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The Midcontinent Rift System of North America is a ~1.1 Ga large igneous province comprising mainly flood basalts and intrusive rocks. We present new data for the Pillar Lake Volcanics and Inspiration Sill from the northern edge of the Midcontinent Rift in the northwestern Nipigon Embayment. The Pillar Lake Volcanics comprise a ~20-40 m thick, flat-lying sequence of mafic pillowed and massive flows, pillowed flow breccia, and hyaloclastite breccia. They are characterized by [SiO.sub.2] of 52-54 wt%, [TiO.sub.2] of 1.2-1.3 wt%, and [K.sub.2]O of 0.9-1.1 wt%. They are light rare earth element (LREE) enriched, with La/Smn of 3.0-4.4 with fractionated heavy rare earth elements (HREE) (Gd/[Yb.sub.n] = 1.4-1.7). The Inspiration diabase sill is < 50 m thick and is in direct contact with the underlying Pillar Lake Volcanics. Baddeleyite and zircon data from the Inspiration Sill yield a combined U-Pb upper intercept age of 1105.6 [+ or -] 1.6 Ma. The Inspiration Sill is characterized by uniform [SiO.sub.2] of 52-53 wt%, [TiO.sub.2] of 1.1-1.2 wt%, and [K.sub.2]O of 0.9-1.2 wt%. Inspiration Sill samples are LREE enriched with La/[Sm.sub.n] of 3.2-3.3 and fractionated HREE (Gd/[Yb.sub.n] = 1.6). The Pillar Lake Volcanics are at least 1120 Ma, and perhaps as old as 1130 Ma, and represent an early, thin, and restricted mafic volcanic sequence, largely preserved below the younger Inspiration Sill. The Pillar Lake Volcanics and Inspiration Sill display a marked geochemical similarity, suggesting that they may represent magmatism associated with the earliest stages of Midcontinent rifting. Key words: Pillar Lake Volcanics, Inspiration Sill, Midcontinent Rift, geochemistry, geochronology. Le rift mediocontinental nord-americain est une grande province ignee de ~1,1 Ga comptant de nombreux basaltes de plateau et roches intrusives. Nous presentons de nouvelles donnees sur les roches volcaniques du lac Pillar et le filon-couche d' Inspiration, a la limite nord du rift mediocontinental dans le nord-ouest de l'echancrure de Nipigon. Les roches volcaniques du lac Pillar consistent en une sequence horizontale de ~20-40 m d'epaisseur de coulees mafiques massives et a coussins, de breches de coulees a coussins et de breches de hyalocastites. Elles sont caracterisees par des teneurs en SiO2 de 52-54 % poids, en [TiO.sub.2] de 1,2-1,3 % poids et en [K.sub.2]O de 0,9-1,1 % poids. Elles sont enrichies en terres rares legeres et presentent des rapports La/Smn allant de 3,0-4,4 et des terres rares lourdes fractionnees (Gd/[Yb.sub.n] = 1,4-1,7). Le filoncouche diabasique d'Inspiration fait < 50 m d' epaisseur et est en contact direct avec les roches volcaniques du lac Pillar sous-jacentes. Des donnees sur de la baddeleyite et du zircon du filon-couche d' Inspiration produisent un age U-Pb d'intersection superieure de 1105,6 [+ or -] 1,6 Ma. Le filon-couche d' Inspiration est caracterise par des teneurs uniformes en [SiO.sub.2] de 52-53 % poids, en [TiO.sub.2] de 1,1 a 1,2 % poids et en [K.sub.2]O de 0,9-1,2 % poids. Les echantillons du filon-couche d' Inspiration sont enrichis en terres rares legeres et presentent des rapports La/Smn allant de 3,2-3,3 et des terres rares lourdes fractionnees (Gd/[Yb.sub.n] = 1,6). L' age des roches volcaniques du lac Pillar est d'au moins 1120 Ma, pouvant possiblement atteindre 1130 Ma, et ces roches representent une sequence volcanique mafique precoce mince et de faible etendue, principalement preservee sous le filon-couche d'Inspiration, plus jeune. Les roches volcaniques du lac Pillar et le filon-couche d'Inspiration presentent une similitude geochimique marquee qui donne a penser qu'ils pourraient representer un magmatisme associe aux toutes premieres phases du rifting mediocontinental. [Traduit par la Redaction] Mots-cles: roches volcaniques du lac Pillar, filon-couche d' Inspiration, rift mediocontinental, geochimie, geochronologie., Introduction The Midcontinent Rift System (MRS) of North America comprises ~1500 000 km (3) of flood basalts, flows, and intrusive rocks emplaced in the Lake Superior region during the Mesoproterozoic [...]

Abstract: Rifting near hotspots results in mantle melting to create thick mafic igneous crust at volcanic rifted margins (VRMs). This mafic crust is transitional between rifted continental crust with mafic [...]

Observations of the south pole of the Saturnian moon Enceladus revealed large rifts in the south-polar terrain, informally called 'tiger stripes', named Alexandria, Baghdad, Cairo and Damascus Sulci. These fractures [...]

The questions of whether Venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change. Nine 'hotspots'--areas analogous to Hawaii, with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes at depth--have been identified as possibly active. This study used variations in the thermal emissivity of the surface observed by the Visible and Infrared Thermal Imaging Spectrometer on the European Space Agency's Venus Express spacecraft to identify compositional differences in lava flows at three hotspots. The anomalies are interpreted as a lack of surface weathering. We estimate the flows to be younger than 2.5 million years and probably much younger, about 250,000 years or less, indicating that Venus is actively resurfacing. doi: 10.1126/science.1186785

A common pyroclastic facies in subaqueous volcanic successions comprises massive to graded, very thick (several to tens of meters), laterally extensive (several kilometers) beds of nonwelded pumice lapilli with volumes ranging to tens of cubic kilometers. This facies may be overlain by laminated ash or bimodal ash and giant (>1 m) pumice clasts, and underlain by coarse lithic breccia. The association is inferred to be the typical product of sustained magmatic volatile--driven explosive eruptions from vents at water depths of ~1300-200 m. We propose the term 'neptunian' for such eruptions and their products. The eruption column rapidly mixes with the surrounding water, cools, increases in density, and collapses, while remaining under water. Lithic clasts that are too heavy to be entrained in the column are deposited close to the source, forming a neptunian lithic breccia. Pumice lapilli are rapidly waterlogged and form the dominant component in the collapsing column and in eruption-fed, water-supported density currents (neptunian density currents). Hot, buoyant, giant pumice clasts continue to rise and may reach the water surface before being waterlogged and settling, along with temporarily suspended ash, forming neptunian suspension deposits. Eruption magnitude, fragmentation mechanisms, and juvenile pyroclast characteristics, especially vesicularity, are very similar in neptunian and Plinian-style eruptions, but column behavior differs primarily because of the contrasting physical properties of the ambient fluid (water versus air).

We determined model ages of mare deposits on the farside of the Moon on the basis of the crater frequency distributions in 10-meter-resolution images obtained by the Terrain Camera on SELENE (Setenotogical and Engineering Explorer) (Kaguya). Most mare volcanism that formed mare deposits on the lunar farside ceased at ~3.0 billion years ago, suggesting that mare volcanism on the Moon was markedly reduced globally during this period. However, several mare deposits at various Locations on the Lunar farside also show a much younger age, clustering at ~2.5 billion years ago. These young ages indicate that mare volcanism on the lunar farside tasted longer than was previously considered and may have occurred episodically.

Hawaiian volcanoes evolve through stages that have been delimited by the compositions of their erupted lavas. New in situ [sup.238]U-[sup.230]Th and U-Pb dating of single zircons from leucocratic plutonic xenoliths erupted at Mauna Kea and Hnalalai volcanoes, Hawaii, reveals that important episodes of magmatic evolution are not necessarily reflected in the stratigraphy or compositions of erupted lavas. Zircons from Mauna Kea diorites form a heterogeneous population with apparently bimodal ages of ca. 125 ka and ca. 65 ka, suggesting fractionation, intrusion, and crystal recycling about the time of transition of post shield volcanism from basaltic to hawaiitic compositions. Hualalai syenogabbros and diorites record extreme fractionation and generation of alkalic magma at 41 [+ or -] 9 ka and 261 [+ or -] 28 ka, indicating that alkalic magma was generated ~130,000 yr before the shield to postshield transition inferred from lava stratigraphy, and that coeval evolution of chemically distinct magma reservoirs at shallow and deep levels may have characterized the shield stage. These episodes at Hualalai did not cause eruption of evolved lavas, indicating that extreme differentiation in Hawaiian volcanoes is not necessarily followed by eruption of highly evolved magma. Keywords: uranium-series method, magma chambers, magmatic differentiation, cumulates, volcanism.

The Cassini Titan Radar Mapper obtained Synthetic Aperture Radar images of Titan's surface during four fly-bys during the mission's first year. These images show that Titan's surface is very complex geologically, showing evidence of major planetary geologic processes, including cryovolcanism. This paper discusses the variety of cryovolcanic features identified from SAR images, their possible origin, and their geologic context. The features which we identify as cryovolcanic in origin include a large (180 km diameter) volcanic construct (dome or shield), several extensive flows, and three calderas which appear to be the source of flows. The composition of the cryomagma on Titan is still unknown, but constraints on rheological properties can be estimated using flow thickness. Rheological properties of one flow were estimated and appear inconsistent with ammonia-water slurries, and possibly more consistent with ammonia-water-methanol slurries. The extent of cryovolcanism on Titan is still not known, as only a small fraction of the surface has been imaged at sufficient resolution. Energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of Titan. Keywords: Titan; Volcanism; Satellites of Saturn

Loki is the largest patera and the most energetic hotspot on Jupiter's moon Io, in turn the most volcanically active body in the Solar System, but the nature of the activity remains enigmatic. We present detailed analysis of Galileo Near-Infrared Mapping Spectrometer (NIMS) and PhotoPolarimeter/Radiometer (PPR) observations covering the 1.5-100 [micro]m wavelength range during the I24, I27, and I32 flybys. The general pattern of activity during these flybys is consistent with previously proposed models of a resurfacing wave periodically crossing a silicate lava lake. In particular our analysis of the I32 NIMS observations shows, over much of the observed patera, surface temperatures and implied ages closely matching those expected for a wave advancing counterclockwise at 0.94-1.38 kin/day. The age pattern is different than other published analyses which do not show as clearly this azimuthal pattern. Our analysis also shows two additional distinctly different patera surfaces. The first is located along the inner and outer margins where components with a 3.00-4.70-[micro]m color temperature of 425 K exist. The second is located at the southwestern margin where components with a 550-K color temperature exist. Although the high temperatures could be caused by disruption of a lava lake crust, some additional mechanism is required to explain why the southwest margin is different from the inner or outer ones. Finally, analysis of the temperature profiles across the patera reveal a smoothness that is difficult to explain by simple lava cooling models. Paradoxically, at a subpixel level, wide temperature distributions exist which may be difficult to explain by just the presence of hot cracks in the lava crust. The resurfacing wave and lava cooling models explain well the overall characteristics of the observations. However, additional physical processes, perhaps involving heat transport by volatiles, are needed to explain the more subtle features. Keywords: Io; Volcanism; Infrared observations; Jupiter, satellites; Satellites, surfaces; Geological processes

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.013 Byline: James A. Skinner, Kenneth L. Tanaka Keywords: Mars; Mars; surface; Geological processes; Regoliths Abstract: Several types of spatially associated landforms in the southern Utopia Planitia highland-lowland boundary (HLB) plain appear to have resulted from localized geologic activity, including (1) fractured rises, (2) elliptical mounds, (3) pitted cones with emanating lobate materials, and (4) isolated and coalesced cavi (depressions). Stratigraphic analysis indicates these features are Hesperian or younger and may be associated with resurfacing that preferentially destroyed smaller ( Author Affiliation: Astrogeology Team, U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA Article History: Received 23 November 2005; Revised 2 August 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.023 Byline: David A. Williams (a), Laszlo P. Keszthelyi (b), David A. Crown (c), Windy L. Jaeger (b), Paul M. Schenk (d) Keywords: Jupiter; satellites; Io; Geological processes; Volcanism; Satellite; surfaces Abstract: We produced the first geologic map of the Amirani-Gish Bar region of Io, the last of four regional maps generated from Galileo mission data. The Amirani-Gish Bar region has five primary types of geologic materials: plains, mountains, patera floors, flows, and diffuse deposits. The flows and patera floors are thought to be compositionally similar, but are subdivided based on interpretations regarding their emplacement environments and mechanisms. Our mapping shows that volcanic activity in the Amirani-Gish Bar region is dominated by the Amirani Eruptive Center (AEC), now recognized to be part of an extensive, combined Amirani-Maui flow field. A mappable flow connects Amirani and Maui, suggesting that Maui is fed from Amirani, such that the post-Voyager designation 'Maui Eruptive Center' should be revised. Amirani contains at least four hot spots detected by Galileo, and is the source of widespread bright (sulfur?) flows and active dark (silicate?) flows being emplaced in the Promethean style (slowly emplaced, compound flow fields). The floor of Gish Bar Patera has been partially resurfaced by dark lava flows, although other parts of its floor are bright and appeared unchanged during the Galileo mission. This suggests that the floor did not undergo complete resurfacing as a lava lake as proposed for other ionian paterae. There are several other hot spots in the region that are the sources of both active dark flows (confined within paterae), and SO.sub.2- and S.sub.2-rich diffuse deposits. Mapped diffuse deposits around fractures on mountains and in the plains appear to serve as the source for gas venting without the release of magma, an association previously unrecognized in this region. The six mountains mapped in this region exhibit various states of degradation. In addition to gaining insight into this region of Io, all four maps are studied to assess the best methodology to use to produce a new global geologic map of Io based on the newly released, combined Galileo-Voyager global mosaics. To convey the complexity of ionian surface geology, we find that a new global geologic map of Io should include a map sheet displaying the global abundances and types of surface features as well as a complementary GIS database as a means to catalog the record of surface changes observed since the Voyager flybys and during the Galileo mission. Author Affiliation: (a) School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287, USA (b) Astrogeology Team, U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86002, USA (c) Planetary Science Institute, 1700 East Fort Lowell Road, Suite 106, Tucson, AZ 85719, USA (d) Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA Article History: Received 8 March 2006; Revised 21 July 2006

We produced the first geologic map of the Amirani-Gish Bar region of Io, the last of four regional maps generated from Galileo mission data. The Amirani--Gish Bar region has five primary types of geologic materials: plains, mountains, patera floors, flows, and diffuse deposits. The flows and patera floors are thought to be compositionally similar, but are subdivided based on interpretations regarding their emplacement environments and mechanisms. Our mapping shows that volcanic activity in the Amirani-Gish Bar region is dominated by the Amirani Eruptive Center (AEC), now recognized to be part of an extensive, combined Amirani-Mani flow field. A mappable flow connects Amirani and Mani, suggesting that Maul is fed from Amirani, such that the post-Voyager designation 'Maui Eruptive Center' should be revised. Amirani contains at least four hot spots detected by Galileo, and is the source of widespread bright (sulfur?) flows and active dark (silicate?) flows being emplaced in the Promethean style (slowly emplaced, compound flow fields). The floor of Gish Bar Patera has been partially resurfaced by dark lava flows, although other parts of its floor are bright and appeared unchanged during the Galileo mission. This suggests that the floor did not undergo complete resurfacing as a lava lake as proposed for other ionian paterae. There are several other hot spots in the region that are the sources of both active dark flows (confined within paterae), and S[O.sub.2]- and [S.sub.2]-rich diffuse deposits. Mapped diffuse deposits around fractures on mountains and in the plains appear to serve as the source for gas venting without the release of magma, an association previously unrecognized in this region. The six mountains mapped in this region exhibit various states of degradation. In addition to gaining insight into this region of Io, all four maps are studied to assess the best methodology to use to produce a new global geologic map of Io based on the newly released, combined Galileo-Voyager global mosaics. To convey the complexity of ionian surface geology, we find that a new global geologic map of Io should include a map sheet displaying the global abundances and types of surface features as well as a complementary GIS database as a means to catalog the record of surface changes observed since the Voyager flybys and during the Galileo mission. Keywords: Jupiter, satellites; Io; Geological processes; Volcanism; Satellite, surfaces

The two main volcanic centers on Mars, Tharsis and Elysium, are often interpreted in terms of mantle plume hotspots, even though there are several problems with the plume hypothesis for Mars. We present results of 2D cylindrical shell numerical mantle convection experiments in which we try to ascertain whether flushing of the hot lower mantle could provide a mechanism for the generation of a small number of plume-like features, i.e., localized upwelling of hot material. In this scenario the formation of hot upwellings is driven from the top by cold downwellings rather than from a hot thermal boundary layer at the CMB. First we construct a range of Mars interior structure models consistent with observations in order to demonstrate that the presence of a thin lower mantle in the martian interior is a viable scenario. Then we use a series of numerical convection experiments to investigate the effects of solid-state phase transitions, different stratified and temperature-dependent viscosity models, and the presence of a thick southern hemisphere crust on the operation of such a mechanism. Our results show that it is possible to generate hot strong localized upwellings from top-down dynamics if the lithosphere is thin or actively involved in the convective pattern. The presence of a thick, immobile, insulating southern hemisphere crust reduces the number of upwellings, and the perovskite phase transition causes a focusing of the upwellings. Further experiments demonstrate that an initial 500 Myr phase of mobile lid is sufficient to start this process create an upwelling which is stable for billions of years. Keywords: Mars, interior; Volcanism; Geophysics

Evidence of volcano ground ice interactions on Mars can provide important constraints on the tinting and distribution of martian volcanic processes and climate characteristics. Northwest of the Elysium Rise is Hrad Vallis, a ~370 m deep, 800 km long sinuous valley thai begins in a source region at 34[degrees] N, 218[degrees] W. Flanking both sides of the source region is a lobate deposit that extends ~50 km perpendicular from the source and is an average of ~40 m thick. Previous studies have suggested the formation of the Hrad Vallis source region was the result of explosive magma--ice interaction and that the lobate deposit is a mudflow; here we use newly available MOLA, MOC, and THEMIS data to investigate the evidence supporting this hypothesis. Within the lobate deposit we have identified 12 craters with thermal infrared signatures and morphologies that are distinct from any other craters or depressions in the region. The thermally distinct craters are distinguished by their cool interiors surrounded by warm ejecta in the nighttime THEMIS IR data and warm interiors surrounded by cool ejecta in the daytime THEMIS IR data. The craters are typically 1100-1800 m in diameter (one crater is ~2300 m across) and 30-40 m deep, but may be up to 70 m. The craters are typically circular and have central depressions (several with interior dune fill) surrounded by ~1 to >6 concentric fracture sets. The distribution of the craters and their morphology suggests that they are likely the result of the interaction between a hot mudflow and ground ice. Keywords: Cratering; Geological processes; Mars, surface; Volcanism

We have quantitatively assessed the resurfacing sources and styles in eighteen mapped venusian quadrangles, about 30% of the venusian surface. Each quadrangle was split into 0.5[degrees] by 0.5[degrees] boxes, which were then identified as corona materials, large volcano materials (> 100 km diameter), intermediate volcano materials (10-100 km), small edifice materials (< 10 km), flow materials from rifts or fractures, plains without an identifiable source, impact crater materials and highly deformed materials, or data gaps. We find that coronae resurface approximately 21%, small edifices 22% and large volcanoes about 6% of the surfaces analyzed. Plains with no identifiable source account for an average of 35% of the surface assessed. Small edifices resurface on a scale of 10-100 s of [km.sup.2]; large edifices resurface areas of [10.sup.4]-[10.sup.5] [km.sup.2]. Coronae have greatly varying amounts of associated volcanism, with some coronae producing negligible flow deposits and others producing deposits of [10.sup.4]-[10.sup.6] [km.sup.2]. The areas identified as plains with no visible source occur on small scales ([10.sup.2] [km.sup.2]) to large scales (> [10.sup.5] [km.sup.2]). Our results indicate that the majority of plains resurfacing by volcanism can be tied to an identifiable source, that fields of small edifices contribute more to resurfacing than we had anticipated, and that resurfacing styles do not appear to have evolved over the time period represented by the surface geology in the mapped quadrangles. All of the units that we quantified occur throughout the histories of the regions mapped. We favor plains resurfacing to have occurred over at least 100 myr, which implies terrestrially reasonable resurfacing rates. Keywords: Venus, surface; Surfaces, planets; Geological processes

Using speckle imaging techniques on the 10-m W.M. Keck I telescope, we observed near-infrared emission at 2.2 [micro] m from volcanic hotspots on Io in July--August 1998. Using several hundreds of short-exposure images we reconstructed diffraction-limited images of Io on each of three nights. We measured the positions of individual hotspots to [+ or -] 0.004' or better, corresponding to a relative positional error of ~20 km on Io's surface. The sensitivity of normal ground-based images of Io is limited by confusion between overlapping sources; by resolving these multiple points we detected up to 17 distinct hotspots, the largest number ever seen in a single image. During the month-long span of our 1998 observations, several events occurred. Loki was at the end of a long brightening, and we observed it to fade in flux by a factor of 2.8 over the course of one month. At the 3-sigma level we see evidence that Loki's position shifts by ~ 100 km. This suggests that the brightening may not have been located at the 'primary' Loki emission center but at a different source within the Loki caldera. We also see a bright transient source near Loki. Among many other sources we detect a dim source on the limb of Io at the latitude of Pele; this source is consistent with 2.7% of the thermal emission from the Pele volcano complex being scattered by the Pele plume, which would be the first detection of a plume through scattered infrared hotspot emission. Keywords: Io; Volcanism; Infrared observations

Topography as measured by the Mars Orbiter Laser Altimeter (MOLA), when supplemented with imaging data, can be used to infer physical emplacement processes in lava flows on Mars with a level of detail analogous to what can be done with unobserved lava flow eruptions on Earth. MOLA, Viking Orbiter and Mars Orbiter Camera (MOC) data are used to develop new inferences regarding the rheology of a typical lava flow near Elysium Mons on Mars. We present a technique that uses MOLA Precision Experiment Data Records (PEDRs) to directly determine the longitudinal thickness profile of lava flows. This technique is preferable to using gridded topography derived from MOLA, particularly for features such as lava flows, with thickness variations at the same scale as their surroundings. Thickness profiles and underlying slope estimates can then be compared with results from theologic models. The longitudinal thickness profile of the Elysium example discussed here exhibits a concave-up flow surface that is consistent with an exponential viscosity increase. The viscosity shows a relative increase of about 50 times over the length of flow examined when the density of the lava increases as a result of lava degassing. Keywords: Mars; MOLA; Rheology; Lava flow; Elysium Mons

The early volcanic history and structural development of Olympus Mons, Mars, has been obscured by the formation of the large circum-Olympus aureole deposits in the Early Amazonian. Mars Orbiter Laser Altimeter data reveal an enormous preaureole extrusive flow unit in Amazonis Planitia that is more than 300 km wide and extends ~1800 km radially away from the Olympus Mons aureole. We interpret this volcanic unit to represent proto-Olympus Mons lava flows emplaced during the latest Hesperian or earliest Amazonian. The orientation and localization of the deposits appear to be due to channeling of the flows into a broad depression between the generally north dipping slope of Amazonis Planitia and the southwestward-dipping slope of the Alba Patera flanks. Formation of the aureole blocked this depression and caused subsequent summit flows to pond in the circum-Olympus trough and flow around the aureole lobes. Emplacement of this proto-Olympus flow unit formed a barrier along the northern margin of Amazonis Planitia, causing ponding of later lava flows and outflow channel events debouching there. The large volume and great lateral extent of the unit imply abundant magma supply and high effusion rates during the initial stages of Olympus Mons construction; this unit may be the result of the initial impingement of a melt-rich mantle plume head. Keywords: volcanism, Olympus Mons, Mars, plumes, lava flows.

Mesozoic picritic and alkali basalts from central Lebanon represent a significant part of an extension-related Upper Jurassic to Upper Cretaceous discontinuous volcanic belt which occurs throughout the Middle East. Volcanism was associated with an episode of intraplate extension that followed a period of continental break-up, where Mesozoic micro-continental blocks separated from Gondwana as the Neotethys ocean opened in Jurassic times. This volcanic episode produced mafic lava flows ranging in thickness from 5 to 20 m, along with some minor pyroclastic flows. These flows are stratigraphically intercalated with thick carbonate platform deposits. The basalts are made up of about 15-20% olivine ([Fo.sub.78-91]), 30-35% clinopyroxene (salite), 40-50% plagioclase ([An.sub.56-71]) and opaqua Fe-Ti oxides (~5%). Geochemically, the rocks exhibit a relatively wide range of Si[O.sub.2] (40.4 to 50.5 wt%) and MgO (5.1 to 15.5 wt%) contents, are relatively enriched in Ti[O.sub.2] (1.7 to 3.7 wt%) and vary in composition from alkali picrite and basanite to alkali basalt. The Mg numbers range from 0.56 to 0.70, with an average of 0.63. The rocks are enriched in incompatible trace elements such as Zr (86-247 ppm), Nb (16-66 ppm) and Y (19-30 ppm). Such compositions are typical of those of HIMU-OIB and plume-related magmas. The REE patterns are fractionated ([(La/Yb).sub.N] = 11), LREE enriched, and are generally-parallel to subparallel. Elemental ratios such as K/P (1.1-4.7), La/Ta (11-13), La/Nb (0.57-0.70), Nb/Y (0.68-1.55) and Th/Nb (0.20-0.36) suggest that crustal contamination was minor or absent. This may be related to a rapid ascent of the magma, in agreement with the nature (mafic, oceanic-like) and the small thickness (about 12 km) of the Mesozoic crust of the Eastern Mediterranean region. The [sup.143]Nd/[sup.144]Nd isotopic compositions of the lavas range from 0.512826 to 0.512886, and [sup.87]Sr/[sup.86]Sr from 0.702971 to 0.703669, suggesting a HIMU-like mantle source. Trace element compositions indicate a melt segregation depth of 100-110 km, well within the garnet lherzolite stability field. The geochemical characteristics of the rocks are typical of within-plate alkali basalts, and suggest that the magmas were derived from a fertile, possibly plume-related, enriched mantle source. Petrogenetic modelling indicates that the magmas were produced by very small degrees of batch partial melting (F = 1.5%) of a primitive garnet-bearing mantle source (garnet lherzolite). Keywords: Lebanon, alkali basalts, petrogenesis, Sr/Nd, geochemistry, mantle plumes.

Io, the innermost Galilean satellite of Jupiter, is a fascinating world. Data taken by Voyager and Galileo instruments have established that it is by far the most volcanic body in the Solar System and suggest that the nature of this volcanism could radically differ from volcanism on Earth. We report on near-IR observations taken in February 2001 from the Earth-based 10-m W. M. Keck II telescope using its adaptive optics system. After application of an appropriate deconvolution technique (MISTRAL), the resolution, ~100 km on Io's disk, compares well with the best Galileo/NIMS resolution for global imaging and allows us for the first time to investigate the very nature of individual eruptions. On 19 February, we detected two volcanoes, Amirani and Tvashtar, with temperatures differing from the Galileo observations. On 20 February, we noticed a slight brightening near the Surt volcano. Two days later it had turned into an extremely bright volcanic outburst. The hot spot temperatures (> 1400 K) are consistent with a basaltic eruption and, being lower limits, do not exclude an ultramafic eruption. These outburst data have been fitted with a silicate-cooling model, which indicates that this is a highly vigorous eruption with a highly dynamic emplacement mechanism, akin to fire-fountaining. Its integrated thermal output was close to the total estimated output of Io, making this the largest ionian thermal outburst yet witnessed. Key Words: Io; volcanism; infrared observations.