. In silicic volcanic rocks not affected by alteration, biotite phenocrysts are often relatively more dehydroxylated than are magnesiohornblende phenocrysts of similar size; this is likely due to the ca 10 times larger overall bulk H diffusion coefficient in biotite. A simplified model of dehydrogenation in hydrous phenocrysts above reaction closure temperature suggests that eruption and quench of magma ascended to the surface in a few hours is too short a time for substantial H loss from amphibole. In contrast, slowly ascended magma can have extremely dehydrogenated and possibly dehydrated biotite, relatively less dehydrogenated magnesiohornblende and reaction rims on both phases. Eruptive products containing the highest proportions of mottled dehydrogenated crystals could indicate that within a few days

Dissolved volatile concentrations in an ore-forming magma

USGS Publications Warehouse

Lowenstern, J. B.

1994-01-01

Infrared spectroscopic measurements of glass inclusions within quartz phenocrysts from the Plinian fallout of the 22 Ma tuff of Pine Grove show that the trapped silicate melt contained high concentrations of H2O and CO2. Intrusive porphyries from the Pine Grove system are nearly identical in age, composition, and mineralogy to the tephra, and some contain high-grade Mo mineralization. Assuming that the porphyry magmas originally contained similar abundances of volatile components as the erupted rocks, they would have been saturated with fluid at pressures far greater than those at which the porphyries were emplaced and mineralized. The data are consistent with formation of Climax-type Mo porphyry deposits by prolonged fluid flux from a large volume of relatively Mo-poor (1-5 ppm) magma. -from Author

Volcanic-plutonic connections and metal fertility of highly evolved magma systems: A case study from the Herberton Sn-W-Mo Mineral Field, Queensland, Australia

NASA Astrophysics Data System (ADS)

Cheng, Yanbo; Spandler, Carl; Chang, Zhaoshan; Clarke, Gavin

2018-03-01

Understanding the connection between the highly evolved intrusive and extrusive systems is essential to explore the evolution of high silicic magma systems, which plays an important role in discussions of planetary differentiation, the growth of continents, crustal evolution, and the formation of highly evolved magma associated Sn-W-Mo mineral systems. To discern differences between "fertile" and "non-fertile" igneous rocks associated with Sn-W-Mo mineralization and reveal the genetic links between coeval intrusive and extrusive rocks, we integrate whole rock geochemistry, geochronology and Hf isotope signatures of igneous zircons from contemporaneous plutonic and volcanic rocks from the world-class Herberton Mineral Field of Queensland, Australia. The 310-300 Ma intrusive rocks and associated intra-plutonic W-Mo mineralization formed from relatively oxidized magmas after moderate degrees of crystal fractionation. The geochemical and isotopic features of the coeval volcanic succession are best reconciled utilizing the widely-accepted volcanic-plutonic connection model, whereby the volcanic rocks represent fractionated derivatives of the intrusive rocks. Older intrusions emplaced at 335-315 Ma formed from relatively low fO2 magmas that fractionated extensively to produce highly evolved granites that host Sn mineralization. Coeval volcanic rocks of this suite are compositionally less evolved than the intrusive rocks, thereby requiring a different model to link these plutonic-volcanic sequences. In this case, we propose that the most fractionated magmas were not lost to volcanism, but instead were effectively retained at the plutonic level, which allowed further localized build-up of volatiles and lithophile metals in the plutonic environment. This disconnection to the volcanism and degassing may be a crucial step for forming granite-hosted Sn mineralization. The transition between these two igneous regimes in Herberton region over a ∼30 m.y. period is attributed to

Magma degassing triggered by static decompression at Kīlauea Volcano, Hawai‘i

USGS Publications Warehouse

Poland, Michael P.; Jeff, Sutton A.; Gerlach, Terrence M.

2009-01-01

During mid-June 2007, the summit of Kīlauea Volcano, Hawai‘i, deflated rapidly as magma drained from the subsurface to feed an east rift zone intrusion and eruption. Coincident with the deflation, summit SO2 emission rates rose by a factor of four before decaying to background levels over several weeks. We propose that SO2 release was triggered by static decompression caused by magma withdrawal from Kīlauea's shallow summit reservoir. Models of the deflation suggest a pressure drop of 0.5–3 MPa, which is sufficient to trigger exsolution of the observed excess SO2 from a relatively small volume of magma at the modeled source depth beneath Kīlauea's summit. Static decompression may also explain other episodes of deflation accompanied by heightened gas emission, including the precursory phases of Kīlauea's 2008 summit eruption. Hazards associated with unexpected volcanic gas emission argue for increased awareness of magma reservoir pressure fluctuations.

On the relation between crustal deformation and seismicity during the 2012-2014 magmatic intrusions in El Hierro island.

NASA Astrophysics Data System (ADS)

Domínguez Cerdeña, Itahiza; García-Cañada, Laura; Ángeles Benito Saz, María; Del Fresno, Carmen

2017-04-01

The last volcanic eruption in the Canary Islands took place in 2011 less than 2 km offshore El Hierro island, after 3 months of measuring surface deformation (up to 5 cm) and locating more than 10 000 earthquakes. In the two years following the end of the submarine eruption on 5 March 2012, six deep magmatic intrusions were recorded beneath the island. Despite the short time duration of these intrusions, these events have been more energetic that the 2011 pre-eruptive intrusive event but none of them ended in a new eruption. These post-eruptive reactivations are some of the few examples in the world of well monitored magmatic intrusions related with monogenetic volcanism. In order to understand these processes we have analyzed the geodetic and seismic data with different techniques. First, we did a joint hypocentral relocation of the six seismic swarms, including more than 6 300 events, to analyze the relative distribution of the earthquakes from different intrusions. The uncertainties of the earthquakes relocations was reduced to an average value of 300 m. New earthquakes' distribution shows the alignments of the different intrusions and a temporal migration of the events to larger depths. Moreover, we show the results of the ground deformation using GPS data from the network installed on the island (for each of the six intrusive events) and their inversion considering spherical models. In most of the intrusions the optimal source model was shallower and southern than the corresponding seismicity hypocenters. The intruded magma volume ranges from 0.02 to 0.13 km3. Finally, we also computed the b value from the Gutenberg Richter equation by means of a bootstrap method. The spatial and temporal evolution of the b value for the seismicity show a clear correlation with the temporal evolution of the crustal deformation. The six magma intrusions can be grouped, depending on their location, in three pairs each one associated with each of the three active rifts of El

Dike Intrusion Process of 2000 Miyakejima - Kozujima Event estimated from GPS measurements in Kozujima - Niijima Islands, central Japan

NASA Astrophysics Data System (ADS)

Murase, M.; Nakao, S.; Kato, T.; Tabei, T.; Kimata, F.; Fujii, N.

2003-12-01

Kozujima - Niijima Islands of Izu Volcano Islands are located about 180 km southeast of Tokyo, Japan. Although the last volcano eruptions in Kozujima and Niijima volcanoes are recorded more than 1000 year before, the ground deformation of 2-3 cm is detected at Kozujima - Niijima Islands by GPS measurements since 1996. On June 26, 2000, earthquake swarm and large ground deformation more than 20 cm are observed at Miyakejima volcano located 40 km east-southeastward of Kozu Island, and volcano eruption are continued since July 7. Remarkable earthquake swarm including five earthquakes more than M5 is stretching to Kozushima Island from Miyakejima Island. From the rapid ground deformation detected by continuous GPS measurements at Miyakejima Island on June 26, magma intrusion models of two or three dikes are discussed in the south and west part of Miyakejima volcano by Irwan et al.(2003) and Ueda et al.(2003). They also estimate dike intrusions are propagated from southern part of Miyakejima volcano to western part, and finally dike intrusion is stretching to 20 km distance toward Kozujima Island. From the ground deformation detected by GPS daily solution of Nation-wide dense GPS network (GEONET), some dike intrusion models are discussed. Ito et al.(2002) estimate the huge dike intrusion with length of about 20 km and volume of 1 km3 in the sea area between the Miyake Island and Kozu Island. (And) Nishimura et al.(2001) introduce not only dike but also aseismic creep source to explain the deformation in Shikinejima. Yamaoka et al.(2002) discuss the dike and spherical deflation source under the dike, because of no evidence supported large aseismic creep. They indicate a dike and spherical deflation source model is as good as dike and creep source model. In case of dike and creep, magma supply is only from the chamber under the Miyakejima volcano. In dike and spherical deflation source model, magma supply is from under Miyakejima volcano and under the dike. Furuya et al

Magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Lie-Meng; Teng, Fang-Zhen; Song, Xie-Yan; Hu, Rui-Zhong; Yu, Song-Yue; Zhu, Dan; Kang, Jian

2018-04-01

Magnesium isotopic compositions of olivine, clinopyroxene, and ilmenite from the Baima intrusion, SW China, for the first time, are investigated to constrain the magnitude and mechanisms of Mg isotope fractionation among cumulus minerals in layered mafic intrusions and to evaluate their geological implications. Olivine and clinopyroxene have limited Mg isotope variations, with δ26Mg ranging from -0.33 to +0.05‰ and from -0.29 to -0.13‰, respectively, similar to those of mantle xenolithic peridotites. By contrast, ilmenites display extremely large Mg isotopic variation, with δ26Mg ranging from -0.50 to +1.90‰. The large inter-mineral fractionations of Mg isotopes between ilmenite and silicates may reflect both equilibrium and kinetic processes. A few ilmenites have lighter Mg isotopic compositions than coexisting silicates and contain high MgO contents without compositional zoning, indicating equilibrium fractionation. The implication is that the light Mg isotopic compositions of lunar high-Ti basalts may result from an isotopically light source enriched in cumulate ilmenites. On the other hand, most ilmenites have heavy Mg isotopic compositions, coupled with high MgO concentration and chemical zoning, which can be quantitatively modeled by kinetic Mg isotope fractionations induced by subsolidus Mg-Fe exchange between ilmenite and ferromagnesian silicates during the cooling of the Baima intrusion. The extensive occurrence of kinetic Mg isotope fractionation in ilmenites implies the possibility of widespread compositional disequilibrium among igneous minerals in magma chambers. Consequently, disequilibrium effects need to be considered in studies of basaltic magma evolution, magma chamber processes, and magmatic Fe-Ti oxide ore genesis.

Seismic Tremors and Three-Dimensional Magma Wagging

NASA Astrophysics Data System (ADS)

Liao, Y.; Bercovici, D.

2015-12-01

Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

The Fish Canyon magma body, San Juan volcanic field, Colorado: Rejuvenation and eruption of an upper-crustal batholith

USGS Publications Warehouse

Bachmann, Olivier; Dungan, M.A.; Lipman, P.W.

2002-01-01

More than 5000 km3 of nearly compositionally homogeneous crystalrich dacite (~68 wt % SiO2: ~45% Pl + Kfs + Qtz + Hbl + Bt + Spn + Mag + Ilm + Ap + Zrn + Po) erupted from the Fish Canyon magma body during three phases: (1) the pre-caldera Pagosa Peak Dacite (an unusual poorly fragmented pyroclastic deposit, ~ 200 km3); (2) the syn-collapse Fish Canyon Tuff (one of the largest known ignimbrites, ~ 5000 km3); (3) the post-collapse Nutras Creek Dacite (a volumetrically minor lava). The late evolution of the Fish Canyon magma is characterized by rejuvenation of a near-solidus upper-crustal intrusive body (mainly crystal mush) of batholithic dimensions. The necessary thermal input was supplied by a shallow intrusion of more mafic magma represented at the surface by sparse andesitic enclaves in late-erupted Fish Canyon Tuff and by the post-caldera Huerto Andesite. The solidified margins of this intrusion are represented by holocrystalline xenoliths with Fish Canyon mineralogy and mineral chemistry and widely dispersed partially remelted polymineralic aggregates, but dehydration melting was not an important mechanism in the rejuvenation of the Fish Canyon magma. Underlying mafic magma may have evolved H2O-F-S-Cl-rich fluids that fluxed melting in the overlying crystal mush. Manifestations of the late up-temperature magma evolution are: (1) resorbed quartz, as well as feldspars displaying a wide spectrum of textures indicative of both resorption and growth, including Rapakivi textures and reverse growth zoning (An27-28 to An32-33) at the margins of many plagioclase phenocrysts; (2) high Sr, Ba, and Eu contents in the high-SiO2 rhyolite matrix glass, which are inconsistent with extreme fractional crystallization of feldspar; (3) oscillatory and reverse growth zoning toward the margins of many euhedral hornblende phenocrysts (rimward increases from ~5??5-6 to 7??7-8??5 wt % Al2O3). Homogeneity in magma composition at the chamber-wide scale, contrasting with extreme textural

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

NASA Astrophysics Data System (ADS)

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen G.; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages. The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

USGS Publications Warehouse

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages.The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The

Fracturing of doleritic intrusions and associated contact zones: Implications for fluid flow in volcanic basins

NASA Astrophysics Data System (ADS)

Senger, Kim; Buckley, Simon J.; Chevallier, Luc; Fagereng, Åke; Galland, Olivier; Kurz, Tobias H.; Ogata, Kei; Planke, Sverre; Tveranger, Jan

2015-02-01

Igneous intrusions act as both carriers and barriers to subsurface fluid flow and are therefore expected to significantly influence the distribution and migration of groundwater and hydrocarbons in volcanic basins. Given the low matrix permeability of igneous rocks, the effective permeability in- and around intrusions is intimately linked to the characteristics of their associated fracture networks. Natural fracturing is caused by numerous processes including magma cooling, thermal contraction, magma emplacement and mechanical disturbance of the host rock. Fracturing may be locally enhanced along intrusion-host rock interfaces, at dyke-sill junctions, or at the base of curving sills, thereby potentially enhancing permeability associated with these features. In order to improve our understanding of fractures associated with intrusive bodies emplaced in sedimentary host rocks, we have investigated a series of outcrops from the Karoo Basin of the Eastern Cape province of South Africa, where the siliciclastic Burgersdorp Formation has been intruded by various intrusions (thin dykes, mid-sized sheet intrusions and thick sills) belonging to the Karoo dolerite. We present a quantified analysis of fracturing in- and around these igneous intrusions based on five outcrops at three individual study sites, utilizing a combination of field data, high-resolution lidar virtual outcrop models and image processing. Our results show a significant difference between the three sites in terms of fracture orientation. The observed differences can be attributed to contrasting intrusion geometries, outcrop geometry (for lidar data) and tectonic setting. Two main fracture sets were identified in the dolerite at two of the sites, oriented parallel and perpendicular to the contact respectively. Fracture spacing was consistent between the three sites, and exhibits a higher degree of variation in the dolerites compared to the host rock. At one of the study sites, fracture frequency in the

Gravity and the mechanics of dike intrusion

NASA Astrophysics Data System (ADS)

Townsend, M.

2017-12-01

Dikes are a diverse yet ubiquitous feature of terrestrial volcanic and magmatic settings, ranging in size from decimeter-thick aplite dikes in silicic plutons, to meters-thick dikes at basaltic shield volcanoes and rift zones, to 100-meter-thick "giant" dikes in swarms that can exceed over 2000 km in length. Dike profiles may be planar or curved, elliptical or teardrop-shaped, and blunt or tapered at the tips. The variety of size, shape, composition, and intrusion environment is in contrast with the ubiquitous observation that dikes tend to be vertically inclined, emanate from central reservoirs, and propagate laterally for distances that are 10 to over 100 times their height. In this talk, I will briefly review the geological and geophysical observations of dike geometry and propagation directions. These data motivate a 2D mechanical model for vertical dikes in which the primary loading is due to gravity. Using this model, I will explore fundamental relationships between density structure within the magma and surrounding crust, driving pressure, topographic and tectonic loading, and the size, shape, and depth at which dikes become vertically stable such that subsequent propagation is lateral. Modeling results highlight a dual effect of gravity, as both a source of diversity in stable dike geometries and as a robust mechanism for trapping dikes in the subsurface.

Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

NASA Astrophysics Data System (ADS)

Andersen, Jens C. Ø.; Rollinson, Gavyn K.; McDonald, Iain; Tegner, Christian; Lesher, Charles E.

2017-08-01

Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1-2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10-50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110-220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.

Degassing system from the magma reservoir of Miyakejima volcano revealed by GPS observations

NASA Astrophysics Data System (ADS)

Oikawa, J.; Nakao, S.; Matsushima, T.

2013-12-01

Miyake-jima is a volcanic island located approximately 180 km south of Tokyo. The island is an active basaltic volcano that was dormant for a 17-year period between an eruption in 1983 and June 26, 2000, when it again became active. The volcanic activity that occurred in 2000 is divided into the following four stages: the magma intrusion stage, summit subsidence stage, summit eruptive stage, and degassing stage (Nakada et al., 2001). Earthquake swarm activity began on June 26, 2000, accompanied by large-scale crustal deformation. This led to a summit eruption on July 8, 2000. Based on the pattern of hypocenter migration and the nature of crustal deformation, it was estimated that magma migrated from beneath the summit of Miyake-jima to the northwest during the magma intrusion stage. The rapid collapse of the summit took place between July 8 and the beginning of August 2000 (summit subsidence stage). Large-scale eruptions took place on August 10, 18, and 29, 2000 (explosion stage). The eruptions largely ceased after August 29, followed by the release of large amounts of gas from the summit crater (degassing stage). In this study, we examined the location of the magma reservoir during the degassing stage based on crustal deformation observed by GPS. By comparing the amounts of degassing and volume change of the magma reservoir, as determined from crustal deformation, we determined the mechanism of degassing and the nature of the magma reservoir-vent system. According to observations by the Japan Meteorological Agency, a large amount of volcanic gas began to be released from Miyake-jima in September 2000 (Kazahaya et al., 2003). Approximately 42,000 tons/day of SO2 was released during the period between September 2000 and January 2001. Analysis of GPS data during the period [Figure 1] indicates a source of crustal deformation on the south side of the summit crater wall at a depth of 5.2 km. The rate of volume change was -3.8 x 106 m3/month [Figure 2]. As the volume is

Magma deformation and emplacement in rhyolitic dykes

NASA Astrophysics Data System (ADS)

McGowan, Ellen; Tuffen, Hugh; James, Mike; Wynn, Peter

2016-04-01

Silicic eruption mechanisms are determined by the rheological and degassing behaviour of highly-viscous magma ascending within shallow dykes and conduits. However, we have little knowledge of how magmatic behaviour shifts during eruptions as dykes and conduits evolve. To address this we have analysed the micro- to macro-scale textures in shallow, dissected rhyolitic dykes at the Tertiary Húsafell central volcano in west Iceland. Dyke intrusion at ~3 Ma was associated with the emplacement of subaerial rhyolitic pyroclastic deposits following caldera formation[1]. The dykes are dissected to ~500 m depth, 2-3 m wide, and crop out in two stream valleys with 5-30 m-long exposures. Dykes intrude diverse country rock types, including a welded ignimbrite, basaltic lavas, and glacial conglomerate. Each of the six studied dykes is broadly similar, exhibiting obsidian margins and microcrystalline cores. Dykes within pre-fractured lava are surrounded by external tuffisite vein networks, which are absent from dykes within conglomerate, whereas dykes failed to penetrate the ignimbrite. Obsidian at dyke margins comprises layers of discrete colour. These display dramatic thickness variations and collapsed bubble structures, and are locally separated by zones of welded, brecciated and flow-banded obsidian. We use textural associations to present a detailed model of dyke emplacement and evolution. Dykes initially propagated with the passage of fragmented, gas-charged magma and generation of external tuffisite veins, whose distribution was strongly influenced by pre-existing fractures in the country rock. External tuffisites retained permeability throughout dyke emplacement due to their high lithic content. The geochemically homogenous dykes then evolved via incremental magma emplacement, with shear deformation localised along emplacement boundary layers. Shear zones migrated between different boundary layers, and bubble deformation promoted magma mobility. Brittle

On the conditions of magma mixing and its bearing on andesite production in the crust.

PubMed

Laumonier, Mickael; Scaillet, Bruno; Pichavant, Michel; Champallier, Rémi; Andujar, Joan; Arbaret, Laurent

2014-12-15

Mixing between magmas is thought to affect a variety of processes, from the growth of continental crust to the triggering of volcanic eruptions, but its thermophysical viability remains unclear. Here, by using high-pressure mixing experiments and thermal calculations, we show that hybridization during single-intrusive events requires injection of high proportions of the replenishing magma during short periods, producing magmas with 55-58 wt% SiO2 when the mafic end-member is basaltic. High strain rates and gas-rich conditions may produce more felsic hybrids. The incremental growth of crustal reservoirs limits the production of hybrids to the waning stage of pluton assembly and to small portions of it. Large-scale mixing appears to be more efficient at lower crustal conditions, but requires higher proportions of mafic melt, producing more mafic hybrids than in shallow reservoirs. Altogether, our results show that hybrid arc magmas correspond to periods of enhanced magma production at depth.

Magma ascent and emplacement in a continental rift setting: lessons from alkaline complexes in active and ancient rift zones

NASA Astrophysics Data System (ADS)

Hutchison, William; Lloyd, Ryan; Birhanu, Yelebe; Biggs, Juliet; Mather, Tamsin; Pyle, David; Lewi, Elias; Yirgu, Gezahgen; Finch, Adrian

2017-04-01

A key feature of continental rift evolution is the development of large chemically-evolved alkaline magmatic systems in the shallow crust. At active alkaline systems, for example in the East African Rift, the volcanic complexes pose significant hazards to local populations but can also sustain major geothermal resources. In ancient rifts, for example the Gardar province in Southern Greenland, these alkaline magma bodies can host some of the world's largest rare element deposits in resources such as rare earths, niobium and tantalum. Despite their significance, there are major uncertainties about how such magmas are emplaced, the mechanisms that trigger eruptions and the magmatic and hydrothermal processes that generate geothermal and mineral resources. Here we compare observations from active caldera volcanoes in the Ethiopian Rift with compositionally equivalent ancient (1300-1100 Ma) plutonic systems in the Gardar Rift province (Greenland). In the Ethiopian Rift Valley we use InSAR and GPS data to evaluate the temporal and spatial evolution of ground deformation at Aluto and Corbetti calderas. We show that unrest at Aluto is characterized by short (3-6 month) accelerating uplift pulses likely caused by magmatic fluid intrusion at 5 km. At Corbetti, uplift is steady ( 6.6 cm/yr) and sustained over many years with analytical source models suggesting deformation is linked to sill intrusion at depths of 7 km. To evaluate the validity of these contrasting deformation mechanisms (i.e. magmatic fluid intrusion and sill emplacement) we carried out extensive field, structural and geochemical analysis in the roof zones of two alkaline plutons (Ilímaussaq and Motzfeldt) in Greenland. Our results show that the volatile contents (F, Cl, OH and S) of these magmas were exceptionally high and that there is evidence for ponding of magmatic fluids in the roof zone of the magma reservoir. We also identified extensive sill networks at the contact between the magma reservoir and the

Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

USGS Publications Warehouse

Chang, Wu-Lung; Smith, Robert B.; Wicks, Charles; Farrell, J.M.; Puskas, C.M.

2007-01-01

The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

Petrological evidence for non-linear increase of magmatic intrusion rates before eruption at open vent mafic volcanoe

NASA Astrophysics Data System (ADS)

Ruth, D. C. S.; Costa Rodriguez, F.

2015-12-01

The most active volcanoes on earth erupt in a yearly to decadal time scales, typically erupt mafic magmas and are open-vent systems with prominent degassing plumes (e.g. Mayon, Arenal, Llaima, Etna). Here we investigate the plumbing systems, dynamics, and processes that drive eruptions at these systems. These are key questions for improving hazard evaluation, and better understanding the unrest associated with these types of volcanoes. The petrology and geochemistry from six historical eruptions (1947-2006) of Mayon volcano (Philippines) shows that all lavas are basaltic andesite with phenocrysts of plagioclase + orthopyroxene (Opx) + clinopyroxene. Opx crystals show a variety of compositions and zoning patterns (reverse, normal or complex) with Mg# (= 100 *Mg/[Mg+Fe]) varying from 67 to 81. The simplest interpretation is that the low Mg# parts of the crystals resided on an upper crustal and crystal rich reservoir that was intruded by more primitive magmas from which the high Mg# parts of the crystals grew. Modelling Mg-Fe diffusion in Opx shows that times since magma injection and eruption range from a few days up to 3.5 years in all of the investigated eruptions. The longest diffusion times are shorter than the repose times between the eruptions, which implies that crystal recycling between eruptive events is negligible. This is a surprising result that shows that for each eruption a different part of the evolved crystal-rich plumbing system is activated. This can be due to random intrusion location or an irreversibility of the plumbing system that prevents multiple eruptions from the same crystal-rich part. Moreover, we find that the number of intrusions markedly increases before each eruption in a non-linear manner. Such an increased rate of intrusions with time might reflect non-linear rheological properties of the crystal-rich system, of the enclosing rocks, or the non-linear evolution of crystal-melt reaction-dissolution fronts during magma intrusions.

Lateral variation of H2O/K2O ratios in Quaternary Magma of the Northeastern Japan arc

NASA Astrophysics Data System (ADS)

Miyagi, I.

2012-12-01

Water plays a fundamental role in the magma genesis beneath subduction zones. In order to estimate a spatial distribution of the density of water flux in the wedge mantle of the Northeastern Japan arc, this study examines a lateral variation of pre-eruptive bulk rock H2O/K2O contents among volcanoes located both in the frontal and in back arc settings. The analytical targets are the frontal volcanoes Nigorikawa (N42.12 E140.45), Zenikame (N41.74 E140.85), Adachi (N38.22 E140.65), and Nanashigure (N40.07 E141.11), and the back arc ones Hijiori (N38.61 E140.17) and Kanpu (N39.93 E139.88). The bulk magmatic H2O content (TH2O) is calculated from a mass balance of hydrogen isotopic ratios among three phases in a batch of magma; dissolved water in melt, excess H2O vapor, and hydrous phenocrysts such as amphiboles (Miyagi and Matsubaya, 2003). Since the amount of H2O in hydrous phenocryst is negligible, the bulk magmatic H2O content can be written as TH2O = (30 XD CD) / (15 - dT + dMW), where dMW is the measured hydrogen isotopic ratio of hydrous phenocrysts, XD is a melt fraction of magma, CD is a water concentration of the melt, and dT is hydrogen isotopic ratios of a bulk magma (assumed to be -50 per-mil). Both XD and CD are estimated from bulk rock chemistry of the sample using the MELTS program (Ghiorso and Sack, 1995). Hydrogen isotopic fractionation factors are assumed to be -15 and -30 per-mil for vapor and hydrous mineral, and vapor and silicate melt, respectively. There observed a clear difference among the H2O/K2O ratios of bulk magmas from the frontal and back arc volcanoes. For instance higher H2O/K2O wt ratios was observed in the frontal volcanoes (Nigorikawa 5.3, Zenikame 11-12, Adachi 8-10, and Nanashigure 4-18), while lower H2O/K2O wt ratios was observed in the back arc ones (Kanpu 0-2.5 and Hijiori 1.4). The lateral variation of H2O/K2O ratios infer the higher water flux through the frontal side of wedge mantle, which can be a potential cause of the

Magma transfer processes at persistently active volcanoes: insights from gravity observations

NASA Astrophysics Data System (ADS)

Locke, Corinne A.; Rymer, Hazel; Cassidy, John

2003-09-01

Magma transfer processes at persistently active volcanoes are distinguished by the large magma flux required to sustain the prodigious quantities of heat and gas emitted at the surface. Although the resulting degassed magma has been conjectured to accumulate either deep within the volcanic edifice or in the upper levels of the sub-edifice system, no direct evidence for such active accumulation has been reported. Temporal gravity data are unique in being able to quantify mass changes and have been successfully used to model shallow magma movements on different temporal scales, but have not generally been applied to the investigation of postulated long-term accumulation of magma at greater spatial scales within volcanic systems. Here, we model the critical data acquisition parameters required to detect mass flux at volcanoes, we review existing data from a number of volcanoes that exemplify the measurement of shallow mass changes and present new data from Poas and Telica volcanoes. We show that if a substantial proportion of degassed magma lodges within the sub-edifice region, it would result in measurable annual to decadal gravity increases occurring over spatial scales of tens of kilometres and propose that existing microgravity data from Sakurajima and, possibly, Etna volcanoes could be interpreted in these terms. Furthermore, such repeat microgravity data could be used to determine whether the accumulation rate is in equilibrium with the rate of production of degassed magma as calculated from the surface gas flux and hence identify the build-up of gas-rich magma at depth that may be significant in terms of eruption potential. We also argue that large magma bodies, both molten and frozen, modelled beneath volcanoes from seismic and gravity data, could represent endogenous or cryptic intrusions of degassed magma based on order of magnitude calculations using present-day emission rates and typical volcano lifetimes.

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Xu, Ting; Xu, Wen-Liang; Wang, Feng; Ge, Wen-Chun; Sorokin, A. A.

2018-02-01

This paper presents new geochronological and geochemical data for early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East, with the aim of elucidating the Paleozoic evolution and tectonic attributes of the Khanka Massif. New U-Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages: 502, 492, 462-445, and 430 Ma. The 502 Ma pyroxene diorites contain 58.28-59.64 wt% SiO2, 2.84-3.69 wt% MgO, and relatively high Cr and Ni contents. Negative εHf(t) values (- 1.8 to - 0.4), along with other geochemical data, indicate that the primary magma was derived from partial melting of mafic lower crust with the addition of mantle material. The 492 Ma syenogranites have high SiO2 and K2O contents, and show positive Eu anomalies, indicating the primary magma was generated by partial melting of lower crust at relatively low pressure. The 445 Ma Na-rich trondhjemites display high Sr/Y ratios and positive εHf(t) values (+ 1.8 to + 3.9), indicating the primary magma was generated by partial melting of thickened hydrous mafic crust. The 430 Ma granitoids have high SiO2 and K2O contents, zircon εHf(t) values of - 5.4 to + 5.8, and two-stage model ages of 1757-1045 Ma, suggesting the primary magma was produced by partial melting of heterogeneous Proterozoic lower crustal material. The geochemistry of these early Paleozoic intrusive assemblages indicates their formation in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif. The εHf(t) values show an increasingly negative trend with increasing latitude, revealing a lateral heterogeneity of the lower crust beneath the Khanka Massif. Regional comparisons of the magmatic events indicate that the Khanka Massif in the Russian Far East has a tectonic affinity to the Songnen-Zhangguangcai Range Massif rather than the adjacent Jiamusi Massif.

Meso to Neoproterozoic layered mafic-ultramafic rocks from the Virorco back-arc intrusion, Argentina

NASA Astrophysics Data System (ADS)

Ferracutti, Gabriela; Bjerg, Ernesto; Hauzenberger, Christoph; Mogessie, Aberra; Cacace, Francisco; Asiain, Lucía

2017-11-01

The Virorco layered mafic-ultramafic intrusion is part of a belt that extends over 100 km from NE to SW in the Eastern Sierras Pampeanas of San Luis, Argentina. The rocks of this belt carry a Fe-Cu-Ni sulphide mineralization in veins and as disseminated and massive ore. Platinum group minerals are associated with the sulphides. The Virorco intrusion exhibits modal, textural and cryptic layering. New results allow the characterization of six layered units (Modal Layered Unit, Pyroxenitic Macro-Layered Unit, Gabbroic Unit, Banded Unit, Hornblende Norite Unit and Gabbronorite Unit) present in three sectors of the intrusion (Eastern, Central and Western). The units from the Western Sector (Banded Unit, Hornblende Norite Unit and Gabbronorite Unit) and the Modal Layered Unit from the Eastern Sector belong to the Marginal Border Series of the intrusion. Meanwhile, the Central sector units (Pyroxenitic Macro-Layered Unit and Gabbroic Unit) are from the Layered Series. The presence of crescumulate texture (Modal Layered Unit) and colloform banding (Banded Unit) are evidences of "in situ" crystallization due to supercooling of a MgO-rich hydrated mafic magma, where cooling proceeded from the walls towards the interior of the magma chamber. In previous studies the mafic-ultramafic rocks have been considered to be Cambrian to Ordovician. Here we present a Sm-Nd whole rock isochron which shows that the formation age of these intrusions is 1002 ± 150 Ma and that the protolith age of the Pringles Metamorphic Complex metasedimentary rocks is 1289 ± 97 Ma. Our study also indicates that the San Luis mafic-ultramafic layered intrusives most probably formed in a back-arc tectonic setting, from an enriched sub-continental mantle, influenced by a subducting slab and/or crust injection into the Pampia Terrane prior to its collision with the Rio de la Plata Craton.

Lunar magma transport phenomena

NASA Technical Reports Server (NTRS)

Spera, Frank J.

1992-01-01

An outline of magma transport theory relevant to the evolution of a possible Lunar Magma Ocean and the origin and transport history of the later phase of mare basaltic volcanism is presented. A simple model is proposed to evaluate the extent of fractionation as magma traverses the cold lunar lithosphere. If Apollo green glasses are primitive and have not undergone significant fractionation en route to the surface, then mean ascent rates of 10 m/s and cracks of widths greater than 40 m are indicated. Lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics. The predominant vapor species appear to be CO CO2, and COS. Near the lunar surface, the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high-speed ejection of vapor and pyroclasts to form lunary fire fountain deposits such as the Apollo 17 orange and black glasses and Apollo 15 green glass.

Granite intrusion in a metamorphic core complex: the example of the Mykonos laccolith (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Denèle, Yoann; Lecomte, Emmanuel; Jolivet, Laurent; Huet, Benjamin; Labrousse, Loïc.; Le Pourhiet, Laetitia; Lacombe, Olivier

2010-05-01

deformation at the top of the laccolith after cooling due to heat exchange with country rocks and exhumation of the Mykonos MCC. The study of fabric evolution in the laccolith suggests that the laccolith structuration results from the interaction between regional deformation and lateral extension of magmas. Fabrics are indeed strongly planar close to the detachment, show an evolution toward plano-linear close to the bottom of the laccolith and are strongly linear in the root zone. Structural data suggest an evolution of the Mykonos MCC in three stages as follows: (i) a first stage characterized by the formation of a migmatitic "a-type dome" with a major axis parallel to the lineation such as Naxos dome by competition between regional N20 extension and EW shortening; (ii) a second stage marked by the emplacement of the Mykonos laccolith at 13 Ma at the top of the migmatitic paragneiss in the Blueschist Unit (iii) a progressive localisation of the deformation occured at the top of the laccolith in semi-ductile conditions on a thickness at about 500 m and thus in brittle conditions in the major detachment plane. Our study shows that intensity of submagmatic to high temperature deformation observed in the laccolith remains low compared to the deformation observed in country-rocks. This suggests that intrusion of a laccolith in the roof of a MCC in partially molten rocks does not localize the deformation. By contrast the geometry of the intrusion shows that the magmas are sucked into the direction of regional extension and that the intrusion of magmas will inevitably cause a local acceleration of the MCC development. Finally, during its cooling the laccolith will localize the brittle ductile transition in its roof and caused the formation of a strong deformation zone first ductile and then brittle.

A Chill Sequence to the Bushveld Complex - Insight into the First Stages of Emplacement and the Parental Magmas to the World's Largest Layered Intrusion

NASA Astrophysics Data System (ADS)

Wilson, A.

2012-04-01

Evidence of the initial stages of magma emplacement in large mafic chambers is commonly lacking because of resorption of early-formed chills and complicated by the fact that the first magmas that entered the chamber were usually more evolved than the true parental magma. Deep drilling has revealed a rare occurrence of a chill sequence from the eastern Bushveld Complex at the base of a previously unrecognized thick succession of ultramafic rocks that forms part of the Lower Zone. The chill sequence (1.8 m thick) includes a true chill against quartzite floor rock, crystalline quench textured and orthopyroxene spinifex textured rocks. Importantly the chill composition represents a relatively evolved magma formed by the separation of high-Mg olivines prior to its emplacement, probably in a conduit or a pre-chamber. An overlying pyroxene dunite represents the extract that gave rise to the chill and was emplaced either as a crystal slurry derived from the feeder conduit or as the crystallization product from a slightly later influx of primitive magma of komatiitic composition. This highly-Mg rich pyroxene dunite most likely acted as a barrier to the thermal erosion of the chill sequence as the chamber filled. The olivine in the pyroxene dunite layer is the most primitive yet recorded for the Bushveld Complex at Mg# 0.915, and the cores of associated orthopyroxene are Mg# 0.93. Compositions of the orthopyroxene in the quench and spinifex textured units range from Mg# 0.91 to 0.72 and preserve cores close to the original liquidus as well as tracking the complete in-situ solidification process. Olivine contains abundant dendritic exsolution structures of Cr-spinel and Al-rich clinopyroxene indicating that they formed at high temperature from incorporation of Ca, Al and Cr into olivine, with little time to equilibrate before emplacement. Chromite in the section is the most primitive yet recorded for the Bushveld Complex. The komatiite magma that was initially emplaced into

Rapid dike intrusion into Sakurajima volcano on August 15, 2015, as detected by multi-parameter ground deformation observations

NASA Astrophysics Data System (ADS)

Hotta, Kohei; Iguchi, Masato; Tameguri, Takeshi

2016-04-01

We present observations of ground deformation at Sakurajima in August 2015 and model the deformation using a combination of GNSS, tilt and strain data in order to interpret a rapid deformation event on August 15, 2015. The pattern of horizontal displacement during the period from August 14 to 16, 2015, shows a WNW-ESE extension, which suggests the opening of a dike. Using a genetic algorithm, we obtained the position, dip, strike length, width and opening of a dislocation source based on the combined data. A nearly vertical dike with a NNE-SSW strike was found at a depth of 1.0 km below sea level beneath the Showa crater. The length and width are 2.3 and 0.6 km, respectively, and a dike opening of 1.97 m yields a volume increase of 2.7 × 106 m3. 887 volcano-tectonic (VT) earthquakes beside the dike suggest that the rapid opening of the dike caused an accumulation of strain in the surrounding rocks, and the VT earthquakes were generated to release this strain. Half of the total amount of deformation was concentrated between 10:27 and 11:54 on August 15. It is estimated that the magma intrusion rate was 1 × 106 m3/h during this period. This is 200 times larger than the magma intrusion rate prior to one of the biggest eruptions at the summit crater of Minami-dake on July 24, 2012, and 2200 times larger than the average magma intrusion rate during the period from October 2011 to March 2012. The previous Mogi-type ground deformation is considered to be a process of magma accumulation in preexisting spherical reservoirs. Conversely, the August 2015 event was a dike intrusion and occurred in a different location to the preexisting reservoirs. The direction of the opening of the dike coincides with the T-axes and direction of faults creating a graben structure.

Efficiency of differentiation in the Skaergaard magma chamber

NASA Astrophysics Data System (ADS)

Tegner, C.; Lesher, C. E.; Holness, M. B.; Jakobsen, J. K.; Salmonsen, L.; Humphreys, M.; Thy, P.

2011-12-01

Although it is largely agreed that crystallization occurs inwardly in crystal mushes along the margins of magma chambers, the efficiency and mechanisms of differentiation are not well constrained. The fractionation paradigm hinges on mass exchange between the crystal mush and the main magma reservoir resulting in coarse-grained, refractory (cumulate) rocks of primary crystals, and complementary enrichment of incompatible elements in the main reservoir of magma. Diffusion, convection, liquid immiscibility and compaction have been proposed as mechanisms driving this mass exchange. Here we examine the efficiency of differentiation in basaltic crystal mushes in different regions of the Skaergaard magma chamber. The contents of incompatible elements such as phosphorus and calculated residual porosities are high in the lowermost cumulate rocks of the floor (47-30%) and decrease upsection, persisting at low values in the uppermost two-thirds of the floor rock stratigraphy (~5% residual porosity). The residual porosity is intermediate at the walls (~15%) and highest and more variable at the roof (10-100%). This is best explained by compaction and expulsion of interstitial liquid from the accumulating crystal mush at the floor and the inefficiency of these processes elsewhere in the intrusion. In addition, the roof data imply upwards infiltration of interstitial liquid. Remarkably uniform residual porosity of ~15% for cumulates formed along the walls suggest that their preservation is related to the rheological properties of the mush, i.e. at ≤ 15% porosity the mush is rigid enough to adhere to the wall, while at higher porosity it is easily swept away. We conclude that the efficiency of compaction and differentiation can be extremely variable along the margins of magma chambers. This should be taken into account in models of magma chamber evolution.

Igneous layering in the peralkaline intrusions ,Kola Peninsula :leading role of gravitational differentiation

NASA Astrophysics Data System (ADS)

Kogarko, L. N..

2012-04-01

In the center of Kola Peninsula there are two large layered intrusions of agpaitic nepheline syenites - Khibina and Lovozero. . The Khibina alkaline massif (Kola Peninsula,Russia) hosts the world's largest and economically most important apatite deposit. The Khibina massif is a complex multiphase body built up from a number of ring-like and conical intrusions. The apatite bearing intrusion is ring-like and is represented by a layered body of ijolitic composition with a thickness of about 1 - 2 km. The upper zone is represented by different types of apatite ores. These rocks consist of 60-90% euhedral very small (tenths of mm)apatite crystals. The lower zone has mostly ijolitic composition. The lower zone grades into underlying massive urtite consisting of 75-90% large (several mm) euhedral nepheline. Our experimental studies of systems with apatite demonstrated the near-eutectic nature of the apatite-bearing intrusion, resulting in practically simultaneous crystallization of nepheline, apatite and pyroxene. The mathematical model of the formation of the layered apatite-bearing intrusion based on the processes of sedimentation under the conditions of steady state convection taking account of crystal sizes is proposed. Under the conditions of steady-state convection large crystals of nepheline continuously had been settling forming massive underlying urtite whereas smaller crystals of pyroxenes, nepheline and apatite had been stirred in the convecting melt. During the cooling the intensity of convection decreased causing a settling of smaller crystals of nepheline and pyroxene and later very small crystalls of apatite in the upper part of alkaline magma chamber. The Lovozero massif, the largest of the Globe layered peralkaline intrusion, comprises super-large rare-metal (Nb, Ta, REE) deposit. The main ore mineral is loparite (Na, Ce, Ca)2 (Ti, Nb)2O6 which was mined during many years. The composition of cumulus loparite changed systematically upward through the

Petrological constraints on the recycling of mafic crystal mushes, magma ascent and intrusion of braided sills in the Torres del Paine mafic complex (Patagonia)

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Müntener, Othmar; Baumgartner, Lukas; Putlitz, Benita

2014-05-01

Cumulate and crystal mush disruption and reactivation are difficult to recognise in coarse grained shallow plutonic rocks. Mafic minerals included in hornblende and zoned plagioclase provide snapshots of early crystallization and cumulate formation, but are difficult to interpret in terms of the dynamics of magma ascent and possible links between silicic and mafic rock emplacement. We will present the field relations, the microtextures and the mineral chemistry of the Miocene mafic sill complex of the Torres del Paine intrusive complex (Patagonia, Chile) and its sub-vertical feeder-zone. The mafic sill complex was built up by a succession of braided sills of shoshonitic and high-K calc-alkaline porphyritic hornblende-gabbro and fine grained monzodioritic sills. The mafic units were over-accreted over 41±11 ka, underplating the overlying granite. Local diapiric structures and felsic magma accumulation between sills indicate limited separation of intercumulus liquid from the mafic sills. Anhedral hornblende cores, with olivine + clinopyroxene ± plagioclase ± apatite inclusions, crystallized at temperatures >900°C and pressures of ~300 to ~500 MPa. The corresponding rims and monzodiorite matrix crystallized at <830°C, ~70 MPa. This abrupt compositional variation suggests stability and instability of hornblende during mafic roots recycling and subsequent decompression. The near lack of intercumulus crystals in the sub-vertical feeder zone layered gabbronorite and pyroxene-hornblende gabbronorite stocks testifies that melt is more efficiently extracted than in sills, resulting in a cumulate signature in the feeding system. The emplacement age of the sill complex topmost granitic unit is identical, within uncertainties, to the feeder zone mafic cumulates. Granitic liquids formed by AFC processes and were extracted at high temperature (T>950°C) from the middle crust reservoir to the emplacement level. We show that hornblende-plagioclase thermobarometry is a useful

Derivation of S and Pb in phanerozoic intrusion-related metal deposits from neoproterozoic sedimentary pyrite, Great Basin, United States

USGS Publications Warehouse

Vikre, Peter G.; Poulson, S.R.; Koenig, Alan E.

2011-01-01

The thick (≤8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high δ34S values (−11.6 to 40.8‰, >70% exceed 10‰; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes (207Pb/204Pb >19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits.Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and

Biot number and thermos bottle effect: implications for magma-chamber convection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carrigan, C.R.

1988-09-01

Thermal boundary conditions model the coupling between a convecting magmatic body and its host. Such conditions need to be considered in models of igneous systems that involve thermal histories, crystallization and fractionation of melt, formation of aureoles by contact metamorphism, and any other processes in which transport of heat plays a role. Usually, investigations of magmatic systems have tended to emphasize modeling the interior convective regime relative to treatment of the thermal coupling. Yet it is found that the thermal nature of an intrusion is likely to be influenced more by coupling to its host than by the details ofmore » internal convective flows. Evaluation of a parameter having the form of a Biot number (Bi) provides a basis for estimating which boundary conditions are most appropriate. It is found that Bi less than or equal to 0.1 (constant heat-flux limit) for models of several caldera systems. For such values of the Biot number, the host regime behaves somewhat like a thermos bottle by limiting the flow of heat through the magma-host system so that convective stirring of magma has little effect on the cooling rate of the intrusion. Because of this insulating effect, boundary temperatures assumed in convection models should approach magmatic values even if an active hydrothermal system is present. However, high boundary temperatures do not imply that melting and assimilation of host rock by magma must occur. Despite the thermos bottle effect, magmatic convection can still be quite vigorous.« less

The growth history of the Lago Della Vacca (Southern Adamello Massive, Italy) intrusion from field observations, thermal and rheological modelling

NASA Astrophysics Data System (ADS)

Rust, A.; Annen, C.; Blundy, J. D.; Caricchi, L.

2010-12-01

The Lago Della Vacca granitoid is an intrusive body emplaced at about 4-6 km in up to 1 My. The core of the body is characterised by the presence of dyke-like structures, enclave-swarms and randomly distributed enclaves, which appear undeformed. Enclaves become oblate with the short axis perpendicular to the foliation, which, in turn follows the margin of the plutonic body (John and Blundy, 1993). Geothermometry and experimental data have been used to constrain the temperature of injection of the mafic component (1273-1323 K), the temperature of the host granitic magma (1173-1223), and to characterise the evolution of crystallinity with temperature for both magmas (Blundy and Sparks, 1992). Based on these data thermal and rheological modelling have been combined to interpret the growth and deformation history of the Lago della Vacca intrusive body. The pluton was modeled as a series of incrementally emplaced nested cylinders with 1D-cylindrical conductive heat transfer. The evolution of temperature and melt fraction distribution in the pluton and country rock were determined and used as input parameters for the rheological modelling. The rheology of each magma depends on the viscosity of the melt and, more importantly, on crystallinity. Field observations suggest that the mafic magma was injected as dykes. Their partial or total disaggregation produced mafic enclaves. The presence of randomly distributed enclaves in the core of Lago Della Vacca body indicates that convection was active in this portion of the intrusion. The undeformed nature of the enclaves in this region also implies that the contrast in temperature between host magma and mafic material produced a sudden (hours) rheological inversion with the mafic magma becoming more viscous than the felsic end-member. In these conditions, the enclaves would be transported passively by the felsic-host without suffering any substantial deformation. Thermal modelling indicates that to maintain the core of the pluton

Origin of a late Neoproterozoic (605 ± 13 Ma) intrusive carbonate-albitite complex in Southern Sinai, Egypt

NASA Astrophysics Data System (ADS)

Azer, Mokhles Kamal; Stern, Robert J.; Kimura, Jun-Ichi

2010-03-01

New geochemical, isotopic, and geochronological data and interpretations are presented for late Neoproterozoic intrusive carbonates and related rocks of southern Sinai, Egypt (northernmost Arabian-Nubian Shield). The Tarr carbonates are coarsely crystalline and related to explosive emplacement of hypabyssal and volcanic albitite at 605 ± 13 Ma. The carbonates associated with the albitites are divisible into two types: primary dolomitite and secondary breunneritite (Fe-rich magnesite). The dolomitite was clearly intrusive but differs from classic igneous carbonatites, containing much lower abundances of incompatible elements, such as REE, U, Th, Rb, Nb, Y, P, Sr, Zr, Ba, and total alkalies. The breunneritite is a secondary replacement of dolomitite, probably marking the roots of a vigorous hydrothermal system. Albitites show pristine abundances of major and trace elements and were not subjected to a major metamorphic overprint. They are relatively more fractionated, alkaline and related to within-plate A-type magmas, were emplaced in an extensional or non-compressive tectonic regime in the cupola of high-level A-type granite. Tarr albitites may represent residual magma remaining after near-total crystallization of an A-type granite pluton at depth, forcibly emplaced into the roof above the cooling pluton. The intrusive dolomitite exsolved from highly differentiated albitite melt, in the apical regions of a still-buried alkaline “A-type” granite pluton that was rich in CO2; these volatiles migrated upwards and towards the cooler margins of the magma body. Late NNE-SSW extension allowed a shallow-level cupola to form, into which albitite melts and carbonate fluids migrated, culminating in explosive emplacement of albitite breccia and intrusive carbonate. Isotopic compositions of Tarr dolomitite and albitite indicate these are consanguineous and ultimately of mantle origin. Magmatic volatiles fenitized the wall rock, while submarine hydrothermal activity

Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland.

PubMed

Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S; Ófeigsson, Benedikt G; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A; Geirsson, Halldór; La Femina, Peter C; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J; Möllhoff, Martin; Braiden, Aoife K; Eibl, Eva P S

2015-01-08

Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

NASA Astrophysics Data System (ADS)

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni; Rico, Ciro; Scandone, Roberto; Terrasi, Filippo

2017-04-01

this gap, we focused on the last eruption of 1538, reconstructing its pre-eruptive deformation pattern. For this, we exploited the unique historical, archaeological, geological and long-term geodetic record of the caldera to carefully determine the height variations (and related errors) of 20 selected sites along its coastline. The integration of this large dataset permitted the first reconstruction of pre-eruptive short- and long-term ground deformation of the CFc and to model the magma transfer before the eruption. Our data suggest a progressive magma accumulation from 1251 to 1536 in a 4.6±0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8±0.6 km deep magmatic source 4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4±0.3 km deep. This reconstruction corroborates the existence of a stationary oblate source, below the caldera centre, that was feeding lateral eruptions for the last 5 ka, and suggests: repeated emplacement of magma through intrusions below the caldera centre; occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

The link between multistep magma ascent and eruption intensity: examples from the recent activity of Piton de la Fournaise (La Réunion Island).

NASA Astrophysics Data System (ADS)

Di Muro, Andrea

2014-05-01

Caldera collapses represent catastrophic events, which induce drastic modification in a volcano plumbing system and can result in major and fast evolution of the system dynamics. At Piton de la Fournaise (PdF) volcano, the 2007 eruptive sequence extruded the largest lava volume (240 Mm3) since at least 3 centuries, provoking the collapse of a small (1 km wide; 340 m deep) summit caldera. In about 35 days, the 2007 major eruption generated i) the greatest lava output rate, ii) the strongest lava fountaining activity (> 200 m high), iii) the largest SO2 volume (> 230 kt) ever documented at PdF. This event ended a 9 year-long period (1998-2007) of continuous edifice inflation and sustained eruptive activity (3 eruptions per year on average). Unexpectedly and in spite of the large volume of magma erupted in 2007, volcano unrest and eruptive activity resumed quickly in 2008, soon after caldera collapse, and produced several closely spaced intracaldera eruptions and shallow intrusions. The post-2007 activity is associated with a trend of continuous volcano deflation and consists in small-volume (<3 Mm3) weak (< 20 m high fountains; strombolian activity) summit/proximal eruptions of moderate/low MgO magmas and frequent shallow magma intrusions. Non-eruptive tremor and increase in SO2 emissions were interpreted as evidences of magma intrusions at shallow depth (< 2.0 km) preceding the eruptions. The 2007-2011 phase of activity represents an ideal case-study to analyze the influence of magma ascent kinetics on the evolution of volcano dynamics at a persistently active basaltic volcano. In order to track magma storage and ascent, we compare geochemical data on fast quenched glasses (melt inclusions, Pele's hairs, coarse ash fragments produced by lava-sea water interaction, glassy crust of lavas, high-temperature lavas quenched in water, matrix glasses) with the geophysical record of volcano unrest. Petro-chemical data suggest that the shallow PdF plumbing system is formed by

Magma Mixing: Why Picrites are Not So Hot

NASA Astrophysics Data System (ADS)

Natland, J. H.

2010-12-01

porosity in regions where crustal-level magma chambers and flanking rift zones do not have a chance to form. Low-magma supply is favored. In the ocean basins, such upper mantle mainlining occurs only at certain fracture zones, deep propagating rifts at microplates, or ultra-slow spreading ridges, but no liquids (glasses) with >10% MgO occur at any of these places. On continents, rift structures through cratons might allow this, but so far no picrite, ferropicrite, or meimichite that has been adequately described from these places lacks evidence for end-member mixing. Low-temperature iron-rich magmas can accumulate in the deep lower crust and later rise to form substantial intrusions (e.g. Skaergaard) or erupt as flood basalts (Columbia River). Some komatiites might represent high-temperature liquids, but many are so altered that original liquid compositions cannot be deduced (e.g., Gorgona). The hottest intraplate volcano is Kilauea, Hawaii, where rare picrite glass with 15% MgO has an estimated eruptive temperature (1) of ~1350C and a potential temperature at 1 GPa of ~1420C. Lavas at all other linear island chains, Iceland and even west Greenland where picrites are abundant, are cooler than this. (1) Beattie, P., 1993. CMP 115: 103-111.

Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent Rift System, Minnesota

NASA Astrophysics Data System (ADS)

Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean

2015-01-01

The Tamarack Intrusive Complex (TIC, 1105.6 ± 1.2 Ma) in NE Minnesota, was emplaced during the early stages of the development of the Midcontinent Rift System (MRS, "Early Stage": 1110-1106 Ma). Country rocks of the TIC are those of the Paleoproterozoic Thomson Formation, part of the Animikie Group including sulfide-bearing metasedimentary black shale. The magmatic system is composed of at least two principal mafic-ultramafic intrusive sequences: the sulfide-barren Bowl Intrusion in the south and the "dike" area intrusions in the north which host Ni-Cu-Platinum Group Elements (PGE) mineralization with up to 2.33% Ni, 1.24% Cu, 0.34 g/t Pt, 0.23 g/t Pd and 0.18 g/t Au. Two distinct intrusive units in the "dike" area are the CGO (coarse-grained olivine-bearing) Intrusion, a sub-vertical dike-like body, and the overlying sub-horizontal FGO (fine-grained olivine-bearing) Intrusion. Both intrusions comprise peridotite, feldspathic peridotite, feldspathic pyroxenite, melatroctolite and melagabbro. Massive sulfides are volumetrically minor and mainly occur as lenses emplaced into the country rocks associated with both intrusions. Semi-massive (net-textured) sulfides are distributed at the core of the CGO Intrusion, surrounded by a halo of the disseminated sulfides. Disseminated sulfides also occur in lenses along the base of the FGO Intrusion. Olivine compositions in the CGO Intrusion are between Fo89 and Fo82 and in the FGO Intrusion from Fo84 to Fo82. TIC intrusions have more primitive olivine compositions than that of olivine in the sheet-like intrusions in the Duluth Complex (below Fo70), as well as olivine from the smaller, conduit-related, Eagle and East Eagle Intrusions in Northern Michigan (Fo86 to Fo75). The FeO/MgO ratios of the CGO and FGO Intrusion parental magmas, inferred from olivine compositions, are similar to those of picritic basalts erupted during the early stages of the MRS formation. Trace element ratios differ slightly from other intrusions in the

Magma hybridization in the Western Tatra Mts. granitoid intrusion (S-Poland, Western Carpathians).

PubMed

Burda, Jolanta; Gawęda, Aleksandra; Klötzli, Urs

In the Variscan Western Tatra granites hybridization phenomena such as mixing and mingling can be observed at the contact of mafic precursors of dioritic composition and more felsic granitic host rocks. The textural evidence of hybridization include: plagioclase-K-feldspar-sphene ocelli, hornblende- and biotite-rimmed quartz ocelli, plagioclase with Ca-rich spike zonation, inversely zoned K-feldspar crystals, mafic clots, poikilitic plagioclase and quartz crystals, mixed apatite morphologies, zoned K-feldspar phenocrysts. The apparent pressure range of the magma hybridization event was calculated at 6.1 kbar to 4.6 kbar, while the temperature, calculated by independent methods, is in the range of 810°C-770°C. U-Pb age data of the hybrid rocks were obtained by in-situ LA-MC-ICP-MS analysis of zircon. The oscillatory zoned zircon crystals yield a concordia age of 368 ± 8 Ma (MSWD = 1.1), interpreted as the age of magma hybridization and timing of formation of the magmatic precursors. It is the oldest Variscan magmatic event in that part of the Tatra Mountains.

In-situ seismic record of potential sill intrusion at the ultraslow spreading Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Meier, M.; Schlindwein, V. S. N.

2017-12-01

Ultraslow spreading mid-ocean ridges with full spreading rates up to 15 mm/yr are described as the melt poor endmember of the entire mid-ocean ridge system. The melt supply along ultraslow spreading ridges is uneven resulting in the formation of volcanic centres and amagmatic segments. Amagmatic segments show thicker brittle lithosphere of up to 30 km, whereas magmatic segments have much thinner lithosphere of up to less than 15 km. It is supposed that melt travels along the lithosphere asthenosphere boundary from amagmatic segments to magmatic segments, where it can reach the seafloor and erupt. These spreading events are rare at ultraslow spreading ridges compared to faster spreading ridges and insitu observations hardly exist. During an ocean bottom seismometer (OBS) experiment at the eastern Southwest Indian Ridge two earthquake swarms were accidentally recorded. The swarms occurred in January and April 2013 and both lasted for a few days. The events of the earthquake swarms were relatively located with HypoDD for better spatial resolution. This unique dataset allowed for studying active spreading processes at an ultraslow spreading ridge. The earthquakes occurred in depths, where the magma chamber of the nearby Segment-8 volcano is located. This magma chamber potentially fed a sill intrusion, which was recorded as earthquake swarms. During the first hours of the first earthquake swarm a migration pattern was identified. The hypocentres migrated away from the Segment-8 volcanic centre and slightly downwards. Later events occurred more randomly in the active area. Simultaneously seismic tremor was recorded at the station closest to the swarm locations. The tremor lasted longer for the shorter earthquake swarm in April. During both tremor phases the signal was modulated with a 12 hour period. We speculate that a hydrothermal system was affected by the intrusion and fluid flow modulated by the tides produced the tremor signal.

Interaction of coeval felsic and mafic magmas from the Kanker granite, Pithora region, Bastar Craton, Central India

NASA Astrophysics Data System (ADS)

Elangovan, R.; Krishna, Kumar; Vishwakarma, Neeraj; Hari, K. R.; Ram Mohan, M.

2017-10-01

Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes.

Forced-folding by laccolith and saucer-shaped sill intrusions on the Earth, planets and icy satellites

NASA Astrophysics Data System (ADS)

Michaut, Chloé

2017-04-01

Horizontal intrusions probably initially start as cracks, with negligible surface deformation. Once their horizontal extents become large enough compared to their depths, they make room for themselves by lifting up their overlying roofs, creating characteristic surface deformations that can be observed at the surface of planets. We present a model where magma flows below a thin elastic overlying layer characterized by a flexural wavelength Λ and study the dynamics and morphology of such a magmatic intrusion. Our results show that, depending on its size, the intrusion present different shapes and thickness-to-radius relationships. During a first phase, elastic bending of the overlying layer is the main source of driving pressure in the flow; the pressure decreases as the flow radius increases, the intrusion is bell-shaped and its thickness is close to being proportional to its radius. When the intrusion radius becomes larger than 4 times Λ, the flow enters a gravity current regime and progressively develops a pancake shape with a flat top. We study the effect of topography on flow spreading in particular in the case where the flow is constrained by a lithostatic barrier within a depression, such as an impact crater on planets or a caldera on Earth. We show that the resulting shape for the flow depends on the ratio between the flexural wavelength of the layer overlying the intrusion and the depression radius. The model is tested against terrestrial data and is shown to well explain the size and morphology of laccoliths and saucer-shaped sills on Earth. We use our results to detect and characterize shallow solidified magma reservoirs in the crust of terrestrial planets and potential shallow water reservoirs in the ice shell of icy satellites.

Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry

USGS Publications Warehouse

Lu, Z.; Masterlark, Timothy; Dzurisin, D.; Rykhus, Russ; Wicks, C.

2003-01-01

A group of satellite radar interferograms that span the time period from 1991 to 2000 shows that Westdahl volcano, Alaska, deflated during its 1991-1992 eruption and is reinflating at a rate that could produce another eruption within the next several years. The rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days, respectively. This behavior is consistent with a deep, constant-pressure magma source connected to a shallow reservoir by a magma-filled conduit. An elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath Westdahl Peak. We propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir. The pressure gradient, and hence the flow rate, are greatest immediately after eruptions. Pressurization of the reservoir decreases both the pressure gradient and the flow rate, but eventually the reservoir ruptures and an eruption or intrusion ensues. The eruption rate is controlled partly by the pressure gradient between the reservoir and surface, and therefore it, too, decreases with time. When the supply of eruptible magma is exhausted, the eruption stops, the reservoir begins to repressurize at a high rate, and the cycle repeats. This model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems.

Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China

NASA Astrophysics Data System (ADS)

Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao

2017-06-01

The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by <10% partial melting of both phlogopite-lherzolite and garnet-lherzolite mantle sources. These sources are best interpreted to be in a subduction-related arc environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

Reduced granitic magmas in an arc setting: The Catface porphyry Cu-Mo deposit of the Paleogene Cascade Arc

NASA Astrophysics Data System (ADS)

Smith, C. M.; Canil, D.; Rowins, S. M.; Friedman, R.

2012-12-01

The Catface porphyry Cu (Mo-Au) deposit, Vancouver Island, British Columbia was studied to characterize the age, geometry and geochemical affinity of its different intrusive phases, and their tectonic setting. Four different intrusive phases of quartz diorite are broadly calc-alkaline, moderately metaluminous, and have typical arc geochemical affinity. U-Pb age dating of zircons showing two intrusive phases was emplaced at 41.26 ± 0.11 and 41.15 ± 0.10 Ma, and a second two 40.93 ± 0.11 and 40.88 ± 0.10 (95% confidence). The latter ages are identical to the Re-Os age of molybdenite mineralization of 40.9 ± 0.2 Ma. The depth of emplacement is less than 4 km, as determined by amphibole-plagioclase thermobarometry (630-815 °C and 50-300 MPa). A reduced magmatic-hydrothermal system is evidenced by: (1) presence of pyrrhotite and absence of anhydrite and hematite, (2) low SO3 (< 450 ppm) in apatite, and (3) oxygen fugacities (fO2) of 0.5-3.0 log units below the quartz-fayalite-magnetite (QFM) buffer recorded by the assemblage K-feldspar-biotite-ilmenite-quartz. Reduced porphyry-related magmas on Vancouver Island of similar age to those at North Fork, Washington (37 Ma) suggests consanguinity of reduced arc magmatism and related ore deposits within the Paleogene Cascade arc of the Pacific Northwest. Reduced evolved magmas at Catface are atypical in an arc setting, but can be attributed to thorough degassing of S from the magmas as evidenced by low S in apatite.

Emplacement and magnetic fabrics of rapakivi granite intrusions within Wiborg and Åland rapakivi granite batholiths in Finland

NASA Astrophysics Data System (ADS)

Karell, Fredrik; Ehlers, Carl; Airo, Meri-Liisa

2014-02-01

Anisotropy of magnetic susceptibility (AMS) studies were carried out in two areas in Finland: the Ruotsinpyhtää intrusion within the Wiborg rapakivi granite batholith and the Saltvik intrusions within the Åland rapakivi granite batholith. The main aim of this study was to understand the emplacement history of these mid-Proterozoic rapakivi granites. Aeromagnetic images reveal structures of ca. 5-10 km intrusions that build up the large rapakivi granite batholiths of Åland and Wiborg. Magnetic susceptibility data from the database of the Geological Survey of Finland, including more than 1700 samples from the Wiborg rapakivi batholith and almost 900 samples from the Åland rapakivi batholith, were compared with measurements from the present study. The mean susceptibility is ca. 1500 μSI for the Wiborg batholith and ca. 10,000 μSI for the Åland batholith. Samples taken for this study demonstrate that the mean value for the Ruotsinpyhtää intrusion is ca. 1200 μSI and for the Saltvik intrusions ca. 24,000 μSI. Thermomagnetic measurements reveal that the magnetic susceptibility is mainly derived either from paramagnetic minerals or from magnetite. The absence of solid-state deformation features such as breccia or contact deformation indicates a cauldron-type subsidence emplacement. The AMS measurements from Ruotsinpyhtää confirm these proposals, with concentric gently dipping magnetic foliations that support a ring complex structure above a piston-type subsidence system. The Saltvik area consists of a number of smaller elliptical intrusions of different rapakivi granites forming a multiple intrusive complex. The magnetic fabric shows a general westward dipping of the pyterlite and eastward dipping of the contiguous even-grained rapakivi granite, which indicates a central inflow of magma batches towards the east and west resulting from a laccolitic emplacement of magma batches, while the main mechanism for space creation was derived from subsidence.

Development of a 3D numerical model to evaluate the Stromboli NW flank instability in relation to magma intrusion

NASA Astrophysics Data System (ADS)

Apuani, T.; Merri, A.

2009-04-01

A stress-strain analysis of the Stromboli volcano was performed using a three-dimensional explicit finite difference numerical code (FLAC 3D, ITASCA, 2005), to evaluate the effects associated to the presence of magma pressure in magmatic conduit and to foresee the evolution of the magmatic feeding complex. The simulations considered both the ordinary state for the Stromboli, characterized by a partial fill of the active dyke with regular emission of gas and lava fountains and the paroxysmal conditions observed during the March 2007's eruptive crisis, with the magma level in the active dyke reaching the topographic surface along the Sciara del Fuoco depression. The modeling contributes to identify the most probable directions of propagation of new dikes, and the effects of their propagation on the stability of the volcano edifice. The numerical model extends 6 x 6 x 2.6 km3, with a mesh resolution of 100 m, adjusting the grid to fit the shape of the object to be modeled. An elasto-plastic constitutive law was adopted and an homogeneous Mohr-Coulomb strength criterion was chosen for the volcanic cone, assuming one lithotechnical unit (alternation of lava and breccia layers "lava-breccia unit"- Apuani et al 2005). The dykes are represented as discontinuities of the grid, and are modeled by means of interfaces. The magmatic pressure is imposed to the model as normal pressure applied on both sides of the interfaces. The magmastatic pressure was calculated as Pm=d•h, where d is the magma unit weight assumed equal to 25 KN/m3, and h (m) is the height of the magma column. Values of overpressure between 0 and 1 MPa were added to simulate the paroxysmal eruption. The simulation was implemented in successive stages, assuming the results of the previous stages as condition for the next one. A progressive propagation of the dike was simulated, in accordance with the stress conditions identified step by step, and in accordance with the evidences detected by in situ survey, and

Magma plumbing for the 2014-2015 Holuhraun eruption, Iceland

NASA Astrophysics Data System (ADS)

Geiger, Harri; Mattsson, Tobias; Deegan, Frances M.; Troll, Valentin R.; Burchardt, Steffi; Gudmundsson, Ólafur; Tryggvason, Ari; Krumbholz, Michael; Harris, Chris

2016-08-01

The 2014-2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Bárðarbunga and Holuhraun, we present mineral textures and compositions, mineral-melt-equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Bárðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system. Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption, wherein clinopyroxene and plagioclase crystallized at average depths of ˜17 km and ˜5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated magma mixing and assimilation of low-δ18O Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical magma ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.

The Relationship Between Carbonatitic, Melilititic and Potassic Trachytic Magma Types at the Saltpeterkop Carbonatite Complex, Sutherland, South Africa

NASA Astrophysics Data System (ADS)

Janney, P. E.; Marageni, M.

2016-12-01

The 74 Ma Saltpeterkop Carbonatite Complex near Sutherland, South Africa, is unusual in that it is one of the few southern African carbonatites with preserved volcanic features, including a 1 km-diameter tuff ring composed of silicified volcaniclastic breccia. Around the complex, the regionally flat-lying Karoo strata have been dramatically upwarped, with dips away from the Complex as high as 45°. Further, within about a 10 km radius of the center of the complex are hundreds of dikes, sills and diatremes composed mainly of carbonatite, potassic trachyte and olivine melilitite, with the spatial density of these intrusions decreasing with increasing distance. We have recently completed an in-depth geochemical reconnaissance of the Saltpeterkop complex, involving field sampling and whole-rock major and trace element analysis, with radiogenic and stable isotope measurements in progress. While the association with potassic trachytes is relatively common in southern African carbonatites, the presence of significant amounts of primitive olivine melilitite (30-40 wt.% SiO2, Mg# = 61-74) is unusual. Our preliminary model for the origin of the complex involves (1) ascent and intrusion of a mantle-derived carbonated and potassic magma into the mid-to upper crust, (2a) separation of an alkali carbonatite phase from this magma, resulting in intensive local fenitization and partial melting of mid-crustal rocks (thereby forming potassic trachytes), and possibly triggering the initial eruption, (2b) small amounts of primitive, but now less potassic, mantle-derived magma are emplaced as olivine melilitite dikes and diatremes, and (3) differentiation of the mantle-derived magma to generate significant quantities of mainly calcio- and ferro-carbonatite magmas emplaced as dykes and sills.

Centrifuge models simulating magma emplacement during oblique rifting

NASA Astrophysics Data System (ADS)

Corti, Giacomo; Bonini, Marco; Innocenti, Fabrizio; Manetti, Piero; Mulugeta, Genene

2001-07-01

A series of centrifuge analogue experiments have been performed to model the mechanics of continental oblique extension (in the range of 0° to 60°) in the presence of underplated magma at the base of the continental crust. The experiments reproduced the main characteristics of oblique rifting, such as (1) en-echelon arrangement of structures, (2) mean fault trends oblique to the extension vector, (3) strain partitioning between different sets of faults and (4) fault dips higher than in purely normal faults (e.g. Tron, V., Brun, J.-P., 1991. Experiments on oblique rifting in brittle-ductile systems. Tectonophysics 188, 71-84). The model results show that the pattern of deformation is strongly controlled by the angle of obliquity ( α), which determines the ratio between the shearing and stretching components of movement. For α⩽35°, the deformation is partitioned between oblique-slip and normal faults, whereas for α⩾45° a strain partitioning arises between oblique-slip and strike-slip faults. The experimental results show that for α⩽35°, there is a strong coupling between deformation and the underplated magma: the presence of magma determines a strain localisation and a reduced strain partitioning; deformation, in turn, focuses magma emplacement. Magmatic chambers form in the core of lower crust domes with an oblique trend to the initial magma reservoir and, in some cases, an en-echelon arrangement. Typically, intrusions show an elongated shape with a high length/width ratio. In nature, this pattern is expected to result in magmatic and volcanic belts oblique to the rift axis and arranged en-echelon, in agreement with some selected natural examples of continental rifts (i.e. Main Ethiopian Rift) and oceanic ridges (i.e. Mohns and Reykjanes Ridges).

Cathedral Peak Granodiorite, Sierra Nevada Batholith, California: A Big, Mushy, Magma System?

NASA Astrophysics Data System (ADS)

Burgess, S. D.; Miller, J. S.; Matzel, J. P.

2006-12-01

The Cathedral Peak Granodiorite (Kcp) is the largest mapped unit of the >1200 km2 Tuolumne Batholith (TB), which is one of a belt of Cretaceous zoned intrusions within the Sierra Nevada Batholith. Previous workers [1,2] proposed that the zonation in the TB was mainly produced in-situ either by inward differentiation of a large mass of magma and/or large-scale magma mixing between compositionally distinct map units. Recent geochronology has shown that the entire TB was intruded over 8-9 Ma, leading to the hypothesis that it was constructed continuously over this time period by many small increments [3], with variations in chemical and isotopic composition attributed to processes in the melt source. This hypothesis is also supported by scatter in trace elements vs. longitude from the margins to inner TB and appreciable variability in Nd and Sr isotopic data between the mapped units of the TB [e.g., 4]. Thus attributing chemical variations between major intrusive units to simple closed system fractionation or binary magma mixing is precluded. New field, geochemical and geochronologic work along a 5 km transect from the porphyritic Half Dome Granodiorite (Khdp) margin to the innermost Kcp, and approximately perpendicular to the Kcp-Khdp contact shows that: (1) magmatic foliation is moderately- to steeply-dipping (>60°); (2) zircon ages at each end of the transect are indistinguishable; (3) bulk composition varies only modestly but trace elements show variable degrees of scatter with greatest scatter observed among feldspar-compatible and highly incompatible elements (Sr, Ba, Th); (5) ɛNd(t) is invariant (Sr(i) has small variation); (6) abundant field evidence for transport and mixing of melt and crystals is observed (multiple generations of steep planar, tube- like, and chaotically folded schlieren, rafts and monomineralic clusters of K-feldspar, irregular and mingled contacts between sheets of texturally variable granite and schlieren). The broad geochemical and

Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals.

PubMed

Rubin, Allison E; Cooper, Kari M; Till, Christy B; Kent, Adam J R; Costa, Fidel; Bose, Maitrayee; Gravley, Darren; Deering, Chad; Cole, Jim

2017-06-16

Silicic volcanic eruptions pose considerable hazards, yet the processes leading to these eruptions remain poorly known. A missing link is knowledge of the thermal history of magma feeding such eruptions, which largely controls crystallinity and therefore eruptability. We have determined the thermal history of individual zircon crystals from an eruption of the Taupo Volcanic Zone, New Zealand. Results show that although zircons resided in the magmatic system for 10 3 to 10 5 years, they experienced temperatures >650° to 750°C for only years to centuries. This implies near-solidus long-term crystal storage, punctuated by rapid heating and cooling. Reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales, and our approach can help to quantify heat input to and output from magma reservoirs. Copyright © 2017, American Association for the Advancement of Science.

U-Pb (zircon) and geochemical constraints on the age, origin, and evolution of Paleozoic arc magmas in the Oyu Tolgoi porphyry Cu-Au district, southern Mongolia

USGS Publications Warehouse

Wainwright, A.J.; Tosdal, R.M.; Wooden, J.L.; Mazdab, F.K.; Friedman, R.M.

2011-01-01

Uranium-Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu-Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (??Nd(t) range from +3.1 to +7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have <1.5% TiO2) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu-Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium-Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu-Au deposits are ~372Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu-Au mineralization are ~366Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu-Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late

Mafic enclaves record syn-eruptive basalt intrusion and mixing

NASA Astrophysics Data System (ADS)

Plail, Melissa; Edmonds, Marie; Woods, Andrew W.; Barclay, Jenni; Humphreys, Madeleine C. S.; Herd, Richard A.; Christopher, Thomas

2018-02-01

Mafic enclaves hosted by andesite erupted at the Soufrière Hills Volcano between 1995 and 2010 yield insights into syn-eruptive mafic underplating of an andesite magma reservoir, magma mixing and its role in sustaining eruptions that may be widely applicable in volcanic arc settings. The mafic enclaves range in composition from basalt to andesite and are generated from a hybrid thermal boundary layer at the interface between the two magmas, where the basalt quenches against the cooler andesite, and the two magmas mix. We show, using an analytical model, that the enclaves are generated when the hybrid layer, just a few tens of centimetres thick, becomes buoyant and forms plumes which rise up into the andesite. Mafic enclave geochemistry suggests that vapour-saturated basalt was underplated quasi-continuously throughout the first three eruptive phases of the eruption (the end member basalt became more Mg and V-rich over time). The andesite erupted during the final phases of the eruption contained more abundant and larger enclaves, and the enclaves were more extensively hybridised with the andesite, suggesting that at some time during the final few years of the eruption, the intrusion of mafic magma at depth ceased, allowing the hybrid layer to reach a greater thickness, generating larger mafic enclaves. The temporal trends in mafic enclave composition and abundance suggests that basalt recharge and underplating sustained the eruption by the transfer of heat and volatiles across the interface and when the recharge ceased, the eruption waned. Our study has important implications for the petrological monitoring of long-lived arc eruptions.

Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption.

PubMed

Sigmundsson, Freysteinn; Hreinsdóttir, Sigrún; Hooper, Andrew; Arnadóttir, Thóra; Pedersen, Rikke; Roberts, Matthew J; Oskarsson, Níels; Auriac, Amandine; Decriem, Judicael; Einarsson, Páll; Geirsson, Halldór; Hensch, Martin; Ofeigsson, Benedikt G; Sturkell, Erik; Sveinbjörnsson, Hjörleifur; Feigl, Kurt L

2010-11-18

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (>5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ∼0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajökull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.

Deformation of host rocks and flow of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico

USGS Publications Warehouse

Delaney, Paul T.; Pollard, David D.

1981-01-01

We have studied a small group of minette dikes and plugs that crop out within a flat-lying sequence of siltstone and shale near Ship Rock, a prominent volcanic throat of tuff breccia in northwestern New Mexico. Seven dikes form a radial pattern about Ship Rock we describe in detail the northeastern dike, which has an outcrop length of about 2,900 m, an average thickness of 2.3 m, and a maximum thickness of 7.2 m. The dike is composed of 35 discrete segments arranged in echelon; orientation. of dike segments ranges systematically from N. 52? E. to N. 66? E. A prominent joint set strikes parallel to the segments and is localized within several tens of meters of the dike. Regional joint patterns display no obvious relation to dike orientation. Small offsets of segment contacts, as well as wedge-shaped bodies of crumpled host rock within segments mark the sites of coalescence of smaller segments during dike growth. Bulges in the dike contact, which represent a nondilational component of growth, indicate that wall rocks were brecciated and eroded during the flow of magma. Breccias make up about 9 percent of the 7,176-m 2 area of the dike, are concentrated in its southwest half, and are commonly associated with its thickest parts. We also describe three subcircular plugs; each plug is smaller than 30 m in diameter, is laterally associated with a dike, and contains abundant breccias. Field evidence indicates that these plugs grew from the dikes by brecciation and erosion of wallrocks and that the bulges in the contact of the northeastern dike represent an initial stage of this process. From continuum-mechanical models of host-rock deformation, we conclude that dike propagation was the dominant mechanism for creating conduits for magma ascent where the host rock was brittle and elastic. At a given driving pressure, dikes dilate to accept greater volumes of magma than plugs, and for a given dilation, less work is done on the host rocks. In addition, the pressure required

The transition from diapirism to dike intrusion: Implications for planetary volcanism

NASA Technical Reports Server (NTRS)

Rubin, Allan M.

1994-01-01

Magma transport processes influence the rate of magma transport and how far the magma travels before it freezes, the degree to which the magma communicates chemically with the host rock, the morphology of volcanic landforms on planetary surfaces, the interplay between magmatism and regional tectonics, and even the direction the magma moves. The primary question motivating this research is: How does magma rheology influence the mechanisms by which it is transported through planetary lithospheres? It is widely recognized that on Earth basaltic intrusions typically take the form of narrow dikes, while granites are typically found in more equidimensional plutons. Several explanations for this observation were offered over the last 50 years. While basalts and rhyolites vary somewhat in temperature and density, the major difference is the 2 to 8 orders of magnitude contrast in viscosity. The significant ductile strains associated with many granitic plutons has led to the statement that the occurrence of granites in diapirs rather than dikes results from the fact that there is insufficient viscosity contrast between the magma and wall rock for the granite to intrude narrow cracks. A second explanation states that granites are so viscous that they cannot propagate far before freezing. Despite the length of time these explanations have been around, there has been relatively little effort to investigate them quantitatively. My goal has been to evaluate these explanations through a series of well-posed numerical models. These models can be tested by the decades of field data collected by structural geologists that have yet to be integrated into any coherent theory, and the results should have important implications for volcanism on the terrestrial planets.

Magma Emplacement Processes of the Oligocene Zákupy and Miocene Měrunice Diatremes, Czech Republic: Revealed via Petrography, Anisotropy of Magnetic Susceptibility, Paleomegnetic, and Ground Magnetometry Data

NASA Astrophysics Data System (ADS)

Shields, Sarah; Petronis, Michael; Rapprich, Vladislav; Valenta, Jan

2016-04-01

The emplacement of silica-undersaturated magma in continental rift volcanoes remains poorly understood because the roots of these systems are not often accessible. The Miocene Měrunice and Oligocene Zákupy diatremes, Czech Republic, are located within or on the SE shoulder of the Eger Rift. These diatremes provide a unique opportunity to conduct a comparative emplacement study, in near 3-dimensions, of their sub-volcanic magma plumbing systems. Studies across the rift reveal that magma compositions show a temporal evolution trend that coincides with three rift phases: melilitic-nephelinites during pre-rift (79-49 Ma); two magmas, weakly alkaline olivine basalts and strongly alkaline nephlelinite-tephrite-phonolites during syn-rift (42-16 Ma), and olivine foidites during late rift (16-0.3 Ma). Here we report preliminary data on how varying degrees of alkaline magma generation paired with a dynamic rift stress regime yield unique emplacement mechanisms of presumed monogenetic rift diatremes. Field observations and laboratory data at both diatremes indicate multiple emplacement and eruptive events, as shown by variation in eruptive materials and cross cutting relationships between dikes and sills that differ in emplacement dynamics. Anisotropy of magnetic susceptibility (AMS) data were collected from 25 Zákupy diatreme sites and reveal primarily oblate magnetic fabrics that we interpret to indicate that magma flowed up, down, and laterally away from the suspected main conduit. Preliminary paleomagnetic data reveal that the intrusions are of reversed polarity and show some scatter about the expected reverse polarity reference direction that could be related to sub-volcanic deformation of the diatreme. In addition, ground magnetometry data indicate that the main conduit is likely located at the center of the quarry as shown by a magnetic low with a magnetic high radiating around the probable conduit. Curie point estimates show that the magnetic mineral phases

Rethinking Volcanic Plumbing Systems: The Prevalence of Offset Magma Reservoirs at Holocene Volcanoes

NASA Astrophysics Data System (ADS)

Lerner, A. H.; Karlstrom, L.; Hurwitz, S.; Anderson, K. R.; Ebmeier, S. K.

2016-12-01

Mechanical models of volcanic overpressure and interpretations of volcanic deposits are generally rooted in the classic paradigm of a magma reservoir being located directly beneath the main topographic high and central conduit of a volcano. We test this framework against recent decades of research on volcanic deformation, seismic tomography, earthquake hypocenter locations, and magnetotellurics, which have provided unprecedented geophysical views of volcanic plumbing systems. In a literature survey of Holocene strato- and shield volcanoes in arc, backarc, continental rift, and intraplate settings, we find that shallow to mid-crustal (< 20 km) magma reservoirs are equally likely to be laterally offset from principle volcanic edifices (n = 20) as they are to be centrally located beneath volcanic topographic highs (n = 19). We classify offset reservoirs as having imaged or modeled centroids that are at least 2 km laterally offset from the central volcanic edifice. The scale and geometry of offset magma reservoirs range widely, with a number of systems having discrete reservoirs laterally offset up to 15 km from the main volcanic edifice, at depths of 2 to 15 km. Other systems appear to have inclined magmatic reservoirs and/or fluid transport zones that continuously extend from beneath the main edifice to lateral distances up to 20 km, at depths of 3 to 18 km. Additionally, over a third of the studied systems have small, centrally located shallow magma or fluid reservoirs at depths of 1 to 5 km. Overall, we find that offset magma reservoirs are more common than is classically perceived, and offset reservoirs are more prevalent in intermediate to evolved stratovolcanoes (19 of 28) than in basaltic shield volcanoes (2 of 7). The reason for the formation of long-lived edifices that are offset from their source magma reservoir(s) is an open question; correlation to regional principal stresses or local tectonics, edifice size, lithology, and morphology, and climate may

Magma ascent and magmatism controlled by cratering on the Moon

NASA Astrophysics Data System (ADS)

Michaut, C.; Pinel, V.

2016-12-01

The lunar primary crust was formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a relatively light and thick crust. This crust acted as a barrier for the denser primary mantle melts: mare basalts erupted primarily within large impact basins where at least part of this crust was removed. Thus, lunar magmas likely stored at the base of or deep in the lunar crust and the ascent of magma to shallow depths probably required local or regional tensional stresses. On the Moon, evidences of shallow sites of magmatism are mostly concentrated within old and degraded simple and complex craters that surround the Mare basalts. Impacts, that were numerous in the early times of the Moon, created depressions at the lunar surface that induced specific states of stress. Below a crater, magma ascent is helped by the tensional stresses caused by the depression up to a depth that is close to the crater radius. However, many craters that are the sites of shallow magmatism are less than 10 to 20 km in radius and are equally situated in regions of thin (i.e. 20 km) or thick (i.e. 60km) crust suggesting that the depression, although significant enough to control magma emplacement, was not large enough to induce it. Since the sites of magmatism surround the mare basalts, we explore the common idea that the weight of the Mare induced a tensile state of stress in the surrounding regions. We constrain the regional state of stress that was necessary to help magma ascent to shallow depths but was low enough for the local depression due to a crater to control magma emplacement. This state of stress is consistent with a relatively thin but extended mare load. We also show that the depression due to the crater probably caused the horizontalization and hence the storage of the magmatic intrusion at shallow depth below the crater. In the end, because of the neutral buoyancy of magmas in the crust and the lack of tectonic processes, impact processes largely

Unconventional maar diatreme and associated intrusions in the soft sediment-hosted Mardoux structure (Gergovie, France)

NASA Astrophysics Data System (ADS)

Valentine, Greg A.; van Wyk de Vries, Benjamin

2014-03-01

A Miocene age volcanic-hypabyssal structure comprising volcaniclastic deposits and mafic intrusions is exposed with vertical relief of ˜110 m on the side of Gergovie Plateau (Auvergne, France). Three main volcaniclastic facies are: (1) Fluidal tuff breccia composed of juvenile basalt and sediment clasts with dominantly fluidal shapes, with several combinations of basalt and sediment within individual clasts. (2) Thickly bedded lapilli tuff composed of varying proportions of fine-grained sediment derived from Oligocene-Miocene lacustrine marls and mudstones and basaltic lapilli, blocks, and bombs. (3) Planar-bedded tuff forming thin beds of fine to coarse ash-size sedimentary material and basalt clasts. Intrusive bodies in the thickly bedded lapilli tuff range from irregularly shaped and anastomosing dikes and sills of meters to tens of meters in length, to a main feeder dike that is up to ˜20 m wide, and that flares into a spoon-shaped sill at ˜100 m in diameter and 10-20 m thick in the eastern part of the structure. Volcaniclastic deposits and structural features suggest that ascending magma entrained soft, saturated sediment host material into the feeder dike and erupted fluidal magma and wet sediment via weak, Strombolian-like explosions. Host sediment and erupted material subsided to replace the extracted sediments, producing the growth subsidence structure that is similar to upper diatreme facies in typical maar diatremes but lacks evidence for explosive disruption of diatreme fill. Irregularly shaped small intrusions extended from the main feeder dike into the diatreme, and many were disaggregated due to shifting and subsidence of diatreme fill and recycled via eruption. The Mardoux structure is an "unconventional" maar diatreme in that it was produced mainly by weak explosive activity rather than by violent phreatomagmatic explosions and is an example of complex coupling between soft sediment and ascending magma.

The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology

NASA Astrophysics Data System (ADS)

Maier, W. D.; Prevec, S. A.; Scoates, J. S.; Wall, C. J.; Barnes, S.-J.; Gomwe, T.

2018-01-01

The Uitkomst intrusion is a tubular mafic-ultramafic layered body that hosts one of South Africa's largest Ni-Cu-Cr-PGE deposits, Nkomati. The sulphide ore occurs in the form of massive lenses in the immediate quartzitic footwall and as disseminations within peridotite. The chromite ore forms an up to ˜10-m-thick layer in the lower portion of the intrusion. Uitkomst has generally been interpreted as a magma conduit, possibly related to the Bushveld event. Here, we present a new high-precision U-Pb zircon date of 2057.64 ± 0.69 Ma that overlaps with the age of the Merensky Reef of the Bushveld Complex and thus demonstrates a coeval relationship between the intrusions. Based on incompatible trace elements as well as O- and Nd isotope data (ɛNd -4.5 to -6.2), we show that the Uitkomst parent magmas were contaminated with up to 20% Archean upper crust prior to emplacement, and with up to 15% dolomitic country rock during emplacement. Ore formation at Nkomati was critically aided by substantial devolatisation and removal of dolomitic floor rocks leading to hydrodynamic concentration of sulphide and chromite during slumping of crystal mushes into the trough-like centre of the subsiding intrusion and its footwall.

Paleozoic mafic-intermediate intrusions (320-287 Ma) in the Kalatongke area, southern Altai, NW China: Products of protracted magmatism in a convergent tectonic setting

NASA Astrophysics Data System (ADS)

Qian, Zhuangzhi; Duan, Jun; Li, Chusi; Xu, Gang; Feng, Yanqing; Ren, Meng

2018-06-01

Numerous small mafic-intermediate intrusions are present in the Kalatongke area in the southern part of the Paleozoic Altai Orogenic Belt, NW China. Previous studies reveal that most of these intrusions were emplaced at ∼287 Ma, broadly coeval with the eruption of alkaline flood basalts at ⩽282 Ma in the Tarim Craton. The similar ages have led some researchers to believe that the Tarim flood basalts and the Kalatongke mafic-intermediate intrusions are related to the same mantle plume. New and existing geochronological and geochemical data for the mafic-intermediate intrusions in the Kalatongke area together do not support such interpretation. Most of the intrusions in this small area (4.5 × 2 km) were emplaced at ∼287 Ma but our new data reveal that older intrusive rocks with zircon U-Pb ages from 290 ± 1.5 to 320 ± 2 Ma are also present. The temporal and spatial distribution of these intrusions does not show a hotspot track as expected by the mantle plume model. The intrusive rocks have similar Nd-Hf isotope compositions (εNd = 3-9, εHf = 15-19) and are all characterized by light REE enrichments relative to heavy REE, plus pronounced negative Nb-Ta anomalies. The oldest intrusion (∼320 Ma) also shows negative Zr-Hf anomalies, which are common in arc basalts but absent in continental flood basalts. The results of mixing calculations based on Sr-Nd-Hf isotopes and selected trace elements (Th, Nb and Yb) indicate that the parental magmas for these intrusions were all enriched in Th and depleted in Nb prior to crustal contamination, similar to the magmas generated in a convergent tectonic setting from subduction to post-subduction elsewhere in the world. The results from this study remind us that temporal correlation is not a reliable tool to determine the size of a mantle plume.

The Consequences of Increased Magma Supply to Kilauea Volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Poland, M.; Miklius, A.; Sutton, A. J.; Orr, T.

2007-12-01

The summer of 2007 was a time of intense activity at Kilauea. By mid-2007, ~4 years of summit inflation had uplifted and extended the caldera by 30 cm and 55 cm, respectively. Lava continued to erupt from the Pu`u `O`o vent on the east rift zone (ERZ) during the inflation. On May 24, 2007, two M4+ normal-faulting earthquakes occurred on caldera-bounding faults southeast of the summit. The seismicity did not affect summit inflation, which continued until June 17 when a dike intruded the upper and middle ERZ, causing a pause in the eruption, collapse of Pu`u `O`o's floor, and a small eruption 6 km uprift of Pu`u `O`o. The inflated state of the summit, relative timing of summit deflation and east rift zone extension, and abundant co-intrusive earthquake activity suggest forcible intrusion of magma. Lava returned to Pu`u `O`o by July 2, forming a lake that gradually refilled much of the collapsed crater. Early on July 21, the lake drained suddenly, the cone began to collapse, and a 2-km-long series of discontinuous eruptive fissures opened on and beyond the east flank of Pu`u `O`o. Sesimicity in Kilauea's south flank has been elevated since June and several M3+ earthquakes have occurred there, including a M5.4 on August 13. An increase in magma supply to Kilauea's shallow magmatic system is the probable cause for the events of summer 2007. Summit inflation since 2003 occurred during a period of constant or increasing magma supply to Pu`u `O`o, based on SO2 emissions from the ERZ. The rate of inflation increased markedly in early 2006, and uplift also began in the southwest rift zone. CO2 emissions at the summit, indicative of the quantity of magma degassing beneath Kilauea's caldera, more than doubled between 2003 and 2006. Also since 2003, the ERZ immediately downrift of Pu`u `O`o extended, and subsidence in the lower ERZ ceased. Together, these factors suggest that the magma supply rate to Kilauea's shallow magmatic system (the summit and rift zones above about 5 km

Review of the geochemistry and metallogeny of approximately 1.4 Ga granitoid intrusions of the conterminous United States

USGS Publications Warehouse

du Bray, Edward A.; Holm-Denoma, Christopher S.; Lund, Karen; Premo, Wayne R.

2018-03-27

primitive, mantle-derived components and evolved, crust-derived components.Each compositional subtype can be ascribed to a relatively unique petrogenetic history. The numerically dominant ferroan, peraluminous granites probably represent low-degree, relatively high-pressure partial melting of preexisting, crust-derived, intermediate-composition granitoids. The moderately numerous, weakly magnesian, peraluminous granites probably reflect similar partial melting but at a higher degree and in a lower pressure environment. In contrast, the ferroan but metaluminous granites may be the result of extensive differentiation of tholeiitic basalt. Finally, the peralkaline igneous rocks at Mountain Pass have compositions potentially derived by differentiation of alkali basalt. The varying alkalic character of each subtype probably reflects polybaric petrogenesis and the corresponding effect of diverse mineral stabilities on ultimate melt compositions. Mantle-derived mafic magma and variably assimilated partial melts of mainly juvenile Paleoproterozoic crustal components are required to generate the relatively low initial strontium (87Sr/86Sr) and distinctive neodymium isotope compositions characteristic of the U.S. 1.4 Ga granitoid intrusions. The characteristics of these intrusions are consistent with crustal melting in an extensional/decompressional, intracratonic setting that was triggered by mantle upwelling and emplacement of tholeiitic basaltic magma at or near the base of the crust. Composite magmas, formed by mingling and mixing mantle components with partial melts of Paleoproterozoic crust, produced variably homogenized storage reservoirs that continued polybaric evolution as intrusions lodged at various crustal depths.

Deep magma transport at Kilauea volcano, Hawaii

NASA Astrophysics Data System (ADS)

Wright, Thomas L.; Klein, Fred W.

2006-03-01

The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5° and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325°, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0

Deep magma transport at Kilauea volcano, Hawaii

USGS Publications Warehouse

Wright, T.L.; Klein, F.W.

2006-01-01

The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5?? and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325??, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0

Magma Fragmentation

NASA Astrophysics Data System (ADS)

Gonnermann, Helge M.

2015-05-01

Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

How to build a mid-crustal intrusive suite: geologic mapping, U-Pb geo-/thermochronology, and thermal modeling of the Bergell Intrusion, Central Alps

NASA Astrophysics Data System (ADS)

Samperton, K. M.; Schoene, B.; Annen, C.

2015-12-01

Insights into the characteristic rates and processes of crustal magmatic systems can best be made through the integration of observational, analytical and modeling perspectives. We present such an approach in reconstructing the emplacement, differentiation and cooling history of the Bergell Intrusion (N Italy/SE Switzerland), a normally-zoned pluton preserving a ~10 km mid-crustal transect. U-Pb zircon, titanite and allanite geo-/thermochronology of Bergell granitoids provide key empirical constraints for informing numerical simulations of pulse-wise, incremental assembly. Protracted zircon crystallization histories, representing the time between magma zircon saturation and cooling to the solidus, provide a direct petrologic link to forward models of magma emplacement, both of which can be used to derive quantitative magmatic cooling rates for the middle crust. Titanite and allanite dates provide additional constraints on the timing of solidification. Geochronology and modeling are performed in the context of detailed field and structural observations, including those previously interpreted as evidence of upward, pluton-scale melt migration via floor convergence/roof ballooning. Combined Bergell data and modeling demonstrate that pulsed assembly can lead to the formation of substantial melt reservoirs in the middle crust: this finding is largely in contrast to similar models of shallow crustal plutons, highlighting the importance of factors such as ambient country rock temperature in affecting melt residence timescales. This work emphasizes the importance of implementing joint data/modeling studies to intrusive rocks across the full range of spatial scales, emplacement levels and tectonic settings observed on Earth.

The amphiboles of the REE-rich A-type peralkaline Strange Lake pluton - fingerprints of magma evolution

NASA Astrophysics Data System (ADS)

Siegel, Karin; Williams-Jones, Anthony E.; van Hinsberg, Vincent J.

2017-09-01

Major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions. In this study, we use the amphibole-group minerals from the Strange Lake, REE-enriched peralkaline granitic pluton to gain insights into the evolution of the magma. This 1240 Ma old pluton consists of two main intrusive facies, an early hypersolvus granite, which occurs as separate northern and southern intrusions, and a more evolved transsolvus granite. In the hypersolvus granite the amphibole is a late interstitial phase, whereas in the transsolvus granite, it is present as phenocrysts. The amphibole compositions vary from calcic-sodic (ferro-ferri-katophorite) in the southern hypersolvus granite to sodic (arfvedsonite, ferro-ferri-leakeite) in the other, more evolved granitic units. High Na, Si, Li, and low Al and Ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite, despite the fact that these crystals formed early. We interpret the increasing Fe3+/Fe2+ ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects (Na/Ca-ratio) and increasingly oxidizing conditions in the magma, whereas in the phenocrysts of the transsolvus granite, the increasing ratio was the product of increasing proportions of F- and OH- in the melt. The amphiboles of all the granite units have elevated Nb, Zr, Hf and REE concentrations compared to the bulk rock, suggesting that these elements are compatible in amphibole. By contrast the much lower Ti concentration was due to saturation of the magma in sodium-titanosilicates. The amphibole REE concentrations vary greatly among the granite units. Amphibole of the southern and northern hypersolvus granite contains 0.16 and 0.07 wt.% ∑ REE + Y, on average, respectively, and in the transsolvus granite, the average ∑ REE content is only 0.01 wt.%, despite the more evolved nature of its host

Taxonomy of Magma Mixing II: Thermochemistry of Mixed Crystal-Bearing Magmas Using the Magma Chamber Simulator

NASA Astrophysics Data System (ADS)

Bohrson, W. A.; Spera, F. J.; Neilson, R.; Ghiorso, M. S.

2013-12-01

Magma recharge and magma mixing contribute to the diversity of melt and crystal populations, the abundance and phase state of volatiles, and thermal and mass characteristics of crustal magma systems. The literature is replete with studies documenting mixing end-members and associated products, from mingled to hybridized, and a catalytic link between recharge/mixing and eruption is likely. Given its importance and the investment represented by thousands of detailed magma mixing studies, a multicomponent, multiphase magma mixing taxonomy is necessary to systematize the array of governing parameters (e.g., pressure (P), temperature (T), composition (X)) and attendant outcomes. While documenting the blending of two melts to form a third melt is straightforward, quantification of the mixing of two magmas and the subsequent evolution of hybrid magma requires application of an open-system thermodynamic model. The Magma Chamber Simulator (MCS) is a thermodynamic, energy, and mass constrained code that defines thermal, mass and compositional (major, trace element and isotope) characteristics of melt×minerals×fluid phase in a composite magma body-recharge magma-crustal wallrock system undergoing recharge (magma mixing), assimilation, and crystallization. In order to explore fully hybridized products, in MCS, energy and mass of recharge magma (R) are instantaneously delivered to resident magma (M), and M and R are chemically homogenized and thermally equilibrated. The hybrid product achieves a new equilibrium state, which may include crystal resorption or precipitation and/or evolution of a fluid phase. Hundreds of simulations systematize the roles that PTX (and hence mineral identity and abundance) and the mixing ratio (mass of M/mass of R) have in producing mixed products. Combinations of these parameters define regime diagrams that illustrate possible outcomes, including: (1) Mixed melt composition is not necessarily a mass weighted mixture of M and R magmas because

Soliton-mediated conduit flow: Deep Hawaiian magma migration

NASA Astrophysics Data System (ADS)

Ryan, M.; Stanley, B.

2006-12-01

Solitons have first-order attributes that include shape- and volume-conserving packets of fluid that migrate with characteristic wavelengths, amplitudes, wave numbers, and pulse durations. For ascent in dike-like magma- filled fractures, the soliton pulse duration is directly proportional to the conduit wall region viscosity and inversely proportional to the density contrast that drives the flow. Second-order effects that modify pathways include heat loss to conduit wall rocks, and progressive crystallization episodes along conduit walls. Long-lived (and intermediate duration) historical eruption episodes of Kilauea volcano, Hawai'i, include the 1959 Kilauea summit series at Kilauea Iki, the 1969-1974 series at Mauna Ulu and the 1983-to-present series at Pu'u `O'o-Kupaianaha. For each locale, the eruptions display a variable time-series in their erupted volumes, as well as fountain heights and vent flow rates. Inter-episode repose periods, however, often show broad regularity over extended periods. We suggest that these dynamics represent serendipitous windows into the characteristic system dynamics of deep magma migration beneath Hawai'i: all made possible by the chance clearance of mechanical obstructions allowing virtually open-system behavior. The rhythmic `beat' of eruptive episodes within a long-lived series (and their roughly regular repose periods) arise directly from the soliton migration mechanism. For non-summit locales such as Mauna Ulu and Pu'u `O'o-Kupaianaha, the fluid contents of the sub-caldera reservoir and the shallow molten rift zone core modulate the observed intrusion- eruption dynamics as volumetric displacements transmit down-rift the pressure pulses first felt beneath Halemaumau and the summit caldera. Analytic calculations of wave speed, wave length, batch volume, parcel shapes and repose periods reveal the dependence on material properties appropriate for Kilauea intrusions and eruptions. Analogue laboratory experiments using stiff

Magma Reservoirs from the Perspective of Supervolcanoes and Granitic Plutons: "Big Red Blobs" and "Balloons and Soda Straws" are Real

NASA Astrophysics Data System (ADS)

Christiansen, E. H.

2016-12-01

Simple models describing silicic magma reservoirs and their connections with volcanic rocks have been denigrated as "big red blobs" and "balloons-and-soda straws." Although these models are certainly generalized to convey complex relations, there are multiple reasons to accept the existence of large magma chambers and direct connections between volcanoes and plutonic rocks. These include:-Geophysical evidence (seismic, magnetotelluric, and geodetic) for the existence of large bodies of magma in the crust today. Magma is a mixture of liquids, solids, and fluids. It does not have to be melt rich, nor does it need to be mobile and eruptible; it just has to have melt present. -Eruptions of large volumes (>1,000 km3) of dacitic to rhyolitic magma and large collapse calderas (30-50 km across). -The thermal lifetimes of large bodies are extended by high recharge rates. Individual bodies of magma may exist for tens to hundreds of thousands of years.-Geochronological evidence that pluton lifetimes are similar to those of volcanic fields.-Evidence for incremental emplacement of a pluton is not evidence against the former existence of a large magma reservoir, but the natural consequence of ongoing replenishment and crystallization after eruptions cease. Thus, what might have been a large liquid-dominated system at the time of eruption of a large ignimbrite, is subsequently intruded by new batches of magma as it crystallizes and closes down. This destroys the evidence for a large red blob and creates a composite pluton. -Direct and indirect evidence connect plutons to large eruptions. This is shown by field relations, geochronology, as well as chemical, mineralogical, and isotopic similarities of volcanic and plutonic rocks. -Volcanic and plutonic differentiation patterns are very similar, but differ in some ways because cumulates are preserved in the plutonic record and because intrusions continue to differentiate (liquids separate from solids) until the last bit of liquid is

Volcano-tectonic earthquakes: A new tool for estimating intrusive volumes and forecasting eruptions

NASA Astrophysics Data System (ADS)

White, Randall; McCausland, Wendy

2016-01-01

We present data on 136 high-frequency earthquakes and swarms, termed volcano-tectonic (VT) seismicity, which preceded 111 eruptions at 83 volcanoes, plus data on VT swarms that preceded intrusions at 21 other volcanoes. We find that VT seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more, and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from VEI 0 to ultraplinian VEI 6 at such previously long-dormant volcanoes. Because large eruptions occur most commonly during resumption of activity at long-dormant volcanoes, VT seismicity is an important precursor for the Earth's most dangerous eruptions. VT seismicity precedes all explosive eruptions of VEI ≥ 5 and most if not all VEI 4 eruptions in our data set. Surprisingly we find that the VT seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption, and rarely if ever starts beneath the eruption site itself. The distal VT swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance, beyond which hypocenter depths level out. We summarize several important characteristics of this distal VT seismicity including: swarm-like nature, onset days to years prior to the beginning of magmatic eruptions, peaking of activity at the time of the initial eruption whether phreatic or magmatic, and large non-double couple component to focal mechanisms. Most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the VT seismicity from: Log10 V = 0.77 Log ΣMoment - 5.32, with volume, V, in cubic meters and seismic moment in Newton meters. Because the cumulative seismic moment can be approximated from the size of just the few largest events, and is quite insensitive to precise locations

A fully coupled petrological geodynamical model to investigate the evolution of crustal magma chambers

NASA Astrophysics Data System (ADS)

Rummel, Lisa; Kaus, Boris J. P.; White, Richard W.

2017-04-01

The evolution of crustal magma chambers can be considered from a range of different physical and chemical perspectives. Most previous studies focus either on the petrological side (assuming only thermal effects and ignoring mechanics), or on the mechanical evolution (assuming a fixed melt chemistry). Here, we develop a method that fully couples petrological with geodynamic modelling, by combining a finite element code, MVEP2, with a thermodynamic modelling approach (Perple_X) that takes the evolving chemistry into account. The evolution of melt chemistry in a crustal magma chamber is analyzed by focusing on the effects of depth and temperature as well as size and shape of the magma chamber(s). The models show that each of these factors influences the melting behavior of rocks, the magma composition and their effects on the mechanics in the upper lithosphere. Interactions with country rocks (assimilation), ongoing rock depletion (fractional melting) and a possible open system behavior (fractional crystallization) and their effects on magma chemistry are taken into account. The chemical and mineralogical evolution of the melt source, composition (10 oxide component system) of intrusive and extrusive rocks as well as melt fraction and density are tracked on particles using a marker-in-cell-method in the geodynamic code. After each melt extraction event, the employed phase diagram is updated or recalculated based on the residuum chemistry that shifts the solidus to higher temperatures with sequential melt extraction. The resulting wide range in chemical compositions and the volume of intrusive and extrusive rocks are tracked in time and space over the melting region. The newly generated crust employs phase diagrams which are directly computed from the chemistry of extracted melts. Plutons are able to melt again as long as the local temperature is higher in the model than the solidus temperature in the employed phase diagram. As a result, our models make testable

Linking precious metal enrichment and halogen cycling in mafic magmatic systems: insights from the Rum layered intrusion, NW Scotland

NASA Astrophysics Data System (ADS)

Kelly, A. P.; O'Driscoll, B.; Clay, P. L.; Burgess, R.

2017-12-01

Layered intrusions host the world's largest known concentrations of the platinum-group elements (PGE). Emphasis has been attached to the role of halogen-bearing fluids in concentrating the precious metals, but whether this occurs at the magmatic stage, or via subsequent metasomatism, is actively debated. One obstacle to progress has been the analytical difficulty of measuring low abundances of the halogens in the cumulate products of layered intrusions. To elucidate the importance of the halogens in facilitating PGE-mineralisation, as well as fingerprint halogen provenance and assess the importance of halogen cycling in mafic magma systems more generally, a suite of samples encompassing different stages of activity of the Palaeogene Rum layered intrusion was investigated. Halogen abundances were measured by neutron irradiation noble gas mass spectrometric analysis, permitting the detection of relatively low (ppm-ppb) abundances of Cl, Br and I in mg-sized samples. The samples include PGE-enriched chromite seams, various cumulates (e.g., peridotites), picrites (approximating the Rum parental magma), and pegmatites representing volatile-rich melts that circulated the intrusion at a late-stage in its solidification history. The new data reveal that PGE-bearing chromite seams contain relatively low Cl concentrations (2-3 ppm), with high molar ratios of Br/Cl and I/Cl (0.005 and 0.009, respectively). The picrites and cumulates have Br/Cl and I/Cl ratios close to sub-continental lithospheric mantle values of approximately 0.0013 and 0.00002, respectively, and thus likely reflect the Rum magma source region. A positive correlation between Cl and Br signifies comparable partitioning behaviour in all samples. However, I is more variable, displaying a positive correlation with Cl for more primitive samples (e.g. picrite and peridotite), and seemingly decoupling from Br and Cl in chromite seams and pegmatites. The relative enrichment of I over Cl in the chromite seams points

The Role of Spinel Minerals in Lunar Magma Evolution

NASA Astrophysics Data System (ADS)

Taylor, L. A.; Head, J. W.; Pieters, C. M.; Sunshine, J. M.; Staid, M.; Isaacson, P.; Petro, N. E.

2009-12-01

The Moon Mineralogy Mapper (M3), a NASA guest instrument on Chandrayaan-1, India’s first mission to the Moon, was designed to map the surface mineralogy of the Moon using reflected solar radiation at visible and near-infrared wavelengths, which contain highly diagnostic absorptions due to minerals. The M3 spectrometer has discovered several new and unexpected aspects of the geology and petrology of the Moon, some involving specific oxide phases. Spinel minerals, with the general formula, AB2O4, present clues as to the oxygen fugacity, the nature of magmatic systems, and their evolution, particularly during the early stages of crystallization. On the Moon, with its total lack of Fe3+ and minerals such as magnetite, observed spinels range between spinel, MgAl2O4; hercynite, FeAl2O4; Chromite, FeCr2O4; and ulvöspinel, Fe(FeTi)2O4. They manifest themselves in three distinctly different igneous rock types: highlands rocks of anorthosites/troctolites, gabbro-norites; mare basalts with various TiO2 contents; and basaltic pyroclastic volcanic glasses. Although spinels occur as minor minerals in the Apollo collection, unique rock types dominated by Mg-spinel (with olivine and pyroxene abundances below detection limits, assumed to be ~5%) have been identified by M3 on the Moon. Because the spinel-bearing rocks detected by M3 have no signature of a significant olivine component, they must be dominated by plagioclase and spinel. Pink Mg-spinels typically occur as a minor phase in troctolites (plagioclase + olivine), a highland rock formed after the initial Ferroan Anorthosite (FAN) crust, presumably by serial magmatism deep within the crust, with intrusion upward. FANs were formed by floatation of plagioclase in the lunar magma ocean (LMO), whereas spinels would sink due to their much higher density. Thus, a plagioclase-rich rock type with a strong Mg-spinel spectral signature would have to be part of later highland intrusives. The excess Mg-spinel could be the product of

Drilling into Rhyolitic Magma at Shallow depth at Krafla Volcanic Complex, NE-Iceland

NASA Astrophysics Data System (ADS)

Mortensen, A. K.; Markússon, S. H.; Gudmundsson, Á.; Pálsson, B.

2017-12-01

Krafla volcanic complex in NE-Iceland is an active volcano but the latest eruption was the Krafla Fires in 1975-1984. Though recent volcanic activity has consisted of basaltic fissure eruptions, then it is rhyolitic magma that has been intercepted on at least two occasions while drilling geothermal production wells in the geothermal field suggesting a layered magma plumbing system beneath the Krafla volcanic complex. In 2008 quenched rhyolitic glass was retrieved from the bottom of well KJ-39, which is 2865 m deep ( 2571 m true vertical depth). In 2009 magma was again encountered at an even shallower depth and in more than 2,5 km distance from the bottom of well KJ-39, but in 2009 well IDDP-1 was drilled into magma three times just below 2100 m depth. Only on the last occasion was quenched glass retrieved to confirm that magma had been encountered. In well KJ-39 the quenched glass was rhyolitic in composition. The glass contained resorbed minerals of plagioclase, clinopyroxene and titanomagnetite, but the composition of the glass resembles magma that has formed by partial melting of hydrated basalt. The melt was encountered among cuttings from impermeable, coarse basaltic intrusives at a depth, where the well was anticipated to penetrate the Hólseldar volcanic fissure. In IDDP-1 the quenched glass was also rhyolitic in composition. The glass contained less than 5% of phenocrysts, but the phenocryst assemblage included andesine plagioclase, augite, pigeonite, and titanomagnetite. At IDDP-1 the melt was encountered below a permeable zone composed of fine to coarse grained felsite and granophyre. The disclosure of magma in two wells at Krafla volcanic complex verify that rhyolitic magma can be encountered at shallow depth across a larger area within the caldera. The encounter of magma at shallow depth conforms with that superheated conditions have been found at >2000 m depth in large parts of Krafla geothermal field.

Stuck in the spin cycle: Avoidance and intrusions following breast cancer diagnosis.

PubMed

Bauer, Margaret R; Wiley, Joshua F; Weihs, Karen L; Stanton, Annette L

2017-09-01

Theories and research regarding cognitive and emotional processing during the experience of profound stressors suggest that the presence of intrusive thoughts and feelings predicts greater use of avoidance and that the use of avoidance paradoxically predicts more intrusions. However, empirical investigations of their purported bidirectional relationship are limited. This study presents a longitudinal investigation of the reciprocal relationship between intrusions and avoidance coping over a 6-month period in the year following breast cancer diagnosis. Breast cancer patients (N = 460) completed measures of cancer-related intrusions and avoidance at study entry, 3 months, and 6 months later (i.e., an average of 2, 5, and 8 months after diagnosis, respectively). Cross-lagged panel analyses revealed that intrusive thoughts, feelings, and images at study entry predicted greater avoidance 3 months later, and avoidance coping at study entry predicted intrusions 3 months later, controlling for the stability of intrusions and avoidance as well as time since diagnosis. Findings were not statistically significant for avoidance predicting intrusions, or vice versa, between the 3-month and the 6-month assessment period, during which they declined. These findings provide empirical support for the theoretical contention that avoidance and intrusive thoughts and emotions reciprocally influence one another following stressful events. Additionally, in the months shortly after breast cancer diagnosis, intrusions and avoidance are positively related. However, the relationships attenuate over time, which could indicate resolved cognitive and emotional processing of the cancer experience. Statement of contribution What is already known on this subject? Following stressful life events, individuals often experience intrusive thoughts and feelings related to the event and they report avoidance of such reminders. Many studies demonstrate that greater intrusions predict more

Buffered and unbuffered dike emplacement on Earth and Venus - Implications for magma reservoir size, depth, and rate of magma replenishment

NASA Technical Reports Server (NTRS)

Parfitt, E. A.; Head, J. W., III

1993-01-01

Models of the emplacement of lateral dikes from magma chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source magma reservoir. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.

The chemical and isotopic differentiation of an epizonal magma body: Organ Needle pluton, New Mexico

USGS Publications Warehouse

Verplanck, P.L.; Farmer, G.L.; McCurry, M.; Mertzman, S.A.

1999-01-01

Major and trace element, and Nd and Sr isotopic compositions of whole rocks and mineral separates from the Oligocene, alkaline Organ Needle pluton (ONP), southern New Mexico, constrain models for the differentiation of the magma body parental to this compositionally zoned and layered epizonal intrusive body. The data reveal that the pluton is rimmed by lower ??(Nd) (~-5) and higher 87Sr/86Sr (~0.7085) syenitic rocks than those in its interior (??(Nd) ~ 2, 87Sr/86Sr ~0.7060) and that the bulk compositions of the marginal rocks become more felsic with decreasing structural depth. At the deepest exposed levels of the pluton, the ??(Nd)~-5 lithology is a compositionally heterogeneous inequigranular syenite. Modal, compositional and isotopic data from separates of rare earth element (REE)-bearing major and accesory mineral phases (hornblende, titanite, apatite, zircon) demonstrate that this decoupling of trace and major elements in the inequigranular syenite results from accumulation of light REE (LREE)-bearing minerals that were evidently separated from silicic magmas as the latter rose along the sides of the magma chamber. Chemical and isotopic data for microgranular mafic enclaves, as well as for restite xenoliths of Precambrian granite wall rock, indicate that the isotopic distinction between the marginal and interior facies of the ONP probably reflects assimilation of the wall rock by ??(Nd) ~-2 mafic magmas near the base of the magma system. Fractional crystallization and crystal liquid separation of the crystally contaminated magma at the base and along the margins of the chamber generated the highly silicic magmas that ultimately pooled at the chamber top.

Two hundred years of magma transport and storage at Kīlauea Volcano, Hawai'i, 1790-2008

USGS Publications Warehouse

Wright, Thomas L.; Klein, Fred W.

2014-01-01

Kīlauea’s history can be considered in cycles of equilibrium, crisis, and recovery. The approach of a crisis is driven by a magma supply rate that greatly exceeds the capacity of the plumbing to deliver magma to the surface. Crises can be anticipated by inflation measured at Kīlauea’s summit coupled with an increase in overall seismicity, particularly manifest by intrusion and eruption in the southwest sector of the volcano. Unfortunately the nature of the crisis—for example, large earthquake, new eruption, or edifice-changing intrusion—cannot be specified ahead of time. We conclude that Kīlauea’s cycles are controlled by nonlinear dynamics, which underscores the difficulty in predicting eruptions and earthquakes.

Making mushy magma chambers in the lower continental crust: Cold storage and compositional bimodality

NASA Astrophysics Data System (ADS)

Jackson, Matthew; Blundy, Jon; Sparks, Steve

2017-04-01

Increasing geological and geophysical evidence suggests that crustal magma reservoirs are normally low melt fraction 'mushes' rather than high melt fraction 'magma chambers'. Yet high melt fractions must form within these mush reservoirs to explain the observed flow and eruption of low crystallinity magmas. In many models, crystallinity is linked directly to temperature, with higher temperature corresponding to lower crystallinity (higher melt fraction). However, increasing temperature yields less evolved (silicic) melt composition for a given starting material. If mobile, low crystallinity magmas require high temperature, it is difficult to explain how they can have evolved composition. Here we use numerical modelling to show that reactive melt flow in a porous and permeable mush reservoir formed by the intrusion of numerous basaltic sills into the lower continental crust produces magma in high melt fraction (> 0.5) layers akin to conventional magma chambers. These magma-chamber-like layers contain evolved (silicic) melt compositions and form at low (close to solidus) temperatures near the top of the mush reservoir. Evolved magma is therefore kept in 'cold storage' at low temperature, but also at low crystallinity so the magma is mobile and can leave the mush reservoir. Buoyancy-driven reactive flow and accumulation of melt in the mush reservoir controls the temperature and composition of magma that can leave the reservoir. The modelling also shows that processes in lower crustal mush reservoirs produce mobile magmas that contain melt of either silicic or mafic composition. Intermediate melt compositions are present but are not within mobile magmas. Silicic melt compositions are found at high melt fraction within the magma-chamber like layers near the top of the mush reservoir. Mafic melt compositions are found at high melt fraction within the cooling sills. Melt elsewhere in the reservoir has intermediate composition, but remains trapped in the reservoir because

Mechanisms of differentiation in the Skaergaard magma chamber

NASA Astrophysics Data System (ADS)

Tegner, C.; Lesher, C. E.; Holness, M. B.; Jakobsen, J. K.; Salmonsen, L. P.; Humphreys, M. C. S.; Thy, P.

2012-04-01

The Skaergaard intrusion is a superb natural laboratory for studying mechanisms of magma chamber differentiation. The magnificent exposures and new systematic sample sets of rocks that solidified inwards from the roof, walls and floor of the chamber provide means to test the relative roles of crystal settling, diffusion, convection, liquid immiscibility and compaction in different regions of the chamber and in opposite positions relative to gravity. Examination of the melt inclusions and interstitial pockets has demonstrated that a large portion of intrusion crystallized from an emulsified magma chamber composed of immiscible silica- and iron-rich melts. The similarity of ratios of elements with opposite partitioning between the immiscible melts (e.g. P and Rb) in wall, floor and roof rocks, however, indicate that large-scale separation did not occur. Yet, on a smaller scale of metres to hundred of metres and close to the interface between the roof and floor rocks (the Sandwich Horizon), irregular layers and pods of granophyre hosted by extremely iron-rich cumulates point to some separation of the two liquid phases. Similar proportions of the primocryst (cumulus) minerals in roof, wall and floor rocks indicate that crystal settling was not an important mechanism. Likewise, the lack of fractionation of elements with different behavior indicate that diffusion and fluid-driven metasomatism played relatively minor roles. Compositional convection and/or compaction within the solidifying crystal mush boundary layer are likely the most important mechanisms. A correlation of low trapped liquid fractions (calculated from strongly incompatible elements) in floor rocks with high fractionation density (the density difference between the crystal framework and the liquid) indicate that compaction is the dominating process in expelling evolved liquid from the crystal mush layer. This is supported by high and variable trapped liquid contents in the roof rocks, where gravity

Mafic microgranular enclave swarms in the Chenar granitoid stock, NW of Kerman, Iran: evidence for magma mingling

NASA Astrophysics Data System (ADS)

Arvin, M.; Dargahi, S.; Babaei, A. A.

2004-10-01

Mafic microgranular enclaves (MME) are common in the Early to Middle Miocene Chenar granitoid stock, northwest of Kerman, which is a part of Central Iranian Eocene volcanic belt. They occur individually and in homogeneous or heterogeneous swarms. The MME form a number of two-dimensional structural arrangements, such as dykes, small rafts, vortices, folded lens-shapes and late swarms. The enclaves are elongated, rounded to non-elongated and subrounded in shape and often show some size-sorting parallel to direction of flow. Variation in the elongation of enclaves could reflect variations in the viscosity of the enclave, the time available for enclave deformation and differential strain during flow of the host granitoid magma. The most effective mechanism in the formation of enclave swarms in the Chenar granitoid stock was velocity gradient-related convection currents in the granitoid magma chamber. Gravitational sorting and the break-up of heterogeneous dykes also form MME swarms. The MME (mainly diorite to diorite gabbro) have igneous mineralogy and texture, and are marked by sharp contacts next to their host granitoid rocks. The contact is often marked by a chilled margin with no sign of solid state deformation. Evidence of disequilibrium is manifested in feldspars by oscillatory zoning, resorbed rims, mantling and punctuated growth, together with overgrowth of clinopyroxene/amphibole on quartz crystals, the acicular habit of apatites and the development of Fe-Ti oxides along clinopyroxene cleavages. These observations suggest that the MMEs are derived from a hybrid-magma formed as a result of the intrusion of a mafic magma into the base of a felsic magma chamber. The density contrast between hybrid-magma and the overlying felsic magma was reduced by the release of dissolved fluids and the ascent of exsolved gas bubbles from the mafic magma into the hybrid zone. Further convection in the magma chamber dispersed the hybridized magma as globules in the upper parts of

The fluid dynamics of a basaltic magma chamber replenished by influx of hot, dense ultrabasic magma

NASA Astrophysics Data System (ADS)

Huppert, Herbert E.; Sparks, R. Stephen J.

1981-09-01

This paper describes a fluid dynamical investigation of the influx of hot, dense ultrabasic magma into a reservoir containing lighter, fractionated basaltic magma. This situation is compared with that which develops when hot salty water is introduced under cold fresh water. Theoretical and empirical models for salt/water systems are adapted to develop a model for magmatic systems. A feature of the model is that the ultrabasic melt does not immediately mix with the basalt, but spreads out over the floor of the chamber, forming an independent layer. A non-turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion. Both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock. The convection continues until the two layers have almost the same temperature. The compositions of the layers remain distinct due to the low diffusivity of mass compared to heat. The temperatures of the layers as functions of time and their cooling rate depend on their viscosities, their thermal properties, the density difference between the layers and their thicknesses. For a layer of ultrabasic melt (18% MgO) a few tens of metres thick at the base of a basaltic (10% MgO) magma chamber a few kilometres thick, the temperature of the layers will become nearly identical over a period of between a few months and a few years. During this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling. Olivines only settle after the two layers have nearly reached thermal equilibrium. At this stage residual basaltic melt segregates as the olivines sediment in the lower layer. Depending on its density, the released basalt can either mix convectively with the overlying basalt layer, or can continue as a separate

Magma surge from the mantle: the Father's Day Eruption, Kīlauea Volcano, Hawai'i

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

2015-12-01

The geometry of the shallow plumbing system of Kīlauea Volcano, Hawai'i, is constrained by both geophysical and petrologic studies, yet the loci of lower crustal magma storage and timescales of magma ascent are almost entirely unknown. The petrography and texture of erupted magmas are largely overprinted by processes in the shallow reservoir and conduit. Direct petrological evidence for lower crustal storage and transport is enigmatic but exists in the form of fine-scale crystal zoning in the cores of olivine phenocrysts, in the geochemical heterogeneity of melt inclusions and in fluid inclusion density. The 2007 Father's Day intrusion and eruption occurred at the culmination of a surge in magma supply to the summit reservoir and during a period of heightened CO2 outgassing flux. The erupted lavas provide an opportunity to analyze atypically primitive melts, with > 8.5 wt% MgO in the whole rock, which have undergone relatively little shallow crustal processing. We characterise melt inclusions and their host olivine crystals through a detailed study of olivine morphology, diffusion modelling, and melt and fluid inclusion geochemistry. We show that the melt inclusions preserve primitive geochemical heterogeneity, which we use to reconstruct fractionation, mixing and degassing processes through the crust. We infer timescales and pressures of magma ascent, storage, and CO2 degassing through the crustal plumbing system. These observations are interpreted in the context of the exceptionally detailed set of volcano monitoring data at Kīlauea Volcano.

Disequilibrium dihedral angles in layered intrusions: the microstructural record of fractionation

NASA Astrophysics Data System (ADS)

Holness, Marian; Namur, Olivier; Cawthorn, Grant

2013-04-01

The dihedral angle formed at junctions between two plagioclase grains and a grain of augite is only rarely in textural equilibrium in gabbros from km-scale crustal layered intrusions. The median of a population of these disequilibrium angles, Θcpp, varies systematically within individual layered intrusions, remaining constant over large stretches of stratigraphy with significant increases or decreases associated with the addition or reduction respectively of the number of phases on the liquidus of the bulk magma. The step-wise changes in Θcpp are present in Upper Zone of the Bushveld Complex, the Megacyclic Unit I of the Sept Iles Intrusion, and the Layered Series of the Skaergaard Intrusion. The plagioclase-bearing cumulates of Rum have a bimodal distribution of Θcpp, dependent on whether the cumulus assemblage includes clinopyroxene. The presence of the step-wise changes is independent of the order of arrival of cumulus phases and of the composition of either the cumulus phases or the interstitial liquid inferred to be present in the crystal mush. Step-wise changes in the rate of change in enthalpy with temperature (ΔH) of the cooling and crystallizing magma correspond to the observed variation of Θcpp, with increases of both ΔH and Θcpp associated with the addition of another liquidus phase, and decreases of both associated with the removal of a liquidus phase. The replacement of one phase by another (e.g. olivine ⇔ orthpyroxene) has little effect on ΔH and no discernible effect on Θcpp. An increase of ΔH is manifest by an increase in the fraction of the total enthalpy budget that is the latent heat of crystallization (the fractional latent heat). It also results in an increase in the amount crystallized in each incremental temperature drop (the crystal productivity). An increased fractional latent heat and crystal productivity result in an increased rate of plagioclase growth compared to that of augite during the final stages of solidification

Magma wagging and whirling in volcanic conduits

NASA Astrophysics Data System (ADS)

Liao, Yang; Bercovici, David; Jellinek, Mark

2018-02-01

Seismic tremor characterized by 0.5-7 Hz ground oscillations commonly occur before and during eruptions at silicic volcanoes with widely ranging vent geometries and edifice structures. The ubiquitous characteristics of this tremor imply that its causes are potentially common to silicic volcanoes. Here we revisit and extend to three dimensions the magma-wagging model for tremor (Jellinek and Bercovici, 2011; Bercovici et al., 2013), wherein a stiff magma column rising in a vertical conduit oscillates against a surrounding foamy annulus of bubbly magma, giving rise to tremor. While prior studies were restricted to two-dimensional lateral oscillations, here we explore three-dimensional motion and additional modes of oscillations. In the absence of viscous damping, the magma column undergoes 'whirling' motion: the center of each horizontal section of the column traces an elliptical trajectory. In the presence of viscous effect we identify new 'coiling' and 'uncoiling' column bending shapes with relatively higher and comparable rates of dissipation to the original two-dimensional magma wagging model. We also calculate the seismic P-wave response of the crustal material around the volcanic conduit to the new whirling motions and propose seismic diagnostics for different wagging patterns using the time-lag between seismic stations. We test our model by analyzing pre-eruptive seismic data from the 2009 eruption of Redoubt Volcano. In addition to suggesting that the occurrence of elliptical whirling motion more than 1 week before the eruption, our analysis of seismic time-lags also implies that the 2009 eruption was accompanied by qualitative changes in the magma wagging behavior including fluctuations in eccentricity and a reversal in the direction of elliptical whirling motion when the eruption was immediately impending.

Extremely High Magma Emplacement Rates Recorded in the Golden Horn Batholith, WA

NASA Astrophysics Data System (ADS)

Eddy, M. P.; Bowring, S. A.; Tepper, J. H.; Miller, R. B.

2015-12-01

High SiO2 rhyolites emplaced during 'super-eruptions' demonstrate that large volumes of eruptible magma can exist in the upper crust. However, the timescale over which the magma reservoirs that source these eruptions are built remains controversial. Thermal models suggest that magma emplacement rates need to be > 0.005-0.01 km3/yr in order to accumulate enough eruptible magma to source a 'super-eruption'. Yet, these rates are higher than the time-averaged rates (< 0.001 km3/yr) for nearly all well-studied granitoid plutonic complexes. This disparity contradicts geologic evidence suggesting that the high SiO2 rhyolites emplaced during 'super-eruptions' are extracted from crystal rich magma chambers that should be preserved in the geologic record as granodioritic and granitic plutons. We quantify time-averaged magma emplacement rates for the upper crustal Golden Horn batholith, WA based on new geologic mapping and U-Pb zircon CA-IDTIMS geochronology. The batholith is exposed over 310 km3 and can be separated in the field into five intrusive units. High topography allows the 3D geometry of each phase to be constrained and their volumes range from < 100 km3 to > 400 km3. U-Pb zircon geochronology reveals that four of the five phases were assembled incrementally and distinct zircon populations from samples within these phases suggest that individual magmatic pulses had fully crystallized before the next arrived. However, six nearly identical U-Pb zircon dates from a > 400 km3 rapakivi granite show that this phase was built in ca. 50 kyr and that large portions may have been emplaced nearly simultaneously. The implied emplacement rate for this phase (≥ 0.008 km3/yr) is in agreement with those predicted for assembly of the upper crustal magma chambers that source 'super-eruptions', and it may provide a rare and unprecedented opportunity to study the processes that occur in such chambers.

Microgravity changes at the Laguna del Maule volcanic field: Magma-induced stress changes facilitate mass addition

NASA Astrophysics Data System (ADS)

Miller, C. A.; Le Mével, H.; Currenti, G.; Williams-Jones, G.; Tikoff, B.

2017-04-01

Time-dependent, or 4-D, microgravity changes observed at the Laguna del Maule volcanic field, Chile, since 2013, indicate significant (1.5 × 1011 kg) ongoing mass injection. Mass injection is focused along the Troncoso fault, and subparallel structures beneath the lake at 1.5-2 km depth, and is best modeled by a vertical rectangular prism source. The low-density change (156 to 307 kg/m3) and limited depth extent suggest a mechanism of hydrothermal fluid intrusion into existing voids, or voids created by the substantial uplift, rather than deeper-sourced dike intrusion of rhyolite or basalt magma. Although the gravity changes are broadly spatially coincident with ongoing surface deformation, existing models that explain the deformation are deeper sourced and cannot explain the gravity changes. To account for this discrepancy and the correspondence in time of the deformation and gravity changes, we explore a coupled magmatectonic interaction mechanism that allows for shallow mass addition, facilitated by deeper magma injection. Computing the strain, and mean, normal, and Coulomb stress changes on northeast trending faults, caused by the opening of a sill at 5 km depth, shows an increase in strain and mean and normal stresses along these faults, coincident with the areas of mass addition. Seismic swarms in mid-2012 to the west and southwest of the mass intrusion area may be responsible for dynamically increasing permeability on the Troncoso fault, promoting influx of hydrothermal fluids, which in turn causes larger gravity changes in the 2013 to 2014 interval, compared to the subsequent intervals.

Origin of the Mackenzie large igneous province and sourcing of flood basalts from layered intrusions

NASA Astrophysics Data System (ADS)

Day, J. M.; Pearson, D.

2013-12-01

The 1.27 Ga Coppermine continental flood basalt (CFB) in northern Canada represents the extrusive manifestation of the Mackenzie large igneous province (LIP) that includes the Mackenzie dyke swarm and the Muskox layered intrusion. New Re-Os isotope and highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data are reported together with whole-rock major- and trace-element abundances and Nd isotopes to examine the behaviour of the HSE during magmatic differentiation and to place constraints on the extent of crustal interaction with mantle-derived melts. Mineral-chemical data are also reported for an unusual andesite glass flow (4.9 wt.% MgO) found in proximity to newly recognised picrites (>20 wt.% MgO) in the lowermost stratigraphy of the Coppermine CFB. Compositions of mineral phases in the andesite are similar to equivalent phases found in Muskox Intrusion chromitites and the melt composition is identical to Muskox chromite melt inclusions. Elevated HSE contents (e.g., 3.8 ppb Os) and the mantle-like initial Os isotope composition of this andesitic glass contrast strongly with oxygen isotope and lithophile element evidence for extensive crustal contamination. These signatures implicate an origin for the glass as a magma mingling product formed within the Muskox Intrusion during chromitite genesis. The combination of crust and mantle signatures define roles for both these reservoirs in chromitite genesis, but the HSE appear to be dominantly mantle-sourced. Combined with Nd isotope data that places the feeder for lower Coppermine CFB picrites and basalts within the Muskox Intrusion, this provides the strongest evidence yet for direct processing of some CFB within upper-crustal magma chambers. Modeling of absolute and relative HSE abundances in CFB reveal that HSE concentrations decrease with increasing fractionation for melts with <8×1 wt.% MgO in the Coppermine CFB, with picrites (>13.5wt.% MgO) from CFB having higher Os abundances than ocean island

First steps in using machine learning on fMRI data to predict intrusive memories of traumatic film footage

PubMed Central

Clark, Ian A.; Niehaus, Katherine E.; Duff, Eugene P.; Di Simplicio, Martina C.; Clifford, Gari D.; Smith, Stephen M.; Mackay, Clare E.; Woolrich, Mark W.; Holmes, Emily A.

2014-01-01

After psychological trauma, why do some only some parts of the traumatic event return as intrusive memories while others do not? Intrusive memories are key to cognitive behavioural treatment for post-traumatic stress disorder, and an aetiological understanding is warranted. We present here analyses using multivariate pattern analysis (MVPA) and a machine learning classifier to investigate whether peri-traumatic brain activation was able to predict later intrusive memories (i.e. before they had happened). To provide a methodological basis for understanding the context of the current results, we first show how functional magnetic resonance imaging (fMRI) during an experimental analogue of trauma (a trauma film) via a prospective event-related design was able to capture an individual's later intrusive memories. Results showed widespread increases in brain activation at encoding when viewing a scene in the scanner that would later return as an intrusive memory in the real world. These fMRI results were replicated in a second study. While traditional mass univariate regression analysis highlighted an association between brain processing and symptomatology, this is not the same as prediction. Using MVPA and a machine learning classifier, it was possible to predict later intrusive memories across participants with 68% accuracy, and within a participant with 97% accuracy; i.e. the classifier could identify out of multiple scenes those that would later return as an intrusive memory. We also report here brain networks key in intrusive memory prediction. MVPA opens the possibility of decoding brain activity to reconstruct idiosyncratic cognitive events with relevance to understanding and predicting mental health symptoms. PMID:25151915

The crustal magma storage system of Volcán Quizapu, Chile, and the effects of magma mixing on magma diversity

USGS Publications Warehouse

Bergantz, George W.; Cooper, Kari M.; Hildreth, Edward; Ruprecht, Phillipp

2012-01-01

Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km3) of Volcán Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcán Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An25–40) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcán Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic

Empirical equations to predict the sulfur content of mafic magmas at sulfide saturation and applications to magmatic sulfide deposits

NASA Astrophysics Data System (ADS)

Li, Chusi; Ripley, Edward M.

2005-03-01

Empirical equations to predict the sulfur content of a mafic magma at the time of sulfide saturation have been developed based on several sets of published experimental data. The S content at sulfide saturation (SCSS) can be expressed as: ln X_{text S} = 1.229 - 0.74(10^4/T) - 0.021(P) - 0.311 ln X_{{text{FeO}}} - 6.166X_{{text{SiO}}_{text{2}}} - 9.153X_{{text{Na}}_{text{2}} {text{O + K}}_{text{2}} {text{O}}} - 1.914X_{{text{MgO}}} + 6.594X_{{text{FeO}}} where T is in degrees Kelvin, X is mole fraction and P is in kbar. The squared multiple correlation coefficient ( r 2) for the equation is 0.88. Application of the equation to data from sulfide-saturated mid-ocean ridge basalts (MORB) samples show that the SCSS is closely predicted for primitive MORBs, but that accuracy decreases for lower T (<1,130°C) and more evolved MORB samples. This suggests that because the calibrations are based on anhydrous experimental runs done at temperatures of 1,200°C and above, it is not possible to extrapolate them to significantly lower temperatures and hydrous conditions. Because the SCSS of a primitive MORB magma increases with decreasing P, sulfide saturation in MORB appears to be a function of the degree of en route assimilation of S from country rocks as well as the degree of fractional crystallization in shallow staging chambers. Application of the equation to the high- T impact melt sheet that produced the Sudbury Igneous Complex and associated Ni-Cu sulfide ores indicates that sulfide-saturation was reached at 1,500°C, well above the start of orthopyroxene crystallization at 1,190°C. This would permit ample time for the gravitational settling and collection of immiscible sulfide liquid that produced the high-grade ore bodies. The development of a platinum group element (PGE)-enriched layer in the Sonju Lake Intrusion of the Duluth Complex is thought to be due to the attainment of sulfide saturation in the magma after a period of fractional crystallization. Using the

Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

USGS Publications Warehouse

Kusky, Timothy M.; Bradley, Dwight C.; Donely, D. Thomas; Rowley, David; Haeussler, Peter J.

2003-01-01

have sheeted margins and appear to have intruded along extensional jogs in margin-parallel strike-slip faults, whereas others form significant angles with the main faults and may have been influenced by minor faults of other orientations. Some of the plutons of the Sanak-Baranof belt have their long axes oriented parallel to faults of an orthorhombic fault set, implying that these faults may have provided a conduit for magma emplacement. This orthorhombic set of late faults is interpreted to have initially formed during the ridge subduction event, and continued to be active for a short time after passage of the triple junction. ENE-striking dextral faults of this orthorhombic fault system exhibit mutually crosscutting relationships with Eocene dikes related to ridge subduction, and mineralized strike-slip and normal faults of this system have yielded 40Ar/39Ar ages identical to near-trench intrusives related to ridge subduction. Movement on the orthorhombic fault system accommodated exhumation of deeper levels of the southern Alaska accretionary wedge, which is interpreted as a critical taper adjustment to subduction of younger oceanic lithosphere during ridge subduction. These faults therefore accommodate both deformation of the wedge and assisted emplacement of near-trench plutons. Structures that crosscut the plutons and aureoles include the orthorhombic fault set and dextral strike-slip faults, reflecting a new kinematic regime established after ridge subduction, during underthrusting of the trailing oceanic plate with new dextral-oblique convergence vectors with the overriding plate. The observation that the orthorhombic fault set both cuts and is cut by Eocene intrusives demonstrates the importance of these faults for magma emplacement in the forearc.A younger, ca. 35 Ma suite of plutons intrudes the Chugach terrane in the Prince William Sound region, and their intrusion geometry was strongly influenced by pre-existing faults developed during ridge subduction

Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 2. Coeruptive deflation, July-August 2008

USGS Publications Warehouse

Lu, Zhong; Dzurisin, Daniel

2010-01-01

A hydrovolcanic eruption near Cone D on the floor of Okmok caldera, Alaska, began on 12 July 2008 and continued until late August 2008. The eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and ∼3 km below sea level (bsl), which began immediately after Okmok's previous eruption in 1997. In this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar (InSAR) techniques to produce a suite of 2008 coeruption deformation maps. Most of the surface deformation that occurred during the eruption is explained by deflation of a Mogi-type source located beneath the center of the caldera and 2–3 km bsl, i.e., essentially the same source that inflated prior to the eruption. During the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1/e time constant of ∼13 days. We envision a sponge-like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath Okmok caldera. The rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface. A similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring-fracture system.

The variation of magma discharge during basaltic eruptions

NASA Technical Reports Server (NTRS)

Wadge, G.

1981-01-01

The rate at which basaltic magma is discharged during many eruptions varies substantially. An individual eruption has an eruption rate, which is the volumetric rate of discharge averaged over the whole or a major part of an eruption, and an effusion rate, which is the volumetric flux rate at any given time. In many cases, the effusion rate soon reaches a maximum after a short period of waxing flow (partly because of magmatic expansion); it then falls more slowly in the later parts of the eruption. The release of elastic strain energy from stored magma and the subvolcanic reservoir during eruption can give a waning flow of this type an exponential form. A comparison of the eruption rates of eruptions of Mauna Loa, Kilauea and Etna shows that for each volcano there is a trend of decreasing effusion rate with increasing duration of eruption. It is noted that this relationship is not predicted by a simple elastic model of magma release. Two other processes are invoked to explain the eruptive histories of these volcanoes: modification of the eruptive conduits and the continued supply of magma from depth during eruption.

Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Zhao, Yan; Sun, Yong; Diwu, Chunrong; Zhu, Tao; Ao, Wenhao; Zhang, Hong; Yan, Jianghao

2017-05-01

The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic. Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430-410 Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet + amphibole + rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370-360 Ma) and middle Carboniferous stage (ca. 335-315 Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of

Craters of elevation / forced folds: more examples of shallow magma accumulation and its consequences

NASA Astrophysics Data System (ADS)

van Wyk de Vries, Benjamin; Marquez, Alvaro; Craig, Magee; Valdislav, Rapprich; Hetherington, Rachel; Bastow, Ian

2016-04-01

Craters of elevation are uplifts with apical depressions that are caused by shallow magma intrusion. Forced folds are dome-like folds caused by magma intrusion that also have apical extensional structures. They are the same feature described from the different viewpoints of the volcanologist and the structural geologist. While working on such features in the Chaîne des Puys (Central France), and Ethiopia we have been searching for other examples in the world. This is our most up to date review of such phenomena taken from a global search in the world of volcanology where some stunning examples are seen in the landscape, and in outcrop. We also show such features from tectonics data and literature, where such features are superbly displayed in seismic data. We take three examples, the Puy de Gouttes, in the Chaîne des Puys, the Montana Encantada in Lanzarote, which we have mapped in the field, and the Diamond Craters National Monument in Oregon to show the different structures and possible evolutionary trends that such features can follow. We use the observations to integrate the possible eruptive, deformational and structural events that can combine in a forced fold to create the surface features observed at such craters of elevation. The hazard implications of the growth and destruction of such features are assessed.

The interplay between crystallization, replenishment and hybridization in large felsic magma chambers

NASA Astrophysics Data System (ADS)

Bateman, R.

1995-09-01

While hybridized granitoid magmas are readily identifiable, the mechanisms of hybridization in large crustal magma chambers are so not clearly understood. Characteristic features of hybrid granitoids are (1) both the granitoid and included enclaves are commonly hybrids, as shown by mineralogy, geochemistry and isotopes; (2) mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early; (3) zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution; (4) mafic end-members in hybrids are commonly fractionated magmas and (5) stratification in subvolcanic granitoid magma chambers is not uncommon, and stratification has been identified in some deeper level plutons. Hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma. Experimental work with magma analogues and theoretical considerations reveal very severe thermal, rheological and dynamical limitations on mixing: only very similar (composition, temperature) magmas are likely to mix to homogeneity, and only moderately silicic hybrids are likely to be produced. However, "impossibly" silicic hybrids do exist. Synchronous, interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas, in the following manner. A mafic magma intrudes into the base of a stratified felsic magma and is cooled against it. Crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber. Subsequently, melt released by crystallization pf this, now-hybrid zone mixes with adjacent, more felsic zones. Thus, a suite of hybrid magmas are progressively formed. Density inhibitions are overcome by the generation of relatively low density residual melts. As crystallization proceeds, later injections are preserved as dykes and enclaves composed of hybrid magma. In

Forecasting deflation, intrusion and eruption at inflating volcanoes

NASA Astrophysics Data System (ADS)

Blake, Stephen; Cortés, Joaquín A.

2018-01-01

A principal goal of volcanology is to successfully forecast the start of volcanic eruptions. This paper introduces a general forecasting method, which relies on a stream of monitoring data and a statistical description of a given threshold criterion for an eruption to start. Specifically we investigate the timing of intrusive and eruptive events at inflating volcanoes. The gradual inflation of the ground surface is a well-known phenomenon at many volcanoes and is attributable to pressurised magma accumulating within a shallow chamber. Inflation usually culminates in a rapid deflation event caused by magma escaping from the chamber to produce a shallow intrusion and, in some cases, a volcanic eruption. We show that the ground elevation during 15 inflation periods at Krafla volcano, Iceland, increased with time towards a limiting value by following a decaying exponential with characteristic timescale τ. The available data for Krafla, Kilauea and Mauna Loa volcanoes show that the duration of inflation (t*) is approximately equal to τ. The distribution of t* / τ values follows a log-logistic distribution in which the central 60% of the data lie between 0.99

SHRIMP U-Pb zircon geochronology and thermal modeling of multilayer granitoid intrusions. Implications for the building and thermal evolution of the Central System batholith, Iberian Massif, Spain

NASA Astrophysics Data System (ADS)

Díaz Alvarado, Juan; Fernández, Carlos; Castro, Antonio; Moreno-Ventas, Ignacio

2013-08-01

This work shows the results of a U-Pb SHRIMP zircon geochronological study of the central part of the Gredos massif (Spanish Central System batholith). The studied batholith is composed of several granodiorite and monzogranite tabular bodies, around 1 km thick each, intruded into partially molten pelitic metasediments. Granodiorites and monzogranites, belonging to three distinct intrusive bodies, and samples of anatectic leucogranites have been selected for SHRIMP U-Pb zircon geochronology. Distinct age groups, separated by up to 20 Ma, have been distinguished in each sample. Important age differences have also been determined among the most representative age groups of the three analyzed granitoid bodies: 312.6 ± 2.8 Ma for the Circo de Gredos Bt-granodiorites (floor intrusive layer), 306.9 ± 1.5 Ma for the Barbellido-Plataforma granitoids (top intrusive layer) and 303.5 ± 2.8 Ma for Las Pozas Crd-monzogranites (middle intrusive layer). These age differences are interpreted in terms of sequential emplacement of the three intrusive bodies, contemporary with the Late Paleozoic D3 deformation phase. The anatectic leucogranites are coeval to slightly younger than the adjacent intrusive granodiorites and monzogranites (305.4 ± 1.6 Ma for Refugio del Rey leucogranites and 303 ± 2 Ma for migmatitic hornfelses). It is suggested that these anatectic magmas were generated in response to the thermal effects of granodiorite intrusions. Thermal modeling with COMSOL Multiphysics® reveals that sequential emplacement was able to keep the thermal conditions of the batholith around the temperature of zircon crystallization in granitic melts (around 750 °C) for several million of years, favoring the partial melting of host rocks and the existence of large magma chambers composed of crystal mush prone to be rejuvenated after new intrusions.

Orthodontic intrusion of maxillary incisors: a 3D finite element method study

PubMed Central

Saga, Armando Yukio; Maruo, Hiroshi; Argenta, Marco André; Maruo, Ivan Toshio; Tanaka, Orlando Motohiro

2016-01-01

Objective: In orthodontic treatment, intrusion movement of maxillary incisors is often necessary. Therefore, the objective of this investigation is to evaluate the initial distribution patterns and magnitude of compressive stress in the periodontal ligament (PDL) in a simulation of orthodontic intrusion of maxillary incisors, considering the points of force application. Methods: Anatomic 3D models reconstructed from cone-beam computed tomography scans were used to simulate maxillary incisors intrusion loading. The points of force application selected were: centered between central incisors brackets (LOAD 1); bilaterally between the brackets of central and lateral incisors (LOAD 2); bilaterally distal to the brackets of lateral incisors (LOAD 3); bilaterally 7 mm distal to the center of brackets of lateral incisors (LOAD 4). Results and Conclusions: Stress concentrated at the PDL apex region, irrespective of the point of orthodontic force application. The four load models showed distinct contour plots and compressive stress values over the midsagittal reference line. The contour plots of central and lateral incisors were not similar in the same load model. LOAD 3 resulted in more balanced compressive stress distribution. PMID:27007765

Transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers: An experimental study

NASA Astrophysics Data System (ADS)

Guo, Haihao; Audétat, Andreas

2017-02-01

In order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic, upper crustal magma chambers, fluid-rock partition coefficients (Dfluid/rock) of Li, B, Na, S, Cl, K, Mn, Fe, Rb, Sr, Ba, Ce, Cu, Zn, Ag, Cd, Mo, As, Se, Sb, Te, W, Tl, Pb and Bi were determined experimentally at 2 kbar and 850 °C close to the solidus of mafic magma. In a first step, volatile-bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile-bearing fluids at 1200 °C/10 kbar in piston cylinder presses. The hydrous glasses were then equilibrated in subsequent experiments at 850 °C/2 kbar in cold-seal pressure vessels, which caused 80-90% of the melt to crystallize. After 0.5-2.0 days of equilibration, the exsolved fluid was trapped by means of in-situ fracturing in the form of synthetic fluid inclusions in quartz. Both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser-ablation ICP-MS for major and trace elements. Reverse experiments were conducted by equilibrating metal-bearing aqueous solutions with rock powder and then trapping the fluid. In two additional experiments, information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic magma with overlying silicic melts. The combined results suggest that under the studied conditions S, Cl, Cu, Se, Br, Cd and Te are most volatile (Dfluid/rock >10), followed by Li, B, Zn, As, Ag, Sb, Cs, W, Tl, Pb and Bi (Dfluid/rock = 1-10). Less volatile are Na, Mg, K, Ca, Mn, Fe, Rb, Sr, Mo and Rb (Dfluid/rock 0.1-1), and the least fluid-mobile elements are Al, Si, Ti, Zr, Ba and Ce (Dfluid/rock <0.1). This trend is broadly consistent with relative element volatilities determined on natural high-temperature fumarole gases, although some differences exist. Based on the volatility data and measured mineral-melt and sulfide-melt partition coefficients, volatile fluxing in

Phase equilibria modeling in igneous petrology: use of COMAGMAT model for simulating fractionation of ferro-basaltic magmas and the genesis of high-alumina basalt

NASA Astrophysics Data System (ADS)

Ariskin, Alexei A.

1999-05-01

A new version of COMAGMAT-3.5 model designed for computer simulations of equilibrium and fractional crystallization of basaltic magmas at low to high pressures is presented. The most important modifications of COMAGMAT include an ability to calculate more accurately the crystallization of magnetite and ilmenite, allowing the user to study numerically the effect of oxygen fugacity on basalt magma fractionation trends. Methodological principles of the use of COMAGMAT were discussed based on its thermodynamical and empirical basis, including specific details of the model calibration. Using COMAGMAT-3.5 a set of phase equilibria calculations (called Geochemical Thermometry) has been conducted for six cumulative rocks from the Marginal Border Series of the Skaergaard intrusion. As a result, initial magma temperature (1165±10°C) and trapped melt composition proposed to be parental magma to the Skaergaard intrusion were determined. Computer simulations of perfect fractionation of this composition as well as another proposed parent produced petrochemical trends opposite to those followed from natural observations. This is interpreted as evidence for an initial Skaergaard magma containing a large amount of olivine and plagioclase crystals (about 40-45%), so that the proposed and calculated parents are related through the melt trapped in the crystal-liquid mixture. This promotes the conclusion that the Skaergaard magma fractionation process was intermediate between equilibrium and fractional crystallization. In this case the classic Wager's trend should be considered an exception rather than a rule for the differentiation of ferro-basaltic magmas. A polybaric version of COMAGMAT has been applied for the genetic interpretation of a volcanic suite from the Klyuchevskoi volcano, Kamchatka, Russia. To identify petrological processes responsible for the observed suite ranging from high-magnesia to high-alumina basalts, we used the model to simulate the Klyuchevskoi suite

The effect of giant flank collapses on magma pathways and location of volcanic vents

NASA Astrophysics Data System (ADS)

Maccaferri, Francesco; Richter, Nicole; Walter, Thomas

2017-04-01

Flank collapses have been identified at tall volcanoes and ocean islands worldwide. They are recurrent processes, significantly contributing to the morphological and structural evolution of volcanic edifices, and they often occur in interaction with magmatic activity. Moreover, it has been observed that the intrusion pathways and eruption's sites often differ before and after flank collapses. While it is understood that dyke intrusions might destabilise a volcano flank, and a moving flank might create the space needed for further intrusions, the effect of collapses on the magma pathways has been rarely addressed. Here we use a boundary element model for dyke propagation to study the effect of the stress redistribution due to a flank collapse on the location of eruptive vents. We use our model to simulate the path of magmatic intrusion after the collapse of the eastern flank of Fogo Volcano, Cabe Verde. We find that the competition between loading stress due to the volcanic edifice and unloading due to the collapse of a flank favours magmatic activity to cluster within the collapse scar, displaced with respect to the pre-collapse volcanic centre. Our results are compared with geomorphological observations at Fogo Island and are discussed in the general context of the long-term evolution intraplate volcanic ocean islands worldwide.

Oxygen isotope study of the Long Valley magma system, California: isotope thermometry and convection in large silicic magma bodies

NASA Astrophysics Data System (ADS)

Bindeman, Ilya; Valley, John

2002-07-01

Products of voluminous pyroclastic eruptions with eruptive draw-down of several kilometers provide a snap-shot view of batholith-scale magma chambers, and quench pre-eruptive isotopic fractionations (i.e., temperatures) between minerals. We report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite, pyroxene, and zircon from individual pumice clasts of ignimbrite and fall units of caldera-forming 0.76 Ma Bishop Tuff (BT), pre-caldera Glass Mountain (2.1-0.78 Ma), and post-caldera rhyolites (0.65-0.04 Ma) to characterize the long-lived, batholith-scale magma chamber beneath Long Valley Caldera in California. Values of δ18O show a subtle 1‰ decrease from the oldest Glass Mountain lavas to the youngest post-caldera rhyolites. Older Glass Mountain lavas exhibit larger ( 1‰) variability of δ18O(quartz). The youngest domes of Glass Mountain are similar to BT in δ18O(quartz) values and reflect convective homogenization during formation of BT magma chamber surrounded by extremely heterogeneous country rocks (ranging from 2 to +29‰). Oxygen isotope thermometry of BT confirms a temperature gradient between "Late" (815 °C) and "Early" (715 °C) BT. The δ18O(quartz) values of "Early" and "Late" BT are +8.33 and 8.21‰, consistent with a constant δ18O(melt)=7.8+/-0.1‰ and 100 °C temperature difference. Zircon-melt saturation equilibria gives a similar temperature range. Values of δ18O(quartz) for different stratigraphic units of BT, and in pumice clasts ranging in pre-eruptive depths from 6 to 11 km (based on melt inclusions), and document vertical and lateral homogeneity of δ18O(melt). Worldwide, five other large-volume rhyolites, Lava Creek, Lower Bandelier, Fish Canyon, Cerro Galan, and Toba, exhibit equal δ18O(melt) values of earlier and later erupted portions in each of the these climactic caldera-forming eruptions. We interpret the large-scale δ18O homogeneity of BT and other large magma chambers as evidence

Melt-induced seismic anisotropy and magma assisted rifting in Ethiopia: Evidence from surface waves

NASA Astrophysics Data System (ADS)

Bastow, I. D.; Pilidou, S.; Kendall, J.-M.; Stuart, G. W.

2010-06-01

The East African rift in Ethiopia is unique worldwide because it captures the final stages of transition from continental rifting to seafloor spreading. A recent study there has shown that magma intrusion plays an important role during the final stages of continental breakup, but the mechanism by which it is incorporated into the extending plate remains ambiguous: wide-angle seismic data and complementary geophysical tools such as gravity analysis are not strongly sensitive to the geometry of subsurface melt intrusions. Studies of shear wave splitting in near-vertical SKS phases beneath the transitional Main Ethiopian Rift (MER) provide strong and consistent evidence for a rift-parallel fast anisotropic direction. However, it is difficult to discriminate between oriented melt pocket (OMP) and lattice preferred orientation (LPO) causes of anisotropy based on SKS study alone. The speeds of horizontally propagating Love (SH) and Rayleigh (SV) waves vary in similar fashions with azimuth for LPO- and OMP-induced anisotropy, but their relative change is distinctive for each mechanism. This diagnostic is exploited by studying the propagation of surface waves from a suite of azimuths across the MER. Anisotropy is roughly perpendicular to the absolute plate motion direction, thus ruling out anisotropy due to the slowly moving African Plate. Instead, three mechanisms for anisotropy act beneath the MER: periodic thin layering of seismically fast and slow material in the uppermost ˜10 km, OMP between ˜20-75 km depth, and olivine LPO in the upper mantle beneath. The results are explained best by a model in which low aspect ratio melt inclusions (dykes and veins) are being intruded into an extending plate during late stage breakup. The observations from Ethiopia join a growing body of evidence from rifts and passive margins worldwide that shows magma intrusion plays an important role in accommodating extension without marked crustal thinning.

Magnetic fabric in granitoid plutons emplaced during Variscan orogeny and timing of their intrusions: Eastern Variscan front

NASA Astrophysics Data System (ADS)

Hrouda, F.; Schulmann, K.; Chlupacova, M.; Aichler, J.; Mixa, P.; Pecina, V.; Zacek, V.; Kroener, A.

2003-04-01

The eastern Variscan front at the Czech and Polish border is characterised by oblique underthrusting of Neo-Proterozoic continental margin below thickened crustal root. The underthrust plate is subsequently imbricated and forms obliquely convergent crustal wedge which was further thrust over the foreland. Several granitic plutons of arc geochemical affinity are intruded during different stages of crustal thickening and exhumation. Analysis of anisotropy of magnetic susceptibility was carried out to study the relationships between host rock deformation and magma emplacement fabrics in different crustal levels and geographical positions with respect to crustal wedge and westerly orogenic root. Deep seated granodiorite sheets (Javornik intrusion 348 Ma, and Stare Mesto sill 340 Ma) are emplaced in the deepest and more internal high grade parts of the orogen along the margin of thickened crustal root. They show AMS fabrics entirely concordant with surrounding high grade gneisses and were emplaced during contractional (transpressive) regime.The Sumperk granodiorite is a more shallow intrusion emplaced in the central part of the crustal wedge. This sheet-like intrusion shows its AMS fabrics conformable to transpressional fabrics of surrounding mylonitised barovian schists and gneisses. The Zulova Pluton 330 Ma, representing the shallowest intrusion, intrudes the most external part of the crustal wedge. It shows the magnetic fabrics virtually perpendicular to compressional structures in the neighbouring areas. In addition, these fabrics are clearly concordant with large-scale detachment zone along which the Devonian meta-sedimentary cover slided to the west. The AMS fabrics of granitoids thus testify the progressive oblique convergence prograding to the east followed by collapse of external part of orogenic wedge. The AMS fabric data allow us to evaluate the mechanical role of arc magmas syntectonically emplaced during oblique convergence and finally during normal

Activating attachment representations during memory retrieval modulates intrusive traumatic memories.

PubMed

Bryant, Richard A; Chan, Iris

2017-10-01

Although priming mental representations of attachment security reduces arousal, research has not examined the effect of attachment on the retrieval of emotionally arousing memories. This study investigated the effect of priming attachment security on the retrieval of emotional memories. Seventy-five participants viewed negative and neutral images, and two days later received either an attachment prime or a control prime immediately prior to free recall of the images. Two days later, participants reported how frequently they experienced intrusions of the negative images. The attachment group had less distress, and reported fewer subsequent intrusions than the control group. Attachment style moderated these effects such that individuals with an avoidant attachment style were not impacted by the attachment prime. These findings suggest that priming attachment security decreases distress during memory reactivation, and this may reduce subsequent intrusive memories. Copyright © 2017 Elsevier Inc. All rights reserved.

Transfer Rates of Magma From Planetary Mantles to the Surface.

NASA Astrophysics Data System (ADS)

Wilson, L.; Head, J. W.; Parfitt, E. A.

2008-12-01

We discuss the speed at which magma can be transferred to a planetary surface from the deep interior. Current literature describes a combination of slow percolation of melt in the mantle where convection-driven pressure-release melting is occurring, concentration of melt by source region deformation, initiation and growth of magma-filled brittle fractures (dikes) providing wider pathways for melt movement, additional growth and interconnection of dikes with decreasing depth, rise of magma to storage zones (reservoirs) located at levels of neutral buoyancy at the base of or within the crust, and transfer from the storage zones in dikes to feed eruptions or intrusions. We do not take issue with these mechanisms but think that their relative importance in various circumstances is poorly appreciated. On Earth, preservation of diamonds in kimberlites implies very rapid (hours) transfer of melts from depths of 100-300 km, and there is strong geochemical evidence that magmas at mid-ocean ridges reach shallow depths faster than is possible by percolation alone. On the Moon, the petrology of pyroclasts involved in dark-mantle-forming eruptions implies rapid (again probably hours) magma transfer from depths of up to 400 km. The ureilite meteorites, samples of the mantle of a disrupted asteroid 200 km in diameter, have compositions only consistent with the rapid (months) extraction of mafic melt from the mantle. All of these examples imply that brittle fractures (dikes) can sometimes be initiated at depths where mantle rheology would normally be expected to be plastic rather than elastic, and that melt can be fed into these dikes extremely efficiently. Further evidence for this is provided by the giant radial dike swarms observed on Earth, Mars and Venus. The dikes observed (on Earth) and inferred from the presence of radiating graben systems (Mars) and radiating fracture and graben systems (Venus) are so voluminous that they can only be understood if they are fed from

From Magma Fracture to a Seismic Magma Flow Meter

NASA Astrophysics Data System (ADS)

Neuberg, J. W.

2007-12-01

Seismic swarms of low-frequency events occur during periods of enhanced volcanic activity and have been related to the flow of magma at depth. Often they precede a dome collapse on volcanoes like Soufriere Hills, Montserrat, or Mt St Helens. This contribution is based on the conceptual model of magma rupture as a trigger mechanism. Several source mechanisms and radiation patterns at the focus of a single event are discussed. We investigate the accelerating event rate and seismic amplitudes during one swarm, as well as over a time period of several swarms. The seismic slip vector will be linked to magma flow parameters resulting in estimates of magma flux for a variety of flow models such as plug flow, parabolic- or friction controlled flow. In this way we try to relate conceptual models to quantitative estimations which could lead to estimations of magma flux at depth from seismic low-frequency signals.

Intrusive Memories of Distressing Information: An fMRI Study

PubMed Central

Battaglini, Eva; Liddell, Belinda; Das, Pritha; Malhi, Gin; Felmingham, Kim

2016-01-01

Although intrusive memories are characteristic of many psychological disorders, the neurobiological underpinning of these involuntary recollections are largely unknown. In this study we used functional magentic resonance imaging (fMRI) to identify the neural networks associated with encoding of negative stimuli that are subsequently experienced as intrusive memories. Healthy partipants (N = 42) viewed negative and neutral images during a visual/verbal processing task in an fMRI context. Two days later they were assessed on the Impact of Event Scale for occurrence of intrusive memories of the encoded images. A sub-group of participants who reported significant intrusions (n = 13) demonstrated stronger activation in the amygdala, bilateral ACC and parahippocampal gyrus during verbal encoding relative to a group who reported no intrusions (n = 13). Within-group analyses also revealed that the high intrusion group showed greater activity in the dorsomedial (dmPFC) and dorsolateral prefrontal cortex (dlPFC), inferior frontal gyrus and occipital regions during negative verbal processing compared to neutral verbal processing. These results do not accord with models of intrusions that emphasise visual processing of information at encoding but are consistent with models that highlight the role of inhibitory and suppression processes in the formation of subsequent intrusive memories. PMID:27685784

Detecting deep crustal magma movement: Exploring linkages between increased gas emission, deep seismicity, and deformation (Invited)

NASA Astrophysics Data System (ADS)

Werner, C. A.; Poland, M. P.; Power, J. A.; Sutton, A. J.; Elias, T.; Grapenthin, R.; Thelen, W. A.

2013-12-01

Typically in the weeks to days before a volcanic eruption there are indisputable signals of unrest that can be identified in geophysical and geochemical data. Detection of signals of volcanic unrest months to years prior to an eruption, however, relies on our ability to recognize and link more subtle changes. Deep long-period earthquakes, typically 10-45 km beneath volcanoes, are thought to represent magma movement and may indicate near future unrest. Carbon dioxide (CO2 ) exsolves from most magmas at similar depths and increases in CO2 discharge may also provide a months-to-years precursor as it emits at the surface in advance of the magma from which it exsolved. Without the use of sensitive monitoring equipment and routine measurements, changes in CO2 can easily go undetected. Finally, inflation of the surface, through use of InSAR or GPS stations (especially at sites tens of km from the volcano) can also indicate accumulation of magma in the deep crust. Here we present three recent examples, from Redoubt, Kilauea, and Mammoth Mountain volcanoes, where increases in CO2 emission, deep long-period earthquakes, and surface deformation data indicate either the intrusion of magma into the deep crust in the months to years preceding volcanic eruptions or a change in ongoing volcanic unrest. At Redoubt volcano, Alaska, elevated CO2 emission (~ 1200 t/d, or roughly 20 times the background emission) was measured in October, 2008, over 5 months prior to the first magmatic eruption in March, 2009. In addition to CO2 release, deep long-period earthquakes were first recorded in December, 2008, and a deep deformation signal was detected starting in May 2008, albeit retrospectively. At Kilauea, Hawaii, increases in CO2 emissions from the summit (up to nearly 25 kt/d, over three times the background emission) were measured mid-2004, roughly coincident with a change in deformation behavior from deflation to inflation. Nearly 3 years later, a change in eruptive activity occurred

Magma-magma interaction in the mantle beneath eastern China

NASA Astrophysics Data System (ADS)

Zeng, Gang; Chen, Li-Hui; Yu, Xun; Liu, Jian-Qiang; Xu, Xi-Sheng; Erdmann, Saskia

2017-04-01

In addition to magma-rock and rock-rock reaction, magma-magma interaction at mantle depth has recently been proposed as an alternative mechanism to produce the compositional diversity of intraplate basalts. However, up to now no compelling geochemical evidence supports this novel hypothesis. Here we present geochemistry for the Longhai basalts from Fujian Province, southeastern China, which demonstrates the interaction between two types of magma at mantle depth. At Longhai, the basalts form two groups, low-Ti basalts (TiO2/MgO < 0.25) and high-Ti basalts (TiO2/MgO > 0.25). Calculated primary compositions of the low-Ti basalts have compositions close to L + Opx + Cpx + Grt cotectic, and they also have low CaO contents (7.1-8.1 wt %), suggesting a mainly pyroxenite source. Correlations of Ti/Gd and Zr/Hf with the Sm/Yb ratios, however, record binary mixing between the pyroxenite-derived melt and a second, subordinate source-derived melt. Melts from this second source component have low Ti/Gd and high Zr/Hf and Ca/Al ratios, thus likely representing a carbonated component. The Sr, Nd, Hf, and Pb isotopic compositions of the high-Ti basalts are close to the low-Ti basalts. The Sm/Yb ratio of the high-Ti basalts, however, is markedly elevated and characterized by crossing rare earth element patterns at Ho, suggesting that they have source components comparable to the low-Ti basalts, but that they have experienced garnet and clinopyroxene fractionation. We posit that mingling of SiO2-saturated tholeiitic magma with SiO2-undersaturated alkaline magma might trigger such fractionation. Therefore, the model of magma-magma interaction and associated deep evolution of magma in the mantle is proposed to explain the formation of Longhai basalts. It may, moreover, serve as a conceptual model for the formation of tholeiitic to alkaline intraplate basalts worldwide.

Imaging of magma intrusions beneath Harrat Al-Madinah in Saudi Arabia

NASA Astrophysics Data System (ADS)

Abdelwahed, Mohamed F.; El-Masry, Nabil; Moufti, Mohamed Rashad; Kenedi, Catherine Lewis; Zhao, Dapeng; Zahran, Hani; Shawali, Jamal

2016-04-01

High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.

Lu-Hf isotopic memory of plume-lithosphere interaction in the source of layered mafic intrusions, Windimurra Igneous Complex, Yilgarn Craton, Australia

NASA Astrophysics Data System (ADS)

Nebel, O.; Arculus, R. J.; Ivanic, T. J.; Nebel-Jacobsen, Y. J.

2013-10-01

Most layered mafic intrusions (LMI) are formed via multiple magma injections into crustal magma chambers. These magmas are originally sourced from the mantle, likely via plume activity, but may interact with the overriding lithosphere during ascent and emplacement in the crust. The magma injections lead to the establishment of different layers and zones with complex macroscopic, microscopic and cryptic compositional layering through magmatic differentiation and associated cumulate formation, sometimes accompanied by crustal assimilation. These complex mineralogical and petrological processes obscure the nature of the mantle sources of LMI, and typically have limited the degree to which parental liquids can be fully characterised. Here, we present Lu-Hf isotope data for samples from distinct layers of the Upper Zone of the Windimurra Igneous Complex (WIC), an immense late-Archean LMI in the West Australian Yilgarn Craton. Lu-Hf isotope systematics of whole rocks are well correlated (MSWD=5.6, n=17) with an age of ˜3.05±0.05 Ga and initial ɛHf˜+8. This age, however, is older than whole rock Sm-Nd and zircon U-Pb ages of the intrusion, both of which are ca. 2.8 Ga. Stratigraphically-controlled initial Hf isotope variations (associated with multiple episodes of emplacement at ca. 2.8 Ga) indicate isotope mixing between a near-chondritic and an ultra-radiogenic component, the latter with ɛHf[2.8 Ga]>+15. This Hf isotope mixing creates a pseudochron-relationship at the time of intrusion of ˜250 Myr that is superimposed on subsequent radiogenic ingrowth after crystallisation, generating an age that predates the actual emplacement event. Mixing between late-stage crystallisation products (melt + crystals) from the Middle Zone and replenishing, plume-derived liquids was followed by crystal accumulation in a chemically evolving magma chamber. The ultra-radiogenic Hf isotope endmember in the WIC mantle source requires parent-daughter ratios consistent with very early

The dynamics of magma ascent in the crust: Characterising fluid flow and host-rock deformation using scaled analogue experiments

NASA Astrophysics Data System (ADS)

Kavanagh, Janine; Dennis, David

2015-04-01

We present the results from a series of analogue experiments that use gelatine injected by water to study magma ascent dynamics in the crust. Gelatine is a viscoelastic material that displays predominantly elastic deformation when used at low temperatures (5-10 °C) and mid-to-low concentrations (2-5 wt%). To study dyke propagation we have used a combination of Particle Image Velocimentry (PIV) and Digital Image Correlation (DIC) to characterise the dynamics of fluid flow within the intrusion and contemporaneous deformation of the host gelatine. Experiments are prepared by filling a 40 cm x 40 cm x 30 cm clear-Perspex tank with a gelatine mixture that has been seeded with neutrally buoyant fluorescent particles. Water, also seeded with tracer particles, is then injected into the solid gelatine from below under a constant flux or constant head pressure. This causes a vertical penny-shaped crack (dyke) to propagate through the gelatine and erupt at the surface. During the experiment, a vertical high-power laser sheet positioned along the centre of the tank is triggered to illuminate the seeding particles with short intense pulses, and two Dantec CCD cameras record successive images. Using PIV and DIC, vector fields of fluid flow within the intrusion and strain within the gelatine host is calculated by cross-correlation between successive images at a defined time interval. The experiments indicate that, prior to eruption, dyke propagation is characterised by rapid centralised and upwards fluid flow with accompanying downwards motion at the intrusion margin. Deformation of the gelatine solid is focused at a small head region, with the tail remaining relatively static as the dyke grows. Upon eruption, rapid centralised fluid evacuation occurs with contemporaneous contraction of the dyke and relaxation of the host gelatine. Models that can couple fluid dynamics and host deformation during magma ascent and eruption will make an important step towards improving our

Magma Chambers, Thermal Energy, and the Unsuccessful Search for a Magma Chamber Thermostat

NASA Astrophysics Data System (ADS)

Glazner, A. F.

2015-12-01

Although the traditional concept that plutons are the frozen corpses of huge, highly liquid magma chambers ("big red blobs") is losing favor, the related notion that magma bodies can spend long periods of time (~106years) in a mushy, highly crystalline state is widely accepted. However, analysis of the thermal balance of magmatic systems indicates that it is difficult to maintain a significant portion in a simmering, mushy state, whether or not the system is eutectic-like. Magma bodies cool primarily by loss of heat to the Earth's surface. The balance between cooling via energy loss to the surface and heating via magma accretion can be denoted as M = ρLa/q, where ρ is magma density, L is latent heat of crystallization, a is the vertical rate of magma accretion, and q is surface heat flux. If M>1, then magma accretion outpaces cooling and a magma chamber forms. For reasonable values of ρ, L, and q, the rate of accretion amust be > ~15 mm/yr to form a persistent volume above the solidus. This rate is extremely high, an order of magnitude faster than estimated pluton-filling rates, and would produce a body 10 km thick in 700 ka, an order of magnitude faster than geochronology indicates. Regardless of the rate of magma supply, the proportion of crystals in the system must vary dramatically with depth at any given time owing to transfer of heat. Mechanical stirring (e.g., by convection) could serve to homogenize crystal content in a magma body, but this is unachievable in crystal-rich, locked-up magma. Without convection the lower part of the magma body becomes much hotter than the top—a process familiar to anyone who has scorched a pot of oatmeal. Thermal models that succeed in producing persistent, large bodies of magma rely on scenarios that are unrealistic (e.g., omitting heat loss to the planet's surface), self-fulfilling prophecies (e.g., setting unnaturally high temperatures as fixed boundary conditions), or physically unreasonable (e.g., magma is intruded

The 2010-2011 Microearthquake Swarm in Krýsuvík, SW Iceland: Was it Triggered by Crustal Magma Injection?

NASA Astrophysics Data System (ADS)

Liu, J.; Michael, F.; Hager, B. H.

2013-12-01

Iceland, the on-land continuation of the Mid-Atlantic Ridge, is the result of the interaction between the Mid-Atlantic Ridge and the North-Atlantic mantle plume. The superposition and relative motion of the spreading plate boundary over the mantle plume are manifested by the volcanism and seismicity in Iceland. The Krýsuvík geothermal field is one of the most active geothermal fields in southwest Iceland. In 2010, Massachusetts Institute of Technology, Reykjanes University, Uppsala University, and the Iceland Geosurvey (ISOR) deployed 38 temporary seismic stations on the Reykjanes Peninsula. Using data from 18 of the temporary seismic stations and from 5 stations of the South Iceland Lowland network around Krýsuvík, we captured an earthquake swarm that occurred between November, 2010 and February, 2011. We applied double difference tomography to relocate the events and determine the velocity structure in the region. Activity is clustered around the center of the Krýsuvík volcano system. Our seismic tomography result indicates a low velocity zone at a depth of about 6 km, right under the earthquake swarm. We consider that this low velocity zone contains some crustal magma that may be the thermal source for the geothermal field. At the same time, our relocated events delineate faults above and around this magma chamber. The system is within the stress field of a combination of left-lateral shear and extension; the majority of the strike-slip faults are right-lateral and most dip-slip faults are normal faults. Published geodetic measurements for the time period between 2009 and 2012 show a few centimeters uplift and extension in the area of the seismic swarm. We modeled the observed deformation using the Coulomb 3.3 software (U.S. Geological Survey). Our result indicates that a Mogi source of about 20×10^6 m^3 at a depth of about 6 km, consistent with the location and size of the tomography result, can explain the main deformation. The normal and the right-lateral

Saltwater intrusion in coastal regions of North America

USGS Publications Warehouse

Barlow, Paul M.; Reichard, Eric G.

2010-01-01

Saltwater has intruded into many of the coastal aquifers of the United States, Mexico, and Canada, but the extent of saltwater intrusion varies widely among localities and hydrogeologic settings. In many instances, the area contaminated by saltwater is limited to small parts of an aquifer and to specific wells and has had little or no effect on overall groundwater supplies; in other instances, saltwater contamination is of regional extent and has resulted in the closure of many groundwater supply wells. The variability of hydrogeologic settings, three-dimensional distribution of saline water, and history of groundwater withdrawals and freshwater drainage has resulted in a variety of modes of saltwater intrusion into coastal aquifers. These include lateral intrusion from the ocean; upward intrusion from deeper, more saline zones of a groundwater system; and downward intrusion from coastal waters. Saltwater contamination also has occurred along open boreholes and within abandoned, improperly constructed, or corroded wells that provide pathways for vertical migration across interconnected aquifers. Communities within the coastal regions of North America are taking actions to manage and prevent saltwater intrusion to ensure a sustainable source of groundwater for the future. These actions can be grouped broadly into scientific monitoring and assessment, engineering techniques, and regulatory approaches.

The Role of Magma During Continent-Ocean Transition: Evidence from Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Kendall, J. M.; Bastow, I. D.; Keir, D.; Stuart, G. W.

2010-12-01

Passive margins worldwide are often considered magmatic because they are characterised by thick sequences of extrusive and intrusive igneous rocks emplaced around the time of continental breakup. Despite the global abundance of such margins, however, it is difficult to discriminate between different models of both extension and melt generation, since most ruptured during Gondwana breakup >100Ma and the continent-ocean transition (COT) is now hidden by thick, basaltic seaward dipping reflectors (SDRs). The Main Ethiopian Rift offers a unique opportunity to address this problem because it captures sub-aerially the final stages of transition from continental rifting to seafloor spreading. Recent studies there have shown that magma intrusion plays an important role during the final stages of continental breakup, but the mechanism by which it is incorporated into the extending plate remains ambiguous: wide angle seismic data and complementary geophysical tools such as gravity analysis are not strongly sensitive to the geometry of subsurface melt intrusions. Studies of shear wave splitting in near-vertical SKS phases beneath the transitional Main Ethiopian Rift (MER) provide strong and consistent evidence for a rift-parallel fast anisotropic direction. However, it is difficult to discriminate between oriented melt pocket (OMP) and lattice preferred orientation (LPO) causes of anisotropy based on SKS study alone. The speeds of horizontally propagating Love (SH) and Rayleigh (SV) waves vary in similar fashions with azimuth for LPO- and OMP-induced anisotropy, but their relative change is distinctive for each mechanism. This diagnostic is exploited by studying the propagation of surface waves from a suite of azimuths across the MER. Anisotropy is roughly perpendicular to the absolute plate motion direction, thus ruling out anisotropy due to the slowly moving African Plate. Instead, three mechanisms for anisotropy act beneath the MER: periodic thin layering of seismically

Hydrogen, Oxygen and Silicon Isotope Systematics of Groundwater-Magma Interaction in Icelandic Hydrothermal Systems

NASA Astrophysics Data System (ADS)

Kleine, B. I.; Stefansson, A.; Halldorsson, S. A.; Martin, W.; Barnes, J.; Jónasson, K.; Franzson, H.

2016-12-01

Magma often encounters groundwater (meteoric or seawater derived) when intruded into the crust. Magma-groundwater interactions result in the formation of hydrothermal fluids which can lead to contact metamorphism and elemental transport in the country rock. In fact, magma-hydrothermal fluid interaction (rather than magma-magmatic fluid interaction) may lead to classic contact metamorphic reactions. In order to explore the importance of hydrothermal fluid during contact metamorphism we use stable isotopes (δD, δ18O, δ30Si) from both active and extinct magma chambers and hydrothermal systems from across Iceland. Quartz grains from various hydrothermal systems, from crustal xenoliths from the Askja central volcano and from the Hafnarfjall pluton, as well as quartz grains associated with low-T zeolites were analysed for δ18O and δ30Si in-situ using SIMS. Whole rock material of these samples was analysed for δD values using a TCEA coupled to an IRMS. Our results indicate that low-T quartz (<150°C) are dominated by negative δ30Si values whereas positive δ30Si values prevail in quartz precipitated at higher T (>300°C). Combining the results from the analyses of δ18O and δD allows further division of samples into (i) seawater and/or rock dominated and (ii) meteoric water dominated hydrothermal systems. In order to isolate the effects of fluid-rock interaction, fluid source and formation temperature at the magma-groundwater contact, δD, δ18O and δ30Si values of rocks and fluids were modeled using the PHREEQC software. Comparison of analytical and model results shows that the isotopic compositions are influenced by multiple processes. In some cases, groundwater penetrates the contact zone and causes alteration at >400°C by groundwater-magma heat interaction. Other cases document "baked" contact zones without groundwater. Our analyses and modeling demonstrates that groundwater flow and permeability are crucial in setting the style of contact metamorphism

Intrusive Images in Psychological Disorders

PubMed Central

Brewin, Chris R.; Gregory, James D.; Lipton, Michelle; Burgess, Neil

2010-01-01

Involuntary images and visual memories are prominent in many types of psychopathology. Patients with posttraumatic stress disorder, other anxiety disorders, depression, eating disorders, and psychosis frequently report repeated visual intrusions corresponding to a small number of real or imaginary events, usually extremely vivid, detailed, and with highly distressing content. Both memory and imagery appear to rely on common networks involving medial prefrontal regions, posterior regions in the medial and lateral parietal cortices, the lateral temporal cortex, and the medial temporal lobe. Evidence from cognitive psychology and neuroscience implies distinct neural bases to abstract, flexible, contextualized representations (C-reps) and to inflexible, sensory-bound representations (S-reps). We revise our previous dual representation theory of posttraumatic stress disorder to place it within a neural systems model of healthy memory and imagery. The revised model is used to explain how the different types of distressing visual intrusions associated with clinical disorders arise, in terms of the need for correct interaction between the neural systems supporting S-reps and C-reps via visuospatial working memory. Finally, we discuss the treatment implications of the new model and relate it to existing forms of psychological therapy. PMID:20063969

Construction of the Devonian bimodal Gouldsboro pluton via multiple intrusion, coastal Maine, USA

NASA Astrophysics Data System (ADS)

Koteas, C.

2006-12-01

The Gouldsboro pluton (377 ± 19 ma) (Metzger et al., 1982) of the eastern coastal Maine magmatic province preserves abundant evidence of mechanical interaction between mafic and felsic magmas, as well as the stoping and doming of country rock. Coastal Maine is a unique location where subequal volumes of felsic and mafic material have interacted and are preserved in both plutonic and volcanic complexes. The effects of generation and mobilization of large volumes of magma in the shallow crust are well-preserved. The Gouldsboro pluton provides an excellent perspective from the highest to lowest sections (southwest to northeast) of a hybrid magmatic system. The Gouldsboro magmatic complex is hosted by undated greenstone to the north that is overlain by the 477 ± 18 ma (Metzger, 1977) meta-volcanic/meta-sedimentary Bar Harbor formation. Blocks of both units are discernable as 10 cm to 2 m-diameter blocks within the pluton. The Gouldsboro granite is dominantly a fine to medium grained feldspar- rich leucocratic hornblende granite, although biotite is sometimes present. Miarolitic cavities are common in the highest exposure of the system, especially in the south where the finest grained, most leucocratic granite occurs. Other units include, from lowest to highest in the system, hybrid diorite-gabbro, hybrid granite-granodiorite, granite hosting 30 cm to 3 m-diameter globular basaltic pillows, and a previously unrecognized pyroclastic unit, very similar to the lowermost member of the Cranberry Isle series, a volcanic breccia (Seaman et al., 1999). The pyroclastic unit is intruded by medium grained granite hosting angular fragments of volcanic, mafic plutonic, and country rock. While the contact between gabbro near the base of the pluton and granite in the middle of the pluton is commonly gradational, there are complex intrusive breccias in some areas where fine to coarse, angular diorite to gabbro xenoliths are hosted by granodiorite and granite. Enclave-rich zones

Magma differentiation in shallow sills controlled by compaction and surface tension: San Rafael desert, Utah

NASA Astrophysics Data System (ADS)

Diez, M.; Savov, I. P.; Connor, C.

2010-12-01

Veinlets, veins, sheet or layers of syenite are common structures found in alkaline basalt sills. The mechanism usually invoked to explain their formation are liquid immiscibility, multiple intrusion or crystal fractionation from primitive mafic melt. Syenite veins of few centimeters to sheets of up to 1-2 m thick are ubiquitous in remarkably well-exposed sills of the San Rafael subvolcanic field in the Colorado Plateau, Utah. In some of these exposures we have found an intriguing configuration in which the main body of the alkaline sill is underlain by a lower density sheet of syenite of ~ 1 m thick. The contact is flat and is not a chilled margin, therefore a multiple intrusion scenario with long intervals between injections can be disregarded. This implies that both layers were fluid at the time of magma emplacement. As the more felsic less dense syenite is at the bottom of the sill any mechanism governed exclusively by bouyancy would be problematic. In an attempt to shed light on this apparent riddle we propose the following geological scenario: The sill is built by continuous injections. Magma starts to cool and fractional crystallization operates at this stage to differentiate the alkaline magma into syenite. By the time ~60% of crystallization is attained the system can be described as two-phase flow consisting of pore-syenite melt in hot-creeping matrix. The forces acting to segregate melt into veins or sheets are the gravitational force and surface tension. When surface tension is stronger than the gravitational force, differences in average curvature or surface tension translates into pressure differences that drive melt flow from low to high porosity regions. If the last injections occur at the bottom of the sill a syenite layer may be formed. With the aid of dimensional analysis and two-phase numerical models that account for gravitational compaction and surface tension effects, we explore the conditions that allow for centimeter-scale veins to meter

Seismic images of multiple magma sills beneath the East Pacific Rise

NASA Astrophysics Data System (ADS)

Marjanovic, M.; Carbotte, S. M.; Carton, H. D.; Mutter, J. C.; Nedimovic, M. R.; Canales, J.

2013-12-01

Along fast and intermediate spreading centers, thin and narrow axial magma lenses (AMLs) are detected beneath much of the ridge axis, and the notion that the AML is the primary melt reservoir for dike intrusions and volcanic eruptions that build the upper crust is commonly accepted. However the role of the AML in construction of the lower crust is still actively debated. Some models based on geochemistry and structural observations from ophiolites suggest that formation of the lower crustal gabbro section takes place in situ, from multiple small magma sills, with the AML being the shallowest of these. Here, we present new observations from multichannel seismic data collected in 2008 along the East Pacific Rise (EPR) for seismic reflectors below the AML or sub-axial magma lens (SAML). The most prominent SAML events are found between latitudes 9°20' and 9°56'N, where they appear as moderately bright, discontinuous reflectors, at ~ 50 to 300 ms (~ 200-600 m) below the AML. From an analysis of the characteristics of these events, we rule out possible 'artifact' origins for the SAML including, seafloor side scattering, out-of-plane imaging of the AML or other crustal horizons, internal multiples, and the presence of a P-to-S converted phase (PAMLS). We interpret these deep melt lenses to have a low crystalline component (i.e. they are mostly molten). Disruptions in the SAML reflector, represented by relatively abrupt steps in two-way travel time are collocated with small-scale discontinuities in the AML and further support the notion of crustal accretion through small magmatic units. In addition, within the area of documented volcanic eruptions in 1991-1992 and 2005-2006, two prominent gaps centered at 9°46' and 9°50.5' N in the SAML reflectors are identified. We hypothesize that magma from these deeper lenses have also contributed to the eruption, implying hydraulic connectivity between the AML and SAMLs during eruption events. We suggest that the SAMLs play an

Wind-forced salt intrusion into a tributary estuary

NASA Astrophysics Data System (ADS)

Sanford, Lawrence P.; Boicourt, William C.

1990-08-01

Moored measurements and hydrographic surveys were carried out during the summers of 1986 and 1987 to examine interaction between the mainstem of the Chesapeake Bay and the Choptank River, an eastern shore tributary estuary. The data show that an important mode of interaction is through wind-forced intrusion of saline, hypoxic water from below the pycnocline of the Bay into the lower river. Intrusions are driven by lateral tilting of the pycnocline in the Bay, when high salinity water is upwelled on the eastern side of the Bay in response to a southward pulse of wind stress. The resulting internal surges propagate up the relict Choptank entrance channel at a speed of about 20 cm/s and spill onto the broad sill inside the mouth of the river. Intrusion-favorable pycnocline tilts in the Bay do not always result in lower layer intrusion into the Choptank, but may be blocked or choked in the entrance channel on occasion. The data suggest that wind-forced intrusion of salt leads to increased gravitational circulation in the Choptank during the summer months, providing a mechanism through which high frequency energy may be directly translated into lower frequency motion.

Origin of Fe-Ti Oxide Mineralization in the Middle Paleoproterozoic Elet'ozero Syenite-Gabbro Intrusive Complex (Northern Karelia, Russia)

NASA Astrophysics Data System (ADS)

Sharkov, E. V.; Chistyakov, A. V.; Shchiptsov, V. V.; Bogina, M. M.; Frolov, P. V.

2018-03-01

Magmatic oxide mineralization widely developed in syenite-gabbro intrusive complexes is an important Fe and Ti resource. However, its origin is hotly debatable. Some researchers believe that the oxide ores were formed through precipitation of dense Ti-magnetite in an initial ferrogabbroic magma (Bai et al., 2012), whereas others consider them as a product of immiscible splitting of Fe-rich liquid during crystallization of Fe-Ti basaltic magma (Zhou et al., 2013). We consider this problem with a study of the Middle Paleoproterozoic (2086 ± 30 Ma) Elet'ozero Ti-bearing layered intrusive complex in northern Karelia (Baltic Shield). The first ore-bearing phase of the complex is mainly made up of diverse ferrogabbros, with subordinate clinopyroxenites and peridotites. Fe-Ti oxides (magnetite, Ti-magnetite, and ilmenite) usually account for 10-15 vol %, reaching 30-70% in ore varieties. The second intrusive phase is formed by alkaline and nepheline syenites. Petrographical, mineralogical, and geochemical data indicate that the first phase of the intrusion was derived from a moderately alkaline Fe-Ti basaltic melt, while the parental melt of the second phase was close in composition to alkaline trachyte. The orebodies comprise disseminated and massive ores. The disseminated Fe-Ti oxide ores make up lenses and layers conformable to general layering. Massive ores occur in subordinate amounts as layers and lenses, as well as cross-cutting veins. Elevated Nb and Ta contents in Fe-Ti oxides makes it possible to consider them complex ores. It is shown that the Fe-Ti oxide mineralization is related to the formation of a residual (Fe,Ti)-rich liquid, which lasted for the entire solidification history of the first intrusive phase. The liquid originated through multiple enrichment of Fe and Ti in the crystallization zone of the intrusion owing to the following processes: (1) precipitation of silicate minerals in the crystallization zone with a corresponding increase in the Fe and

Moderate-magnitude earthquakes induced by magma reservoir inflation at Kīlauea Volcano, Hawai‘i

USGS Publications Warehouse

Wauthier, Christelle; Roman, Diana C.; Poland, Michael P.

2013-01-01

Although volcano-tectonic (VT) earthquakes often occur in response to magma intrusion, it is rare for them to have magnitudes larger than ~M4. On 24 May 2007, two shallow M4+ earthquakes occurred beneath the upper part of the east rift zone of Kīlauea Volcano, Hawai‘i. An integrated analysis of geodetic, seismic, and field data, together with Coulomb stress modeling, demonstrates that the earthquakes occurred due to strike-slip motion on pre-existing faults that bound Kīlauea Caldera to the southeast and that the pressurization of Kīlauea's summit magma system may have been sufficient to promote faulting. For the first time, we infer a plausible origin to generate rare moderate-magnitude VTs at Kīlauea by reactivation of suitably oriented pre-existing caldera-bounding faults. Rare moderate- to large-magnitude VTs at Kīlauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes.

Magma-driven antiform structures in the Afar rift: The Ali Sabieh range, Djibouti

NASA Astrophysics Data System (ADS)

Le Gall, Bernard; Daoud, Mohamed Ahmed; Maury, René C.; Rolet, Joël; Guillou, Hervé; Sue, Christian

2010-06-01

The Ali Sabieh Range, SE Afar, is an antiform involving Mesozoic sedimentary rocks and synrift volcanics. Previous studies have postulated a tectonic origin for this structure, in either a contractional or extensional regime. New stratigraphic, mapping and structural data demonstrate that large-scale doming took place at an early stage of rifting, in response to a mafic laccolithic intrusion dated between 28 and 20 Ma from new K-Ar age determinations. Our 'laccolith' model is chiefly supported by: (i) the geometry of the intrusion roof, (ii) the recognition of roof pendants in its axial part, and (iii) the mapping relationships between the intrusion, the associated dyke-sill network, and the upper volcanic/volcaniclastic sequences. The laccolith is assumed to have inflated with time, and to have upwardly bent its sedimentary roof rocks. From the architecture of the ˜1 km-thick Mesozoic overburden sequences, ca. 2 km of roof lifting are assumed to have occurred, probably in association with reactivated transverse discontinuities. Computed paleostress tensors indicate that the minimum principal stress axis is consistently horizontal and oriented E-W, with a dominance of extensional versus strike-slip regimes. The Ali Sabieh laccolith is the first regional-scale magma-driven antiform structure reported so far in the Afro-Arabian rift system.

Detailed Segmentation and Episodic Propagation of the 2014 Bárðarbunga Dike Intrusion and Seismicity Accompanying the Sustained Holuhraun Eruption, Central Icleand

NASA Astrophysics Data System (ADS)

Ágústsdóttir, T.; Woods, J.; Greenfield, T. S.; Green, R. G.; White, R. S.; Brandsdottir, B.

2015-12-01

An intense swarm of seismicity on 16 August 2014 marked the intrusion of a large dike from the subglacial Bárðarbunga volcano, central Iceland. Melt propagated laterally from the central volcano at the brittle-ductile boundary at ~6 km b.s.l. and created over 30,000 earthquakes along a 46 km path heading NE from Bárðarbunga. On 31 August a fissure eruption began at Holuhraun and the seismicity rate within the dike dropped instantaneously to a much lower level suggesting that once a pathway to the surface had formed, magma was able to flow freely and largely aseismically. Melt was fed from the subsiding Bárðarbunga volcano to Holuhraun for 6 months, until the eruption ceased on 27 February 2015. We discuss the relationship between bursts of seismicity in the feeder volcano and periods of rapid dike propagation. We use a dense seismic network and relative earthquake relocations to map in detail the segmentation of the dike on all scales. New dike segments were initiated with a rapid advance of the dike tip at typically 1 km/h, separated by pauses of up to 78 h. During the stalled periods the magma pressure built until it was sufficient to fracture a new segment, which then propagated rapidly forward. Large segments became seismically quiet once a new segment had intruded beyond it as extensional stresses had been relieved and melt was able to flow freely. Each rapid propagation phase was accompanied by a drop in the seismicity rate directly behind the dike tip, most likely due to a stress shadow being formed behind the dike tip. Moment tensor solutions show that the dominant failure mechanism is left-lateral strike slip faulting at the leading edge, orientated parallel to the dike, with a combination of right-lateral, left-lateral and normal faulting behind the dike tip, contradicting many widely used models. Much of the seismicity behind the tip may represent fracture of frozen melt as the dike inflated and propagated forward

Percolation of isotopically heterogeneous interstitial melts in the crystal mush of the Rum layered intrusion, NW Scotland

NASA Astrophysics Data System (ADS)

O'Driscoll, B.; Hepworth, L. N.; Daly, J. S.; Gertisser, R.; Emeleus, C. H.

2017-12-01

The cumulate stratigraphy of layered intrusions offers a means of interrogating the replenishment and solidification histories of mafic magma chambers. Cumulates comprise cumulus minerals, which accumulate to form a silicate framework, and intercumulus minerals, which represent melt crystallised within the crystal mush. This fundamental textural distinction lies at the heart of cumulus theory and underpins some of the classic models of crystal-liquid differentiation that are based on layered intrusions. In order to shed further light on the importance of postcumulus processes in layered intrusions, and to demonstrate that crystal mushes may behave as open-systems during the crystallisation of cumulates, we investigated mineral-scale textural and geochemical heterogeneity in Unit 10 of the 60 Ma Rum layered intrusion. Numerous ( 1 mm thick) Cr-spinel seams occur throughout the 65 m Unit 10 peridotite stratigraphy. Unusually, intercumulus plagioclase and clinopyroxene crystals in the peridotite several centimetres above and below these seams exhibit complex optical and major element zoning. Sampling of individual intra-crystal zones in these phases was carried out using a New Wave Micromill, for analysis of their 87Sr/86Sr compositions to be measured on unspiked samples by TIMS. Both minerals reveal intra-crystalline isotopic heterogeneity. The maximum range (with 2σ uncertainties) of 87Sr/86Sr in the Unit 10 plagioclase is 0.704026±17-0.704591±8 and in clinopyroxene is 0.703533±23-0.704517±17. Within a single, oscillatory-zoned plagioclase, three discrete zones yield 87Sr/86Sr values of 0.704337±20, 0.704095±20 and 0.704052±11. A complex patchily-zoned clinopyroxene yields a 87Sr/86Sr range of 0.703533±23-0.703894±23. The new data demonstrate that multiple generations of isotopically distinct melts percolated through the Unit 10 crystal mush, suggesting solidification from cumulates that underwent repeated cycles of resorption and recrystallisation at the

Plutonic-squishy lid and beyond: implications of intrusive magmatism and characterization of a new global-tectonic regime on Earth-like planets

NASA Astrophysics Data System (ADS)

Louro Lourenço, Diogo; Rozel, Antoine; Ballmer, Maxim; Tackley, Paul

2017-04-01

-plastic rheology: stagnant-lid regime (a one-plate planet), episodic lid (where the lithosphere is unstable and frequently overturns into the mantle), and mobile-lid regime (similar to plate tectonics). At high intrusion efficiencies, we observe and characterise a new additional regime called here "plutonic-squishy lid". This regime is characterised by a set of strong plates separated by warm and weak regions due to plutonism. Eclogitic drippings and lithospheric delaminations often occur around these weak regions. These processes lead to significant surface velocities, even if subduction is not active. The location of plate boundaries is strongly time-dependent and mainly occurs in magma intrusion regions. This regime is also distinctive because it generates a thin lithosphere, which results in high conductive heat fluxes and lower internal temperatures when compared to a stagnant lid. The plutonic-squishy-lid regime has the potential to be applicable to the Archean Earth and Venus, as it combines elements of both protoplate tectonic and vertical tectonic models, such as horizontal plate motion and reprocessing of the lithosphere for the former, and lithospheric diapirism, volcanism, and basal delamination for the later.

Lateral extrusion of a thermally weakened pluton overburden (Campiglia Marittima, Tuscany)

NASA Astrophysics Data System (ADS)

Vezzoni, Simone; Rocchi, Sergio; Dini, Andrea

2017-10-01

The ascent and emplacement of magmas in the upper crust modify the local pre-existing thermal and rheological settings. Such changes have important effects in producing anomalous structures, mass extrusion, rock fracturing, and in some conditions, hydrothermal mineralizations. In the Campiglia Marittima area, detailed field mapping led to the reconstruction of a local deformation history that overlaps, chronologically and spatially, with regional extension. This local deformation was triggered at the Miocene-Pliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence. The emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks, producing transient ductile conditions in the very shallow crust. The carbonate rocks were thermally weakened and flowed laterally, accumulating downslope of the pluton roof, mainly toward the east. As the thermal anomaly was decaying, the brittle-ductile boundary moved progressively back towards the pluton, and large tension gash-shaped volumes of fractured marble were generated. These fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots. This work presents the Campiglia Marittima case study as a prime example of structural interference between regional extensional structures and local, lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement.

Lateral extrusion of a thermally weakened pluton overburden (Campiglia Marittima, Tuscany)

NASA Astrophysics Data System (ADS)

Vezzoni, Simone; Rocchi, Sergio; Dini, Andrea

2018-06-01

The ascent and emplacement of magmas in the upper crust modify the local pre-existing thermal and rheological settings. Such changes have important effects in producing anomalous structures, mass extrusion, rock fracturing, and in some conditions, hydrothermal mineralizations. In the Campiglia Marittima area, detailed field mapping led to the reconstruction of a local deformation history that overlaps, chronologically and spatially, with regional extension. This local deformation was triggered at the Miocene-Pliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence. The emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks, producing transient ductile conditions in the very shallow crust. The carbonate rocks were thermally weakened and flowed laterally, accumulating downslope of the pluton roof, mainly toward the east. As the thermal anomaly was decaying, the brittle-ductile boundary moved progressively back towards the pluton, and large tension gash-shaped volumes of fractured marble were generated. These fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots. This work presents the Campiglia Marittima case study as a prime example of structural interference between regional extensional structures and local, lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement.

Zircon U-Pb ages and Hf isotopes for the Diablillos Intrusive Complex, Southern Puna, Argentina: Crustal evolution of the Lower Paleozoic Orogen, Southwestern Gondwana margin

NASA Astrophysics Data System (ADS)

Ortiz, Agustín; Hauser, Natalia; Becchio, Raúl; Suzaño, Néstor; Nieves, Alexis; Sola, Alfonso; Pimentel, Marcio; Reimold, Wolf

2017-12-01

The evolution of the rocks of the Lower Paleozoic Orogen in Puna, at the Southwestern Gondwana margin, has been widely debated. In particular, the scarce amount of geological and geochemical data available for the Diablillos Intrusive Complex, Eastern Magmatic Belt, Southern Puna, require a further study for new evidence towards the understanding of sources, magmatic processes and emplacement of magmas, in order to better comprehend the crustal evolution in this setting. We present new combined U-Pb and Hf isotope analyses on zircon by LA-MC-ICP-MS from monzogranite, granodiorite and diorite rocks of the Diablillos Intrusive Complex. We obtained 206Pb/238U concordant weighted average ages of 517 ± 3 Ma and 515 ± 6 Ma for the monzogranite and diorite, respectively, and a concordant age of 521 ± 4 Ma for the granodiorite. These ages permit to constrain the climax of magmatic activity in the Diablillos Complex around ∼515-520 Ma, while the emplacement of the complex took place between ∼540 Ma and 490 Ma (representing a ca. 50 Ma magmatic event). Major and trace element data, initial 87Sr/86Sr values varying from 0.70446 to 0.71278, positive and negative ɛNd(t) values between +2.5 and -4, as well as ɛHf(t) for zircon data between + 3 and -3 indicate that the analyzed samples represent contaminated magmas. The ɛHf(t) and the ɛNd(t) values for this complex specify that these rocks are derived from interaction of a dominant Mesoproterozoic crystalline and/or a metasedimentary source and juvenile mantle-derived magmas, with a TDM model age range of ∼1.2-1.5 Ga, with later reworking during lower Paleozoic times. The combined data obtained in this contribution together with previous data, allow us to suggest that the formation of the Eastern Magmatic Belt of the Puna was part of a long-lived magmatic event during Early Paleozoic times. Whereby the granitoids of the Eastern Magmatic Belt formed through intra-crustal recycling at an active continental margin, with

Formation of continental crust in a temporally linked arc magma system from 5 to 30 km depth: ~ 90 Ma plutonism in the Cascades Crystalline Core composite arc section

NASA Astrophysics Data System (ADS)

Ratschbacher, B. C.; Miller, J. S.; Kent, A. J.; Miller, R. B.; Anderson, J. L.; Paterson, S. R.

2015-12-01

Continental crust has an andesitic bulk composition with a mafic lower crust and a granodioritic upper crust. The formation of stratified continental crust in general and the vertical extent of processes active in arc crustal columns leading to the differentiation of primitive, mantle-derived melts entering the lower crust are highly debated. To investigate where in the crustal column magma mixing, fractionation, assimilation and crystal growth occur and to what extent, we study the ~ 90 Ma magmatic flare-up event of the Cascades arc, a magma plumbing system from ~ 5 to 30 km depth. We focus on three intrusive complexes, emplaced at different depths during major regional shortening in an exceptionally thick crust (≥ 55 km1) but which are temporally related: the upper crustal Black Peak intrusion (1-3 kbar at 3.7 to 11 km; ~ 86.8 to 91.7 Ma2), the mid-crustal Mt. Stuart intrusion (3.5-4.0 kbar at 13 to 15 km; 90.8 and 96.3 Ma3) and the deep crustal Tenpeak intrusion (7 to 10 kbar at 25 to 37 km; 89.7 to 92.3 Ma4). These intrusive complexes are well characterized by geochronology showing that they have been constructed incrementally by multiple magma batches over their lifespans and thus allow the monitoring and comparison of geochemical parameters over time at different depths. We use a combination of whole rock major and trace element data and isotopes combined with detailed investigation of amphibole, which has been recognized to be important in the generation of calc-alkaline rocks in arcs to test the following hypotheses: (a) compositional bimodality is produced in the lower crust, whereas upper crustal levels are dominated by mixing to form intermediate compositions, or (b) differentiation occurs throughout the crustal column with different crystallizing phases and their compositions controlling the bulk chemistry. 1. Miller et al. 2009: GSA Special Paper 456, p. 125-149 2. Shea 2014: PhD thesis, Massachusetts Institute of Technology 3. Anderson et al. 2012

Lower Crstal Reflectity bands and Magma Emplacement in Norweigian sea, NE Atlantic

NASA Astrophysics Data System (ADS)

Rai, A.; Breivik, A. J.; Mjelde, R.

2013-12-01

In this study we present the OBS data collected along seismic profiles in the norweigian sea. The traveltime modelling of the OBS data provides first-hand information about seismic structure of the subsurface. However, waveform modelling is used to further constrain the fine scale structure, velocity constrast and velocity gradients. By forward modelling and inversion of the seismic waveforms, we show that the multiple bands of reflectivity could be due to multiple episodes of magma emplacements that might have frozen in the form of sills. These mafic intrusions probably intruded into the ductile lower crust during the main rifting phase of Europe and Greenland.

Comparative Magma Oceanography

NASA Technical Reports Server (NTRS)

Jones, J. H.

1999-01-01

The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot

Coeval Formation of Zircon Megacrysts and Host Magmas in the Eifel Volcanic Field (Germany) Based on High Spatial Resolution Petrochronology

NASA Astrophysics Data System (ADS)

Schmitt, Axel; Klitzke, Malte; Gerdes, Axel; Ludwig, Thomas; Schäfer, Christof

2017-04-01

-derived. The porous structure and relatively small grain size of the host enclaves suggests that they originated from subvolcanic intrusions. Moreover, the preservation of zircon in hot, zircon undersaturated magmas requires brief residence times. Zircon megacrysts thus appear to have crystallized in highly differentiated magmas or nearly solidified intrusions from which crystals or rock aggregates were incorporated into more primitive magmas en route to surface. This implies that chemical signatures of apparently primitive magmas in basaltic volcanic fields can be modified by interaction with evolved melts that differentiated prior to eruption, mostly within an interval less than the ca. 10-25 ka uncertainty range of the radiometric ages.

Magma storage prior to the 1912 eruption at Novarupta, Alaska

USGS Publications Warehouse

Hammer, J.E.; Rutherford, M.J.; Hildreth, W.

2002-01-01

New analytical and experimental data constrain the storage and equilibration conditions of the magmas erupted in 1912 from Novarupta in the 20th century's largest volcanic event. Phase relations at H2O+CO2 fluid saturation were determined for an andesite (58.7 wt% SiO2) and a dacite (67.7 wt%) from the compositional extremes of intermediate magmas erupted. The phase assemblages, matrix melt composition and modes of natural andesite were reproduced experimentally under H2O-saturated conditions (i.e., PH2O=PTOT) in a negatively sloping region in T-P space from 930 ??C/100 MPa to 960 ??C/75 MPa with fO2???N NO + 1. The H2O-saturated equilibration conditions of the dacite are constrained to a T-P region from 850 ??C/ 50 MPa to 880 ??C/25 MPa. If H2O-saturated, these magmas equilibrated at (and above) the level where coerupted rhyolite equilibrated (???100 MPa), suggesting that the andesite-dacite magma reservoir was displaced laterally rather than vertically from the rhyolite magma body. Natural mineral and melt compositions of intermediate magmas were also reproduced experimentally under saturation conditions with a mixed (H2O + CO2) fluid for the same range in PH2O. Thus, a storage model in which vertically stratified mafic to silicic intermediate magmas underlay H2O-saturated rhyolite is consistent with experimental findings only if the intermediates have XH2Ofl=0.7 and 0.9 for the extreme compositions, respectively. Disequilibrium features in natural pumice and scoria include pristine minerals existing outside their stability fields, and compositional zoning of titanomagnetite in contact with ilmenite. Variable rates of chemical equilibration which would eliminate these features constrain the apparent thermal excursion and re-distribution of minerals to the time scale of days.

Toddler Inhibited Temperament, Maternal Cortisol Reactivity and Embarrassment, and Intrusive Parenting

PubMed Central

Kiel, Elizabeth J.; Buss, Kristin A.

2013-01-01

The relevance of parenting behavior to toddlers’ development necessitates a better understanding of the influences on parents during parent-child interactions. Toddlers’ inhibited temperament may relate to parenting behaviors, such as intrusiveness, that predict outcomes later in childhood. The conditions under which inhibited temperament relates to intrusiveness, however, remain understudied. A multi-method approach would acknowledge that several levels of processes determine mothers’ experiences during situations in which they witness their toddlers interacting with novelty. As such, the current study examined maternal cortisol reactivity and embarrassment about shyness as moderators of the relation between toddlers’ inhibited temperament and maternal intrusive behavior. Participants included 92 24-month-olds toddlers and their mothers. Toddlers’ inhibited temperament and maternal intrusiveness were measured observationally in the laboratory. Mothers supplied saliva samples at the beginning of the laboratory visit and 20 minutes after observation. Maternal cortisol reactivity interacted with inhibited temperament in relation to intrusive behavior, such that mothers with higher levels of cortisol reactivity were observed to be more intrusive with more highly inhibited toddlers. Embarrassment related to intrusive behavior as a main effect. These results highlight the importance of considering child characteristics and psychobiological processes in relation to parenting behavior. PMID:23750532

Geochemical composition, petrography and 40Ar/39Ar age of the Heldburg phonolite: implications on magma mixing and mingling

NASA Astrophysics Data System (ADS)

Abratis, Michael; Viereck, Lothar; Pfänder, Jörg A.; Hentschel, Roland

2015-11-01

Differentiated magmatic rocks such as trachyte and phonolite are volumetrically subordinate to mafic volcanic rocks within the Cenozoic Central European Volcanic Province (exceptions are the East Eifel and the Rhön volcanic fields). Within the volcanic field of the "Heldburg dike swarm" (Heldburger Gangschar), the phonolite of the Burgberg near Heldburg represents the only known occurrence of differentiated magmatic rocks. However, the Heldburg phonolite is famous foremost for containing mantle xenoliths (spinel lherzolite). Former studies proposing a cogenetic relationship between the phonolite and the peridotites concluded that the phonolite magma must have evolved under upper mantle conditions. Herewith, we present petrographic and geochemical evidence for magma mixing and mingling in the Heldburg phonolite melt due to the intrusion of mantle-derived basanitic magma, which is exposed today as dikes at the foot of the Heldburg Burgberg. During this process, the mantle xenoliths were introduced into the phonolite melt as they all contain rims of basanitic magma. Extensive mingling features (e.g., schlieren layers, load casts, flame structures, mafic enclaves) are developed, indicating that the basanite and the zoned phonolitic body were melts at the time of mixing. These petrographic and geochemical indications of two coeval melts of different composition are substantiated by 40Ar/39Ar dating, revealing identical ages of ca. 15 Ma.

Sulfide mineralization associated with arc magmatism in the Qilian Block, western China: zircon U-Pb age and Sr-Nd-Os-S isotope constraints from the Yulonggou and Yaqu gabbroic intrusions

NASA Astrophysics Data System (ADS)

Zhang, Zhao-Wei; Li, Wen-Yuan; Gao, Yong-Bao; Li, Chusi; Ripley, Edward M.; Kamo, Sandra

2014-02-01

The sulfide-bearing Yulonggou and Yaqu mafic intrusions are located in the southern margin of the Qilian Block, Qinghai Province, western China. They are small dike-like bodies mainly composed of gabbros and diorites. Disseminated sulfides (pyrrhotite, pentlandite, and chalcopyrite) are present as concordant lenses within the intrusions. Precise CA-ID-TIMS zircon U-Pb dating yields the crystallization ages of 443.39 ± 0.42 and 440.74 ± 0.33 Ma for the Yulonggou and Yaqu intrusions, respectively. Whole rock samples from both intrusions show light rare earth element (REE) enrichments relative to heavy REE and pronounced negative Nb-Ta anomalies relative to Th and La, which are consistent with the products of arc basaltic magmatism. The Yulonggou intrusion has negative ɛ Nd values from -5.7 to -7.7 and elevated (87Sr/86Sr) i ratios from 0.711 to 0.714. In contrast, the Yaqu intrusion has higher ɛ Nd values from -4.1 to +8.4 and lower (87Sr/86Sr) i ratios from 0.705 to 0.710. The δ34S values of sulfide separates from the Yulonggou and Yaqu deposits vary from 0.8 to 2.4 ‰ and from 2 to 4.3 ‰, respectively. The γ Os values of sulfide separates from the Yulonggou and Yaqu deposits vary between 80 and 123 and between 963 and 1,191, respectively. Higher γ Os values coupled with higher δ34S values for the Yaqu deposit relative to the Yulonggou deposit indicate that external sulfur played a bigger role in sulfide mineralization in the Yaqu intrusion than in the Yulonggou intrusion. Mixing calculations using Sr-Nd isotope data show that contamination with siliceous crustal materials is more pronounced in the Yulonggou intrusion (up to 20 wt%) than in the Yaqu intrusion (<15 wt%). The distribution of sulfides in both intrusions is consistent with multiple emplacements of sulfide-saturated magmas from depth. The Yulonggou and Yaqu sulfide deposits are not economically valuable under current market condition due to small sizes and low Ni grades, which can be explained

Phase petrology reveals shallow magma storage prior to large explosive silicic eruptions at Hekla volcano, Iceland

NASA Astrophysics Data System (ADS)

Weber, Gregor; Castro, Jonathan M.

2017-05-01

Understanding the conditions that culminate in explosive eruptions of silicic magma is of great importance for volcanic hazard assessment and crisis mitigation. However, geological records of active volcanoes typically show a wide range of eruptive behavior and magnitude, which can vary dramatically for individual eruptive centers. In order to evaluate possible future scenarios of eruption precursors, magmatic system variables for different eruption types need to be constrained. Here we use petrological experiments and microanalysis of crystals to clarify the P-T-x state under which rhyodacitic melts accumulated prior to the H3 eruption; the largest Holocene Plinian eruption of Hekla volcano in Iceland. Cobalt-buffered, H2O-saturated phase equilibrium experiments reproduce the natural H3 pumice phenocryst assemblage (pl > fa + cpx > ilm + mt > ap + zrc) and glass chemistry, at 850 ± 15°C and PH2O of 130 to 175 MPa, implying shallow crustal magma storage between 5 and 6.6 km. The systematics of FeO and anorthite (CaAl2Si2O8) content in plagioclase reveal that thermal gradients were more important than compositional mixing or mingling within this magma reservoir. As these petrological findings indicate magma storage much shallower than is currently thought of Hekla's mafic system, we use the constrained storage depth in combination with deformation modeling to forecast permissible surface uplift patterns that could stem from pre-eruptive magma intrusion. Using forward modeling of surface deformation above various magma storage architectures, we show that vertical surface displacements caused by silicic magma accumulation at ∼6 km depth would be narrower than those observed in recent mafic events, which are fed from a lower crustal storage zone. Our results show how petrological reconstruction of magmatic system variables can help link signs of pre-eruptive geophysical unrest to magmatic processes occurring in reservoirs at shallow depths. This will enhance our

Fractal hierarchies of magma transport in Hawaii and critical self-organization of tremor

NASA Astrophysics Data System (ADS)

Shaw, Herbert R.; Chouet, Bernard

1991-06-01

A hierarchical model of magma transport in Hawaii is developed from the seismic records of deep (30-60 km) and intermediate-depth (5-15 km) harmonic tremor between January 1, 1962, and December 31, 1983. We find two kinds of spatial distributions of magma fractions at depths below 5 km, defined by the fractal dimension D3, where the subscript is the embedding dimension. The first is a focused distribution with D3 = 0.28, and the second is a dispersed distribution with D3 = 1.52. The former dimension reflects conduitlike structures where the magma flow converges toward a summit magma chamber and the fractal dimension tends to zero. The latter dimension reflects multifractal clustering of dendritic fractures where hypocentral domains represent subsets of fractures within spherical domains with an average radius of about 1 km. These geometries constitute a percolation network of clustered intermittent fracture and magma transport. The magma volume of the average fracture is about 2 × 104 m3. A tremor model of magma transport is developed from mass balances of percolation that are proportional to tremor durations. It gives reasonable magma fractions and residence times for a vertical drift velocity of 4 km yr-1 and yields patterns of intermittency that are in accord with singularity analyses of the 22-year time series record. According to the model, sustained tremor is generated by the relaxation oscillations of the percolation network with a dominant frequency of about 1 Hz to obtain internally consistent values of fracture geometry, fracture opening force, and magma supply rate. Calculated tremor frequencies are higher in fracture networks of small volume in harmony with the observed relation between seismic amplitude and dominant frequency of tremor. Tectonic relaxation times of rock stresses versus magma pressures are in fair agreement with the average length of tremor episodes and average period of tremor intermittencies. These observations suggest that a high

Growth of plutons by incremental emplacement of sheets in crystal-rich host: Evidence from Miocene intrusions of the Colorado River region, Nevada, USA

NASA Astrophysics Data System (ADS)

Miller, Calvin F.; Furbish, David J.; Walker, Barry A.; Claiborne, Lily L.; Koteas, G. Christopher; Bleick, Heather A.; Miller, Jonathan S.

2011-03-01

Growing evidence supports the notion that plutons are constructed incrementally, commonly over long periods of time, yet field evidence for the multiple injections that seem to be required is commonly sparse or absent. Timescales of up to several million years, among other arguments, indicate that the dominant volume does not remain largely molten, yet if growing plutons are constructed from rapidly solidifying increments it is unlikely that intrusive contacts would escape notice. A model wherein magma increments are emplaced into melt-bearing but crystal-rich host, rather than either solid or crystal-poor material, provides a plausible explanation for this apparent conundrum. A partially solidified intrusion undoubtedly comprises zones with contrasting melt fraction and therefore strength. Depending on whether these zones behave elastically or ductilely in response to dike emplacement, intruding magma may spread to form sheets by either of two mechanisms. If the melt-bearing host is elastic on the relevant timescale, magma spreads rather than continuing to propagate upward, where it encounters a zone of higher rigidity (higher crystal fraction). Similarly, if the dike at first ascends through rigid, melt-poor material and then encounters a zone that is weak enough (poor enough in crystals) to respond ductilely, the ascending material will also spread because the dike tip ceases to propagate as in rigid material. We propose that ascending magma is thus in essence trapped, by either mechanism, within relatively crystal-poor zones. Contacts will commonly be obscure from the start because the contrast between intruding material (crystal-poorer magma) and host (crystal-richer material) is subtle, and they may be obscured even further by subsequent destabilization of the crystal-melt framework. Field evidence and zircon zoning stratigraphy in plutons of the Colorado River region of southern Nevada support the hypothesis that emplacement of magma replenishments into a

Drilling the Bushveld Complex- the world's largest layered mafic intrusion

NASA Astrophysics Data System (ADS)

Ashwal, L. D.; Webb, S. J.; Trumbull, R. B.

2013-12-01

The fact that surprising new discoveries can be made in layered mafic intrusions (e.g., subtle 100-150 m cyclicity in apparently homogeneous cumulates over 1000s of m) means that we are still in the first-order characterization phase of understanding these objects. Accordingly, we have secured funding from ICDP for a planning workshop to be held in Johannesburg in early 2014, aimed at scientific drilling of the Bushveld Complex, the world's largest layered mafic intrusion. Science objectives include, but are not limited to: 1. Magma chamber processes & melt evolution. How many melts/magmas/mushes were involved, what were their compositions and how did they interact? What, if anything, is missing from the Complex, and where did it go? Did Bushveld magmatism have an effect upon Earth's atmosphere at 2 Ga? 2. Crust-mantle interactions & origin of Bushveld granitoids. Are Bushveld granites & rhyolites crustal melts, differentiates from the mafic magmas or products of immiscibility? How can the evolved isotopic signatures in the mafic rocks (e.g., epsilon Nd to -8) be understood? 3. Origin of ore deposits. What were the relative roles of gravity settling, magma mixing, immiscibility and hydrothermal fluid transport in producing the PGE, Cr and V deposits? We have identified 3 potential drilling targets representing a total of ~12 km of drill core. Exact locations of drill sites are to be discussed at the workshop. Target A- East-Central Bushveld Complex. We propose 3 overlapping 3 km boreholes that will provide the first roof-to-floor continuous coverage of the Rustenburg Layered Suite. These boreholes will represent a curated, internationally available reference collection of Bushveld material for present and future research. Target B- Southeastern Bushveld Complex. We propose a single borehole of ~2 km depth, collared in Rooiberg felsite, and positioned to intersect the Roof Zone, Upper Zone, Main Zone and floor of the Complex. Amongst other things, this site will

Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

NASA Technical Reports Server (NTRS)

Danielson, Lisa R.; Metcalf, Rodney V.; Miller, Calvin F.; Rhodes Gregory T.; Wooden, J. L.

2013-01-01

The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the

Intrusive images and intrusive thoughts as different phenomena: two experimental studies.

PubMed

Hagenaars, Muriel A; Brewin, Chris R; van Minnen, Agnes; Holmes, Emily A; Hoogduin, Kees A L

2010-01-01

According to the dual representation theory of PTSD, intrusive trauma images and intrusive verbal thoughts are produced by separate memory systems. In a previous article it was shown that after watching an aversive film, participants in non-movement conditions reported more intrusive images than participants in a free-to-move control condition (Hagenaars, Van Minnen, Holmes, Brewin, & Hoogduin, 2008). The present study investigates whether the experimental conditions of the Hagenaars et al. study had a different effect on intrusive thoughts than on intrusive images. Experiment 2 further investigated the image-thoughts distinction by manipulating stimulus valence (trauma film versus neutral film) and assessing the subsequent development of intrusive images and thoughts. In addition, both experiments studied the impact of peri-traumatic emotions on subsequent intrusive images and thoughts frequency across conditions. Results showed that experimental manipulations (non-movement and trauma film) caused higher levels of intrusive images relative to control conditions (free movement and neutral film) but they did not affect intrusive thoughts. Peri-traumatic anxiety and horror were associated with subsequent higher levels of intrusive images, but not intrusive thoughts. Correlations were inconclusive for anger and sadness. The results suggest intrusive images and thoughts can be manipulated independently and as such can be considered different phenomena.

Mass Intrusion at Mount St. Helens (WA) From Temporal Gravity Variations

NASA Astrophysics Data System (ADS)

Battaglia, M.; Lisowski, M.; Dzurisin, D.; Poland, M. P.; Schilling, S. P.; Diefenbach, A. K.; Wynn, J.

2015-12-01

Repeated high-precision gravity measurements made at Mount St. Helens (WA) have revealed systematic temporal variations in the gravity field several years after the end of the 2004-2008 dome-building eruption. Changes in gravity with respect to a stable reference station 36 km NW of the volcano were measured at 10 sites on the volcanic edifice and at 4 sites far afield (10 to 36 km) from the summit in August 2010, August 2012 and August 2014. After simulating and removing the gravity signal associated with changes in mass of the crater glacier, the local hydrothermal aquifer, and vertical deformation, the residual gravity field observed at sites near the volcano's summit significantly increased with respect to the stable reference site during 2010-2012 (maximum change 48 ± 15 mgal). No significant change was measured during 2012-2014. The pattern of gravity increase is radially symmetrical, with a half-width of about 2.5 km and a point of maximum change centered at the 2004-2008 lava dome. Forward modeling of residual gravity data using the same source geometry, depth, and location as that inferred from geodetic data (a spheroidal source centered 7.5 km beneath the 2004-2008 dome) indicates a mass increase rate of the order of 1011 kg/year. For a reasonable magma density (~2250 kg/m3), the volume rate of magma intrusion beneath the summit region inferred from gravity (~ 0.1 km3/yr) greatly exceeds the volume inferred from inversion of geodetic data (0.001 km3/yr between 2008-2011), suggesting that either magma compressibility or other processes are important aspects of magma storage at Mount St. Helens, or that the data argue for a different source.

Mesozoic invasion of crust by MORB-source asthenospheric magmas, U.S. Cordilleran interior

NASA Astrophysics Data System (ADS)

Leventhal, Janet A.; Reid, Mary R.; Montana, Art; Holden, Peter

1995-05-01

Mafic and ultramafic xenoliths entrained in lavas of the Cima volcanic field have Nd and Sr isotopic ratios indicative of a source similar to that of mid-ocean ridge basalt (MORB). Nd and Sr internal isochrons demonstrate a Late Cretaceous intrusion age. These results, combined with evidence for emplacement in the lower crust and upper mantle, indicate invasion of the lower crust by asthenospheric magmas in the Late Cretaceous. Constituting the first prima facie evidence for depleted-mantle magmatism in the Basin and Range province prior to late Cenozoic volcanism, these results lend key support to models suggesting crustal heating by ascent of asthenosphere in the Mesozoic Cordilleran interior.

Pyroxene megacrysts in Proterozoic anorthosites: Implications for tectonic setting, magma source and magmatic processes at the Moho

NASA Astrophysics Data System (ADS)

Bybee, G. M.; Ashwal, L. D.; Shirey, S. B.; Horan, M.; Mock, T.; Andersen, T. B.

2014-03-01

Proterozoic anorthosites from the 1630-1650 Ma Mealy Mountains Intrusive Suite (Grenville Province, Canada), the 1289-1363 Ma Nain Plutonic Suite (Nain-Churchill Provinces, Canada) and the 920-949 Ma Rogaland Anorthosite Province (Sveconorwegian Province, Norway), all entrain comagmatic, cumulate, high-alumina orthopyroxene megacrysts (HAOMs). The orthopyroxene megacrysts range in size from 0.2 to 1 m and all contain exsolution lamellae of plagioclase that indicate the incorporation of an excess Ca-Al component inherited from the host magma at pressures in excess of 10 kbar at or near Moho depths (>30-40 km). Suites of HAOMs from each intrusion display a large range in 147Sm/144Nd (0.10 to 0.34) making them amenable for precise age dating with the Sm-Nd system. Sm-Nd isochrons for HAOMs give ages of 1765±12 Ma (Mealy Mountains), 1041±17 Ma (Rogaland) and 1444±100 Ma (Nain), all of them older by about 80 to 120 m.y. than the respective 1630-1650, 920-949 and 1289-1363 Ma crystallization ages of their host anorthosites. Internal mineral Sm-Nd isochrons between plagioclase exsolution lamellae and the orthopyroxene host for HAOMs from the Rogaland and Nain complexes yield ages of 968±43 and 1347±6 Ma, respectively - identical within error to the ages of the anorthosites themselves. This age concordance establishes that decompression exsolution in the HAOM was coincident with magmatic emplacement of the anorthosites, ∼100 m.y. after HAOMs crystallization at the Moho. Correspondence of Pb isotope ages (206Pb/204Pb vs. 207Pb/204Pb) with Sm-Nd ages and other strong lines of evidence indicate that the older megacryst ages represent true crystallization ages and not the effects of time-integrated mixing processes in the magmas. Nd isotopic evolution curves, AFC/mixing calculations and the age relations between the HOAMs and their anorthosite hosts show that the HAOMs are much less contaminated with crustal components and are an older part of the same magmatic system

Subglacial volcanic activity above a lateral dyke path during the 2014-2015 Bárdarbunga-Holuhraun rifting episode, Iceland

NASA Astrophysics Data System (ADS)

Reynolds, Hannah I.; Gudmundsson, Magnús T.; Högnadóttir, Thórdís; Magnússon, Eyjólfur; Pálsson, Finnur

2017-06-01

The rifting episode associated with the Bárdarbunga-Holuhraun eruption in 2014-2015 included the first observations of major dyke propagation under ice. Three shallow ice depressions (ice cauldrons) with volumes ranging from 1 to 18 million m3 formed in Dyngjujökull glacier above the 48-km-long lateral path of the magma, at 4, 7 and 12 km from the northern glacier edge. Aircraft-based radar altimetry profiling was used to map the evolution of the cauldrons and construct a time series of the heat transfer rates. Out of the three scenarios explored: (1) onset or increase of hydrothermal activity, (2) convection within vertical fissures filled with water overlying intruded magma and (3) subglacial eruptions, the last option emerges as the only plausible mechanism to explain the rapid heat transfer observed in a location far from known geothermal areas. The thermal signals at two of the cauldrons are consistent with effusive subglacial eruptions. The formation of the northernmost cauldron was more rapid, indicating faster heat transfer rates. Radio-echo sounding data indicate that in contrast to the other two cauldrons, an intrusion of eruptive products occurred into the glacier, reaching 50-60 m above bedrock with the increased magma-ice contact explaining the more rapid heat transfer. We propose that the 2-m widening associated with graben formation increased the groundwater storage capacity of the bedrock, creating space for the meltwater to be stored, explaining the absence of meltwater pulses draining from Dyngjujökull.

Fronts and intrusions in the upper Deep Polar Water of the Eurasian and Makarov basins

NASA Astrophysics Data System (ADS)

Kuzmina, Natalia; Rudels, Bert; Zhurbas, Natalia; Lyzhkov, Dmitry

2013-04-01

CTD data obtained in the Arctic Basin are analyzed to describe structural features of intrusive layers and fronts encountered in the upper Deep Polar Water. This work is an extension of Arctic intrusions studies by Rudels et al. (1999) and Kuzmina et al. (2011). Numerous examples of fronts and intrusions observed in a deep layer (depth range of 600-1300 m) in the Eurasian and Makarov basins where salinity is increasing, and temperature is decreasing with depth (stable-stable thermohaline stratification), are described. The data are used to estimate hydrological parameters capable of determining different types of fronts and characterizing intrusive layers depending on the front structure. Coherence of intrusive layers is shown to get broken with the change of front structure. An evidence is found that enhanced turbulent mixing above local bottom elevations can prevent from intrusive layering. A linear stability model description of the observed intrusions is developed based on the Merryfield's (2000) assumption that interleaving is caused by differential mixing. Theoretical analysis is focused on prediction of the slopes of unstable modes at baroclinic and thermohaline fronts. Apparent vertical diffusivity due to turbulent mixing at baroclinic and thermohaline fronts is estimated on the basis of comparison of observed intrusion slopes with modeled slopes of the most unstable modes. Apparent lateral diffusivity is estimated too, based on Joyce (1980) approach. These estimates show that intrusive instability of fronts caused by differential mixing can result in sizable values of apparent lateral heat diffusivity in the deep Arctic layer that are quite comparable with those of the upper and intermediate Arctic layers (Walsh, Carmack, 2003; Kuzmina et al., 2011).

Quasi-horizontal circulation cells in 3D seawater intrusion

USGS Publications Warehouse

Abarca, E.; Carrera, J.; Sanchez-Vila, X.; Voss, C.I.

2007-01-01

The seawater intrusion process is characterized by the difference in freshwater and seawater density that causes freshwater to float on seawater. Many confined aquifers have a large horizontal extension with respect to thickness. In these cases, while buoyancy acts in the vertical direction, flow is confined between the upper and bottom boundaries and the effect of gravity is controlled by variations of aquifer elevation. Therefore, the effective gravity is controlled by the slope and the shape of the aquifer boundaries. Variability in the topography of the aquifer boundaries is one case where 3D analysis is necessary. In this work, density-dependent flow processes caused by 3D aquifer geometry are studied numerically and specifically, considering a lateral slope of the aquifer boundaries. Sub-horizontal circulation cells are formed in the saltwater entering the aquifer. The penetration of the saltwater can be quantified by a dimensionless buoyancy number that measures the lateral slope of the aquifer relative to freshwater flux. The penetration of the seawater intrusion wedge is controlled more by this slope than by the aquifer thickness and dispersivity. Thus, the slope must be taken into account in order to accurately evaluate seawater intrusion. ?? 2007 Elsevier B.V. All rights reserved.

The Meaning of "Magma"

NASA Astrophysics Data System (ADS)

Bartley, J. M.; Glazner, A. F.; Coleman, D. S.

2016-12-01

Magma is a fundamental constituent of the Earth, and its properties, origin, evolution, and significance bear on issues ranging from volcanic hazards to planetary evolution. Unfortunately, published usages indicate that the term "magma" means distinctly different things to different people and this can lead to miscommunication among Earth scientists and between scientists and the public. Erupting lava clearly is magma; the question is whether partially molten rock imaged at depth and too crystal-rich to flow should also be called magma. At crystal fractions > 50%, flow can only occur via crystal deformation and solution-reprecipitation. As the solid fraction increases to 90% or more, the material becomes a welded crystal framework with melt in dispersed pores and/or along grain boundaries. Seismic images commonly describe such volumes of a few % melt as magma, yet the rheological differences between melt-rich and melt-poor materials make it vital not to confuse a large rock volume that contains a small melt fraction with melt-rich material. To ensure this, we suggest that "magma" be reserved for melt-rich materials that undergo bulk fluid flow on timescales consonant with volcanic eruptions. Other terms should be used for more crystal-rich and largely immobile partially molten rock (e.g., "crystal mush," "rigid sponge"). The distinction is imprecise but useful. For the press, the public, and even earth scientists who do not study magmatic systems, "magma" conjures up flowing lava; reports of a large "magma" body that contains a few percent melt can engender the mistaken perception of a vast amount of eruptible magma. For researchers, physical processes like crystal settling are commonly invoked to account for features in plutonic rocks, but many such processes are only possible in melt-rich materials.

Longitudinal Relations of Intrusive Parenting and Effortful Control to Ego-Resiliency during Early Childhood

ERIC Educational Resources Information Center

Taylor, Zoe E.; Eisenberg, Nancy; Spinrad, Tracy L.; Widaman, Keith F.

2013-01-01

Longitudinal relations among ego-resiliency (ER), effortful control (EC), and observed intrusive parenting were examined at 18, 30, and 42 months of age ("Ns" = 256, 230, and 210) using structural equation modeling. Intrusive parenting at 18 and 30 months negatively predicted EC a year later, over and above earlier levels. EC at…

Chemical consequences of compaction within the freezing front of a crystallizing magma ocean

NASA Astrophysics Data System (ADS)

Hier-Majumder, S.; Hirschmann, M. M.

2013-12-01

The thermal and compositional evolution of planetary magma oceans have profound influences on the early development and differentiation of terrestrial planets. During crystallization, rejection of elements incompatible in precipitating solids leads to petrologic and geochemical planetary differentiation, including potentially development of a compositionally stratified early mantle and evolution of thick overlying atmospheres. In cases of extremely efficient segregation of melt and crystals, solidified early mantles can be nearly devoid of key incompatible species including heat-producing (U, Th, K) and volatile (H,C,N,& noble gas) elements. A key structural component of a crystallizing magma ocean is the partially molten freezing front. The dynamics of this region influences the distribution of incompatible elements between the earliest mantle and the initial surficial reservoirs. It also can be the locus of heating owing to the dissipation of large amounts of tidal energy potentially available from the early Moon. The dynamics are influenced by the solidification rate, which is coupled to the liberation of volatiles owing to the modulating greenhouse effects in the overlying thick atmosphere. Compaction and melt retention in the freezing front of a magma ocean has received little previous attention. While the front advances during the course of crystallization, coupled conservation of mass, momentum, and energy within the front controls distribution and retention of melt within this layer. Due to compaction within this layer, melt distribution is far from uniform, and the fraction of melt trapped within this front depends on the rate of freezing of the magma ocean. During phases of rapid freezing, high amount of trapped melt within the freezing front retains a larger quantity of dissolved volatiles and the reverse is true during slow periods of crystallization. Similar effects are known from inferred trapped liquid fractions in layered mafic intrusions. Here we

Calderas and magma reservoirs

NASA Astrophysics Data System (ADS)

Cashman, Katharine V.; Giordano, Guido

2014-11-01

Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; petrologists have used the eruptive products to probe conditions of magma storage (and thus processes that drive magma evolution), while volcanologists have used them to study the conditions under which large volumes of magma are transported to, and emplaced on, the Earth's surface. Traditionally, both groups have worked on the assumption that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. Here we explore the implications of complex magma reservoir configurations for eruption dynamics and caldera formation. We first examine mafic systems, where stacked-sill models have long been invoked but which rarely produce explosive eruptions. An exception is the 2010 eruption of Eyjafjallajökull volcano, Iceland, where seismic and petrologic data show that multiple sills at different depths fed a multi-phase (explosive and effusive) eruption. Extension of this concept to larger mafic caldera-forming systems suggests a mechanism to explain many of their unusual features, including their protracted explosivity, spatially variable compositions and pronounced intra-eruptive pauses. We then review studies of more common intermediate and silicic caldera-forming systems to examine inferred conditions of magma storage, time scales of melt accumulation, eruption triggers, eruption dynamics and caldera collapse. By compiling data from large and small, and crystal-rich and crystal-poor, events, we compare eruptions that are well explained by simple evacuation of a zoned

Asymmetric shock heating and the terrestrial magma ocean origin of the Moon.

PubMed

Karato, Shun-ichiro

2014-01-01

One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon.

Tempo of magma degassing and the genesis of porphyry copper deposits.

PubMed

Chelle-Michou, Cyril; Rottier, Bertrand; Caricchi, Luca; Simpson, Guy

2017-01-12

Porphyry deposits are copper-rich orebodies formed by precipitation of metal sulphides from hydrothermal fluids released from magmatic intrusions that cooled at depth within the Earth's crust. Finding new porphyry deposits is essential because they are our largest source of copper and they also contain other strategic metals including gold and molybdenum. However, the discovery of giant porphyry deposits is hindered by a lack of understanding of the factors governing their size. Here, we use thermal modelling and statistical simulations to quantify the tempo and the chemistry of fluids released from cooling magmatic systems. We confirm that typical arc magmas produce fluids similar in composition to those that form porphyry deposits and conclude that the volume and duration of magmatic activity exert a first order control on the endowment (total mass of deposited copper) of economic porphyry copper deposits. Therefore, initial magma enrichment in copper and sulphur, although adding to the metallogenic potential, is not necessary to form a giant deposit. Our results link the respective durations of magmatic and hydrothermal activity from well-known large to supergiant deposits to their metal endowment. This novel approach can readily be implemented as an additional exploration tool that can help assess the economic potential of magmatic-hydrothermal systems.

Tempo of magma degassing and the genesis of porphyry copper deposits

PubMed Central

Chelle-Michou, Cyril; Rottier, Bertrand; Caricchi, Luca; Simpson, Guy

2017-01-01

Porphyry deposits are copper-rich orebodies formed by precipitation of metal sulphides from hydrothermal fluids released from magmatic intrusions that cooled at depth within the Earth’s crust. Finding new porphyry deposits is essential because they are our largest source of copper and they also contain other strategic metals including gold and molybdenum. However, the discovery of giant porphyry deposits is hindered by a lack of understanding of the factors governing their size. Here, we use thermal modelling and statistical simulations to quantify the tempo and the chemistry of fluids released from cooling magmatic systems. We confirm that typical arc magmas produce fluids similar in composition to those that form porphyry deposits and conclude that the volume and duration of magmatic activity exert a first order control on the endowment (total mass of deposited copper) of economic porphyry copper deposits. Therefore, initial magma enrichment in copper and sulphur, although adding to the metallogenic potential, is not necessary to form a giant deposit. Our results link the respective durations of magmatic and hydrothermal activity from well-known large to supergiant deposits to their metal endowment. This novel approach can readily be implemented as an additional exploration tool that can help assess the economic potential of magmatic-hydrothermal systems. PMID:28079160

Magma plumbing in the Grímsvötn volcanic system, Iceland: an overview

NASA Astrophysics Data System (ADS)

Thordarson, T.

2016-12-01

The basaltic Grímsvötn volcanic system (GVS) consists of Grímsvötn central volcano (GCV) and an immature fissure swarm extending 70 km to the southwest from GCV. The GCV has the highest eruption frequency of all central volcanos in Iceland, or 7 events per 100 years. In contrast, the GVS fissure swarm has only featured two events in postglacial times, the 1783-4 Laki and the prehistoric Lambavatnsgígar fissure eruptions. These two events account for 25% of the total Holocene magma output from the GVS and 80% of the output in historic time (i.e. last 1100 years). Although GVS magma plumbing has been a topic of research for four decades, its general structure, extent and geometry is still deliberated. Is mantle-derived magma delivered straight up beneath the GCV to an upper crustal magma chamber and then vertically to eruptions at the GCV and laterally to eruption on the GVS fissure swarm? Or does the system feature two levels of crustal storage, one in the upper crust beneath GCV and another at mid-crustal depth? Or is the structure of the GVS plumbing more complex? The data that we have so far and is pertinent to GVS magma plumbing is summarised below: Geophysical measurements imply that shallowest magma storage beneath GCV is at 3-4 km. The Zr and Nb concentrations in the tephra from the 1998 and 2004 GCV plus Laki eruptions show that the parent magmas for each was produced by different degrees of partial melting of a similar mantle source. It also demonstrates transport to the surface via separate pathways and that neither magma can be derived by fractional crystallization from a Laki-like magma. Detailed petrological studies on the Laki tephra and lava indicate polybaric magma evolution within the mid-crust (at 6 to 15 km depth), with further evolution at shallower depths induced either by disequilibrium crystal growth during ascent of magma from the mid-crust storage or a brief residence at 3-6 km depths. The Laki magma contains significant abundances of

Longitudinal Relations of Intrusive Parenting and Effortful Control to Ego-Resiliency During Early Childhood

PubMed Central

Taylor, Zoe E.; Eisenberg, Nancy; Spinrad, Tracy L.; Widaman, Keith F.

2012-01-01

Longitudinal relations among ego-resiliency, effortful control, and observed intrusive parenting were examined at 18, 30, and 42 months of age (Ns = 256, 230, and 210) using structural equation modeling. Intrusive parenting at 18 and 30 months negatively predicted effortful control a year later, over and above earlier levels. Effortful control at 30 months mediated the negative relation between 18-month intrusive parenting and ego-resiliency at 42 months when controlling for stability of the variables. Ego-resiliency did not predict effortful control. The findings suggest that intrusive parenting may have a negative effect on children’s personality resiliency through its effects on the abilities to regulate attention and behavior. PMID:23379965

Magma genesis, storage and eruption processes at Aluto volcano, Ethiopia: lessons from remote sensing, gas emissions and geochemistry

NASA Astrophysics Data System (ADS)

Hutchison, William; Biggs, Juliet; Mather, Tamsin; Pyle, David; Gleeson, Matthew; Lewi, Elias; Yirgu, Gezahgen; Caliro, Stefano; Chiodini, Giovanni; Fischer, Tobias

2016-04-01

One of the most intriguing aspects of magmatism during the transition from continental rifting to sea-floor spreading is that large silicic magmatic systems develop within the rift zone. In the Main Ethiopian Rift (MER) these silicic volcanoes not only pose a significant hazard to local populations but they also sustain major geothermal resources. Understanding the journey magma takes from source to surface beneath these volcanoes is vital for determining its eruption style and for better evaluating the geothermal resources that these complexes host. We investigate Aluto, a restless silicic volcano in the MER, and combine a wide range of geochemical and geophysical techniques to constrain magma genesis, storage and eruption processes and shed light on magmatic-hydrothermal-tectonic interactions. Magma genesis and storage processes at Aluto were evaluated using new whole-rock geochemical data from recent eruptive products. Geochemical modelling confirms that Aluto's peralkaline rhyolites, that constitute the bulk of recent erupted products, are generated from protracted fractionation (>80 %) of basalt that is compositionally similar to rift-related basalts found on the margins of the complex. Crustal melting did not play a significant role in rhyolite genesis and melt storage depths of ~5 km can reproduce almost all aspects of their geochemistry. InSAR methods were then used to investigate magma storage and fluid movement at Aluto during an episode of ground deformation that took place between 2008 and 2010. Combining new SAR imagery from different viewing geometries we identified an accelerating uplift pulse and found that source models support depths of magmatic and/or fluid intrusion at ~5 km for the uplift and shallower depths of ~4 km for the subsidence. Finally, gas samples collected on Aluto in 2014 were used to evaluate magma and fluid transport processes. Our results show that gases are predominantly emanating from major fault zones on Aluto and that they

Magma differentiation in volcanic conduits - the clinopyroxenite body of Fuerteventura (Canary Islands)

NASA Astrophysics Data System (ADS)

Tornare, Evelyne; Bussy, François

2014-05-01

Fractionation processes and magma differentiation/mixing occur at various levels during magma transportation through the crust. These processes are usually thought to occur in magmatic chambers or reservoirs into which magma stagnates before continuing to ascent and/or erupt. Here we discuss dynamic fractionation and magma differentiation processes in the plumbing system of an ocean island volcano. Fuerteventura, Canary Island, allows insight into the root-zone of an alkaline ocean island volcano. The PX1 pluton is a 22 Ma-old vertically layered mafic intrusion emplaced at ca. 0.1 GPa. This body shows large- and small-scale alternations of cumulate assemblages evolving from ol-rich wehrlite to clinopyroxenite to gabbro. These cumulates are intruded by numerous dykes of various compositions and veins of more evolved melt. Dykes, veins, and the large scale lithological variations define a general NNE-SSW vertical layering within the pluton. In some areas free of layering, numerous wehrlitic and clinopyroxenitic enclaves appear in a slightly more evolved matrix revealing clear mixing features of crystal mushes. Neither horizontal layering nor marginal facies are observed within PX1. Thus, clinopyroxenites do not represent accumulation of crystals through gravitational settling in a magma chamber. Compositions of cpx define a clear differentiation trend among all lithologies, from sp-bearing dunite (average cpx mg#: 85.99) to plg-ol- or kst-clinopyroxenites (mg#: 75.4). Chemically zoned cpx are present in all coarse-grained lithologies. They are characterised by a rather primitive resorbed core (higher Cr and Mg content), surrounded by a more evolved rim (higher Ti, Al and REE contents, similar to cpx in the matrix). Rims sometimes preserve clear oscillatory zoning and resorbtion features. Cores are interpreted as inherited crystals from deeper levels, whereas rims are considered to have crystallized at the final emplacement level in the root zone of the volcano. We

Pressure waves in a supersaturated bubbly magma

USGS Publications Warehouse

Kurzon, I.; Lyakhovsky, V.; Navon, O.; Chouet, B.

2011-01-01

We study the interaction of acoustic pressure waves with an expanding bubbly magma. The expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves. On the one hand, growth in vesicularity leads to increased damping and decreased wave amplitudes, and on the other hand, a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity, which in turn, reduces damping and may lead to wave amplification. The additional acoustic energy originates from the chemical energy released during bubble growth. We examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible. These conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles. Amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material. We examine two amplification phase-dependent effects: (1) a tensile-phase effect in which the inserted wave adds to the process of bubble growth, utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy, and (2) a compressive-phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle, but later enough energy is gained to amplify the second cycle. These two effects provide additional new possible mechanisms for the amplification phase seen in Long-Period (LP) and Very-Long-Period (VLP) seismic signals originating in magma-filled cracks.

Patchy distribution of magma that fed the Bishop Tuff supereruption: Evidence from matrix glass major and trace-element compositions

NASA Astrophysics Data System (ADS)

Gualda, G. A. R.; Ghiorso, M. S.; Hurst, A. A.; Allen, M. C.; Bradshaw, R. W.

2017-12-01

For more than 40 years, the Bishop Tuff has been the archetypical example of a singular, zoned magma body that fed a supereruption. Early-erupted material is pyroxene-free and crystal poor (<20 wt. %), presumably erupted from the upper parts of the magma body; late-erupted material is orthopyroxene and clinopyroxene-bearing, commonly more crystal rich (up to 30 wt. % crystals), and presumably tapped magma from the lower portions of the magma body. Fe-Ti oxide compositions suggest higher crystallization temperatures for late-erupted magmas (as high as 820 °C) than for early-erupted magmas (as low as 700 °C). Pressures and temperatures derived from major element compositions of glass inclusions led Gualda & Ghiorso (2013, CMP) to suggest an alternative model of lateral juxtaposition of two main magma bodies - each one feeding early-erupted and late-erupted units. Chamberlain et al. (2015, JPet) and Evans et al. (2016, AmMin) recently disputed this interpretation. We present a large dataset of matrix glass compositions for 161 pumice clasts that span the stratigraphy of the deposit. We calculate crystallization pressures based on major-element glass compositions using rhyolite-MELTS geobarometry, and crystallization temperatures based on Zr in glass using zircon saturation geothermometry. We apply the same methods to 1538 major-element and 615 trace-element analyses from Chamberlain et al. The results overwhelmingly demonstrate that there is no difference in crystallization temperature or pressure between early and late-erupted magmas. Crystallization pressures and temperatures are unimodal, with modes of 150 MPa and 730 °C (calibration of Watson & Harrison). Our results strongly support lateral juxtaposition of two main magma bodies. Smaller units recognized by Chamberlain et al. crystallized at the same pressures as the main bodies - this suggests the coexistence of larger and smaller magma bodies at the time of the Bishop Tuff supereruption. We compare our

Deformation monitoring at Mount St. Helens in 1981 and 1982

USGS Publications Warehouse

Chadwick, W.W.; Swanson, D.A.; Iwatsubo, E.Y.; Heliker, C.C.; Leighley, T.A.

1983-01-01

For several weeks before each eruption of Mount St. Helens in 1981 and 1982, viscous magma rising in the feeder conduit inflated the lava dome and shoved the crater floor laterally against the immobile crater walls, producing ground cracks and thrust faults. The rates of deformation accelerated before eruptions, and thus it was possible to predict eruptions 3 to 19 days in advance. Lack of deformation outside the crater showed that intrusion of magma during 1981 and 1982 was not voluminous.

Intermediate-term seismic precursors to the 2007 Father's Day intrusion and eruption at Kilauea Volcano, Hawai'i

NASA Astrophysics Data System (ADS)

Roman, D. C.; Wauthier, C.; Poland, M. P.

2012-12-01

For two days beginning on June 17 (Father's Day), 2007, and following a four-year-long period of summit inflation, magma intruded into Kilauea's east rift zone, resulting in a small eruption just north of Makaopuhi Crater (~7 km west of the long-lived Pu'u O'o vent). On the basis of concurrent summit deflation and observations of lava chemistry and temperature, the June 17-19 Father's Day event has been interpreted as the result of forcible intrusion driven by high magma pressure at the summit, as opposed to a passive response to rifting. The Father's Day event was preceded by a) two shallow oblique strike-slip M4+ earthquakes along the outermost caldera faults on 24 May 2007, and b) a strong swarm of shallow volcano-tectonic (VT) earthquakes beginning on June 17 and signaling the onset of intrusion into the ERZ. Little is known, however, about any intermediate-term precursors that may have occurred between these two sets of earthquakes. We analyzed continuous and event-detected seismic data recorded by the Hawaiian Volcano Observatory permanent seismic monitoring network during the first half of 2007 and observe a) a subtle increase in the rate of seismic moment release beginning in April 2007, and b) a subtle decrease in seismic event rate beginning in early June 2007, both of which appear to correspond to changes in shallow (<5 km BSL) and intermediate-depth (>5 km BSL) seismicity. Most located events during this period occur in the upper southwest and east rift zones; however, relocation of newly-detected low-magnitude events also indicates the presence of a 'ring' of seismicity centered on the southeast caldera rim and a cluster of events with epicenters near Kilauea Iki crater. Additional analyses will indicate whether these features are unique to the months preceding the Father's Day event or whether they represent long-term features of Kilauea's seismicity. Finally, Interferometric Synthetic Aperture Radar (InSAR) analyses were used to examine the M4.7 and

Theoretical prediction of gold vein location in deposits originated by a wall magma intrusion

NASA Astrophysics Data System (ADS)

Martin, Pablo; Maass-Artigas, Fernando; Cortés-Vega, Luis

2016-05-01

The isotherm time-evolution resulting from the intrusion of a hot dike in a cold rock is analized considering the general case of nonvertical walls. This is applied to the theoretical prediction of the gold veins location due to isothermal evolution. As in previous treatments earth surface effects are considered and the gold veins are determined by the envelope of the isotherms. The locations of the gold veins in the Callao mines of Venezuela are now well predicted. The new treatment is now more elaborated and complex that in the case of vertical walls, performed in previous papers, but it is more adequated to the real cases as the one in El Callao, where the wall is not vertical.

Magma-poor vs. magma-rich continental rifting and breakup in the Labrador Sea

NASA Astrophysics Data System (ADS)

Gouiza, M.; Paton, D.

2017-12-01

Magma-poor and magma-rich rifted margins show distinct structural and stratigraphic geometries during the rift to breakup period. In magma-poor margins, crustal stretching is accommodated mainly by brittle faulting and the formation of wide rift basins shaped by numerous graben and half-graben structures. Continental breakup and oceanic crust accretion are often preceded by a localised phase of (hyper-) extension where the upper mantle is embrittled, serpentinized, and exhumed to the surface. In magma-rich margins, the rift basin is narrow and extension is accompanied by a large magmatic supply. Continental breakup and oceanic crust accretion is preceded by the emplacement of a thick volcanic crust juxtaposing and underplating a moderately thinned continental crust. Both magma-poor and magma-rich rifting occur in response to lithospheric extension but the driving forces and processes are believed to be different. In the former extension is assumed to be driven by plate boundary forces, while in the latter extension is supposed to be controlled by sublithospheric mantle dynamics. However, this view fails in explaining observations from many Atlantic conjugate margins where magma-poor and magma-rich segments alternate in a relatively abrupt fashion. This is the case of the Labrador margin where the northern segment shows major magmatic supply during most of the syn-rift phase which culminate in the emplacement of a thick volcanic crust in the transitional domain along with high density bodies underplating the thinned continental crust; while the southern segment is characterized mainly by brittle extension, mantle seprentinization and exhumation prior to continental breakup. In this work, we use seismic and potential field data to describe the crustal and structural architectures of the Labrador margin, and investigate the tectonic and mechanical processes of rifting that may have controlled the magmatic supply in the different segments of the margin.

Asymmetric shock heating and the terrestrial magma ocean origin of the Moon

PubMed Central

KARATO, Shun-ichiro

2014-01-01

One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon. PMID:24621956

Growth of plutons by incremental emplacement of sheets in crystal-rich host: Evidence from Miocene intrusions of the Colorado River region, Nevada, USA

USGS Publications Warehouse

Miller, C.F.; Furbish, D.J.; Walker, B.A.; Claiborne, L.L.; Koteas, G.C.; Bleick, H.A.; Miller, J.S.

2011-01-01

Growing evidence supports the notion that plutons are constructed incrementally, commonly over long periods of time, yet field evidence for the multiple injections that seem to be required is commonly sparse or absent. Timescales of up to several million years, among other arguments, indicate that the dominant volume does not remain largely molten, yet if growing plutons are constructed from rapidly solidifying increments it is unlikely that intrusive contacts would escape notice. A model wherein magma increments are emplaced into melt-bearing but crystal-rich host, rather than either solid or crystal-poor material, provides a plausible explanation for this apparent conundrum. A partially solidified intrusion undoubtedly comprises zones with contrasting melt fraction and therefore strength. Depending on whether these zones behave elastically or ductilely in response to dike emplacement, intruding magma may spread to form sheets by either of two mechanisms. If the melt-bearing host is elastic on the relevant timescale, magma spreads rather than continuing to propagate upward, where it encounters a zone of higher rigidity (higher crystal fraction). Similarly, if the dike at first ascends through rigid, melt-poor material and then encounters a zone that is weak enough (poor enough in crystals) to respond ductilely, the ascending material will also spread because the dike tip ceases to propagate as in rigid material. We propose that ascending magma is thus in essence trapped, by either mechanism, within relatively crystal-poor zones. Contacts will commonly be obscure from the start because the contrast between intruding material (crystal-poorer magma) and host (crystal-richer material) is subtle, and they may be obscured even further by subsequent destabilization of the crystal-melt framework. Field evidence and zircon zoning stratigraphy in plutons of the Colorado River region of southern Nevada support the hypothesis that emplacement of magma replenishments into a

The influence of magma viscosity on convection within a magma chamber

NASA Astrophysics Data System (ADS)

Schubert, M.; Driesner, T.; Ulmer, P.

2012-12-01

Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

Numerical simulation of magma chamber dynamics.

NASA Astrophysics Data System (ADS)

Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea

2010-05-01

Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective

Magmatic ore deposits in layered intrusions - Descriptive model for reef-type PGE and contact-type Cu-Ni-PGE deposits

USGS Publications Warehouse

Zientek, Michael L.

2012-01-01

Layered, ultramafic to mafic intrusions are uncommon in the geologic record, but host magmatic ore deposits containing most of the world's economic concentrations of platinum-group elements (PGE) (figs. 1 and 2). These deposits are mined primarily for their platinum, palladium, and rhodium contents (table 1). Magmatic ore deposits are derived from accumulations of crystals of metallic oxides, or immiscible sulfide, or oxide liquids that formed during the cooling and crystallization of magma, typically with mafic to ultramafic compositions. "PGE reefs" are stratabound PGE-enriched lode mineralization in mafic to ultramafic layered intrusions. The term "reef" is derived from Australian and South African literature for this style of mineralization and used to refer to (1) the rock layer that is mineralized and has distinctive texture or mineralogy (Naldrett, 2004), or (2) the PGE-enriched sulfide mineralization that occurs within the rock layer. For example, Viljoen (1999) broadly defined the Merensky Reef as "a mineralized zone within or closely associated with an unconformity surface in the ultramafic cumulate at the base of the Merensky Cyclic Unit." In this report, we will use the term PGE reef to refer to the PGE-enriched mineralization, not the host rock layer. Within a layered igneous intrusion, reef-type mineralization is laterally persistent along strike, extending for the length of the intrusion, typically tens to hundreds of kilometers. However, the mineralized interval is thin, generally centimeters to meters thick, relative to the stratigraphic thickness of layers in an intrusion that vary from hundreds to thousands of meters. PGE-enriched sulfide mineralization is also found near the contacts or margins of layered mafic to ultramafic intrusions (Iljina and Lee, 2005). This contact-type mineralization consists of disseminated to massive concentrations of iron-copper-nickel-PGE-enriched sulfide mineral concentrations in zones that can be tens to hundreds

Externalizing symptoms, effortful control, and intrusive parenting: A test of bidirectional longitudinal relations during early childhood.

PubMed

Eisenberg, Nancy; Taylor, Zoe E; Widaman, Keith F; Spinrad, Tracy L

2015-11-01

At approximately 30, 42, and 54 months of age (N = 231), the relations among children's externalizing symptoms, intrusive maternal parenting, and children's effortful control (EC) were examined. Both intrusive parenting and low EC have been related to psychopathology, but children's externalizing problems and low EC might affect the quality of parenting and one another. Mothers' intrusive behavior with their children was assessed with observations, children's EC was measured with mothers' and caregivers' reports, and children's externalizing symptoms were assessed with mothers', fathers', and caregivers' reports. In a structural equation panel model, bidirectional relations between intrusive parenting and EC were found: EC at 30 and 42 months predicted low levels of intrusive parenting a year later, controlling for prior levels of parenting and vice versa. Moreover, high levels of children's externalizing problems at both 30 and 42 months negatively predicted EC a year later, controlling for prior levels of EC. Although externalizing problems positively predicted high EC over time, this appeared to be a suppression effect because these variables had a strong negative pattern in the zero-order correlations. Moreover, when controlling for the stability of intrusive parenting, EC, and externalizing (all exhibited significant stability across time) and the aforementioned cross-lagged predictive paths, EC and externalizing problems were still negatively related within the 54-month assessment. The findings are consistent with the view that children's externalizing behavior undermines their EC and contributes to intrusive mothering and that relations between intrusive parenting and EC are bidirectional across time. Thus, interventions that focus on modifying children's externalizing problems (as well as the quality of parenting) might affect the quality of parenting they receive and, hence, subsequent problems with adjustment.

Magma Reservoir Processes Revealed by Geochemistry of the Ongoing East Rift Zone Eruption, Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Thornber, C. R.

2002-12-01

limits of repeated MgO and temperature variation imply end-member magma conditions that are regulated by open-system recharge of the shallow magmatic plumbing system. The low-end of MgO variation (7 wt%) approaches the low-pressure multiphase cotectic, which is maintained by open-system replenishment of a persistent magma reservoir. The high-temperature end-member (10 wt% MgO) is probably regulated by olivine fractionation in a zone of turbulent mixing between primitive recharge magma (15 wt% MgO) and resident cotectic magma. The highest temperature magmas are associated with eruption pulses that occur in response to intrusive events at the summit and initiate short-term increases of HINCE/MINCE. Subsequent changes toward lower magmatic temperatures are associated with periods of overall summit deflation, relatively low-level effusion, and frequent eruptive pauses. The long-term trends can be explained by episodic mixing of chemically uniform recharge melt with diminishing proportions of pre-1983 summit magma (maintained at cotectic conditions). Decreasing HINCE/MINCE may signify that a greater proportion of recharge magma is being diverted directly to Pu`u `O`o with minimal summit interaction or that the mass ratio of those mixing end-members has changed due to a depleted summit chamber (or both). The coincidence of long-term summit deflation since the 1982 summit eruption suggests that shallow processes related to summit reservoir depletion may be responsible for decreasing HINCE/MINCE and Pb isotopes in post-1982 steady-state eruption products. Magma derived from a uniform mantle-source, after having flushed out older resident magma, may now completely occupy the shallow magmatic plumbing system.

Nyamulagira’s magma plumbing system inferred from 15 years of InSAR

USGS Publications Warehouse

Wauthier, Christelle; Cayol, Valérie; Poland, Michael; Kervyn, François; D'Oreye, Nicolas; Hooper, Andrew; Samsonov, Sergei; Tiampo, Kristy; Smets, Benoit; Pyle, D. M.; Mather, T.A.; Biggs, J.

2013-01-01

Nyamulagira, located in the east of the Democratic Republic of Congo on the western branch of the East African rift, is Africa’s most active volcano, with an average of one eruption every 3 years since 1938. Owing to the socio-economical context of that region, the volcano lacks ground-based geodetic measurements but has been monitored by interferometric synthetic aperture radar (InSAR) since 1996. A combination of 3D Mixed Boundary Element Method and inverse modelling, taking into account topography and source interactions, is used to interpret InSAR ground displacements associated with eruptive activity in 1996, 2002, 2004, 2006 and 2010. These eruptions can be fitted by models incorporating dyke intrusions, and some (namely the 2006 and 2010 eruptions) require a magma reservoir beneath the summit caldera. We investigate inter-eruptive deformation with a multi-temporal InSAR approach. We propose the following magma plumbing system at Nyamulagira by integrating numerical deformation models with other available data: a deep reservoir (c. 25 km depth) feeds a shallower reservoir (c. 4 km depth); proximal eruptions are fed from the shallow reservoir through dykes while distal eruptions can be fed directly from the deep reservoir. A dyke-like conduit is also present beneath the upper southeastern flank of Nyamulagira.

Bulk Viscosity of Bubbly Magmas and the Amplification of Pressure Waves

NASA Astrophysics Data System (ADS)

Navon, O.; Lensky, N. G.; Neuberg, J. W.; Lyakhovsky, V.

2001-12-01

The bulk viscosity of magma is needed in order to describe the dynamics of a compressible bubbly magma flowing in conduits and to follow the attenuation of pressure waves travelling through a compressible magma. We developed a model for the bulk viscosity of a suspension of gas bubbles in an incompressible Newtonian liquid that exsolves volatiles (e.g. magma). The suspension is modeled as a close pack of spherical cells, consisting of gas bubbles centered in spherical shells of a volatile-bearing liquid. Following a drop in the ambient pressure the resulting dilatational motion and driving pressure are obtained in terms of the two-phase cell parameters, i.e. bubble radius and gas pressure. By definition, the bulk viscosity of a fluid is the relation between changes of the driving pressure with respect to changes in the resulted expansion strain-rate. Thus, we can use the two-phase solution to define the bulk viscosity of a hypothetical cell, composed of a homogeneously compressible, one-phase, continuous fluid. The resulted bulk viscosity is highly non-linear. At the beginning of the expansion process, when gas exsolution is efficient, the expansion rate grows exponentially while the driving pressure decreases slightly. That means that bulk viscosity is formally negative. The negative value reflects the release of the energy stored in the supersaturated liquid (melt) and its conversion to mechanical work during exsolution. Later, when bubbles are large enough and the gas influx decreases significantly, the strain rate decelerates and the bulk viscosity becomes positive as expected in a dissipative system. We demonstrate that amplification of seismic wave travelling through a volcanic conduit filled with a volatile saturated magma may be attributed to the negative bulk viscosity of the compressible magma. Amplification of an expansion wave may, at some level in the conduit, damage the conduit walls and initiate opening of new pathways for magma to erupt.

Magma addition rates in continental arcs: New methods of calculation and global implications

NASA Astrophysics Data System (ADS)

Ratschbacher, B. C.; Paterson, S. R.

2017-12-01

The transport of mass, heat and geochemical constituents (elements and volatiles) from the mantle to the atmosphere occurs via magma addition to the lithosphere. Calculation of magma addition rates (MARs) in continental arcs based on exposed proportions of igneous arc rocks is complex and rarely consistently determined. Multiple factors influence MAR calculations such as crust versus mantle contributions to magmas, a change in MARs across the arc and with depths throughout the arc crustal column, `arc tempos' with periods of high and low magmatic activity, the loss of previous emplaced arc rocks by subsequent magmatism and return to the mantle, arc migration, variations in the intrusive versus extrusive additions and evolving arc widths and thicknesses during tectonism. All of these factors need to be considered when calculating MARs.This study makes a new attempt to calculate MARs in continental arcs by studying three arc sections: the Famatinian arc, Argentina, the Sierra Nevada batholith, California and the Coast Mountain batholith, Washington and British Columbia. Arcs are divided into fore-arc, main arc and back arc sections and `boxes' with a defined width, length and thickness spanning upper middle and lower crustal levels are assigned to each section. Representative exposed crustal slices for each depth are then used to calculate MARs based on outcrop proportions for each box. Geochemical data is used to infer crustal recycling percentages and total thickness of the arc. Preliminary results show a correlation between MARs, crustal thicknesses and magmatic flare-up durations. For instance, the Famatinian arc shows a strong decrease in MARs between the main arc section (9.4 km3/Ma/arc-km) and the fore-arc (0.61 km3/Ma/arc-km) and back-arc (1.52 km3/Ma/arc-km) regions and an increase in the amount of magmatism with depth.Global MARs over geologic timescales have the potential to investigate mantle melt generation rates and the volatile outgassing contribution

Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies

NASA Astrophysics Data System (ADS)

Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel

2015-03-01

Lunar floor-fractured craters are a class of 170 lunar craters with anomalously shallow, fractured floors. Two end-member processes have been proposed for the floor formation: viscous relaxation, and subcrater magmatic intrusion and sill formation. Recent morphometric analysis with new Lunar Reconnaissance Orbiter Laser Altimeter (LOLA) and image (LROC) data supports an origin related to shallow magmatic intrusion and uplift. We find that the distribution and characteristics of the FFC population correlates strongly with crustal thickness and the predicted frequency distribution of overpressurization values of magmatic dikes. For a typical nearside lunar crustal thickness, dikes with high overpressurization values favor surface effusive eruptions, medium values favor intrusion and sill formation, and low values favor formation of solidified dikes concentrated lower in the crust. We develop a model for this process, make predictions for the morphologic, morphometric, volcanic, and geophysical consequences of the process and then compare these predictions with the population of observed floor-fractured craters. In our model, the process of magmatic intrusion and sill formation begins when a dike propagates vertically towards the surface; as the dike encounters the underdense brecciated region beneath the crater, the magmatic driving pressure is insufficient to continue vertical propagation, but pressure in the stalled dike exceeds the local lithostatic pressure. The dike then begins to propagate laterally forming a sill which does not propagate past the crater floor region because increased overburden pressure from the crater wall and rim crest pinch off the dike at this boundary; the sill then continues to inflate, further raising and fracturing the brittle crater floor. When the intrusion diameter to intrusion depth ratio is smaller than a critical value, the intrusion assumes a laccolith shape with a domed central region. When the ratio exceeds a critical value

Crystallisation sequence and magma evolution of the De Beers dyke (Kimberley, South Africa)

NASA Astrophysics Data System (ADS)

Soltys, Ashton; Giuliani, Andrea; Phillips, David

2018-06-01

requirement for detailed petrographic and mineral chemical studies to assess whether individual intrusions are in fact `evolved'; and that dykes are not necessarily produced by differentiated magmas.

Isotopic data for Late Cretaceous intrusions and associated altered and mineralized rocks in the Big Belt Mountains, Montana

USGS Publications Warehouse

du Bray, Edward A.; Unruh, Daniel M.; Hofstra, Albert H.

2017-03-07

The quartz monzodiorite of Mount Edith and the concentrically zoned intrusive suite of Boulder Baldy constitute the principal Late Cretaceous igneous intrusions hosted by Mesoproterozoic sedimentary rocks of the Newland Formation in the Big Belt Mountains, Montana. These calc-alkaline plutonic masses are manifestations of subduction-related magmatism that prevailed along the western edge of North America during the Cretaceous. Radiogenic isotope data for neodymium, strontium, and lead indicate that the petrogenesis of the associated magmas involved a combination of (1) sources that were compositionally heterogeneous at the scale of the geographically restricted intrusive rocks in the Big Belt Mountains and (2) variable contamination by crustal assimilants also having diverse isotopic compositions. Altered and mineralized rocks temporally, spatially, and genetically related to these intrusions manifest at least two isotopically distinct mineralizing events, both of which involve major inputs from spatially associated Late Cretaceous igneous rocks. Alteration and mineralization of rock associated with the intrusive suite of Boulder Baldy requires a component characterized by significantly more radiogenic strontium than that characteristic of the associated igneous rocks. However, the source of such a component was not identified in the Big Belt Mountains. Similarly, altered and mineralized rocks associated with the quartz monzodiorite of Mount Edith include a component characterized by significantly more radiogenic strontium and lead, particularly as defined by 207Pb/204Pb values. The source of this component appears to be fluids that equilibrated with proximal Newland Formation rocks. Oxygen isotope data for rocks of the intrusive suite of Boulder Baldy are similar to those of subduction-related magmatism that include mantle-derived components; oxygen isotope data for altered and mineralized equivalents are slightly lighter.

Evidences of Multiple Magma Injections in Quaternary Balerang and Rajabasa Volcanoes, Indonesia

NASA Astrophysics Data System (ADS)

Hasibuan, R. F.; Ohba, T.; Abdurrachman, M.

2016-12-01

Quaternary Balerang and Rajabasa volcanoes are situated along the nearly north-south lineament with a most explosive Krakatau volcanic complex in the south and effusive Sukadana basalt plateau in the north. Some studies have elucidated that Krakatau volcano has multiple magma storage regions beneath together with evidences of magma mixing process. By considering these circumstances, it is necessary to know lateral variations of magmas and to characterize volcanic rocks from Rajabasa volcanic complex which is located between these distinct magmatic systems, in terms of magmatic processes and evolution. Methodologies we used are X-ray fluorescence to determine the whole rock chemistry, K-Ar isotope dating to determine the lifespan of the volcano, as well as EPMA analysis to obtain the chemical composition of minerals. The rock chemistry or TAS plot shows a linear trend, ranging from basaltic (51 wt.%) to rhyolitic (75 wt.%), indicating a chemical heterogeneity of magma. When SiO2 contents are correlated with the relative ages, we found a broad tendency that SiO2 contents progressively decrease with age. The Rajabasa volcano lifespan is known formed at 0.31 Ma while one of the youngest lava is identified erupted at 0.12 Ma. Some plagioclase crystals exhibit disequilibrium textures, like highly sieved core and clear rim regions, also overgrowth rim on the plagioclase and pyroxene crystals whose composition more primitive than the core's composition, indicating magmatic recharge events. Reverse zoning and resorption textures associated with compositional step zoning or progressive zoning are quite common as well in clinopyroxene and plagioclase crystals. By considering these evidences, we conclude that injection of a hotter basaltic magma into colder and more felsic magma occurred beneath the volcanoes.

Igneous Sheet Intrusions as a Record of Paleostress States

NASA Astrophysics Data System (ADS)

Stephens, T. L.; Walker, R. J.; Healy, D.; Bubeck, A.; England, R. W.; McCaffrey, K. J. W.

2017-12-01

The architecture of igneous sheet intrusion networks provides useful constraints on paleostress during emplacement. Several models for sill emplacement have used the close spatial relationships between sills and dikes in layered (sedimentary) host rocks to propose that dike-sill transitions are driven by layering. Such models require a stress rotation - from horizontal extension for dikes, to horizontal compression for sills - which is assumed to reflect a near-hydrostatic stress state, facilitating the dilation and intrusion of pre-existing structures (e.g. faults, joints, and bedding). Here, we present case examples of sills for which layering is not the main control on emplacement: Isle of Mull (UK), Faroe Islands (European Atlantic margin) and the San Rafael Subvolcanic Field (Utah, USA). In each case, dikes cut, or are cut by, sills; indicating that dikes were not the feeders to sills in the same section. The sills consist of linked, flat and shallowly-dipping segments that always show near-vertical opening directions. Sills cut bedding and formation contacts with consistent low-angle dips, and cut or abut against vertical faults, fractures, and tectonic foliations. From this, we infer that magma pressure during emplacement did not exceed the horizontal stress. To constrain the stress state during emplacement we present a novel approach that combines analysis of local and overall sill geometry data with mechanical models for slip tendency, dilation tendency, and fracture susceptibility. We also present a new depth-independent mechanical model, which estimates paleostress ratio and driving fluid pressure ratio using the opening angles of dilated fluid-filled fractures. Our results show that the studied sills record previously unrecognised local fluctuations in the far-field stress state, during magmatic supply. Sills, therefore, present an important tool for determining paleostress in areas where few brittle deformation structures (e.g. faults), other than

Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber.

PubMed

Zhu, Dan; Bao, Huiming; Liu, Yun

2015-12-01

Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ(57)Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ(57)Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ(57)Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted.

Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber

PubMed Central

Zhu, Dan; Bao, Huiming; Liu, Yun

2015-01-01

Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ57Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ57Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ57Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted. PMID:26620121

Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust

NASA Astrophysics Data System (ADS)

Sarkar, Saheli; Saha, Lopamudra; Satyanarayan, Manavalan; Pati, Jayanta

2015-04-01

Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust Sarkar, S.1, Saha, L.1, Satyanarayan, M2. and Pati, J.K.3 1. Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Haridwar, India, 2. HR-ICPMS Lab, Geochemistry Group, CSIR-National Geophysical Research Institute, Hyderabad-50007, India. 3. Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad-211002, India. Tonalite-Trondhjemite-Granodiorite (TTGs) group of rocks, that mostly constitute the Archaean continental crusts, evolved through a time period of ~3.8 Ga-2.7 Ga with major episodes of juvenile magma generations at ~3.6 Ga and ~2.7 Ga. Geochemical signatures, especially HREE depletions of most TTGs conform to formation of this type of magma by partial melting of amphibolites or eclogites at 15-20 kbar pressure. While TTGs (mostly sodic in compositions) dominates the Eoarchaean (~3.8-3.6 Ga) to Mesoarchaean (~3.2-3.0 Ga) domains, granitic rocks (with significantly high potassium contents) became more dominant in the Neoarchaean period. The most commonly accepted model proposed for the formation of the potassic granite in the Neoarchaean time is by partial melting of TTGs along subduction zones. However Archaean granite intrusive into the gabbro-ultramafic complex from Scourie, NW Scotland has been interpreted to have formed by fractional crystallization of hornblende and plagioclase from co-existing trondhjemitic gneiss. In this study we have studied fractional crystallization paths from a Mesoarchaean trondhjemite from the central Bundelkhand craton, India using MELTS algorithm. Fractional crystallization modeling has been performed at pressure ranges of 20 kbar to 7 kbar. Calculations have shown crystallization of garnet-clinopyroxene bearing assemblages with progressive cooling of the magma at 20 kbar. At pressure ranges 19-16 kbar, solid phases

Million-year melt-presence in monotonous intermediate magma for a volcanic-plutonic assemblage in the Central Andes: Contrasting histories of crystal-rich and crystal-poor super-sized silicic magmas

NASA Astrophysics Data System (ADS)

Kaiser, Jason F.; de Silva, Shanaka; Schmitt, Axel K.; Economos, Rita; Sunagua, Mayel

2017-01-01

crystallized as a granodiorite pluton which was sampled as xenoliths in much later volcanic events. Over the ∼1.1 Ma zircon crystallization history for the PGI, postcaldera lavas and xenoliths, the melt remained in an ∼100-150 °C temperature window as indicated by Ti-in-zircon thermometry. Although chemical trends are consistent with zircon crystallization at variable temperatures, there is no secular cooling, but rather a thermal rejuvenation following the 2.89 Ma PGI eruption. As such these data provide a "low and slow" temporal constraint for models for the pre-eruptive lifetimes of mushy magma in contrast to the "rapid" mobilization of crystal-poor silicic magmas, consistent with a model where the latter are incubated within the former and extracted rapidly prior to eruption. The thermal and chemical monotony of crystal-rich dacites throughout a caldera cycle connotes conditions where near-eutectic melt can be maintained in near-surface magma reservoirs for an extended period of time if the subvolcanic magma reservoir is sufficiently large so that hotter and initially zircon-undersaturated magma can replenish shallow magma vented in a supereruption.

Possible Time Dependent Deformation over Socorro Magma Body from GPS and InSAR

NASA Astrophysics Data System (ADS)

Havazli, E.; Wdowinski, S.; Amelug, F.

2015-12-01

The Socorro Magma Body (SMB) is one of the largest, currently active magma intrusions in the Earth's continental crust. The area of Socorro is a segment of the Rio Grande Rift that display a broad seismic anomaly and ground deformation. The seismic reflector is imaged at 19 km depth coinciding with the occurrence of numerous small earthquake swarms. Broad crustal uplift was also observed above this reflector and led to the hypothesis of the presence of a large mid-crustal sill-like magma body. Previous geodetic studies over the area reveal ground deformation at the rate of 2-3 mm/yr from 1992 to 2006. The magma body was modeled as a penny-shaped crack of 21 km radius at 19 km depth based on InSAR results [Finnegan et. al., 2009]. In this study we expand the uplift measurement period over the SMB to two decades by using additional InSAR and GPS observations. We extended the InSAR observation record by analyzing 27 Envisat scenes acquired during the years 2006-2010. Continuous GPS observation acquired by the SC01 station since 2001 and three more recent Plate Boundary Observatory stations, which were installed between 2005 and 2011, provide high temporal record of uplift over the past decade and a half. We analyzed the InSAR data using ROI_PAC software package and calculated the temporal evolution of the vertical displacement using time series analysis. Preliminary results of 2006-2010 Envisat data show no significant deformation above the 1-2 mm noise level, which disagree with the previous ERS-1/2 results; 2-3 mm/yr during 1992-2006. This disagreement suggests a time dependent uplift of the SMB, which is also supported by GPS observations. The average uplift rate of the SC01 station is 0.9±0.02 mm/yr for 2001-2015 and 0.6±0.08 mm/yr for 2006-2010. Furthermore the SC01 time series exhibits episodic uplift events. The observed time dependent uplift suggests that magma supply in the middle crust may also occur episodically, as in shallow magmatic systems.

Influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension

NASA Astrophysics Data System (ADS)

Magee, Craig; McDermott, Kenneth G.; Stevenson, Carl T. E.; Jackson, Christopher A.-L.

2014-05-01

Continental rifting is commonly accommodated by the nucleation of normal faults, slip on pre-existing fault surfaces and/or magmatic intrusion. Because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent (i.e. higher shear strengths and Young's moduli) than the host rock, it is theoretically plausible that they locally intersect and modify the mechanical properties of pre-existing normal faults. We illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets. Our results show that igneous rocks may initially resist failure, and promote the preferential reactivation of favourably-oriented, pre-existing faults that are not spatially-associated with solidified intrusions. Fault segments situated along strike from laterally restricted fault-intrusion intersections may similarly be reactivated. This spatial and temporal control on strain distribution may generate: (1) supra-intrusion folds in the hanging wall; (2) new dip-slip faults adjacent to the igneous body; or (3) sub-vertical, oblique-slip faults oriented parallel to the extension direction. Importantly, stress accumulation within igneous intrusions may eventually initiate failure and further localise strain. The results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral-bearing fluids.

Petrogenesis of Ore-Bearing and Ore-Barren Intermediate-Acid Intrusive Rocks from Jilongshan Au-Cu Skarn Deposit , the Middle-Lower Yangtze River Metallogenic Belt, Eastern China and their Geological Implications

NASA Astrophysics Data System (ADS)

Zhan, X.; Wei, J.; Chen, M.; Zhao, X.

2017-12-01

Jilongshan Au-Cu skarn deposit in Edong-Jiurui ore district , Middle-Lower Yangtze River Metallogenic Belt(MLYRB) , eastern China ,contains 44 t gold and 32 Mt of copper ores. The mineralization is dominated by massive skarn ores, most of which occurs along the contact zone between the lower Triassic dolomitic limestones and Jilongshan granodioritic intrusion. However, Baiguoshu pluton, no more than 1 km western, has been not found any mineralized occurrence with the same strata. The ore-bearing and ore-barren intrusive rocks are granodiorite porphyries, could not be identified by petrographic characters. Besides, Zircon U-Pb dating results demonstrate that Jilongshan and Baiguoshu intrusion emplaced at 140 ± 1Ma and 141 ± 1 Ma respectively, coeval with the Early Cretaceous magmatism in Edong-Jiurui area. Elements geochemistry present that they are both characterized by high Al2O3, rich Na2O (Na2O/K2O>1.0), enrichment of LILE (Rb, Ba, K, Sr) and depletion of HFSE (Nb, Ta), and weak negative Eu anomalies, which suggest they may be originated from partial melting of enriched mantle and associated with crust-mantle interaction ,evidenced by the Sr-Nd-Hf isotopic composition as well. Although the two are partly geochemically similar with each other, they have some obvious differences. The former have higher K2O and Y, Yb ,lower MgO, and Cr, Ni contents, and more obvious differentiation degree between light and heavy REEs with (La/Yb)N=10.55-15.95 than the latter with (La/Yb)N=8.67-10.47. It is indicated that the magmas of the Jilongshan intrusive rocks were probably derived from deeper source than that of the Baiguoshu, also supported by mineralogical data of biotite. In addition, Jilongshan intrusive rocks have a relatively higher initial Nd (ɛNd (t) = -8.2 - -9.4) and Sr ((87Sr/86Sr)i=0.70822-0.70897) isotopic composition than Baiguoshu (-9.2 - -9.7 and 0.70855-0.70881), as same as Lu-Hf isotopic composition. Therefore, combined with previous studies, we suggest

Crypto-magma chambers beneath Mt. Fuji

NASA Astrophysics Data System (ADS)

Kaneko, Takayuki; Yasuda, Atsushi; Fujii, Toshitsugu; Yoshimoto, Mitsuhiro

2010-06-01

Mt. Fuji consists dominantly of basalt. A study of olivine-hosted melt-inclusions from layers of air-fall scoria, however, shows clear evidence of andesitic liquids. Whole rock compositions show a narrow range of SiO 2, but a wide range of FeO*/MgO and incompatible elements. Phenocrystic plagioclase generally shows bi-modal distributions in compositional frequency, while most olivine phenocrysts show uni-modal distribution with reverse zoning and often contain andesitic melt-inclusions. These suggest that magmas erupted from Fuji are generated through mixing between basaltic and more SiO 2-rich (often andesitic) end-members. We propose that Fuji's magmatic plumbing system consists of at least two magma chambers: a relatively deep (˜20 km) basaltic one and a relatively shallow (˜ 8-9 km) and more SiO 2-rich one. Evolved basalts with wide compositional ranges of incompatible elements are generated in the deep basaltic magma chamber by prevalent fractional crystallization of pyroxenes with olivine and calcic plagioclase at high pressure. Meanwhile basaltic magma left behind by the previous eruption in the conduit accumulates in a shallow magma chamber, and is differentiated to more SiO 2-rich composition by fractional crystallization of olivine, less-calcic plagioclase, and clinopyroxene. Shortly before a new eruption, a large amount of evolved basaltic magma containing calcic plagioclase rises from the deeper magma chamber and is mixed with the more SiO 2-rich magma in the shallow chamber, to generate the hybrid basaltic magma.

Broad accommodation of rift-related extension recorded by dyke intrusion in Saudi Arabia

USGS Publications Warehouse

Pallister, J.S.; McCausland, W.A.; Jonsson, Sigurjon; Lu, Z.; Zahran, H.M.; El, Hadidy S.; Aburukbah, A.; Stewart, I.C.F.; Lundgren, P.R.; White, R.A.; Moufti, M.R.H.

2010-01-01

The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low- and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees.

Exploring Cumulates in Small, Shallow Parts of a Large Mafic Magma System to Provide Baseline Models for Crystallization in Larger Intrusions

NASA Astrophysics Data System (ADS)

Srogi, L.; Willis, K. V.; Lutz, T. M.; Plank, T. A.; Pollock, M.; Connolly, B.; Wood, A. M.

2016-12-01

Small, shallow portions of large magmatic systems cool more rapidly and potentially have less subsolidus overprinting than large mafic intrusions, but it is unclear whether they are small-scale analogs for the same crystallization processes. The Morgantown-Jacksonwald magmatic system (MJS), western Newark Basin, Pennsylvania, is part of the 201-Ma Central Atlantic Magmatic Province (CAMP) formed during Pangean rifting. The MJS consists of several interconnected intrusions exposed in cross-section from the Jacksonwald basalt at the paleosurface to 6 km depth (<0.2 GPa). Mg-rich orthopyroxene (opx) phenocrysts form crystal accumulations in some dikes and in basal and roof zones of sills in the MJS, in many CAMP intrusions, and in younger Ferrar dolerites, Antarctica. Some samples with opx phenocrysts have dm-scale modal layering. Despite ubiquitous occurrence, the opx is little-studied and our work tests most previous authors' assumption that opx was brought in from deeper intrusions. Opx cores with Mg/(Mg+Fe) of 80-77% yield mid-crustal pressures of 0.4-0.6 GPa (using method of Putirka, 2008). LA-ICPMS was used to obtain trace element concentrations in mm-size phenocrysts in a chill margin within 0.5m of the basal contact and cm-size phenocrysts from cumulate about 10m above. REE concentrations are similar in both samples: LREE-depleted cores (normalized La/Sm = 0.05-0.1); variably LREE-enriched rims; some negative Eu anomalies. REE patterns calculated for liquids in equilibrium with opx using published Kd values are roughly parallel to but significantly higher than REE in host chill margin diabase. CSDs of opx and matrix plagioclase from several samples within 10m of the basal contact will be used to evaluate models of crystal growth vs. mechanical sorting. Modes and mineral compositions are not consistent with MELTS fractionation models: opx crystallizes in place of pigeonite; pyroxenes are zoned in Ca not Fe-Mg; late-crystallizing quartz and K-feldspar are

Genesis of the Permian Kemozibayi sulfide-bearing mafic-ultramafic intrusion in Altay, NW China: Evidence from zircon geochronology, Hf and O isotopes and mineral chemistry

NASA Astrophysics Data System (ADS)

Tang, Dongmei; Qin, Kezhang; Xue, Shengchao; Mao, Yajing; Evans, Noreen J.; Niu, Yanjie; Chen, Junlu

2017-11-01

The recently discovered Kemozibayi mafic-ultramafic intrusion and its associated magmatic Cu-Ni sulfide deposits are located at the southern margin of the Chinese Altai Mountain, Central Asian Orogenic Belt in north Xinjiang, NW China. The intrusion is composed of olivine websterite, norite, gabbro and diorite. Disseminated and net-textured Ni-Cu sulfide ores are hosted in the center of the gabbro. In this work, new zircon U-Pb ages, Hf-O isotopic and sulfide S isotopic data, and whole rock and mineral chemical analyses are combined in order to elucidate the characteristics of the mantle source, nature of subduction processes, degree of crustal contamination, geodynamic setting of bimodal magmatism in the region, and the metallogenic potential of economic Cu-Ni sulfide deposit at depth. SIMS zircon U-Pb dating of the gabbro yields Permian ages (278.3 ± 1.9 Ma), coeval with the Kalatongke Cu-Ni deposit and with Cu-Ni deposits in the Eastern Tianshan and Beishan areas. Several lines of evidence (positive εHf(t) from + 7.1 to + 13.3, Al2O3, TiO2 and SiO2 contents in clinopyroxene from olivine websterite, high whole rock TiO2 contents) suggest that the primary magma of the Kemozibayi intrusion was a calc-alkaline basaltic magma derived from depleted mantle, and that the degree of partial melting in the magma source was high. The evolution of the Kemozibayi mafic-ultramafic complex was strongly controlled by fractional crystallization and the crystallization sequence was olivine websterite, norite, and then gabbro. This is evidenced by whole rock Fe2O3 contents that are positively correlated with MgO and negatively correlated with Al2O3, CaO and Na2O, similar LREE enrichment and negative Nb, Ta, Hf anomalies in chondrite and primitive mantle-normalized patterns, and a decrease in total REE and trace elements contents and magnetite content from gabbro through to norite and olivine websterite. Varied and low εHf(t) (+ 7.1 to + 13.3) and high δ18O values (+ 6.4‰ to

Reducing depressive intrusions via a computerized cognitive bias modification of appraisals task: developing a cognitive vaccine.

PubMed

Lang, Tamara J; Moulds, Michelle L; Holmes, Emily A

2009-02-01

A feature of depression is the distressing experience of intrusive, negative memories. The maladaptive appraisals of such intrusions have been associated with symptom persistence. This study aimed to experimentally manipulate appraisals about depressive intrusions via a novel computerized cognitive bias modification (CBM) of appraisals paradigm, and to test the impact on depressive intrusion frequency for a standardized event (a depressive film). Forty-eight participants were randomly assigned to either a session of positive or negative CBM. Participants then watched a depressing film (including scenes of bereavement and bullying) and subsequently monitored the occurrence of depressive intrusions related to the film in a diary for one week. At one-week follow-up, participants completed additional measures of intrusions--the Impact of Event Scale (IES) and an intrusion provocation task. As predicted, compared to the negative condition, participants who underwent positive CBM showed a more positive appraisal bias. Further, one week later, positive CBM participants reported fewer intrusions of the film and had lower IES scores. Our findings demonstrate that it is possible to manipulate maladaptive appraisals about depressive intrusions via a computerized CBM task. Further, this effect transfers to reducing intrusive symptomatology related to a standardized event (a depressive film) over one week, suggesting novel clinical implications.

Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan-Mufushan Batholith in Southeast China and Its Tectonic Significance: 2. Magnetic Fabrics and Gravity Survey

NASA Astrophysics Data System (ADS)

Ji, Wenbin; Chen, Yan; Chen, Ke; Wei, Wei; Faure, Michel; Lin, Wei

2018-01-01

The Late Mesozoic magmatic province is a prominent feature of the South China Block (SCB). However, the tectonic regimes associated with the magmatism are still elusive. A combined anisotropy of magnetic susceptibility and gravity study has been carried out to determine the fabric patterns and shape at depth of the Dayunshan-Mufushan composite batholith in the north-central SCB. This is a companion paper to Part 1 that presented the structural and geochronological data of this batholith. The magnetic fabrics in the batholith interior predominantly reflect magma flow structures. Two distinct patterns of the magnetic lineations are defined, around NNE-SSW and WNW-ESE trends for the early-stage and late-stage intrusions of the batholith, respectively. The gravity survey reveals that the early-stage intrusion has a main feeder zone located below its northern part, while several linear feeder zones trending NNE-SSW are inferred for the late-stage intrusion. Integrating all results, a two-stage construction of the batholith with distinct tectonic regimes has been established. It is concluded that the early-stage intrusion experienced a southward magma transport during its emplacement, partially assisted by far-field compression from the north at ca. 150 Ma. Conversely, the emplacement and exhumation of the late-stage intrusion was accommodated by a NW-SE crustal stretching involving a lateral magma expansion above the multiple feeder zones (likely corresponding to extensional fractures) and ductile shearing during 132-95 Ma localized mainly along the Dayunshan detachment fault. Finally, we discuss the geodynamic linkage between the paleo-Pacific subduction and the Late Mesozoic tectonomagmatism in the SCB.

Volatile content of Hawaiian magmas and volcanic vigor

NASA Astrophysics Data System (ADS)

Blaser, A. P.; Gonnermann, H. M.; Ferguson, D. J.; Plank, T. A.; Hauri, E. H.; Houghton, B. F.; Swanson, D. A.

2014-12-01

We test the hypothesis that magma supply to Kīlauea volcano, Hawai'i may be affected by magma volatile content. We find that volatile content and magma flow from deep source to Kīlauea's summit reservoirs are non-linearly related. For example, a 25-30% change in volatiles leads to a near two-fold increase in magma supply. Hawaiian volcanism provides an opportunity to develop and test hypotheses concerning dynamic and geochemical behavior of hot spot volcanism on different time scales. The Pu'u 'Ō'ō-Kupaianaha eruption (1983-present) is thought to be fed by essentially unfettered magma flow from the asthenosphere into a network of magma reservoirs at approximately 1-4 km below Kīlauea's summit, and from there into Kīlauea's east rift zone, where it erupts. Because Kīlauea's magma becomes saturated in CO2 at about 40 km depth, most CO2 is thought to escape buoyantly from the magma, before entering the east rift zone, and instead is emitted at the summit. Between 2003 and 2006 Kīlauea's summit inflated at unusually high rates and concurrently CO2emissions doubled. This may reflect a change in the balance between magma supply to the summit and outflow to the east rift zone. It remains unknown what caused this surge in magma supply or what controls magma supply to Hawaiian volcanoes in general. We have modeled two-phase magma flow, coupled with H2O-CO2 solubility, to investigate the effect of changes in volatile content on the flow of magma through Kīlauea's magmatic plumbing system. We assume an invariant magma transport capacity from source to vent over the time period of interest. Therefore, changes in magma flow rate are a consequence of changes in magma-static and dynamic pressure throughout Kīlauea's plumbing system. We use measured summit deformation and CO2 emissions as observational constraints, and find from a systematic parameter analysis that even modest increases in volatiles reduce magma-static pressures sufficiently to generate a 'surge' in

Re-appraisal of the Magma-rich versus Magma-poor Paradigm at Rifted Margins: consequences for breakup processes

NASA Astrophysics Data System (ADS)

Tugend, J.; Gillard, M.; Manatschal, G.; Nirrengarten, M.; Harkin, C. J.; Epin, M. E.; Sauter, D.; Autin, J.; Kusznir, N. J.; McDermott, K.

2017-12-01

Rifted margins are often classified based on their magmatic budget only. Magma-rich margins are commonly considered to have excess decompression melting at lithospheric breakup compared with steady state seafloor spreading while magma-poor margins have suppressed melting. New observations derived from high quality geophysical data sets and drill-hole data have revealed the diversity of rifted margin architecture and variable distribution of magmatism. Recent studies suggest, however, that rifted margins have more complex and polyphase tectono-magmatic evolutions than previously assumed and cannot be characterized based on the observed volume of magma alone. We compare the magmatic budget related to lithospheric breakup along two high-resolution long-offset deep reflection seismic profiles across the SE-Indian (magma-poor) and Uruguayan (magma-rich) rifted margins. Resolving the volume of magmatic additions is difficult. Interpretations are non-unique and several of them appear plausible for each case involving variable magmatic volumes and mechanisms to achieve lithospheric breakup. A supposedly 'magma-poor' rifted margin (SE-India) may show a 'magma-rich' lithospheric breakup whereas a 'magma-rich' rifted margin (Uruguay) does not necessarily show excess magmatism at lithospheric breakup compared with steady-state seafloor spreading. This questions the paradigm that rifted margins can be subdivided in either magma-poor or magma-rich margins. The Uruguayan and other magma-rich rifted margins appear characterized by an early onset of decompression melting relative to crustal breakup. For the converse, where the onset of decompression melting is late compared with the timing of crustal breakup, mantle exhumation can occur (e.g. SE-India). Our work highlights the difficulty in determining a magmatic budget at rifted margins based on seismic reflection data alone, showing the limitations of margin classification based solely on magmatic volumes. The timing of

Why Is There an Abrupt Transition from Solid Rock to Low Crystallinity Magma in Drilled Magma Bodies?

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Carrigan, C. R.; Sun, Y.; Lavallée, Y.

2017-12-01

We report on a preliminary evaluation, from basic principles of heat and mass transfer, on the unexpectedly abrupt transition from cuttings of solid rock to fragments of crystal poor glass during drilling into magma bodies. Our analysis is based on conditions determined and inferred for the 2009 IDDP-1 well in Krafla Caldera, which entered apparently liquidus rhyolite magma at about 900oC at a depth of 2104 m. Simple conduction would predict some 30 m of crystallization and partial crystallization since the latest time the magma could have been intruded, approximately 30 years prior to discovery by drilling. Option 1: The expected crystallization of magma has occurred but interstitial melt remains. The pressure difference between lithostatic load of about 50 MPa on the mush and 20 MPa hydrostatic pressure in the well causes pore melt to flow from the permeable mush into the borehole, where it becomes the source of the quenched melt chips. To be viable, this mechanism must work over the time frame of a day. Option 2: The expected crystallization is occurring, but high Rayleigh number thermal convection in the magma chamber continuously displaces crystallizing roof magma by liquidus magma from the interior of the body. To be viable, this mechanism must result in overturning magma in the chamber on a time scale that is much shorter than that of crystallization. Option 3: Flow-induced crystal migration away from zones of high shear created during drilling into magma may preferentially produce low-crystal-content melt at the boundary of the borehole, which is then sampled.

Ridge Jumps Associated with Plume-Ridge Interaction 1: Off-axis Heating due to Lithospheric Magma Penetration

NASA Astrophysics Data System (ADS)

Mittelstaedt, E.; Ito, G.

2005-12-01

In many hot spot-ridge systems, changes in the ridge axis geometry occur between the hot spot centers and nearby mid-ocean ridges in the form of ridge jumps. Such ridge jumps likely occur as a result of anomalous lithospheric stresses associated with mantle plume-lithosphere interaction, as well as weakening of the hot spot lithosphere due to physical and thermal thinning caused by rising buoyant asthenosphere and magma transport through the lithosphere. In this study, we use numerical models to quantify the effects of excess magmatism through the near-ridge lithosphere. Hot spot magmatism can weaken the lithosphere both mechanically through fracturing and thermally through conduction and advection of heat into the plate. Here we focus on the effects of thermal weakening. Using a plane-strain approximation, we examine deformation in a 2-D cross section of a visco-elastic-plastic lithosphere with the finite element code FLAC. The model has isothermal top and bottom boundaries and a prescribed velocity equal to the half spreading rate is imposed on the sides to drive seafloor spreading. The initial condition, as predicted for normal mid-ocean ridges, is a square root of lithospheric age cooling curve with a corner flow velocity field symmetric about the ridge axis. A range of heat inputs are introduced at various plate ages and spreading rates to simulate off-axis magma transport. To reveal the physical conditions that allow for a ridge jump and control its timing, we vary 4 parameters: spreading rate, lithospheric age, crustal thickness and heat input. Results indicate that the heating rate required to produce a ridge jump increases as a function of lithospheric age at the location of magma intrusion. The time necessary for a ridge jump to develop in lithosphere of a particular age decreases with increasing crustal thicknesses. For magma fluxes comparable to those estimated for Galapagos and Iceland, lithospheric heating by the penetrating magma alone is sufficient

The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny

NASA Astrophysics Data System (ADS)

Richards, Jeremy P.

2015-09-01

Global data for measured Fe2O3/FeO ratios and Cu contents in unaltered volcanic and intrusive arc rocks indicate that, on average, they are slightly more oxidized than other magmas derived from depleted upper mantle (such as MORB), but contain similar Cu contents across their compositional ranges. Although Cu scatters to elevated values in some intermediate composition samples, the bulk of the data show a steady but gentle trend to lower concentrations with differentiation, reaching modal values of 50-100 ppm in andesitic rocks. These data suggest that Cu is mildly compatible during partial melting and fractionation processes, likely reflecting minor degrees of sulfide saturation throughout the magmatic cycle. However, the volume of sulfides must be small such that significant proportions of the metal content remain in the magma during fractionation to intermediate compositions. Previous studies have shown that andesitic magmas containing 50 ppm Cu can readily form large porphyry-type Cu deposits upon emplacement in the upper crust. A review of the literature suggests that the elevated oxidation state in the asthenospheric mantle wedge source of arc magmas (ΔFMQ ≈ + 1 ± 1) derives from the subduction of seawater-altered and oxidized oceanic crust, and is transmitted into the mantle wedge via prograde metamorphic dehydration fluids carrying sulfate and other oxidizing components. Progressive hydration and oxidation of the mantle wedge may take up to 10 m.y. to reach a steady state from the onset of subduction, explaining the rarity of porphyry deposits in primitive island arcs, and the late formation of porphyries in continental arc magmatic cycles. Magmas generated from this metasomatized and moderately oxidized mantle source will be hydrous basalts containing high concentrations of sulfur, mainly dissolved as sulfate or sulfite. Some condensed sulfides (melt or minerals) may be present due to the high overall fS2, despite the moderately high oxidation state

Intrusive fathering, children's self-regulation and social skills: a mediation analysis.

PubMed

Stevenson, M; Crnic, K

2013-06-01

Fathers have unique influences on children's development, and particularly in the development of social skills. Although father-child relationship influences on children's social competence have received increased attention in general, research on fathering in families of children with developmental delays (DD) is scant. This study examined the pathway of influence among paternal intrusive behaviour, child social skills and child self-regulatory ability, testing a model whereby child regulatory behaviour mediates relations between fathering and child social skills. Participants were 97 families of children with early identified DD enrolled in an extensive longitudinal study. Father and mother child-directed intrusiveness was coded live in naturalistic home observations at child age 4.5, child behaviour dysregulation was coded from a video-taped laboratory problem-solving task at child age 5, and child social skills were measured using independent teacher reports at child age 6. Analyses tested for mediation of the relationship between fathers' intrusiveness and child social skills by child behaviour dysregulation. Fathers' intrusiveness, controlling for mothers' intrusiveness and child behaviour problems, was related to later child decreased social skills and this relationship was mediated by child behaviour dysregulation. Intrusive fathering appears to carry unique risk for the development of social skills in children with DD. Findings are discussed as they related to theories of fatherhood and parenting in children with DD, as well as implications for intervention and future research. © 2012 The Authors. Journal of Intellectual Disability Research © 2012 John Wiley & Sons Ltd, MENCAP & IASSID.

Caldera resurgence driven by magma viscosity contrasts.

PubMed

Galetto, Federico; Acocella, Valerio; Caricchi, Luca

2017-11-24

Calderas are impressive volcanic depressions commonly produced by major eruptions. Equally impressive is the uplift of the caldera floor that may follow, dubbed caldera resurgence, resulting from magma accumulation and accompanied by minor eruptions. Why magma accumulates, driving resurgence instead of feeding large eruptions, is one of the least understood processes in volcanology. Here we use thermal and experimental models to define the conditions promoting resurgence. Thermal modelling suggests that a magma reservoir develops a growing transition zone with relatively low viscosity contrast with respect to any newly injected magma. Experiments show that this viscosity contrast provides a rheological barrier, impeding the propagation through dikes of the new injected magma, which stagnates and promotes resurgence. In explaining resurgence and its related features, we provide the theoretical background to account for the transition from magma eruption to accumulation, which is essential not only to develop resurgence, but also large magma reservoirs.

Magma differentiation rates from ( 226Ra / 230Th) and the size and power output of magma chambers

NASA Astrophysics Data System (ADS)

Blake, Stephen; Rogers, Nick

2005-08-01

We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of magma. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved magmas ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the magma chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial magma chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the magma body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated

Successive mixing and mingling of magmas in a plutonic complex of Northeast Brazil

NASA Astrophysics Data System (ADS)

Neves, S. P.; Vauchez, A.

1995-02-01

of the porphyritic granite, this time producing a heterogeneous, xenocryst-bearing, dioritic hybrid. Abundant enclaves of diorite in the porphyritic granite, despite their textural diversity, are typically devoid of chilled margins, and were therefore formed relatively early in the crystallisation history of the granite. They are interpreted as liquid droplets separated from the heterogeneous hybrid magma through convection currents and incorporated in the, crystallising granitic magma. Subsequently, during the crystallisation of the porphyritic granite, mafic magma supply to the batholith continued at a declining rate, probably assisted by the development of the Fazenda Nova shear zone. This leads to the production of stromatitic-like structures, with alternating bands of mutually contaminated granite and diorite, then to the intrusion of contorted synplutonic dykes, and, finally, of late-stage dykes, some of which with chilled finer-grained margins.

Mare basalt magma source region and mare basalt magma genesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binder, A.B.

1982-11-15

Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regionsmore » (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.« less

Geology of the ultrabasic to basic Uitkomst complex, eastern Transvaal, South Africa: an overview

NASA Astrophysics Data System (ADS)

Gauert, C. D. K.; De Waal, S. A.; Wallmach, T.

1995-11-01

acted as a conduit for later magma heaves. The first magma pulses, forming the chilled margin of the intrusion, show chemical affinities to a micropyroxenite described from the Bushveld complex. The Lower Harzburgite and Chromitiferous Harzburgite Units, judged from the abundance of xenoliths, originated by crystal settling from a contaminated basic magma. The Main Harzburgite crystallized from a magma of constant, probably also basic, composition, which flowed through the conduit after formation of the lower three lithological units. At a late stage of emplacement, after replenishment in the conduit came to a standstill, closed system conditions developed in the upper part of the complex, resulting in a magma fractionation trend of increasing incompatible elements contents towards the top of the intrusion. The mineralization in the lower three rock units and at the base was most probably caused by a segregating sulphide liquid forced to precipitate by the oxidative degassing of dolomite. Sulphur isotope ratios indicate various degrees of contamination of the magma by the enveloping sedimentary rocks, which provided the necessary amounts of S to reach S saturation.

Magma oceanography. I - Thermal evolution. [of lunar surface

NASA Technical Reports Server (NTRS)

Solomon, S. C.; Longhi, J.

1977-01-01

Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

Evidence of magma intrusion at Fourpeaked volcano, Alaska in 2006-2007 from a rapid-response seismic network and volcanic gases

USGS Publications Warehouse

Gardine, M.; West, M.; Werner, C.; Doukas, M.

2011-01-01

On September 17th, 2006, Fourpeaked volcano had a widely-observed phreatic eruption. At the time, Fourpeaked was an unmonitored volcano with no known Holocene activity, based on limited field work. Airborne gas sampling began within days of the eruption and a modest seismic network was installed in stages. Vigorous steaming continued for months; however, there were no further eruptions similar in scale to the September 17 event. This eruption was followed by several months of sustained seismicity punctuated by vigorous swarms, and SO2 emissions exceeding a thousand tons/day. Based on observations during and after the phreatic eruption, and assuming no recent pre-historical eruptive activity at Fourpeaked, we propose that the activity was caused by a minor injection of new magma at or near 5km depth beneath Fourpeaked, which remained active over several months as this magma equilibrated into the crust. By early 2007 declining seismicity and SO2 emission signaled the end of unrest. Because the Fourpeaked seismic network was installed in stages and the seismicity was punctuated by discrete swarms, we use Fourpeaked to illustrate quantitatively the efficacy and shortcomings of rapid response seismic networks for tracking volcanic earthquakes.

What Can Crystal Size Distributions and Olivine Compositions Tell Us About Magma Solidification Processes in Kilauea Iki Lava Lake, Hawaii?

NASA Astrophysics Data System (ADS)

Vinet, N.; Higgins, M. D.

2009-12-01

Lava lakes offer the opportunity to investigate magma solidification and can be considered as a proxy for small magma chambers or layered intrusions. Here we present data from Kilauea Iki Lava Lake, which formed during the near-summit 1959 picritic eruption of Kilauea Volcano, Hawaii. Microprobe geochemical analyses and crystal size distributions (CSDs) of olivine were determined from three eruption scoria samples, and 34 drill core samples taken from 1967 to 1988. The data provide valuable information on the dynamics and timescales of the intra-lake solidification processes, along with origin of, and temporal constraints on, the distinct olivine populations. Based on their core and rim forsterite (Fo) content, three distinct olivine populations were distinguished: (1) a high-Fo population (Fo85-88); (2) an intermediate-Fo population (Fo77-81); and (3) a low-Fo population (Fo72-76). Groups 1 and 2 both have deformed and undeformed crystals indicating that they formed partly within Kilauea plumbing system before the eruption. The second group seems to be associated with the ‘vertical olivine-rich bodies’ (VORBs) of Helz (1980). These structures raise magma from the lower part of the lake; hence they may have a contrasting composition maintained from the initial filling of the lake. The third population may be the result of rejuvenation within the lake during its cooling. Although the shape of the olivine CSDs is fairly uniform, we note significant variations that allow the recognition and quantification of multiple solidification processes. Our data display evidence of minor accumulation occurring by settling modified by convection currents. The concave-up curvature of at least half of the CSDs is strong evidence for mixing of magmas or crystal populations. The turndown at smallest sizes of the CSD, particularly present for samples at the edge of the lake, is thought to be the result of coarsening. Our CSD and crystal chemistry data suggest that the early

Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany)

USGS Publications Warehouse

Worner, G.; Wright, T.L.

1984-01-01

The final pyroclastic products of the late Quaternary phonolitic Laacher See volcano (East Eifel, W.-Germany) range from feldspar-rich gray phonolite to dark olivine-bearing rocks with variable amounts of feldspar and Al-augite megacrysts. Petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite (MgO 0.9%) to mafic hybrid rock (MgO 7.0%) for all major and trace elements. Both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts. The phonolite-derived phenocrysts are characterized by glass inclusions of evolved composition, rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix. Basanitic (magnesian) clinopyroxene and olivine, in contrast, show skeletal (normally zoned) overgrowths indicative of post-mixing crystallization. In accord with petrographical and other chemical evidence, mass balance calculations suggest mixing of an evolved Laacher See phonolite containing variable amounts of mineral cumulates and a megacryst-bearing basanite magma. Magma mixing occurred just prior to eruption (hours) of the lowermost magma layer of the Laacher See magma chamber but did not trigger the volcanic activity. ?? 1984.

U-Pb zircon, geochemical and Sr-Nd-Hf-O isotopic constraints on age and origin of the ore-bearing intrusions from the Nurkazgan porphyry Cu-Au deposit in Kazakhstan

NASA Astrophysics Data System (ADS)

Shen, Ping; Pan, Hongdi; Seitmuratova, Eleonora; Jakupova, Sholpan

2016-02-01

Nurkazgan, located in northeastern Kazakhstan, is a super-large porphyry Cu-Au deposit with 3.9 Mt metal copper and 229 tonnage gold. We report in situ zircon U-Pb age and Hf-O isotope data, whole rock geochemical and Sr-Nd isotopic data for the ore-bearing intrusions from the Nurkazgan deposit. The ore-bearing intrusions include the granodiorite porphyry, quartz diorite porphyry, quartz diorite, and diorite. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating indicates that the granodiorite porphyry and quartz diorite porphyry emplaced at 440 ± 3 Ma and 437 ± 3 Ma, respectively. All host rocks have low initial 87Sr/86Sr ratios (0.70338-0.70439), high whole-rock εNd(t) values (+5.9 to +6.3) and very high zircon εHf(t) values (+13.4 to +16.5), young whole-rock Nd and zircon Hf model ages, and consistent and slightly high zircon O values (+5.7 to +6.7), indicating that the ore-bearing magmas derived from the mantle without old continental crust involvement and without marked sediment contamination during magma emplacement. The granodiorite porphyry and quartz diorite porphyry are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) and depleted in high-field strength elements (HFSE), Eu, Ba, Nb, Sr, P and Ti. The diorite and quartz diorite have also LILE and LREE enrichment and HFSE, Nb and Ti depletion, but have not negative Eu, Ba, Sr, and P anomalies. These features suggest that the parental magma of the granodiorite porphyry and quartz diorite porphyry originated from melting of a lithospheric mantle and experienced fractional crystallization, whereas the diorite and quartz diorite has a relatively deeper lithospheric mantle source region and has not experienced strong fractional crystallization. Based on these, together with the coeval ophiolites in the area, we propose that a subduction of the Balkhash-Junggar oceanic plate took place during the Early Silurian and the ore-bearing intrusions and associated Nurkazgan

Attenuation in gas-charged magma

NASA Astrophysics Data System (ADS)

Collier, L.; Neuberg, J. W.; Lensky, N.; Lyakhovsky, V.; Navon, O.

2006-05-01

Low frequency seismic events observed on volcanoes, such as Soufriere Hills Volcano, Montserrat, are thought to be caused by a resonating system. The modelling of seismic waves in gas-charged magma is critical for the understanding of seismic resonance effects in conduits, dykes and cracks. Seismic attenuation, which depends mainly on magma viscosity, gas and crystal content, is an essential factor in such modelling attempts. So far only two-phase gas-melt systems with the assumption of no diffusion and transport of volatiles between the melt and the gas bubbles have been considered. In this study, we develop a method of quantifying attenuation within gas-charged magma, including the effects of diffusion and exsolution of gas into the bubbles. The results show that by including such bubble growth processes attenuation levels are increased within magma. The resulting complex behaviour of attenuation with pressure and frequency indicates that two factors are controlling attenuation, the first due to viscous hindrance or the melt, and the second due diffusion processes. The level of attenuation within a gas-charged magma conduit suggests an upper limit on the length of a resonating conduit section of just a few hundred meters.

Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism

NASA Astrophysics Data System (ADS)

Iyer, H. M.

1984-04-01

This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and

Related magma-ice interactions: Possible origins of chasmata, chaos, and surface materials in Xanthe, Margaritifer, Meridiani Terrae, Mars

USGS Publications Warehouse

Chapman, M.G.; Tanaka, K.L.

2002-01-01

We examine here the close spatial and temporal associations among several unique features of Xanthe and Margaritifer Terrae, specifically the Valles Marineris troughs or chasmata and their interior deposits, chaotic terrain, the circum-Chryse outflow channels, and the subdued cratered material that covers Xanthe, Margaritifer, and Meridiani Terrae. Though previous hypotheses have attempted to explain the origin of individual features or subsets of these, we suggest that they may all be related. All of these features taken together present a consistent scenario that includes the processes of sub-ice volcanism and other magma/ice interactions, results of intrusive events during Late Noachian to Early Amazonian times. ?? 2002 Elsevier Science (USA).

Sr-Nd isotope geology and tectonomagmatic setting of the Dehsalm intrusives (Lut Block, Eastern Iran)

NASA Astrophysics Data System (ADS)

Arjmandzadeh, Reza; Francisco Santos, Jose; Ribeiro, Sara

2013-04-01

The Dehsalm porphyritic shallow intrusives belong to the Lut Block volcanic-plutonic belt (central eastern Iran). Previous research on alteration, mineralization and hydrothermal fluids indicates that a Cu-Mo porphyry type mineralization system is related with these intrusives (Arjmandzadeh et al., 2012). The rocks studied in this work range in composition from gabbro-diorite to granite, with dominance of monzonites and quartz monzonites, and have geochemical features of high-K calc alkaline to shoshonitic volcanic arc suites. The trends of major element oxides on Harker diagrams, together with textural evidence, point to the crystal fractionation of clinopyroxene, Ca - plagioclase, hornblende, apatite and oxide minerals. Primitive mantle - normalized trace element spider diagrams display strong enrichment in LILE, such as Rb, Ba and Cs, and depletions in some high field strength elements (HFSE), such as Nb, Ti, Y and HREE. Chondrite-normalized plots show significant LREE enrichments, high LaN/YbN (21.5 to 31.0) and the lack of Eu anomaly. Sr/Y and La/Yb ratios of Dehsalm intrusives are respectively 31.6-72.2 and 21.5-33.5, which reveals that, despite their K-rich composition, these rocks also have some adakitic affinity. A Rb-Sr whole rock-feldspar-biotite age of 33.4±1 Ma was obtained in a quartz monzonite sample; this date may be interpreted as close to the intrusion age, considering that the chosen sample is almost unaltered and should have suffered fast cooling. The obtained age coincides, within error, with a previous geochronological result in a similar rock from the Chah-Shaljami area (Arjmandzadeh et al., 2011), further northwest along the eastern border of the Lut Block. 87Sr/86Sr(33Ma) and ɛNd(33Ma) values range from 0.70481 to 0.70508 and from +1.5 to +2.5, respectively, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that crustal contribution for magma diversification was not relevant. Sr and Nd isotope

Petroleum Vapor Intrusion

EPA Pesticide Factsheets

One type of vapor intrusion is PVI, in which vapors from petroleum hydrocarbons such as gasoline, diesel, or jet fuel enter a building. Intrusion of contaminant vapors into indoor spaces is of concern.

Examining shear processes during magma ascent

NASA Astrophysics Data System (ADS)

Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

2017-12-01

Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

Radiographic visualization of magma dynamics in an erupting volcano.

PubMed

Tanaka, Hiroyuki K M; Kusagaya, Taro; Shinohara, Hiroshi

2014-03-10

Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures.

Radiographic visualization of magma dynamics in an erupting volcano

PubMed Central

Tanaka, Hiroyuki K. M.; Kusagaya, Taro; Shinohara, Hiroshi

2014-01-01

Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

Innovative methods to reduce salt water intrusion in harbours

NASA Astrophysics Data System (ADS)

Groenenboom, J.; Uittenbogaard, R.; Hulsen, L.; van der Kaaij, T.; Kielen, N.

2017-12-01

The availability of fresh water in densely populated estuarine environments will in the future more often be threatened due to both human (e.g. channel deepening) and natural (sea-level rise, storm surges, extremely low river discharges) causes. Here, the salt water intrusion into the New Waterway, the main navigation channel of the port of Rotterdam, is used as a case study to elaborate on two innovative ways to mitigate the effects of salt water intrusion. The first method is based on the concept that vertical mixing of a salt wedge reduces its intrusion length. The idea is to equip a vessel with cranes that hold perforated tubes close to the bed alongside the vessel. By connecting compressors to the perforated tubes, a bubble screen with an adjustable vertical location can be created. Since the horizontal location of the bubble screens is not fixed, the vessel can sail in the vicinity of the moving salt wedge therewith increasing the effectiveness of the method. Another advantage of this intervention is that it can be deployed temporarily when the urgency for the prevention of salt water intrusion is high. The second method originates from the Port of Rotterdam Authority and is inspired by a small bypass that is present between two parallel channels (New Waterway and Caland Canal) connecting the North Sea to the Port of Rotterdam. Due to the different hydrodynamic characteristics of the hinterland of both channels, a difference in salinity and water level is present between both ends of the bypass. As a result, a lateral inflow of water into the New Waterway occurs at the same moment that the flood velocities transport saline water landwards. The lateral inflow of water into this channel has no momentum in the landward direction and therefore decreases the landward flow velocity and therewith the salt water intrusion. In addition, the inflow drives a vertical circulation that mixes the water column close to the bypass. Similar to the bubble screens mentioned

Stress-induced comenditic trachyte effusion triggered by trachybasalt intrusion: multidisciplinary study of the AD 1761 eruption at Terceira Island (Azores)

NASA Astrophysics Data System (ADS)

Pimentel, A.; Zanon, V.; de Groot, L. V.; Hipólito, A.; Di Chiara, A.; Self, S.

2016-03-01

The AD 1761 eruption on Terceira was the only historical subaerial event on the island and one of the last recorded in the Azores. The eruption occurred along the fissure zone that crosses the island and produced a trachybasalt lava flow and scoria cones. Small comenditic trachyte lava domes (known as Mistérios Negros) were also thought by some to have formed simultaneously on the eastern flank of Santa Bárbara Volcano. Following a multidisciplinary approach, we combined geological mapping, paleomagnetic, petrographic, mineral and whole-rock geochemical and structural analyses to study this eruption. The paleomagnetic dating method compared geomagnetic vectors (directions and intensities) recorded by both the AD 1761 lava flow and Mistérios Negros domes and revealed that the two events were indeed coeval. Based on new data and interpretation of historical records, we have accordingly reconstructed the AD 1761 eruptive dynamics and distinguished three phases: (1) a precursory phase characterized by decreased degassing in the fumarolic field of Pico Alto Volcano and a gradual increase of seismic activity, which marked the intrusion of trachybasalt magma; (2) a first eruptive phase that started with phreatic explosions on the eastern flank of Santa Bárbara Volcano, followed by the inconspicuous effusion of comenditic trachyte (66 wt% SiO2), forming a WNW-ESE-oriented chain of lava domes; and (3) a second eruptive phase on the central part of the fissure zone, where a Hawaiian to Strombolian-style eruption formed small scoria cones (E-W to ENE-WSW-oriented) and a trachybasalt lava flow (50 wt% SiO2) which buried 27 houses in Biscoitos village. Petrological analyses show that the two batches of magma were emitted independently without evidence of interaction. We envisage that the dome-forming event was triggered by local stress changes induced by intrusion of the trachybasalt dyke along the fissure zone, which created tensile stress conditions that promoted ascent

Self Sealing Magmas

NASA Astrophysics Data System (ADS)

von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan

2015-04-01

During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

Intrusion-aware alert validation algorithm for cooperative distributed intrusion detection schemes of wireless sensor networks.

PubMed

Shaikh, Riaz Ahmed; Jameel, Hassan; d'Auriol, Brian J; Lee, Heejo; Lee, Sungyoung; Song, Young-Jae

2009-01-01

Existing anomaly and intrusion detection schemes of wireless sensor networks have mainly focused on the detection of intrusions. Once the intrusion is detected, an alerts or claims will be generated. However, any unidentified malicious nodes in the network could send faulty anomaly and intrusion claims about the legitimate nodes to the other nodes. Verifying the validity of such claims is a critical and challenging issue that is not considered in the existing cooperative-based distributed anomaly and intrusion detection schemes of wireless sensor networks. In this paper, we propose a validation algorithm that addresses this problem. This algorithm utilizes the concept of intrusion-aware reliability that helps to provide adequate reliability at a modest communication cost. In this paper, we also provide a security resiliency analysis of the proposed intrusion-aware alert validation algorithm.

Evidence for seismogenic fracture of silicic magma.

PubMed

Tuffen, Hugh; Smith, Rosanna; Sammonds, Peter R

2008-05-22

It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of approximately 600 degrees C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle-ductile fault textures in silicic lavas has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines, leading to models of seismogenic stick-slip along shallow shear zones in the magma. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting.