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A large dyke of quartz tholeiitic gabbronorite has been mapped for 59 km in southern New Brunswick, Canada, between Lepreau River in the northeast and Indian Island in the southwest. Scattered outcrops occur along a positive aeromagnetic lineament, providing a dyke strike of N42[degrees]E overall (segments N30[degrees]E to N72[degrees]E), dips of 80[degrees] to 90[degrees]NNW, and widths of 4 to 30 m. A [new.sup.40]Ar/[.sup.39]Ar plagioclase age of 201.67 6 0.35 Ma for the Lepreau River Dyke is similar to dates for the massive North Mountain Basalt in the Fundy Basin to the east. The dyke is associated with the Ministers Island and Christmas Cove dykes, which are indistinguishable in chemistry, petrology, and probable age, and we regard them as segments of the same co-magmatic dyke system. In addition, their petrology is similar to that of the basalts of the adjacent Early Mesozoic Fundy and Grand Manan basins. We propose that the Lepreau River and associated dykes were sources for the regional basin basalts, which in turn are part of the Central Atlantic Magmatic Province (CAMP) that overlaps the Triassic-Jurassic boundary and associated mass extinction event. Key words: Mesozoic dykes, Central Atlantic Magmatic Province (CAMP), flood basalt, Fundy Basin. Un grand dyke de gabbronorite tholeitique quartzifere a ete cartographie sur une distance de 59 km dans le sud du Nouveau-Brunswick (Canada) entre la riviere Lepreau, au nord-est, et l'ile Indian, au sud-ouest. Des affleurements disperses sont presents le long d'un lineament aeromagnetique positif, qui donnent une orientation globale de N[42.sup.o]E pour le dyke (les differents troncons allant de N30[degrees]E a N72[degrees]E), des pendages de 80[degrees] a 90[degrees] vers le NNO et des largeurs de 4 m a 30 m. Un nouvel [age.sup.40]Ar/[.sup.39]Ar sur plagioclase de 201,67 6 0,35 Ma pour le dyke de la riviere Lepreau est semblable a des ages obtenus pour le basalte massif de North Mountain, dans le bassin de Fundy plus a l'est. Le dyke est associe aux dykes de l'ile Minister et de Christmas Cove, dont la chimie, la petrologie et l'age probable sont essentiellement identiques, et nous estimons qu'ils constituent des troncons d'un meme systeme de dykes comagmatiques. Leur petrologie est en outre semblable a celle des basaltes des bassins de Fundy et de Gand Manan attenants, d'age mesozoique precoce. Nous proposons que le dyke de la riviere Lepreau et les dykes associes constituaient des sources pour les basaltes de bassin regionaux qui, eux, font partie de la province magmatique centre atlantique (PMCA) qui chevauche la limite Trias-Jurassique et l'episode d'extinction massive associe. [Traduit par la Redaction] Mots-cles : dykes mesozoiques, province magmatique centre atlantique (PMCA), basalte de plateau, bassin de Fundy., Introduction Flood basalts in large igneous provinces are produced by fissure eruptions, which can be exceptionally large (tens to hundreds of kilometres long), and with huge eruption volumes of tens [...]

Canadian Malartic is an Archean low-grade bulk tonnage native gold deposit. The deposit is mostly located in altered clastic metasedimentary rocks, mafic-ultramafic dykes, and monzodioritic porphyry intrusions. Airborne magnetic and frequency-domain electromagnetic (EM) data were inverted to reconstruct the geological units associated with the mineralization, especially the intrusive masses. The 3-D inversion of magnetic data, which used a tetrahedral mesh to a depth of 2.4 km, shows that mafic volcanic rocks and iron formation rocks extend to depth in the area, more so than diabase dykes. The magnetic inversion also shows that the diorite and monzodiorite rocks of the Lac Fourniere A pluton are dipping toward the south on its northern edge at the contact with the metasedimentary rocks. The 1-D inversion of the frequency-domain EM data, for both electrical conductivity and magnetic susceptibility, is able to reconstruct geological structures to a depth of approximately 100 m, providing more details and information about these features. The intrusive masses such as diabase dykes, diorite and monzodiorite rocks, and mafic volcanic rocks are reconstructed as electrically conductive structures in the inversion results. The metasedimentary rocks are resistive, and the overburden is conductive in most of the area. The geophysical data and inversion results suggest the presence of some features (such as diabase dykes and monzodiorite rocks) that are not yet present on some parts of the geology map. A comparison of the EM-derived susceptibility and the magnetic-derived susceptibility over the iron formations can reveal the effect of remanent magnetization. Key words: Canadian Malartic area, gold exploration, inversion method, magnetic and electromagnetic methods. Le gisement Canadian Malartic est un gisement d'or natif a fort tonnage et faible teneur. Le gisement est princi-palement encaisse dans des roches metasedimentaires clastiques alterees, des dykes mafiques-ultramafiques et des intrusions de porphyre monzodioritique. Des donnees aeromagnetiques et d'induction electromagnetique (EM) en domaine de frequence ont ete inversees pour reconstituer les unites geologiques associees a la mineralisation, en particulier les masses intrusives. L'inversion 3D des donnees magnetiques, qui emploie une maille tetraedrique jusqu'a une pr1ndeur de 2,4 km, montre que des roches volcaniques mafiques et des roches de formation de fer sont presentes en profondeur dans la region, plus que des dykes de diabase. L'inversion magnetique montre egalement que les roches dioritiques et monzodioritiques du pluton de Lac Fourniere A ont une plongee vers le sud a sa limite nord au contact avec les roches metasedimentaires. L'inversion 1D des donnees EM en domaine de frequence, tant pour la conductivite electrique que pour la susceptibilite magnetique, permet de reconstituer les structures geologiques jusqu'a une profondeur d'environ 100 m, fournissant ainsi plus de details et d'information sur ces elements. Les masses intrusives comme les dykes de diabase, les roches dioritiques et monzodioritiques et lesrochesvolcaniques mafiques sont reconstituees en tant que structures de forte conductivite electrique dans les resultats d'inversion. Les roches metasedimentaires sont resistives et le mort terrain est conducteur dans la majeure partie de la region. Les donnees geophysiques et les resultats d'inversion semblent indiquer la presence de certains elements (tels que des dykes de diabase et des roches monzodioritiques) qui n'apparaissent pas encore dans certains secteurs de la carte geologique. Une comparaison de la susceptibilite obtenue des donnees EM et de la susceptibilite obtenue des donnees magnetiques au-dessus des formations de fer peut reveler l'effet d'une magnetisation remanente. [Traduit par la Redaction] Mots-cles : region du gisement Canadian Malartic, exploration pour l'or, methode d'inversion, methodes magnetiques et electromagnetiques., Introduction The Canadian Malartic Gold Mine is an open pit mine that is owned by the Canadian Malartic General Partnership, a 50/50 joint venture between Agnico Eagle Mines Ltd. (Toronto, [...]

ABSTRACT We present evidence linking vessel forms with ceramic wares resulting from the petrological analysis of 33 sherds from two sixteenth century Spanish colonial sites in the Solomon Islands. Our [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.09.002 Byline: Takaaki Noguchi (a), Akira Tsuchiyama (b), Naru Hirata (c), Hirohide Demura (c), Ryosuke Nakamura (d), Hideaki Miyamoto (e), Hajime Yano (f), Tomoki Nakamura (g), Jun Saito (h), Sho Sasaki (i), Tatsuaki Hashimoto (f), Takashi Kubota (f), Masateru Ishiguro (j), Michael E. Zolensky (k) Keywords: Asteroid Itokawa; Regoliths; Asteroids, Surfaces Abstract: On the sub-kilometer S-type asteroid, 25143 Itokawa, some boulders on rough terrains seem to be exposed without any powdery material covering. Based on surface morphological features, there are two major types of boulders: one has rounded edges and corners (rounded boulders), while the other has angular edges and corners (angular boulders). The surface features of the rounded boulders suggest that they have hardness heterogeneity and that some may be breccias. The angular boulders appear to be more resistant to impact disruption than the rounded ones, which may be due to a difference in lithology. The major constituents of Itokawa may be LL chondrite-like brecciated lithology (rounded boulders) along with a remarkable number of boulders suggesting that lithology is atypical among LL chondrites (angular boulders). Some of both types of boulders contain intersecting and stepped planar foliations. Comparison with meteorite ALH76009 suggests that the planar foliations may be marks where rocks were torn apart. As lithified breccias cannot be formed on present-day sub-kilometer-sized Itokawa, it is reasonable that boulders with various lithologies on Itokawa were formed on its large ancestor(s). The rubble-pile structure of Itokawa suggested by its low density ([approximately equal to]1.9g/cm.sup.3) indicates that boulders on Itokawa are reassembled fragments formed by catastrophic disruption of large ancestor(s). Author Affiliation: (a) College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan (b) Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Japan (c) School of Computer Science and Engineering, University of Aizu, Fukushima 965-8580, Japan (d) National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan (e) University Museum, The University of Tokyo, Tokyo 113-0033, Japan (f) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan (g) Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan (h) School of Engineering, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan (i) Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory of Japan, Iwate 023-0861, Japan (j) School of Earth Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-742, Republic of Korea (k) NASA Johnson Space Center, Houston, TX 77058, USA Article History: Received 25 September 2008; Revised 28 August 2009; Accepted 1 September 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.031 Byline: Kathleen Mandt (a)(b), Shanaka de Silva (c), James Zimbelman (d), Danielle Wyrick (e) Keywords: Mars, Surface; Mars, Climate Abstract: The form of erosional remnants of the Medusae Fossae Formation (MFF) on Mars provide evidence of their development progression and implicate two spatially distinct environments in the equatorial regions of Mars. Ubiquitous yardangs are clearly the product of strong unidirectional winds acting over time on variably indurated deposits. Yardang orientation is used as a proxy to map regional and local wind direction at meso-scale resolution. In other, more limited areas not subjected to strong unidirectional winds, randomly oriented kilometer-scale mesas and buttes are found to be remnants of progressive cliff recession through mass wasting as support is lost from within the MFF lithology at its margins. The differing processes that dominate the formation of the distinctive landforms have implications for meso-scale variations in climate that remain unresolved by current modeling efforts. Additionally, the variability of erosional forms within the deposit emphasizes the overall complexity of this extensive formation. Author Affiliation: (a) University of North Dakota, Department of Space Studies, Grand Forks, ND 58202, United States (b) Space Science and Engineering Department, Southwest Research Institute, San Antonio, TX 78238, United States (c) Department of Geosciences, Oregon State University, Corvallis, OR 97331, United States (d) CEPS/NASM MRC 315, Smithsonian Institution, Washington, DC 20013, United States (e) Geosciences and Engineering Division, Southwest Research Institute, San Antonio, TX 78238, United States Article History: Received 17 January 2009; Revised 10 June 2009; Accepted 16 June 2009

Different methods for quantifying preferred grain orientation (or grain shape fabric) in sandstones are reviewed and their value for the reconstruction of palaeocurrent direction and preferred direction of pore fluid flow is reassessed critically. Based on existing knowledge from literature and new grain fabric data, it is shown that petrographic analysis has distinct merits, because grain fabric can be determined with low equipment costs and population statistics are based on the orientation of individual grains. Several recommendations are given how to standardise procedures for acquisition of grain fabric through microscopy. These recommendations include: (1) the careful selection of cross-section orientations to acquire apparent long grain axes that are representative of true long grain axes; (2) the preferred measurement of the coarsest grains in cross-section; and (3) a new statistically founded method to select a subset of grains that is representative of the total population of grains in a sandstone sample. Magnetic techniques that use anisotropy of magnetic susceptibility (AMS) as a proxy for grain orientation, require specialised equipment and are more restricted in statistical evaluation, but these methods benefit greatly from being able to measure a large number of grains in a three-dimensional space, in a short amount of time and with a lower sensitivity to user bias. Of the two magnetic techniques discussed in this paper, the new enhanced AMS method, in which rock magnetic properties are enhanced by introducing magnetite into the pores and as precipitates on grain surfaces, is regarded to be an improvement over the traditional natural AMS method, in which only the natural assemblage of magnetite particles present in the rock is analysed. Enhanced AMS measures the preferred orientation of essentially all grains in a rock sample, thus providing the shape fabric of a hydrodynamically more accurate representation of framework grains than natural AMS. Through a small technical modification, the enhanced AMS method can be used to obtain a magnetic cast of the pore network of a rock sample, so that the resulting AMS is controlled by the shape anisotropy of the individual pores. It is commonly assumed that long axes of sand grains in sedimentary deposits parallel the direction of the flows that formed the deposits. This concept is challenged by a new systematic study of grain fabric in deep-marine turbidites. It indeed appears that grains in ripple cross-laminated divisions of turbidites dominantly attain a preferred orientation parallel to the palaeoflow direction, but grains in plane-parallel-laminated divisions have an additional flow-perpendicular mode, which suggests a contribution of rolling grain transport. Three different fabric modes occur in massive 'structureless' sandstones and massive divisions in turbidites. Apart from flow-aligned and flow-perpendicular modes, there is a statistically significant, but hydrodynamically enigmatic, flow-oblique mode with an average azimuthal deviation of 40[degrees]. This large variation of fabric types suggests that a similar variation exists in preferred paths of pore fluid flow within turbidites, controlled to at least some degree by depositional process. This is confirmed by independent laboratory measurements of permeability anisotropy on samples for which grain fabric data are available, and thus defines grain fabric analysis as a viable alternative to traditional permeametry techniques. Keywords: review; microscope methods; magnetic susceptibility; fabric; permeability; turbidite

In order to assess the geothermometric potential of the [Na.sub.2]([Mn.sub.2-2x][Fe.sub.1+2x]) [(P[O.sub.4]).sub.3] system (x = 0-1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800[degrees]C, at 1 kbar, under an oxygen fugacity (f([O.sub.2])) controlled by the Ni-NiO (NNO), [Fe.sub2][O.sub.3]-[Fe.sub.3][O.sub.4] (HM), [Cu.sub.2]O-CuO (CT), and Fe-[Fe.sub.3][O.sub.4] (MI) buffers. When f([O.sub.2]) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500[degrees]C, whereas the association alluaudite + maricite appears between 500 and 700[degrees]C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because maricite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, [Na.sub.2]Mn[Fe.sup.2+][Fe.sup.3+] [(P[O.sub.4]).sub.3], has been positioned in the f([O.sub.2])-T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate. Keywords Primary alluaudites * Na-Mn-[Fe.sup.2+]-[Fe.sup.3+] phosphates * Phase relations * Petrological implications * Pegmatites

Iron concentrations in rehomogenized (remelted) melt inclusions hosted in forsterite-rich olivine ([Fo.sub.88 92]) from an alkalic lava have significantly higher Fe contents ([FeO* up to 21 wt%) than found in naturally quenched inclusions, matrix glasses, and bulk lava compositions (6.21-6.66 wt% FEO*). The main objectives of this study were to: (1) determine the source of the anomalous Fe concentrations, and (2) evaluate the significance of this signature with respect to rehomogenization of melt inclusions. Heating experiments conducted from 1125 to 1225 [degrees]C on crystallized inclusions show that Fe and Mg contents in rehomogenized inclusions increase with homogenization temperature, consistent with dissolution of olivine + magnetite in a 1:1 atomic ratio. The dissolution of magnetite contributes significant excess Fe to the homogenized inclusions, and thus the high FeO* contents of the glasses do not reflect the original composition of the trapped melt. The addition of excess Fe also dilutes the concentrations of other major elements, especially evident in Si[O.sub.2], [Al.sub.2[[O.sub.3], and CaO wt%. Although the cause of magnetite formation in the inclusions is unresolved, two models (H* diffusion and co-entrapment of magnetite) for the formation of significant volumes of magnetite are considered. One of the most significant conclusions for this study is that magnetite formation occurred prior to rehomogenization and that the magnetite did not result from post-entrapment fractional crystallization of the inclusion. For these inclusions, a correction must be made for the dissolution of magnetite ([+ or -] pyroxene) and olivine to the silicate melt to accurately reconstruct the original Fe content of the melt. Keywords: Experimental petrology, rehomogenization, major and minor elements. Fe in glass, electron microscopy, melt inclusions, phase equalibria, olivine, magnetite

Extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations. Some of this uncertainty derives from long down-temperature extrapolations, but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition. Numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature, and reveals a systematic dependence of diffusion rates on host garnet composition. A comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for Fe, Mg, Mn, and Ca for nearly all garnet compositions across the full range of geologically relevant temperatures, pressures, and oxygen fugacities. Keywords: Diffusion, Fe, Mg, Mn, and Ca in garnet, kinetics, metamorphic petrology

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2005.03.004 Byline: Michele Lustrino Keywords: delamination; detachment; lithosphere; mantle plume; petrology; lower crust; eclogite; pyroxenite Abstract: The Earth's lithosphere can focus basaltic magmatism along pre-existing weakness zones or discontinuities. However, apart from the influence on the geochemistry of magmas emplaced in subduction tectonic settings (mantle wedge metasomatism related to dehydration of the subducting plates) the role of lithosphere as a magma source for intra-plate (both oceanic and continental), continental margin, and mid-ocean ridge magmatism is not yet fully understood. In many cases intra-plate magmatism has been explained with the existence of deep thermal anomalies (mantle plumes) whose origin has been placed near the upper-lower mantle transition zone (660 km discontinuity) or even deeper, near the mantle-core boundary ([approximately equal to]2900 km). Also in many continental flood basalt provinces (mostly initiated at craton margins) an active role for mantle plumes has been invoked to explain the high melt productivity. In these cases, no active role for melt production has been attributed to the lithospheric mantle. Potential contaminations of asthenospheric or even deeper mantle melts are often considered the only influence of the lithosphere (both crust and mantle) in basalt petrogenesis. In other cases, an active role of the lithospheric mantle has been proposed: the thermal anomalies related to the presence of mantle plumes would trigger partial melting in the lithospheric mantle. At present there is no unequivocal geochemical tracer that reflects the relative role of lithosphere and upper/lower mantle as magma sources. In this paper another role of the lithosphere is proposed. The new model presented here is based on the role of lower crustal and lithospheric mantle recycling by delamination and detachment. This process can explain at least some geochemical peculiarities of basaltic rocks found in large and small volume igneous provinces, as well as in mid-ocean ridge basalts. Metamorphic reactions occurring in the lower continental crust as a consequence of continent-continent can lead to a density increase (up to 3.8 g/cm.sup.3) with the appearance of garnet in the metamorphic assemblage (basalt[right arrow]amphibolite[right arrow]garnet clinopyroxenite/eclogite) leading to gravitative instability of the overthickened lithospheric keel (lower crust+lithospheric mantle). This may detach from the uppermost lithosphere and sink into the upper mantle. Accordingly, metasomatic reactions between SiO.sub.2-rich lower crust partial melts and the uprising asthenospheric mantle (replacing the volume formerly occupied by the sunken lithospheric mantle and the lower crust) lead to formation of orthopyroxene-rich layers with strong crustal signatures. Such metasomatized mantle volumes may remain untapped also for several Ma before being reactivated by geological processes. Partial melts of such sources would bear strong lower crustal signatures giving rise to Enriched Mantle type 1 (EMI)-like basaltic magmatism. Basaltic magmatism with such a geochemical signature is relatively scarce but in some cases (e.g., Indian Ocean) it can be a geographically widespread and long-lasting phenomenon. Author Affiliation: Dipartimento di Scienze della Terra, Universita degli Studi di Roma La Sapienza, P.le A. Moro, 5, 00185 Rome, Italy Istituto di Geologia Ambientale e Geoingegneria (IGAG)-CNR, P.le A. Moro, 5, 00185 Rome, Italy Article History: Received 26 July 2004; Accepted 31 March 2005

A high-resolution three-dimensional reconstruction of the architecture and the deflection of the 25-million-year-old central Swiss Molasse Basin in central Switzerland was performed to demonstrate the importance of sediment supply as a control on the geometrical and stratigraphical evolution. A collection of published chronological and stratigraphical data and sedimentological and petrographical studies were used in the reconstruction. The combination of deflections due to the orogenic load and due to the load of the basin fill was proposed to account for the deflection of the Swiss basin.

The ages of three samples of Sm-Nd garnet from peridotites, pyroxenites and high-pressure granulites from Lower Austria were analyzed to determine the origin of the high-temperature garnet peridotite massifs from Lower Austria. Analysis of the Sm-Nd garnet indicated the fast cooling of the granulites and peridotites during the upper Visean. Furthermore, the periodite massifs underwent near-isothermal decompression during extension in a late Devonian marginal basin.

Large explosive eruptions and base-level change by synsedimentary faulting controlled fluvial geometry in deposits 35 km downstream from the Van Horn Peak cauldron complex, Idaho. Eruptions varied the volume and size of sediment load. The major impact of large eruptions was a marked increase in the proportion of sand-sized pyroclastic material (from 42% to 93%). Smaller eruptions, in contrast, increased only the washload component. Following major eruptions, the river developed into a multichannel system characterized by wide (75+ m) and shallow ([approximately equals]0.5 m) channels. The sedimentary record of this system is a sheet sandstone with width:thickness ratios ranging from 42:1 to 83:1 in the best-exposed sandstone body. The sheets comprise 86% sandstone with low-amplitude stratification. Most of this is planar-laminated sandstone with tabular geometry. This laminated sheet assemblage is an unusual sedimentary accumulation for perennial rivers. The assemblage represents accumulation under a combination of base-level rise associated with faulting and increased sandy sediment loads produced by eruptions. These factors created an environment conducive to rapid aggradation. Declining sandy sediment loads, together with influx of fine ash (mud-sized) sediment caused the river to change to a single-channel system characterized by more stable and deep channels. The sedimentary record of this system is the mudrock-sandstone assemblage that has 46% overbank deposits with a significant mudrock fraction. Channel sandstone bodies in this assemblage are smaller sheets with width:thickness ratios ranging from 8:1 to 25:1.

New 40Ar/39Ar data from The Straits Schist and interlayered formations in the southernmost Connecticut Valley zone of the northern Appalachian orogen, together with published 40Ar/30Ar and U-Pb data, are used to account for relatively rapid Devonian (post-Acadian) cooling of gneisses and schists near the Waterbury dome and slower Devonian through Permian cooling in structurally higher schists south of the dome. Metamorphic hornblende 40Ar/39Ar cooling ages range from 374 Ma 10 km south of the Waterbury dome to 324 Ma 15 to 40 km south of the dome. Muscovite 40Ar/39Ar cooling ages also decrease to the south, from 318 to 254 Ma. The ages from the southernmost Connecticut Valley zone are as much as 50 and 100 m.y. younger than hornblende and muscovite, respectively, from the Waterbury dome. The difference in cooling histories between the Waterbury dome and southern Connecticut Valley zone is interpreted to be a result of relatively slower cooling in the southern Connecticut Valley zone following Acadian metamorphism and/or a static Pennsylvanian (Alleghanian) thermal event that reset the muscovite K/Ar system, promoted growth of fine-grained monazite, and resulted in partial melting of the crust beneath the southern Connecticut Valley zone. Such a thermal event would have been contemporaneous with Alleghanian orogenesis in Appalachian terranes in southeastern New England, but the mechanism for generating a Pennsylvanian thermal pulse is still unknown.

Hydrous partial melting experiments performed between 650 and 750 [degrees] C at 200 MPa ([H.sub.2]O) on synthetic metapelite compositions (quartz + albite + muscovite + biotite mineral mixtures) doped with Ba, Sr, Rb, and Cs yielded alkali feldspar crystals with a wide range of compositions in equilibrium at their rims with peraluminous melt. Measured partition coefficients for normally trace lithophile elements between feldspar and melt [D[(M).sup.Fsp/gl], M = Ba, Sr, Rb, Cs] do not depend on either temperature or bulk composition of melt for the compositions studied. Values of D[(Sr).sup.Fsp/gl] are between 10 and 14 and appear to be independent of the albite and orthoclase contents of the feldspar crystals. In contrast, values of D[(Ba).sup.Fsp/gl] and D[(Rb).sup.Fsp/gl] are strongly dependent on the orthoclase content of feldspar, relationships that can be expressed by the following linear equations: D[(Ba).sup.Fsp/gl] = 0.07 + 0.25(orthoclase) and D[(Rb).sup.Fsp/gl] = 0.03 + 0.01(orthoclase), where orthoclase is in mole percent. These equations reproduce the range of previously reported values for D(Ba) and D(Rb) determined on natural and synthetic samples. A single partition coefficient for Cs was also determined at D[(Cs).sup.Fsp/gl] = 0.13. These data can be used in conjunction with recently published partition coefficients for muscovite, biotite, and plagioclase feldspars (Blundy and Wood 1991; Icenhower and London 1995) to model quantitatively the trace element signatures of peraluminous magmas during anatexis and crystallization. Depending on bulk composition and pressure-temperature trajectories during episodes of partial melting, Ba and Sr (and to a lesser extent, Rb) are retained at the source while Cs and Li are enriched in the first melts. These results explain why peraluminous granitic magmas with S-type (sedimentary) sources carry a distinctive enrichment in Li and Cs.

The structural phase transitions of monoclinic tridymite that occur at elevated temperatures, as well as the structure of the high-temperature modifications, have been studied by 29Si MAS NMR. The sample, originating from the surface of a refractory silica brick, displays sharp discontinuities in the first moment ([M.sub.1]), second moment ([M.sub.2]), or both, of the 29Si MAS NMR spectrum at the following phase transitions: 108 [+ or -] 1 [degrees] C for the monoclinic (MC) to orthorhombic (OP) transition, 165 [+ or -] 5 [degrees] C for the transition from OP to a second orthorhombic phase (OS), and 206 [+ or -] 4 [degrees] C for the transition from OS to a third orthorhombic phase (OC). [M.sub.1] for the OC phase becomes more negative with increasing temperature up to [approximately]323 [degrees] C, at which there is also a small discontinuity in [M.sub.2], indicating a transition from OC to a hexagonal phase (LHP). The spectrum of the MC phase consists of 12 narrow lines of equal area, consistent with the known crystal structure. The spectrum of the OP phase is broad and asymmetric, indicating a distribution of local environments at the Si sites. It can be simulated assuming an incommensurate structural modulation with a maximum amplitude of [approximately]5 x [10.sup.-2] [Angstrom], but it is also consistent with a recent domain-formation model, provided that most disorder occurs at the Si6 site. The spectrum of the OS phase is asymmetric, indicating a nonlinear incommensurate modulation with a maximum amplitude of [approximately]2 x [10.sup.-2] [Angstrom]. The spectra of higher temperature phases are consistent with the single Si site of the known crystal structures, but [M.sub.1] values imply significantly smaller mean Si-O-Si angles e.g., = 152.6 [degrees] at 220 [degrees] C from NMR, compared with 168.0 [degrees] from X-ray diffraction data. This difference is consistent with disorder of O atoms around Si-Si axes.

The observations of the correlation between the degree of O(super 18)-depletion in metasedimentary rocks, O(super 18)O(super 16) homogenization between lithologies and the part of granitoids in any location of the section, are explained by the fluid-mediated exchange between granitoids and metasediment. This exchange occurs by convective recirculation of magnetic fluids on the scale of meters during granitoid crystallization. The generalized model for the isotopic evolution of the the East Humboldt Range core complex is effective to know the influencing factors of depletion and homogenization.

Experimental analysis of dehydration melting of a basaltic composition amphibolite at 1.5 and 2.0 gPa and 850-1150 degrees Celsius temperature reveals the generation of amphacitic clinopyroxene and garnet residues occurring with rhyolitic to andesitic composition melts during dehydration melting. Melts that are similar to adakites lacking MgO and CaO are produced during partial melting of amphibolites. Adakites should acquire MgO and CaO on interaction with the mantle wedge or crust if they are slab melts.

Petrologic studies of recent eruptions from Volcan Tequila, Jalisco, Mexico, reveal the occurrence of magma mixing before or during eruption, as represented by bimodal plagioclase phenocryst rim compositions in the lavas. The large magma storage reservoir branches into several small ones during the later stages of volcanic activity. Calcic plagiodase is crystallized in the presence of significant magmatic water levels. Crystal fraction action of calc-alkaline basalts from the mantle along with crystal material digestion lead to the formation of calc-alkaline magmas.

Crete Island nappes had contrasting lithologies and metamorphisms, and these were obtained southward during the Oligocene-early Miocene north-south compression. This cyclic tectonometamorphic process of alternate extension and compression occurred during the migration of the Hellenic orogenic belt toward external units. Lower nappes experienced high-pressure/low-temperature metamorphism, which was followed by a north-south Miocene crustal extension.

Vesicle size distributions in vent lavas from the Pu'u 'O'o - Kupaianaha eruption of Kilauea volcano are used to estimate nucleation and growth rates of H2O-rich gas bubbles in basaltic magma nearing the earth's surface (less than or equal to 120 m depth). By using well-constrained estimates for the depth of volatile exsolution and magma ascent rate, nucleation rates of 35.9 events center dot cm to the -3 center dot s to the -1 and growth rates of 3.2 x 10 to the -4 cm/s are determined directly from size-distribution data. The results are consistent with diffusion-controlled growth as predicted by a parabolic growth law. This empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings. In addition, perturbations in the measured size distributions are used to examine bubble escape, accumulation, and coalescence prior to the eruption of magma.

Two stratigraphic sequences were sampled through the early Anisian Anton Chico Member of the Moenkopi Formation in northeastern New Mexico. Two polarities of magnetization are present: a normal-polarity interval succeeded by a reversed-polarity interval and followed by a short normal- and reversed-polarity couplet. Detailed thermal demagnetization (10 to 17 steps) was employed to separate magnetic vectors. The secondary magnetization is largely a direction similar to the present-day and/or axial-field directions. Demagnetization above 520 [degrees] C reveals a near-horizontal characteristic magnetization. The lithology of the stratigraphic sequence is such that the reversed polarity is contained almost exclusively within coarse sandstone lithologies, and hence, the reversed-polarity characteristic magnetization direction is rarely completely separated from the secondary magnetization. Because of this, the paleopole was calculated from only the lower normal-polarity portion of the section. The pole, calculated from the samples of two localities, is located at 121.4 [degrees] E, 43.2 [degrees] N, ([[Alpha].sub.95] = 5.3). This Middle Triassic paleopole is in good agreement with published Triassic paleomagnetic poles for cratonic North America and statistically overlaps the Early Triassic paleopoles. The large-scale relative motion during the Triassic between the magnetic pole and the North American plate is constrained by this study to have begun after early Middle Triassic time; it suggests that as much as 10 [degrees] of apparent-polar wander occurred between the late Anisian-Ladinian (late Middle Triassic) and the middle to late Carnian (early Late Triassic), a time interval of between 11 and 14 m.y.

The mineralogical results show that the two diamondiferous harzburgite xenoliths obtained at the Finsch kimberlite, South Africa are coarse peridotites exhibiting compositional equilibrium common in the diamond stability field. The xenoliths are found to be different from other inclusions in Finsch diamonds. The observed differences clearly state that the two recovered xenoliths originate from another diamond source.

The potassium-argon dating done on the mid-Pleistocene Turf Point Formation (TPF) suite showed that Seguam Island in the Aleutians was formed on an extended arc crust. TPF petrology revealed that lavas range from basalt to rhyodacite and are generally tholeiitic. The mineral composition and texture of porphyritic basalt and basaltic andesite lavas exhibited equilibrium crystallization without the presence of assimilation or open-system mixing. The intra-arc extension of the island not only modified the crust structure but also spread heat and density in the lithosphere.

The Punta Falcone gabbroic complex in northern Sardinia, Italy is a parental magma formation that came from the introduction of high-alumina basalt into partially uncrystallized granite magma. The interior and marginal interaction zones in the gabbroic complex feature varied structures due to the low pressure and closed-system crystallization that happened in the interior zone. Cumulus crystals and trapped liquids abound in the chamber, creating different rock protrusions. Chemical and physical processes like crystal fractionation and thermodynamic instability also aid in the structural formation of the gabbroic complex.