Open-system Processes Research Articles

Energy-Constrained Open-System Magmatic Processes I: General Model and Energy-Constrained Assimilation and Fractional Crystallization (EC-AFC) Formulation

recharge mass and Teq, the mass of wallrock heated to Teq is Geochemical data for igneous rocks provide definitive evidence for computed and the geochemical trajectory of melt is determined as the occurrence of open-system processes in magma bodies, including magma temperature approaches Teq from its starting value, Tm°. Replenishment by intrusion of primitive magma, Assimilation of The effects of imperfect extraction of anatectic wallrock melt may anatectic wallrock melt and cumulate formation by Fractional be accounted for by introduction of an extraction efficiency factor. Crystallization. A general class of models (Energy ConservedMathematical details of a simpler model, EC-AFC (no reRAFC or EC-RAFC) can be constructed, which allow simulation plenishment) are provided. Energy-constrained models have the of geochemical paths for trace elements and isotopic ratios for magma advantage of linking thermal and chemical properties of magma undergoing simultaneous replenishment, assimilation and fractional chambers. Compared with ‘classical’ models that conserve mass crystallization during the approach to thermal equilibration. The and species only, they represent more complete assessments of general problem of EC-RAFC is formulated as a set of 3 + t the complex physicochemical dynamics governing the geochemical + i + s coupled nonlinear ordinary differential equations, where evolution of open-system magma bodies. Results of EC-AFC the number of trace elements, radiogenic and stable isotope ratios simulations demonstrate that geochemical trends can differ sigsimultaneously modeled are t, i and s, respectively. Partial melting nificantly from predictions based on ‘classical’ AFC even when of wallrock, modeled as fractional melting, is incorporated, as are recharge plays no role. Incorporation of energy conservation and sensible and latent heat effects. Temperature-dependent partition partial melting into geochemical models allows important coupled coefficients are used to describe trace element distributions. Solution effects to play their natural role. of the set of differential equations, with magma temperature (Tm ) as the independent variable, provides values for the average temperature of wallrock (Ta ), fraction of melt within the magma body (Mm ),

Generalized quantum Onsager coefficients from a symmetrized Campbell-Hausdorff expansion

The analogue of the classical Onsager theory of entropy production is systematically derived for weakly irreversible processes in open quantum systems with finite-dimensional Hilbert space. The dynamics is assumed to be given by a quantum dynamical semigroup with infinitesimal generator of Gorini-Kossakowski-Sudarshan type. The basic Spohn formula for entropy production is used to obtain an expansion in terms of powers of the deviation of the initial state relative to the final stationary state of irreversible dynamics. To this end, an appropriate Lie series is constructed from a particular symmetrization procedure applied to the ordinary Campbell-Hausdorff expansion. In this way, only Hermitian contributions by higher-order commutators are generated, which allow an identification with so-called generalized Onsager coefficients. The explicit derivations concentrate on second-, third- and fourth-order coefficients, whereas complete detailed expressions are worked out for second and third order. In a suitable coherence-vector representation of density matrices the results can be given in terms of the dynamical parameters fixing the infinitesimal semigroup generator and in terms of symmetric and antisymmetric structure constants of the Lie algebra of SU(N). As an illustration, an application to generalized Bloch equations for two-level systems is studied, where the Onsager-like expansion can be compared with exact results for entropy production. We find that convergence is good even for rather large deviations between initial and final state if the calculation includes second- and third-order coefficients only. The formalism presented in this paper generalizes restrictions on admitted final states adopted in much simpler earlier treatments to the most general case of arbitrary unique final states of irreversible processes.

Processes in open systems on crystal surfaces with low miller indices

Exposure characteristics that were obtained when growing various films on natural low Miller index surfaces of several crystals were collected and analyzed. An evolution theory that explains their special form was constructed. The type of dose characteristics obtained suggests that the surface underwent a reconstruction, i.e., a nonequilibrium phase transition that occurs on the surface. A quantitative analysis of the experiments available has been performed. In particular, a quantitative estimation was obtained of to what extent coverage with lead hinders the oxidation of the surface of a nickel crystal. Upon intense light or electron irradiation of silicon, divacancies are the predominant centers of the formation of point and extended radiation defects, as well as of local regions of melting. For some two-dimensional systems (divacancies, sulfur atoms on the surfaces of passivated semiconductors, oxide films), delay times and evolution times for the self-organized structure formed were determined.

Magmatic Na-rich phlogopite in a suite of gabbroic crustal xenoliths from Volcán San Pedro, Chilean Andes: Evidence for a solvus relation between phlogopite and aspidolite

Magmatic Na-rich phlogopite (1-5 wt% Na 2 O) is present as a late-crystallizing mineral in two groups of texturally and mineralogically distinct gabbroic xenoliths at Volcán San Pedro (36°S, Chile), an Andean arc volcano. Phlogopites are characterized by high 100·Mg/(Mg + Fe) (up to 83) and high Cr 2 O 3 contents (up to 0.4 wt%), and they are always found surrounding variably resorbed olivine, pyroxenes, Cr-spinel, and in some cases, plagioclase. We interpret these micas as the result of open-system processes involving infiltration of water-rich evolved melts [with high Na/(Na + K)] and reaction with refractory minerals. The highest 100·Na/(Na + K) (~70) and Na 2 O concentrations (~5 wt%) in phlogopite appear to require reaction with liquids of unrealistically high Na/(Na + K) if no other factor is considered. This, together with the observation that phlogopites consist of alternating Na-rich and Na-poor cleavage-parallel bands, can be best interpreted by the presence of a solvus between the aspidolite (Na) and phlogopite (K) end-members. The high proportions (up to 15 vol%) of Na-rich phlogopite in two different groups of gabbroic xenoliths suggest that it might be a more common and abundant mineral than has been previously recognized, and that it may be used as an indicator of open-system processes.

Homogenization of high-T garnets during deformation, fluid flow and metasomatism Catalonian Coastal Ranges, NE Iberian Peninsula

Progressive homogenization of previous growth zoning patterns in garnets of the HT/LP sillimanite zone of the Osor complex (NE Iberian Peninsula) is interpreted as the product of intracrystalline diffusional processes plus the operation of open system reactions coupled to fluid flow. The infiltrated fluid evolved during syn-tectonic emplacement and crystallization of two-mica peraluminous leucogranitoid sheets. The flow began in a more or less pervasive regime, then the fluid phase became progressively saturated in Si and K–Na species as well as progressively focused along schistose domains subparallel to the developing crenulation cleavage planes. A sequence of open system processes related to this fluid flow took place along the schistose domains syn- to late-tectonically: quartz leaching and further deposition in veins, extreme fibrolitization, muscovite+high Na/Ca plagioclase+biotite blastesis and homogenization of previous garnet growth zoning profiles. Notably the growth profiles have been preserved only in the less permeable quartz-rich, muscovite and plagioclase poor, semi-pelitic geissic domains.

98/03919 Wood as principal energy source for remote regions

We review petrological and geochemical features of silicic pyroclastic deposits of dominantly low to moderate (0–25%) crystallinity, and volumes in the range of 5–1000 km3, erupted from caldera volcanoes. Chemical gradients in zoned deposits with compositions near the water-saturated granite minimum, for example the Bishop and Bandelier Tuffs, are consistent with mineral/melt partitioning predicted from the observed phenocryst assemblages, and are inconsistent with mixing with more mafic magma. Smaller volume alkaline (phonolite and pantellerite) systems show similar behavior. In contrast, high-temperature ignimbrites of the ‘Snake River’-type typically lack compositional zoning. Internal isotopic variations are weak or absent from whole rocks in both types of rhyolite, even in systems where associated volcanic rocks exhibit wide isotopic variation and strong contrasts exist between the isotopic compositions of mantle and crust. An exception to this is 87Sr/86Sr variations in high-silica rhyolite systems, where Sr has been depleted to subchondritic concentrations and is exceptionally sensitive to open-system processes. Both types of ignimbrite commonly contain crystal aggregates, interpreted as fragments of cumulate mush. In zoned systems, these aggregates exhibit evidence for partial resorption of early-formed crystals. We infer that chemical zoning is a near closed-system process and propose that it arises through melting of cognate cumulate mush beneath a crystal-poor body of melt due to heating by invading mafic or intermediate magma with little mass transfer to the eruptible magma. If the crystal mush is fusible (e.g. dominated by sanidine + quartz), part of it melts to yield mobile, water-poor rhyolite that pools at the interface between the mush and overlying rhyolitic liquid. This new, eruptible melt has a cumulate composition and is thus less evolved than the original supernatant melt lens. The result is a chemically zoned crystal-poor rhyolitic magma produced with little mass contribution from the invading magma. This model reconciles evidence for thermal rejuvenation, preserved in crystals, with evidence for the production of zoning by crystallization-differentiation, apparent in whole-rock chemistry. Fusibility of the cumulate is key to the process; high-temperature ‘Snake River’-type rhyolites are not zoned because their cumulates are dominated by a refractory assemblage of pyroxene, plagioclase, and Fe–Ti oxides. Previous models of compositional zoning have envisaged a pot of silicic magma undergoing slow cooling towards thermal senescence. In contrast, we contend that zoning records a history of thermal rejuvenation in which any one recharge event has the potential to trigger a caldera-forming eruption.

Frio Shale Mineralogy and the Stoichiometry of the Smectite-to-Illite Reaction: The Most Important Reaction in Clastic Sedimentary Diagenesis

AbstractBurial diagenesis of shales of the Frio Formation resulted in an increase in the abundance of mixed-layer illite-smectite (I-S), albite and chlorite, and a decrease in the abundance of K-feldspar, illite and kaolinite. Some of the mineralogic trends determined in this study contrast with the results of Hower et al. (1976) and other studies of Frio shales. The differences are due to improvements in laboratory and clay quantification techniques since the time of the earlier research. I-S composition changed from ~20% to ≥80% illite, and mineralogic and chemical reaction of I-S continued throughout burial. Shale diagenesis was an open-system process that required addition of K2O and A12O3, and resulted in loss of SiO2. The amount of SiO2 made available by shale diagenesis is sufficient to be the source of the quartz-overgrowth cements in the associated Frio sandstones. The relationships between I-S diagenesis and fluid flow from shales into sandstones, generation of abnormal formation-water fluid pressure, onset of sandstone diagenesis and distribution of authigenic phases in sandstones indicate that reaction of the I-S in shales is one of the most important components of the sandstone/shale/formation water diagenetic system.

Genesis of Silicic Peralkaline Volcanic Rocks in an Ocean Island Setting by Crustal Melting and Open-system Processes:Socorro Island, Mexico

Silicic volcanic rocks from Socorro Island, Mexico, are dominantly porphyritic (alkali feldspar>sodic pyroxene±fayalite±Fe–Ti oxides±aenigmatite) peralkaline trachytes and rhyolites. Typical of silicic peralkaline rocks, those from Socorro are enriched in Na2O, K2O, FeO*, Zr and Nb, and depleted in Al2O3, Sr and Ba relative to silicic metaluminous rocks. The ranges of Nd and Pb isotope compositions are relatively restricted and similar to those of alkalic basalts from Socorro Island. In contrast, Sr isotope compositions are more radiogenic than those of the alkalic basalts and trend toward the 87Sr/86Sr of modern seawater. Alkali feldspar–whole-rock pairs exhibit marked Sr isotope disequilibria. Gaps in SiO2 and K2O coupled with virtually identical high field strength element (e.g. Zr, Nb, Hf) and Th abundances between differentiated alkalic basalts and the least evolved peralkaline trachytes are inconsistent with an origin for the trachytes by fractional crystallization of the basalts; the most reasonable alternative is partial melting of mafic intrusive rock. Major and trace element compositions are consistent with peralkaline rhyolites being derived from parental trachytes by fractionation of an assemblage dominated by alkali feldspar; phase equilibria suggest that fractionation occurred in a shallow-level magma reservoir. At lest two stages of open system processes are implicated by Sr isotopic and trace element data: (1) interaction between silicic magma and components of the shallow ocean crust may be indicated by abundances of REE in excess of those predicted by fractional crystallization models and negative Ce anomalies; (2) post-eruptive interaction between aqueous fluid and rock is suggested by whole-rock Sr isotope values that trend toward the 87Sr/86Sr by acid leaching. The fluid apparently has Sr isotope characteristics comparable with those of modern seawater and may be similar in composition to hydrothermal fluids present at the summit of Socorro Island.

Towards the mathematical model of rim structure formation

The high burnup LWR UO 2 fuels show a notable micro-structural change around the pellet outer zone which is called the rim structure. It is observed at temperatures as low as 400°C so that fission track and cascade mixing could be the key mechanism. SEM observation revealed that the structure primarily appears on free surfaces of UO 2, indicating that strong sink for point defects may play a big role. And as generic observations, increase of lattice parameter indicates extensive amounts of vacancies are stored in high burnup fuel, which may induce the restructuring interacting with dislocations of high density at high burnup. Considering these observations a model of reaction-diffusion process of defects with irradiation induced transport is proposed. The equations are investigated numerically. The model indicates that an instability starts when the dislocation network starts intensive interaction with vacancy flux which is modified by interstitial diffusion between spatial segments. It appeared to be similar to the Turing type instability which indicates that the rim structure formation is one kind of the self-organizing processes of open reaction-diffusion systems.

Burial diagenesis of illite/smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones

Several gram-size samples of <0.1 μm, nearly monomineralic mixed-layer illite/smectite (I/S)were isolated from nineteen whole-cores of shale of the Frio Formation from the Texas Gulf Coast. Between ∼7,000 ft (2133 m) and ∼15,000 ft (4572 m) burial depth I/S changes from random-interstratification ( R = 0) with low %I to ordered-interstratification ( R = 3) with high %I. The accompanying chemical changes are loss of Si, Mg, and Fe +3, gain of K, Al, and Fe +2, and a shift in the REE content of the mineral. There is no chemical or mineralogical evidence for a cessation of I/S reaction at ∼80% I as is commonly accepted; both chemical and mineralogical changes occur throughout burial. Continuous change in the oxygen isotopic composition of I/S implies that the conversion of smectite-layers to illite-layers is a dissolution and reprecipitation process. Mass balance calculations indicate that burial diagenesis of Frio Formation shales is an open-system process that requires addition of K 2O and Al 2O 3 and results in loss of SiO 2. The amount of SiO 2 made available by shale diagenesis is sufficient to be the source of the quartz-overgrowth cements in the associated Frio sandstones. Iron reduction in I/S is a significant source of the acid required for the diagenesis of both Frio shales and sandstones.

Open systems-a process for achieving affordability [in avionics systems

A major factor that will drive the definition and design of future avionics systems is affordability. Affordability is being addressed on numerous fronts such as hardware re-use, software re-use, COTS leveraging, and reduced cycle times. Each of these thrusts provide potential cost savings along with unique challenges. What is needed is a process that integrates these initiatives while ensuring the overall system objectives are achieved. An Open Systems-based process is key to integrating these initiatives and balancing affordability and system performance goals. Although Open Systems are being widely recognized as a key to affordability, most interpret Open Systems as a set of system attributes that need to be achieved. There are numerous claims of vendors saying they have an Open Systems architecture or how their system will evolve to an Open Systems architecture. This emphasis is not on increasing affordability but on attaching a politically correct label to their product. In this paper, we focus on the Open Systems process as the key to affordability. An Open Systems process is based on Open Systems principles. This paper discusses the Open Systems principles and process in detail and shows how this process integrates numerous affordability initiatives.

Chondrules: Their Diversity and the Role of Open-System Processes during Their Formation

After classification into compositional groups using their cathodoluminescence properties, chondrules were chiseled from sections of the least metamorphosed ordinary chondrites, Semarkona and Krymka. This technique avoided biases due to size and friability and ensured that all classes were adequately sampled. The chondrules were then analyzed by instrumental neutron activation analysis and their major phases (olivine, pyroxene, metal, mesostasis) were analyzed by electron microprobe. Group A1 and A2 chondrules of Semarkona and group A3 chondrules of Krymka have all the properties expected for chondrules which experienced considerable Fe reduction and evaporative loss during their formation (elemental depletions related to volatility, Fe-poor silicates, Ni-poor metal, significant pyroxene, small sizes). This is not the case for group B1, B2, and A5 chondrules (which have unfractionated bulk silicate compositions, FeO-rich silicates, little or no metal, little pyroxene, large sizes). Group A chondrules in Semarkona generally have thicker metal–sulfide-rich rims than group B chondrules, a situation similar to that of the Murchison CM2 chondrite, except that in Murchison aqueous alteration has destroyed the metal and sulfide. Group A chrondrules sometimes show compositional zoning in their mesostases and we suggest that both mesostasis zoning and chondrule rims are the products of recondensation during chondrule formation. Cooling rates differ considerably with chondrule class. Group A1–3 and A5 chondrules cooled relatively slowly and maintained a degree of equilibrium between melt and phenocrysts, while group B1 and B2 chondrules cooled rapidly and underwent considerable supercooling. The chondrule-forming process, whatever it was, was clearly capable of acting with a variety of intensities and produced a range of cooling rates. We suggest that the diversity of chondrules cannot be attributed mainly to variations in the properties and abundances of precursors, although this can sometimes be a factor, but can be derived from a fairly similar precursor of solar composition.

Open Systems: a process for achieving affordability

A major factor that will drive the definition and design of future avionics systems is affordability. Affordability is being addressed on numerous fronts such as hardware re-use, software re-use, COTS leveraging, and reduced cycle times. Each of these thrusts provide potential cost saving along with unique challenges. What is needed is a process that integrates these initiatives while ensuring the overall system objectives are achieved. An Open Systems-based process is key to integrating these initiatives and balancing affordability and system performance goals. Although Open Systems are being widely recognized as a key to affordability, most interpret Open Systems as a set of system attributes that need to be achieved. There are numerous claims of vendors saying they have an Open Systems architecture; or how their system will evolve to an Open Systems architecture. This emphasis is not on increasing affordability, but on attaching a politically-correct label to their product. In this paper, we focus on the Open Systems process as the key to affordability. An Open Systems process is based on Open Systems principles. This paper discusses the Open Systems principles and process in detail and shows how this process integrates numerous affordability initiatives.

Residual-liquid origin for a monzonitic intrusion in a mid-Proterozoic anorthosite complex: The Sybille intrusion, Laramie anorthosite complex, Wyoming

The Sybille intrusion (≈100 km 2) is one of three large monzonitic intrusions in the 1.43 Ga Laramie anorthosite complex of southeastern Wyoming. The petrographic, geochemical, isotopic, and geophysical characteristics of Sybille monzonitic rocks are consistent with an origin by extensive crystallization of liquids residual to nearby anorthositic cumulates (ferrodiorites) and contamination by Archean wall rocks. The exposed part of the intrusion is composed mainly of coarse-grained monzosyenites with abundant alkali feldspar phenocrysts. The monzosyenites preserve mineralogical evidence for high crystallization temperatures (>1000 °C), mid-crustal emplacement pressures (≈3 kbar), relatively reduced crystallization conditions (2 log units below the fayalite + magnetite + quartz [FMQ] oxygen buffer), and they crystallized in the presence of a CO2-rich fluid phase (Fuhrman et al., 1988; Frost and Touret, 1989). The eastern monzosyenites, those adjacent to contemporaneous anorthosite, are distinguished by an anhydrous mineral assemblage (Fo16-Fo8 olivine, high-Ca pyroxene) lacking modal quartz, silica contents of 60 wt%, and smaller Eu anomalies (Eu/Eu* = 1.2 to 1.3). Abundant xenoliths of Archean wall rocks and anorthosite from the adjacent intrusions in all monzosyenites attest to a stoping emplacement mechanism near the roof of the chamber. We propose that the monzosyenites represent a relatively thin, 0.5-1.0-km-thick, roof to a magma chamber dominated by dense ferrodioritic cumulates at depth. Extensive, open-system fractionation of a ferrodioritic parent magma, residual after crystallization of anorthosite, produced Fe-enriched monzodioritic and/or monzonitic magma in the upper part of the chamber and complementary Fe- and Ti-rich cumulates in the lower levels. We have corroborated the production of monzonitic liquids from crystallization of ferrodiorite through a series of reconnaissance equilibrium-crystallization experiments. The presence of dense ferrodioritic cumulates at depth is consistent with the prominent positive gravity anomaly associated with the Sybille intrusion (Hodge et al., 1973). In the upper parts of the chamber, the fractionated monzodioritic and/or monzonitic magmas eventually became saturated in alkali feldspar. Owing to density contrasts, the alkali feldspar phenocrysts floated to the roof of the chamber, thus producing the exposed porphyritic monzosyenites. In addition, the roof of the chamber was the site of significant melting of Archean gneiss and, locally, metapelite. The Sr and Nd isotopic compositions of the monzosyenites, with Sr isotopic ratios becoming increasingly radiogenic from east ( I Sr = 0.7059 and initial ϵNd = −2.5) to west ( I Sr = 0.7092 and initial ϵNd = −2.6), are consistent with a 5% to 15% addition of Archean orthogneiss to a ferrodioritic parent magma that had isotopic characteristics similar to adjacent anorthositic rocks. The stratigraphic and compositional similarity of the Sybille monzosyenites to mangerites in the Bjerkreim-Sokndal intrusion of the Rogaland anorthosite complex, southern Norway, indicates that similar open-system magmatic processes are capable of having produced high-temperature, K-rich monzonitic rocks in other Proterozoic anorthosite complexes.

Petrogenesis of the late-Delamerian gabbroic complex at Black Hill, South Australia: Implications for convective thinning of the lithospheric mantle

A group of funnel-shaped gabbroic plutons at Black Hill, South Australia, consist of a lower series of layered peridotite, troctolite and olivine gabbro cumulates overlain by gabbronorites and potassic gabbronorites, the latter yielding a Sm-Nd isochron of 489 ± 39 Ma. Mineral assemblages in the gabbros record an olivine compositional hiatus (Fo75-55) and a high temperature (1200-1000°C), low pressure (∼1 kbar), continental tholeiitic fractionation trend under moderate fO2 (∼QFM) conditions. The liquid line of descent involved complex open system processes including recharge and crustal assimilation. In one pluton, fine-grained norites may reflect assimilation which resulted in an increaseda SiO2 liquid causing orthopyroxene to crystallize prior to plagioclase.

Open-system magma chamber process in the Freetown Complex of Sierra Leone: evidence from Zone 3

AbstractThe ˜ 7 km thick Freetown layered complex of Sierra Leone consists of four zones each composed of a cyclically layered sequence of troctolite, gabbro, olivine gabbro, gabbronorite, and anorthosite. The complex is thought by previous workers to have solidified in situ from a single parental magma without stratigraphic changes in mineral compositions. Evidence for cryptic variation is presented based on electron microprobe analyses of mega-unit Zone 3. Two reversals in olivine forsterite content, plagioclase anorthite content, and 100 Mg/(Mg Fe2) in clinopyroxene match the variations of Ni in olivine and Cr in clinopyroxene. These changes are consistent with a magma chamber that was open to periodic influxes of new magmas, and the mixing of new and fractionated resident magmas. Expansion of the magma chamber is thought to have occurred at 2000 m, corresponding to the level of a major influx.

Geochemistry of Ferrar Dolerite sills and dykes at Terra Cotta Mountain, south Victoria Land, Antarctica

At Terra Cotta Mountain, in the Taylor Glacier region of south Victoria Land, a 237 m thick Ferrar Dolerite sill is intruded along the unconformity between basement granitoids and overlying Beacon Supergroup sedimentary rocks. Numerous Ferrar Dolerite dykes intrude the Beacon Supergroup and represent later phases of intrusion. Major and trace element data indicate variation both within and between the separate intrusions. Crystal fractionation accounts for much of the geochemical variation between the intrusive events. However, poor correlations between many trace elements require the additional involvement of open system processes. Chromium is decoupled from highly incompatible elements consistent with behaviour predicted for a periodically replenished, tapped and fractionating magma chamber. Large ion lithophile element-enrichment and depletion in Nb, Sr, P and Ti suggests the addition of a crustal component or an enriched mantle source. The trace element characteristics of the Dolerites from Terra Cotta Mountain are similar to those of other Ferrar Group rocks from the central Transantarctic Mountains and north Victoria Land, as well as with the Tasmanian Dolerites. This supports current ideas that the trace element signature of the Ferrar Group is inherited from a uniformly enriched mantle source region.

Elemental mobility in sandstones during burial; whole-rock chemical and isotopic data, Frio Formation, South Texas

ABSTRACT The deepest (> 3.5 km) and most altered Oligocene Frio sandstones from south Texas typically contain authigenic minerals that exceed 30 volume percent of the rock. Elemental and isotopic analyses of whole rocks confirm conclusions based on petrography that authigenesis is accompanied by substantial material transfer involving both import to and export from the sandstone. From petrographic observations, Zr is apparently less mobile than other immobile elements such as Al, Ti, and REE, but nonuniform initial distribution of Zr due to sorting limits its usefulness for normalizing elemental variations. If Zr is assumed to be strictly immobile, and Zr was once uniformly distributed, then volume loss of approximately 38% from the silicate fraction of the deepest sandstones is suggested. Over the range of burial depths for samples used in this study (0.9-4.3 km), elemental trends controlled by feldspar reactions are the most readily documented. Dissolution and replacement of detrital K-feldspar is accompanied by loss of 2-3 weight percent of K2O from the whole rock. Loss of more than half of the initial Rb, Sr, and Pb also correlate with alteration of detrital feldspars. 87Sr/86Sr ratios for whole-rock and silicate fractions increase with depth as loss of nonradiogenic strontium characteristic of the volcanic-rich detrital fraction is overwhelmed by more radiogenic strontium derived from deeper in the basin. Relatively constant Na is compatible with feldspar alteration in which dissolution exceeds albitization. Changes in Nd concentrat ons and Nd also closely track the progress of alteration of detrital feldspar. Magnesium gain accompanies precipitation of authigenic chlorite and very minor ferroan dolomite. Whole-rock calcium values are dominated by calcite that includes both detrital and authigenic components. Significant dissolution of detrital carbonate grains does not occur, and calcium in authigenic carbonate cement exceeds by about 5 times the calcium released by dissolution of detrital silicates, thus requiring considerable import of calcium and CO2. Material transfer on the observed demonstrates that burial diagenesis is an open-system process for several major elements, and introduces a major obstacle to use of elemental data for provenance interpretation. Defining the sources of materials transported into sandstones, and the fate of materials exported, is key to documenting the scale of system closure in sedimentary basins and requires a better understanding of diagenetic processes in mudrocks.

Amphibole zoning in the Garland Peak Syenite, Red Hill complex, New Hampshire: camptonitic parental magmas and differentiation to silica-oversaturated syenites

The Garland Peak Syenite (GPS) of the Red Hill complex, New Hampshire, consists predominantly of amphibole, oligoclase, perthite, and quartz; amphiboles have homogeneous kaersutite cores with strongly zoned rims ranging in composition from pargasite to hastingsite to hornblende. The thin section scale association of kaersutite, an amphibole that typically crystallizes in silica-undersaturated magmas, with quartz suggests that the GPS magma experienced substanital changes in magmatic composition, including silica activity, during its crystallization history. Kaersutite-bearing camptonites are also associated with the Red Hill complex. The camptonite amphiboles are very similar in composition to the core kaersutites in the GPS, suggesting that the earliest GPS liquid may have had camptonitic affinities. In order to elucidate the process where-by silica-undersaturated magmas differentiate to saturation, amphiboles in these rocks were analyzed by electron and ion microprobe techniques. Amphiboles show a progressive increase in REE abundances from the camptonites to the GPS kaersutite cores to the GPS pargasite/hastingsite/hornblende rims. The systematic change in REE concentrations, and the variations in V, Ti, Sr versus Zr, Eu/Eu0 and La/Yb versus Ce, suggest a possible differentiation relationship for the amphiboles and imply that the GPS was derived from magmas similar to camptonites. Rimward depletions in Sr, Ti, V, and Eu/Eu0, and the increase in La/Yb values suggest that parental camptonites fractionated plagioclase, magnetite, and amphibole to produce the silica-oversaturated GPS. Bulk-rock modelling agrees with the trace element record preserved in the amphiboles, that plagioclase, magnetite, and amphibole fractionation caused silica saturation. Minor pegmatitic patches occur in the GPS. Ferrohornblendes in the pegmatites have REE abundances distinct from the other GPS amphiboles, and this difference may be due to open system processes.

A petrologic re-investigation of the Adak volcanic center, central Aleutian arc, Alaska

The Adak volcanic center is located in the central part of the Aleutian arc and consists of three main volcanic vents. Andrew Bay Volcano, the oldest center, has been mostly removed by erosion. The next youngest vent, Mount Adagdak, was built in three major volcanic stages whereas Mount Moffett, the largest volcanic edifice, consists of a main cone and a parasitic cone each with several magmatic phases. Adak is unique compared to other modern Aleutian volcanic centers in that it contains two xenolith suites (Conrad and Kay, 1984; Debari et al., 1987). One suite consisting predominantly of mafic xenoliths occurs on Mount Moffett whereas an assemblage of ultramafic and mafic xenoliths is found on Mount Adagdak. Lavas erupted at Adak span the compositional range from 48.4 to 65.0 wt.% SiO2 and are characterized by significant variations in Al2O3, MgO, Sr, Ni and Cr. On Harker diagrams, this variability produces compositional trends with significant scatter. The Adak suite has total REE contents that vary from 32 to 154 ppm but do not correlate systematically with silica. (LaYb)n ratios range from 2.41 to 21.72 with the majority of lavas between 2.41 and 6.06. On process identification diagrams, the Adak suite plots as steeply sloping trends that contrast with the horizontal patterns of most other Aleutian centers. Measured isotopic ranges are large and nearly equal to those for the entire arc. Although they span similar silica ranges, subtle geochemical and isotopic differences distinguish the different volcanic vents of Adak. On Mount Moffett, a geochemically and isotopically distinct group of andesites (55.5–57.9 SiO2), the mafic andesites, occur on its NE flank. These lavas have elevated MgO, Ni and Cr but are depleted in Al2O3 relative to other Mount Moffett andesites with similar silica. They also have more heterogeneous REE abundances and isotopic ratios than most of the other andesites. Significant compositional differences exist between Adak and the other volcanic centers of the central Aleutian arc. Although these differences are characteristic of all geochemical systems, they are greatest for major and rare-earth elements and isotopic ratios. The lack of coherent relationships on major- and trace-element Harker diagrams, the isotopic variability, as well as the steeply sloping trends on REE process identification diagrams suggest that the Adak volcanic suite was not formed predominantly by closed-system crystal fractionation, but must be the product of a complex open-system process(es). The significant isotopic variability displayed by the suite suggests that contamination by an isotopically distinct contaminant must also have been an important petrologic component in the evolution of the suite. REE data are also suggestive of a role for magma mixing. Such a complex petrologic evolution is consistent with an immature lithospheric plumbing system. Based on REE systematics, the xenolith suites of Adak cannot, as previously proposed, be related to the host lavas or the rest of the Adak suite through crystal fractionation schemes. Rather they are probably accidental fragments derived from various depths along lithospheric conduits. In light of their relation to xenolith-bearing units, the mafic andesites of Adak presumably represent hybrid magmas formed during the interaction of ascending magmas with lithospheric wall rock. They are, therefore, characteristic of immature volcanic centers and unlikely to be related directly to the magmatic processes responsible for the generation of primary arc magmas. Because of the close proximity of the vents and the subtle compositional differences between their lavas, the Adak volcanic center was probably supplied by a single, deep lithospheric plumbing system that fed separate crustal magma chambers. The absence of historic volcanic activity on Adak suggests this plumbing system was abandoned before complete conduit development. This decline in magmatism may reflect a re-adjustment of volcano spacing within this part of the Aleutian arc.