Normative Composition Research Articles

CIPWFULL: A Software Program for Calculation of Comprehensive CIPW Norms of Igneous Rocks

CIPWFULL is a user-friendly, stand-alone FORTRAN program designed to calculate comprehensive CIPW normative compositions of igneous rocks and adheres strictly to the original formulation of the CIPW protocol. This adherence alleviates inaccuracies in norms generated by current programs. Additionally, several important petrological and mineralogical parameters are calculated by the program. Along with major element oxides, all significant minor elements affecting CIPW norms are considered. CIPWFULL also calculates oxidation ratios for rocks reporting only one oxidation state of iron. It also provides an option for normalization of analyses to unity facilitating comparison of norms among rock suites. Other capabilities of the program cater to rare situations, like presence of cancrinite and exclusion of rare rocks from norm calculations. CIPWFULL is very efficient and flexible and allows for a user-defined free-format input of elements, and it permits feeding of minor elements in different notations. Results of calculations are printed in a formatted ASCII text file and may be casted into a space-delimited text file ready for export to general spreadsheet programs. CIPWFULL is implemented on the WINDOWS platform. The program source code resides on the journal web site.

In the Aftermath of Critique We Are Not in Epistemic Free Fall: Human Rights, the Subaltern Subject, and Non-liberal Search for Freedom and Happiness

The article challenges the claim that human rights, which have constituted one of the central tools by which to establish the truth claims of modernity, can produce freedom and meaningful happiness through the acquisition of more rights and more equality. Third World, postcolonial and feminist legal scholars have challenged the accuracy of this claim, amongst others. The critiques expose the discursive operations of human rights as a governance project primarily concerned with ordering the lives of non-European peoples, rather than a liberating force; and that the pre-given rational subject of human rights is contingent and one of the prime effects of power. I examine the problems with the liberal humanism of human rights by examining not only how it is linked to a specific understanding of the `good life’, freedom and happiness, but also how it closes off other emancipatory possibilities. The acquisition of human rights as objects that an individual has by virtue of being human, represent the terminal limits of human rights, rather than the moment when the human subject becomes empowered and liberated. I draw on queer affect theory to make a critique of happiness, to which I argue human rights are linked, and how the failed or unhappy subaltern subject exposes its normative composition. I discuss the resulting depth of the despair produced from the realisation that this political project cannot realise its promise of freedom and meaningful happiness, compelling a `turn away’ from human rights as an emancipatory project and a `turn towards’ other non-liberal philosophical traditions, in the search for alternative understandings of and space for freedom and happiness. I explore these possibilities specifically within the philosophical tradition of non-dualism (Advaita).

Experimental melting of hydrous peridotite–pyroxenite mixed sources: Constraints on the genesis of silica-undersaturated magmas beneath volcanic arcs

The most primitive arc magmas expressed as melt inclusions in forsteritic olivine display silica-undersaturated, nepheline normative compositions, sometimes associated with high CaO contents. Involvement of a heterogeneous mantle source containing an amphibole-bearing clinopyroxene-rich component is often mentioned to account for the origin of these magmas. However, the proportions and the role of such mantle source component in arc magma genesis remains a matter of debate. To better understand the generation of silica-undersaturated magmas in arcs and the role of clinopyroxenites during arc magma genesis, we have performed melting experiments on a heterogeneous hydrous mantle (hydrous lherzolite mixed with variable amounts of amphibole-bearing clinopyroxenite) at 1 GPa under oxidizing conditions (close to the fayalite–magnetite–quartz: FMQ-buffer). Unlike under anhydrous conditions, pyroxenites and peridotites have similar solidus temperatures under hydrous conditions, but the melt productivity still increases with increasing fraction of pyroxenite in the source. For peridotite-rich sources (up to 50% clinopyroxenite) the presence of orthopyroxene buffers the partial melts to compositions identical in terms of major elements to regular peridotite melts. When orthopyroxene leaves the residue (above 50% of pyroxenite), melts become nepheline-normative, with CaO/Al2O3 ratios >1. Comparison between experimental melts produced by melting homogeneous mixed sources (homogeneous melting) and aggregated melts from heterogeneous sources (heterogeneous melting) shows that the later are more silica-undersaturated and richer in CaO. Our experiments confirm that nepheline-normative melt inclusions have sampled pure or poorly-mixed clinopyroxenite melts from a heterogeneous mantle source, while hypersthene-normative lavas are likely to result from a more advanced stage of magma mixing. Amphibole–clinopyroxenite heterogeneities in the mantle wedge could originate by density-driven delamination of lower crustal cumulates consisting of clinopyroxene + amphibole ± olivine. Partial melts of these cumulates can be efficiently extracted and suffer only little interaction with surrounding peridotites before their entrapment as melt inclusions; alternatively, they can react with peridotite to form secondary orthopyroxene-free metasomatic veins, which may also contribute to the source of silica-undersaturated arc magmas.

Les Basaltes de l’Atlas de Béni-Mellal (Haut Atlas Central, Maroc): un Volcanisme Transitionnel Intraplaque Associé aux Stades de L’évolution Géodynamique du Domaine Atlasique

The basaltic rocks emitted at the synclinal basins of the Atlas of Beni-Mellal, show entablatures shapes constituted by interbedded lava flow successions with red silted-sandstone layers (Red Beds). In the synclinal basins of the area, basaltic lavas form two volcanic sequences B1 and B2 which correspond to distinct volcanic events. Pyroclastic deposits are rare. Basaltic outcrops show no pillow lavas. The lava flows were emplaced while the sediments were still soft and unconsolidated. The original flows fissure bet up to the open air, or under very shallow water. Ages of basaltic flows grouped around two distinct values t hat correspond to the Middle Jurassic (B1 basalts) and to the last of the Lower Cretaceous (B2 basalts). Basaltic rocks consist of olivine basalt. Textures are variable and dependent of the type of structure. Lavas flows typically show porphyritic texture at the bottom of entablatures, fluidal structure in its inner parts and vesicules at its upper zone. Clinopyroxene compositions range from augite in B1 to diopside in B2 basaltic horizons. Whole rock compositions mark the transitional character of these volcanic rocks. Normative composition show low nepheline contents (≤ 5%). LREE/HREE ratios are low and clearly less enriched than those obtained for alkaline magmatic series. Spidergram spectra are similar to those of Oceanic Island basalts (OIB). The relative geochemical dissimilitude reported at the both basaltic sequences B1 and B2, indicate, eventually, the changing of the magmatic regime, which becomes from tholeiitic to purely alkaline in Cenozoic, in relation to the geodynamic evolution of atlasic domain. This geodynamic and geochemical evolution is ruled by two major events: the opening of the Central Atlantic and the Mediterranean convergence.

The Chaitén rhyolite lava dome: Eruption sequence, lava dome volumes, rapid effusion rates and source of the rhyolite magma

We use geologic field mapping and sampling, photogrammetric analysis of oblique aerial photographs, and digital elevation models to document the 2008-2009 eruptive sequence at Chaiten Volcano and to estimate volumes and effusion rates for the lava dome. We also present geochemical and petrologic data that contribute to understanding the source of the rhyolite and its unusually rapid effusion rates. The eruption consisted of five major phases: 1. An explosive phase (1-11 May 2008); 2. A transitional phase (11-31 May 2008) in which low-altitude tephra columns and simultaneous lava extrusion took place; 3. An exogenous lava flow phase (June-September 2008); 4. A spine extrusion and endogenous growth phase (October 2008-February 2009); and 5. A mainly endogenous growth phase that began after the collapse of a prominent Peleean spine on 19 February 2009 and continued until the end of the eruption (late 2009 or possibly earliest 2010). The 2008-2009 rhyolite lava dome has a total volume of approximately 0.8 km3. The effusion rate averaged 66 m3s-1 during the first two weeks and averaged 45 m3s-1 for the first four months of the eruption, during which 0.5 km3 of rhyolite lava was erupted. These are among the highest rates measured world-wide for historical eruptions of silicic lava. Chaiten’s 2008-2009 lava is phenocryst-poor obsidian and microcrystalline rhyolite with 75.3±0.3% SiO2. The lava was erupted at relatively high temperature and is remarkably similar in composition and petrography to Chaiten’s pre-historic rhyolite. The rhyolite’s normative composition plots close to that of low pressure (100-200 MPa) minimum melts in the granite system, consistent with estimates of approximately 5 to 10 km source depths based on phase equilibria and geodetic studies. Calcic plagioclase, magnesian orthopyroxene and aluminous amphibole among the sparse phenocrysts suggest derivation of the rhyolite by melt extraction from a more mafic magmatic mush. High temperature and relatively low viscosity enabled rapid magma ascent and high effusion rates during the dome-forming phases of the 2008-2009 eruption.

Geochemistry of Proterozoic granitoids exposed between Dirang and Tawang, western Arunachal Himalaya, north-eastern India: petrogenetic and tectonic significance

Major and trace element geochemistry of Proterozoic granitoids from the Dirang and Galensiniak Formations, of Lesser and Higher Himalayas, respectively, emplaced in and around Dirang and Tawang regions of the western Arunachal Himalaya, is discussed. In general, these granitoids are massive as well as foliated in nature and are characterized by granitic mineralogical compositions. Porphyritic and hypidiomorphic textures are common in massive type, whereas others show porphyroblastic and foliated textures. Augen structure is also observed in a number of samples. Geochemical and normative compositions together with petrographic features classify them as peraluminous granitoids. Major and trace element geochemistry of most of these granitoids shows granitic nature, while few samples also show monzonitic characteristics. Observed geochemical characters, such as their peraluminous and alkali-calcic/calcic-alkalic nature, crudely defined geochemical patterns, different multi-element and rare-earth element patterns, together with low Mg# (Mg number) of these granitoids suggest their derivation from lower crustal material rather than a mantle source. Multi-element and rare-earth element patterns corroborate their genesis from different crustal melts. It is difficult to explain variations observed in granitoid rocks by partial melting alone; definitely different other processes like migration of melts, magma mixing, assimilation and fractional crystallization also played important role in the genesis of these granitoids. These melts were likely generated at low temperature (730–760 °C) and low pressure (2–5 GPa). The chemical compositions suggest that most of these Paleoproterozoic granitoids are emplaced within the syn-collisional tectonic setting, while few granitoid samples also indicate their volcanic-arc nature. Probably, later group of granitoids are slightly younger to the syn-collisional type.

Metasedimentary rocks from the Bol’shoi Cheremshan Group in the East European Platform basement: Initial mineral composition and petrogeochemical properties

The initial normative mineral composition of some metasedimentary rocks (high-alumina crystalline schists, aluminous gneisses, and eulysites) from the Archean Bol’shoi Cheremshan Group is considered. Based on some data (distribution of data points available for these rocks in diagnostic diagrams, values of several indicator ratios, and initial rock composition), it is assumed that examined rocks were partly formed after highly mature sediments (high-alumina crystalline schists and gneisses), while biotite-garnet-andesine gneisses represent products of graywacke sediments. Elevated concentrations of some indicator elements (Fe, Cr, Ni, V, Zn, Pb, and others) imply that material in the sedimentation paleobasin was likely derived from provenances composed of variable lithologies (ultramafic, mafic, intermediate, and acid rocks). It seems that conditions in this paleobasin were favorable for the development of organic life. It is shown that correlation between some elements (Ti, V vs. Al; Ba, Pb vs. K; Sr vs. Ca; La vs. Na; and others) typical of Phanerozoic sedimentary rocks is also observed in the rocks. The possible contents of organic matter (Corg) and U in primary sediments of metasedimentary rocks of the Bol’shoi Cheremshan Group in the East European Platform basement are reconstructed.

Exception handling in pervasive service composition using normative agents

The full integration of pervasive computing services into daily life leads to smart spaces with a wide range of intelligent devices that must be dynamically composed to provide a transparent service to users. To achieve this, pervasive services have to coordinate among themselves in both an automated and autonomous manner, with the aim of satisfying complex user requirements that no single service can fulfill. However, existing pervasive environments are normally ad-hoc and isolated systems incapable of: 1) reacting to dynamic and unforeseen situations that may raise exceptions, and 2) collaborating with pervasive services beyond their physical limits. The contributions of this work are: 1) Proposing a normative agent-based service composition method capable of handling exceptions in open pervasive systems. 2) Using the Web as the underlying infrastructure where pervasive services provided by either smart devices or web services can coexist and interact with each other. 3) Providing a modular and hierarchical agent coordination method based on virtual organizations to sustain coordination among agents belonging to multiple organizations (smart spaces). 4) Integrating exception handling mechanisms based on social norms and formalized by event calculus predicates into virtual organizations to support and guide exception handling in both a dynamic and autonomous manner.

A topaz- and amazonite-bearing leucogranite pluton in eastern Xinjiang, NW China and its zoning

The highly evolved Baishitouquan (BST) beryl-mineralised and topaz-bearing amazonite granite pluton is situated in the eastern Tianshan orogen of northwestern China. This pluton exhibits five well-exposed lithological zones, which, gradational from the lowest level, are leucogranite (zone-a), amazonite-bearing granite (zone-b), amazonite granite (zone-c), topaz-bearing amazonite granite (zone-d) and topaz albite granite (zone-e). The rocks are composed mainly of quartz, albite, and K-feldspar with varying amounts of topaz and amazonite. Quartz and topaz phenocrysts are the earliest phases that crystallised from the melt. Amazonite which replaced albite and K-feldspar was formed at the late magmatic stage or during the magmatic-hydrothermal transition. Geochemically, this pluton is characterised by high F (>2 wt.%) and Rb (499.5–1087.04 ppm), low P 2O 5 (⩽0.06 wt.%), Na 2O > K 2O, A/NKC = 1.00–1.11, low ratios of K/Rb, Al/Ga, Y/Ho, Zr/Ha and Nb/Ta, Σ14 REE = 28.6–231.9 ppm with gull wing-shaped distribution patterns (La CN/Lu CN = 0.11–0.68, Eu/Eu * = 0.0005–0.0110) and tetrad effects, and δ 18O = 9.75–7.32‰. Melt and fluid-melt inclusions coexist with liquid and vapour inclusions. The rocks were originated from a highly evolved granitic magma. The BST pluton exhibits transition in the following aspects from zone-a to zone-e: (1) As quartz and topaz phenocrysts progressively increase in size and crystal euhedral shape, rock textures change from equigranular to porphyritic. (2) Amazonite begins to appear in zone-b and becomes most concentrated in zone-c, whereas topaz begins to appear in zone-d becoming highly concentrated in zone-e. (3) Li and (Al + Ti) increase in white mica. (4) Petrochemically, there are general trends of increasing F, Al 2O 3 and Na 2O, and decreasing SiO 2, (Fe 2O 3 + FeO + MgO + MnO) and K 2O. Plots of normative compositions on the Qz–Ab–Or diagram move gradually towards the Ab apex. (5) Overall, Cr, Ni, Co, V, W, Nb, Zr, U, Th and Y decrease, while F, Li, Rb, Hf, Ta, Sn, Sc, Ga and Zn increase. (6) K/Rb, Al/Ga, Nb/Ta, Zr/Hf and Y/Ho decrease, and K/Cs, Th/U (La/Lu) CN and TE 1,3 (quantification factor of REE tetrad effect) increase. (7) There is a general decrease in whole-rock δ 18O from 9.25‰ to 9.75‰ in zone-a to 7.32‰ in zone-e. (8) Homogenization temperatures of melt inclusions in quartz decrease from about 860 °C for zone-a to about 660 °C for zone-e. It is interpreted that crystallisation of the magma started from zone-a and proceeded upwards to zone-e, and the vertical zoning is produced by fractional crystallisation accompanied by fluid-melt interaction. Some of the distinctive features of zone-e were caused by influx and reaction of meteoric fluid at the post-magmatic stage. Turbulent structures and co-magmatic deformation textures are well recorded in the rocks, and are ascribed to reduced viscosity and enhanced flow rate of the F- and H 2O-rich magma.

Petrological and Geochemical Characteristics of Intrusive Rocks Related to Porphyry Copper Mineralization and the Implications for the Genesis of Deposits in the Namosi area, Viti Levu, Republic of the Fiji Islands

AbstractIn the Namosi district, of Viti Levu Island, Republic of the Fiji Islands, we conducted chemical analysis on intrusive rocks and attempted to clarify the relationship between petrological characteristics and mineralization. Samples were collected from the Waisoi copper deposit, Waivaka corridor, Waisomo, Wailutelevu and Wainabama Southwest localities. The intrusive rocks in the district show the overall characteristics of calc‐alkaline magnetite series. Using the normative composition diagram for granite classification, most of the intrusive rocks plot in the tonalite, granodiorite, quartz monzodiorite and quartz diorite fields. Rare earth element (REE) analysis revealed that at Waisoi the intrusive rocks tend towards an Eu positive anomaly, whereas most of those at Waisomo tend to have a negative anomaly. The (Cecn/Ybcn)/Ybcn ratio shows that the intrusive rocks in the Namosi district may be derived from a mantle origin magma possibly contaminated by crustal materials. Waisoi rocks have less contamination with continental crust and show higher gold content compared to those of the Waivaka corridor. The observed differences between Waisoi and Waivaka corridor in the Cu/Au ratio might also be caused by varying amounts of contamination by crustal materials. There is no clear correlation between the La/Yb ratio and K–Ar ages, however, the La/Yb ratio of the Waivaka corridor rocks has a wide range, suggesting a variable amount of crustal contamination of the magma from 7 to 5 Ma. The less crustal contamination and generation of relatively high silica contents under relatively oxidized conditions in the Waisoi magmas is correlated with Au‐rich porphyry copper mineralization and in contrast more crustal contamination produced Au‐poor porphyry copper mineralization at the Waivaka Corridor in the Namosi district.

The pattern of Ni and Co abundances in lunar olivines

Near liquidus experiments on peridotite and other olivine normative compositions from 1.7 to 6 GPa confirm the applicability of exchange-based empirical models of Ni and Co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite. Given that most estimates of lunar bulk composition are peridotitic, the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization. Calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean, initially 700 km deep, reveals a prominent maximum in Ni concentration versus fraction crystallized or Mg’ (molar MgO/(MgO + FeO)), but a pattern of monotonically increasing Co concentration. These patterns qualitatively match the puzzling patterns of Ni and Co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower Ni and Co abundances than do less magnesian olivines from low-Ti mare basalts, and olivines from the ferroan anorthosite suite (FAS) have lower Ni, but similar Co to mare basalt olivines. The Ni and Co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine-orthopyroxene (harzburgite) layer that is in turn overlain by an upper zone of plagioclase-bearing cumulates. The ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer, which later becomes a portion of the green glass source region, to the bottom of the cumulate pile with Ni- and Co-rich olivine. Meanwhile, the less dense, but hottest, most magnesian olivines with much lower Ni and Co abundances are transported upward to the base of the plagioclase-bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite, norite, and gabbronorite with KREEP (a K–REE–P enriched component widely believed to be derived from the very latest stage magma ocean liquid). These hybrid melts have Al 2O 3, Ni, and Co abundances and Mg’ appropriate for parent magmas of the magnesian suite. Ni and Co abundances in the FAS are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite–norite mixtures without KREEP.

Sr, Nd and Pb isotopic and geochemical constraints for the origin of magmas in Popocatépetl volcano (central Mexico) and their relationship with the adjacent volcanic fields

We present new geochemical data (major- and trace-elements, as well as Sr and Nd isotopic compositions) of volcanic rocks erupted from Popocatépetl volcano during the volcanic event from December 2000 to January 2001. These data along with an exhaustive compilation of geochemical and Sr, Nd, and Pb isotope data reported for Popocatépetl rocks and nearby volcanic areas are used to examine the origin and geochemical evolution of the magmas in the central Mexican volcanic belt (CMVB). During this period of volcanic eruptions Popocatépetl produced ash columns as high as 7 km. Pyroclastic flows and lahars were observed after the completion of the activity. Samples of banded pumice and a bomb fragment transported by the lahar were chemically analysed for this work. Rocks show an andesitic composition with 58.5–61.7 wt.% SiO2 and 5.9–4.0 wt.% MgO. Contents of large ion lithophile elements (LILE), rare-earth elements (REE) and Zr are nearly constant through the compositional range. No significant Eu anomaly is present, but the samples show Nb-anomaly relative to LILE and high-field strength elements (HFSE). Nd- and Sr-isotopic compositions of these samples range from 143Nd/144Nd = 0.51291 to 0.51287 and 87Sr/86Sr = 0.70399 to 0.70422. Comparison of Popocatépetl products with volcanic rocks from the nearby areas shows that the magmas in CMVB were generated in a heterogeneously veined-mantle source enriched in LILE, HFSE, and REE. Additional crustal assimilation as well as fractional crystallization could account for the great chemical variability of rocks in the CMVB. Statistical comparison of the geochemical compositions of the volcanic products ejected from 1994 to 2000 to those ejected during the 2001 event shows that most geochemical parameters (major- and trace-elements, normative minerals, Sr and Nd isotopic composition, as well some elemental ratios) present no statistically significant differences. Statistically significant differences in the mean only were computed for the major-elements SiO2, FeO, MgO, CaO, and K2O, as well as for the rare-earth elements Nd, Sm, Eu, Gd, Dy, Ho, Tm, and Yb.

The normative mineralogy of 10 soil profiles in Fennoscandia and north-western Russia

Abstract The mineralogical composition of soil horizons in different soil types of different ages was estimated by applying the NORMA software, which was developed originally for calculating the normative mineralogical composition of young podsols. Ten soil profiles from six sites in NW Russia, two in Finland, and one in NE Norway were sampled in 1999 as a part of the pilot phase of a large geochemical mapping project. Total element concentrations were determined from the 4 extraction. Extractable concentrations for Al, Ca, Cr, Fe, K, Mn, Mg, Na, P, S, Ti, Zr, and Ba were determined by ICP-MS or ICP-AES after aqua regia (a 1:3 mixture of strong HCl and HNO 3 ) extraction. Total C was determined using a thermal conductivity detector from a sample burned in an O 2 stream. The NORMA software was used to calculate the percentage of normative soluble minerals pyrite, apatite, titanite, calcite, biotite, chlorite, weathered albite, hydrous Al-silicate, goethite and soluble residue. The percentages of non-soluble normative minerals rutile, hornblende, K-feldspar, albite, anorthite, tremolite, wollastonite, kaolinite, magnetite, zircon, quartz, carbon (graphite), and non-soluble residue were calculated after soluble minerals. The calculated mineralogical composition of C-horizon samples in each profile reflected the known geological composition of the bedrock from which the soil parent material was derived during geological processes. Secondary minerals including goethite and hydrous Al-silicates, were detected in upper soil horizons reflecting the development of soils. Rather than age, the local bedrock geology together with the mineralogical composition and chemical properties of the parent material proved to be the controlling factor in the formation of secondary minerals. The results showed that the NORMA method can be used in defining the mineralogy of soil horizons in a large variety of soil types.

Mineralogy of volcanic rocks in Gusev Crater, Mars: Reconciling Mössbauer, Alpha Particle X‐Ray Spectrometer, and Miniature Thermal Emission Spectrometer spectra

Complete sets of mineral abundances for relatively unaltered volcanic or volcaniclastic rocks in Gusev Crater have been determined by modeling Mössbauer subspectral areas as mineral weight percentages, and combining those percentages with the proportions of iron‐free minerals not detected by Mössbauer (normative plagioclase, apatite, and chromite, as calculated from Alpha Particle X‐Ray Spectrometer (APXS) chemical analyses). Comparisons of synthetic thermal emission spectra calculated for these mineral modes with measured Miniature Thermal Emission Spectrometer (Mini‐TES) spectra for the same rock classes show either good agreements or discrepancies that we attribute to sodic plagioclase compositions or unmodeled sulfate, glass, or pigeonite. The normative compositions of olivine, pyroxene, and feldspar calculated from APXS data are consistent with spectroscopic constraints on mineral compositions. Systematic variations between olivine abundances in APXS norms (which sample tens of micrometers depth) and olivine proportions measured by Mössbauer (which sample hundreds of micrometers depth) support the hypothesis that dissolution of olivine by acidic fluids has occurred on weathered rock surfaces.

O granito de duas micas Ney Peixoto, nordeste do Pará: aspectos petrológicos e significado tectônico

The Ney Peixoto granite crops out on the left side of the Guama river, between the cities of Ourem and Sao Miguel do Guama, NE of Para state. It is the only granitic intrusion of Brasiliano age (549 ± 5 Ma) known in the Gurupi region, which was essentially built up during the Paleoproterozoic era. Despite an outcropping area of about 6 km 2 , the contacts with its host rocks cannot be observed due to the alluvium and colluvium cover. This intrusion is slightly foliated and locally banded, having an average modal composition of 35.2% quartz, 32.8% microcline, 20.4% oligoclase, 5.9% muscovite and 5.4% biotite. Its peraluminous rocks (A/CNK > 1.1), which are rich in SiO 2 , Al 2 O 3 , K 2 O and Na 2 O, and poor in MgO and CaO, show normative composition close to the ternary minimum of the SiO 2 -K 2 O-Na 2 O-H 2 O system. Among the trace elements, Ba, Rb, Sr and Zr are the most abundant, affording Rb/Sr and Sr/Ba ratios that range from 0.7 to 1.2 and from 0.24 to 0.37, respectively. The distribution pattern of the rare earth elements displays a moderate fraccionation of the LREE relative to the HREE (La n /Yb n = 27 a 75,5) and a moderate negative Eu anomaly (Eu n /Eu * = 0,46 a 0,62). Derived from a Paleoproterozoic crust, the Ney Peixoto granite was most likely generated by partial melting of the Jeritequara Formation mica-schists of the Gurupi Group. No significant differentiation trend is apparent from bivariate plots using major or trace elements, although FeOt + MgO + TiO 2 decreases as silica increases. This behavior may be due to the variable proportions of biotite in the rock samples. On the other hand, pegmatite pods might represent the residual liquids of the magma crystallization which became so deprived of Fe and Mg that biotite could no longer precipitate. The conditions for the magma crystallization were estimated at temperatures of 600-650°C under pressures around 5 kbar. The mineralogical, structural and chemical characteristics of the Ney Peixoto body, in particular its Nb, Y and Rb contents, allow to interpret it as a syn-collisional intrusion, suggesting a thickening of the crust of the Gurupi region also in Neoproterozoic times.

O granito de duas micas Ney Peixoto, nordeste do Pará: aspectos petrológicos e significado tectônico

The Ney Peixoto granite crops out on the left side of the Guamá river, between the cities of Ourém and São Miguel do Guamá, NE of Pará state. It is the only granitic intrusion of Brasiliano age (549 ± 5 Ma) known in the Gurupi region, which was essentially built up during the Paleoproterozoic era. Despite an outcropping area of about 6 km 2 , the contacts with its host rocks cannot be observed due to the alluvium and colluvium cover. This intrusion is slightly foliated and locally banded, having an average modal composition of 35.2% quartz, 32.8% microcline, 20.4% oligoclase, 5.9% muscovite and 5.4% biotite. Its peraluminous rocks (A/CNK > 1.1), which are rich in SiO 2 , Al 2 O 3 , K 2 O and Na 2 O, and poor in MgO and CaO, show normative composition close to the ternary minimum of the SiO 2 -K 2 O-Na 2 O-H 2 O system. Among the trace elements, Ba, Rb, Sr and Zr are the most abundant, affording Rb/Sr and Sr/Ba ratios that range from 0.7 to 1.2 and from 0.24 to 0.37, respectively. The distribution pattern of the rare earth elements displays a moderate fraccionation of the LREE relative to the HREE (La n /Yb n = 27 a 75,5) and a moderate negative Eu anomaly (Eu n /Eu * = 0,46 a 0,62). Derived from a Paleoproterozoic crust, the Ney Peixoto granite was most likely generated by partial melting of the Jeritequara Formation mica-schists of the Gurupi Group. No significant differentiation trend is apparent from bivariate plots using major or trace elements, although FeOt + MgO + TiO 2 decreases as silica increases. This behavior may be due to the variable proportions of biotite in the rock samples. On the other hand, pegmatite pods might represent the residual liquids of the magma crystallization which became so deprived of Fe and Mg that biotite could no longer precipitate. The conditions for the magma crystallization were estimated at temperatures of 600-650°C under pressures around 5 kbar. The mineralogical, structural and chemical characteristics of the Ney Peixoto body, in particular its Nb, Y and Rb contents, allow to interpret it as a syn-collisional intrusion, suggesting a thickening of the crust of the Gurupi region also in Neoproterozoic times.

Basalt magma genesis and fractionation in collision- and extension-related provinces: A comparison between eastern, central and western Anatolia

Experimental studies of synthetic and natural basalt systems suggest that conditions of magma genesis and fractionation depend fundamentally on mantle temperatures and lithospheric stress fields. In general, compressional settings are more conducive to polybaric fractionation than extensional settings and in this regard, the Anatolian magmatic province offers a natural laboratory for comparing near-coeval basalt eruptions as a function of regional tectonics — compressional (collision-related) régimes dominating in eastern Anatolia and extensional tectonics characterizing a western province related to Aegean Sea opening. Projection of Plio-Quaternary basalt normative compositions from the Western Anatolia Extensional Province (WAEP), the Central Anatolian ‘Ova’ Province (CAOP), and Eastern Anatolia Compressional Province (EACP) are projected onto Ol–Ne–Cpx and Pl–Cpx–Ol planes in the simplified basalt system (Ne–Cpx–Ol–Qz), each showing distinctive liquid lines of descent. WAEP basalts are mostly constrained by low-pressure (< 0.5 GPa) cotectics while CAOP and EACP compositions conform to moderate and/or high-pressure (0.8–3.0 GPa) cotectics. Overall, a quasi-linear shift from moderate and/or high-pressure to low-pressure equilibria matches the westward transgression from compressional east Anatolia to the extensional west Anatolian–Aegean region. Comparison of their respective primary (mantle-equilibrated) magmas–simulated by normalizing their compositions to MgO = 15 wt.% (Mg-15)–with parameterized anhydrous and H 2O-undersaturated experimental melts suggests they segregated from spinel- to garnet-lherzolite mantle facies at pressures between c. 2 and 3 GPa (c. 70–100 km depth) under H 2O-undersaturated conditions. Interpolated potential temperatures ( T p) and lithospheric stretching factors ( β) range as follows: (1) eastern Anatolian basalts associated with the Arabian foreland show T p varying between 1250 and 1400 °C (except for the Karacalidag alkali basalts, south of the Bitlis–Zagros fracture zone, for which T p ranges up to 1450 °C), for β values of 1.2–1.8. T p values for central Anatolia (e.g. Sivas) range between 1300 and 1375 °C (except for Karapinar, Egrikuyu and Hasandag, which show < 1150 °C), and β values of 1.3–1.4. For western Anatolian basalts, T p range mostly between 1250 and 1330 °C, except for a single value for Canakkale of 1400 °C and Kula sample showing T p < 1200 °C, and β values of 1.3–2.0. Variation of these conditions is as great or greater than that between provinces, although there are clearly significant constraints on the inferred polybaric to low-pressure isobaric fractionation régimes. Covariation of total FeO, TiO 2, La/Yb, Ce/Sm, Zr/Y and Zr/Nb reflects small but significant differences in bulk composition and ambient melt fraction while the covariance of Ce/Sm and Sm/Yb is consistent with the segregation of primitive melts at the spinel- to garnet-lherzolite transition.

Crustal contamination of Late Neogene basalts in the Dien Bien Phu Basin, NW Vietnam: Some insights from petrological and geochronological studies

Early Pliocene (Zanclean) basalts in the Dien Bien Phu pull-apart basin in NW Vietnam, associated with the presently sinistral Dien Bien Phu Fault Zone, have been dated by the K–Ar method at 4.4–4.9 and 5.4–5.2 Ma. Rapid migration of basaltic magma to the surface in the Dien Bien Phu Fault Zone may be due to Pliocene transtension of the crust in this region, resulting from asthenospheric upwelling induced by lateral displacement of the mantle. The basalts are moderately phyric ( < 10%) and consist of olivine (hyalosiderite), plagioclase (bytownite–labradorite) and orthopyroxene (bytownite–labradorite) phenocrysts, and a fine-grained crystalline matrix (olivine–hortonolite, plagioclase–labradorite, clinopyroxene–pigeonite and augite, K-feldspar). The presence of Fe-rich olivine and orthopyroxene phenocrysts indicates that the basalts are SiO 2-saturated/oversaturated olivine tholeiites which formed under water-undersaturated conditions. The Dien Bien Phu basalts contain both mantle-derived (pyroxenites, dunites, gabbros) and crustal (sillimanite/mullite + Mg–Fe spinel), wallrock xenoliths, indicative of crustal contamination during the ascent of the basaltic magma. The basalts show selective enrichment in some mobile elements (K, Rb, Sr and Th), a feature considered to be a result of metasomatism. These rocks, classified on the basis of their normative composition as quartz tholeiites, could represent primary olivine tholeiites/basalts, in which the geochemical signatures were modified by the processes of contamination.

Chondrules in the CB/CH-like carbonaceous chondrite Isheyevo: Evidence for various chondrule-forming mechanisms and multiple chondrule generations

The recently discovered metal-rich carbonaceous chondrite Isheyevo consists of Fe, Ni-metal grains, chondrules, heavily hydrated matrix lumps and rare refractory inclusions. It contains several lithologies with mineralogical characteristics intermediate between the CH and CB carbonaceous chondrites; the contacts between the lithologies are often gradual. Here we report the mineralogy and petrography of chondrules in the metal-rich (∼70 vol%) and metal-poor (∼20 vol%) lithologies. The chondrules show large variations in textures [cryptocrystalline, skeletal olivine, barred olivine, porphyritic olivine, porphyritic olivine-pyroxene, porphyritic pyroxene], mineralogy and bulk chemistry (magnesian, ferrous, aluminum-rich, silica-rich). The porphyritic magnesian (Type I) and ferrous (Type II) chondrules, as well as silica- and Al-rich plagioclase-bearing chondrules are texturally and mineralogically similar to those in other chondrite groups and probably formed by melting of mineralogically diverse precursor materials. We note, however, that in contrast to porphyritic chondrules in other chondrite groups, those in Isheyevo show little evidence for multiple melting events; e.g., relict grains are rare and igneous rims or independent compound chondrules have not been found. The magnesian cryptocrystalline and skeletal olivine chondrules are chemically and mineralogically similar to those in the CH and CB carbonaceous chondrites Hammadah al Hamra 237, Queen Alexandra Range 94411 (QUE94411) and MacAlpine Hills 02675 (MAC02675), possibly indicating a common origin from a vapor–melt plume produced by a giant impact between planetary embryos; the interchondrule metal grains, many of which are chemically zoned, probably formed during the same event. The magnesian cryptocrystalline chondrules have olivine–pyroxene normative compositions and are generally highly depleted in Ca, Al, Ti, Mn and Na; they occasionally occur inside chemically zoned Fe, Ni-metal grains. The skeletal olivine chondrules consist of skeletal forsteritic olivine grains overgrown by Al-rich (up to 20 wt% Al 2O 3) low-Ca and high-Ca pyroxene, and interstitial anorthite-rich mesostasis. Since chondrules with such characteristics are absent in ordinary, enstatite and other carbonaceous chondrite groups, the impact-related chondrule-forming mechanism could be unique for the CH and CB chondrites. We conclude that Isheyevo and probably other CH chondrites contain chondrules of several generations, which may have formed at different times, places and by different mechanisms, and subsequently accreted together with the heavily hydrated matrix lumps and refractory inclusions into a CH parent body. Short-lived isotope chronology, oxygen isotope and trace element studies of the Isheyevo chondrules can provide a possible test of this hypothesis.

A method to estimate hydraulic conductivity from bulk geochemical compositions

A new method has been developed to estimate the hydraulic conductivity in unconsolidated aquifers. The method uses bulk geochemical compositions correlated with hydraulic conductivities measured by pumping tests. The concept is based on a general rule that hydraulic conductivity is principally controlled by grain-size distribution and particle shape,both of which relate to mineralogical composition. Using a MINLITH algorithm, normative mineralogical compositions can be derived from bulk geochemical compositions economically and expediently, and then correlated to the hydraulic conductivity determined by pumping tests in the field. In this study, 202 sediment samples from nine unconsolidated aquifers were analyzed by X-ray fluorescence. Although hydraulic conductivity does not show a definite relationship with geochemical compositions, it does demonstrate a linear logarithmic equation to the content of normative earthy minerals. However, linear regressed equations should not be applied to aquifers composed of medium to coarse sand and gravel sizes due to interference from lithic fragments. In addition, this equation tends to overestimate hydraulic conductivity possibly because the effect of compaction is ignored in this study.