Igneous Rock Types Research Articles

Petrographic Analysis and Total organic content (TOC) of Mudstone Inclusions in Igneous Intrusives in Lower Benue Trough, Nigeria

The lower Benue trough is a linear, intracratonic, graben basin, trending ne-sw. The trough is characterized by an uplifted basement block, flanked by deep basin containing about 6km of sediments. The study area which is part of the lower Benue trough comprises of igneous rock types that are predominantly intermediate to basic in nature. From petrological studies, the rocks are made up of intermediate to high temperature minerals. Total organic carbon (TOC) content tests were conducted on the mudstone inclusions in the pyroclastics, and values range from 0.60%wt0.86%wt. The classification of source quality by total organic content (TOC) percent shows that the source quality is fair. This indicates that prior to the eruption, the study area may have had higher organic carbon content but the heat that accompanied the eruption baked the source rock into mudstones thereby reducing the source rock quality. The thermal effect of the igneous intrusions may have increased the temperature above the oil window limit.

Evaluation of radiation dose due to naturally occurring radionuclides in rock samples of different origins collected from Azad Kashmir

The state of Azad Kashmir is rich in three types of rocks, namely, sedimentary, metamorphic, and igneous rocks. These rocks contain extensive deposits of graphite, marble, limestone, quartzite, granite, dolerite, and sandstone, which are widely used for the construction of dwellings in Azad Kashmir and Pakistan. Therefore, knowledge about the presence of natural radioactivity in these materials is desirable to assess the radiological hazards associated with it. In this context, 30 rock samples were collected from different geologic formations of the Muzaffarabad Division, Azad Kashmir. After processing the samples, the specific activities of 226Ra, 232Th, and 40K in them were measured using a P-type coaxial high-purity germanium detector. The observed highest dose rate values for sedimentary, metamorphic, and igneous rocks have been found to be 83.16±1.08, 135.87±1.18, and 115.98±1 nGy ⋅ h–1, respectively. The radium equivalent activity (Raeq) varied from 23.76±1.15 for dolerite sample (igneous rock) to 293.69±2.60Bq ⋅ kg–1 for marble (metamorphic rock). The Raeq values of all rock samples are lower than the limit mentioned in the Organization for Economic Cooperation and Development (OECD, 1979) report (370Bq ⋅ kg–1, equivalent to γ-dose of 1.5mSv ⋅ y–1). The values of external (Hex) and internal hazard indices (Hin) are less than unity. The mean outdoor and indoor annual effective dose equivalents are 0.073mSv ⋅ y–1 and 0.29mSv ⋅ y–1, respectively. The mean (over all types of rock samples) annual effective dose equivalent is reported as 0.36mSv ⋅ y–1.

Petrogenesis of the Early Eocene adakitic rocks in the Napuri area, southern Lhasa: Partial melting of thickened lower crust during slab break-off and implications for crustal thickening in southern Tibet

Cenozoic adakitic rocks in the Lhasa block (southern Tibet) have been widely used to trace the lateral extent of crustal thickening. However, their petrogenesis remains controversial. Here, we report geochronological and geochemical data for the Napuri intrusive rocks in the core area of the Quxu batholith, southern Lhasa. Zircon U–Pb dating suggests that they were generated at approximately 48Ma. The studied samples show significant geochemical variations, manifested by the coexistence of three types of igneous rocks. Groups I and II rocks exhibit variable and high SiO2 (66.4–73.9wt.%), high Al2O3 (14.0–17.4wt.%), K2O (3.9–5.3wt.%), Sr (273–718ppm) and Sr/Y (18.3 to 81.3) values, and low Y (3.6 to 16ppm), heavy rare earth element (REE) (e.g., Yb=0.48 to 1.8ppm), MgO (0.4–1.0wt.%), Cr (2.9–7.4ppm) and Ni (1.6–4.5ppm) contents, which are similar to those of thickened lower crust-derived adakitic rocks. The Group I rocks show higher Sr/Y (77.5–81.3) ratios and lower total REE (55.5–63.2ppm) contents with clearly positive Eu and Sr anomalies, whereas the Group II rocks have relatively lower Sr/Y (18.3–65.7) ratios and higher total REE (115–375ppm) contents with negligible or slightly negative Eu and Sr anomalies. Group III rocks have the highest SiO2 (74.5–76.0wt.%), Y (17.0–23.7ppm) and Yb (2.91–3.30ppm) contents, and the lowest Al2O3 (12.5–13.2wt.%), Sr (81.3–141ppm) and Sr/Y (4.8–5.9) values with distinctly negative Eu and Sr anomalies. Compared with the Jurassic–Cretaceous granitoids in southern Lhasa, the relative enrichment in Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i=0.7049–0.7055, εNd(t)=−0.3±0.7 and εHf(t)zircon=+3.6±11.4) for the Napuri intrusive rocks indicates that they likely contained Indian continental components. The Group I and Group II rocks most probably originated from thickened mafic lower crust (amphibolite eclogites or garnet amphibolites) with garnet+rutile±plagioclase as residual minerals in the source at >1.5GPa, corresponding to depths of >50km, and Group III rocks were probably generated by fractional crystallization of plagioclase from the adakitic magmas. Taking into account the narrow linear nature of the Eocene magmatic belt and reported synchronous asthenosphere-derived basaltic rocks in southern Lhasa, we suggest that upwelling asthenosphere triggered by the break-off of subducted Neo-Tethyan slab probably provided the required thermal conditions for lower crustal melting. The identification of Indian continental components in the Napuri intrusive rocks probably indicates that the Asia–India collision had taken place prior to their emplacement. The dramatic changes in the (La/Yb)N ratios and εNd(t) and εHf(t) values of magmatic rocks in the Gangdese area at ca. 51–46Ma indicate that the Cenozoic crustal thickening associated with the indentation of the Indian continent began in the Early Eocene (ca. 51–46Ma) at the latest.

Igneous mineralogy at Bradbury Rise: The first ChemCam campaign at Gale crater

AbstractTextural and compositional analyses using Chemistry Camera (ChemCam) remote microimager and laser‐induced breakdown spectroscopy (LIBS) have been performed on five float rocks and coarse gravels along the first 100 m of the Curiosity traverse at Bradbury Rise. ChemCam, the first LIBS instrument sent to another planet, offers the opportunity to assess mineralogic diversity at grain‐size scales (~ 100 µm) and, from this, lithologic diversity. Depth profiling indicates that targets are relatively free of surface coatings. One type of igneous rock is volcanic and includes both aphanitic (Coronation) and porphyritic (Mara) samples. The porphyritic sample shows dark grains that are likely pyroxene megacrysts in a fine‐grained mesostasis containing andesine needles. Both types have magnesium‐poor basaltic compositions and in this respect are similar to the evolved Jake Matijevic rock analyzed further along the Curiosity traverse both with Alpha‐Particle X‐ray Spectrometer and ChemCam instruments. The second rock type encountered is a coarse‐grained intrusive rock (Thor Lake) showing equigranular texture with millimeter size crystals of feldspars and Fe‐Ti oxides. Such a rock is not unique at Gale as the surrounding coarse gravels (such as Beaulieu) and the conglomerate Link are dominated by feldspathic (andesine‐bytownite) clasts. Finally, alkali feldspar compositions associated with a silica polymorph have been analyzed in fractured filling material of Preble rock and in Stark, a putative pumice or an impact melt. These observations document magmatic diversity at Gale and describe the first fragments of feldspar‐rich lithologies (possibly an anorthosite) that may be ancient crust transported from the crater rim and now forming float rocks, coarse gravel, or conglomerate clasts.

Petrographic and geochemical comparison between the Copper Age “Ljubljana type” axes and similar lithotypes from Eisenkappler Diabaszug complex (southern Austria)

The petrographic and geochemical features of “Ljubljana type” axes (including Lt1-3 groups), one of the largest assemblage of Copper Age stone artefacts in the Caput Adriae region made from magmatic and metamorphosed igneous rock types, have been compared to rocks specifically sampled from the Eisenkappler Diabaszug complex (southern Austria), recently considered as the most probable provenance area. Both the axes and the geological samples show similar mineralogical and petrographic features and are characterized by a common OIB-like signature, metamorphic and spilitization features. The collected data confirm that the Lt3 group originates from one outcrop located in the eastern part of the complex while the precise provenance of the Lt1-2 axes is still to be identified in the same geological area.

The origin of eucrites, diogenites, and olivine diogenites: Magma ocean crystallization and shallow magma chamber processes on Vesta

AbstractThe asteroid 4 Vesta is one of the very few heavenly bodies to have been linked to samples on Earth: the howardite‐eucrite‐diogenite (HED) meteorite suite. This large and diverse suite of meteorites provides a detailed picture of Vesta's igneous and postigneous history. We have used the range of igneous rock types and compositions in the HED suite to test a series of chemical models for solidification processes following peak melting (magma ocean) conditions on Vesta. Fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive Fe‐enrichment in the melt. Models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates (diogenites). Our best models invoke 60–70% equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers. Fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush (magmatic recharge) can produce all of the igneous HED lithologies (noncumulate and cumulate eucrites, diogenites, dunites, harzburgites, and olivine diogenites). Magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites. We predict an internal structure for Vesta that permits excavation of the HEDs during the formation of the Rheasilvia basin, while remaining consistent with observations from the Dawn mission and most impact models.

Timing of the formation of the Tianhuashan Basin in northern Wuyi as constrained by geochronology of volcanic and plutonic rocks

The Tianhuashan Basin is one of the most important volcanic basins in the northern Wuyi, southeastern China, comprising two successive volcanic units, the Daguding Formation and the overlying Ehuling Formation, along with several small associated igneous intrusions. The Lengshuikeng super-large-scale Ag-Pb-Zn deposit, which is closely related to these volcanic-intrusive rocks, is located in the northwestern part of the basin. In order to understand the basin evolution and magmatism, we determined LA-ICP-MS U-Pb zircon ages for the volcanic successions and associated intrusive rocks. U-Pb zircon dating of volcanic units yielded precise ages of 144±1 Ma for crystal tuff in the lower member of the Daguding Formation, 142±1 Ma for andesite within the upper member of the Daguding Formation, 140±1 Ma for tuffite of the first (i.e., lowermost) member of the Ehuling Formation, and 137±1 Ma for rhyolitic ignimbrite within the third volcano-stratigraphic member of the Ehuling Formation. Three types of intrusive igneous rocks (quartz syenite porphyry, K-feldspar granite porphyry, and rhyolite porphyry) yielded precise weighted mean 206Pb/238U ages of 144±1, 140±1, and 140±1 Ma, respectively, suggesting that these intrusions along with the aforementioned volcanics were all emplaced during the Early Cretaceous. In addition, the weighted mean 206Pb/238U ages determined on zircon from two samples of a granite porphyry intrusion, which hosts ore mineralization of the Lengshuikeng Ag-Pb-Zn deposit, are 158±1 and 157±1 Ma, indicating emplacement in the Late Jurassic. These new geochronological results for igneous rocks of the Tianhuashan Basin constrain the timing of volcanic and plutonic activity in the basin, and have important implications for our understanding the tectonic history of the region, and for identifying metallogenic types and the timing of ore deposition of the Lengshuikeng deposit.

Mineralogical and Chemical Constraints on the Provenance of Copper Age Polished Stone Axes of ‘Ljubljana Type’ from Caput Adriae

In this paper we show the results of a study concerning 42 axes, mainly discovered in the Copper Age pile dwellings of Ljubljansko barje (central Slovenia) and in the neighbouring areas of Caput Adriae. The studied shaft‐hole axes, characterized by homogeneous typology but slightly different raw materials, have been called ‘Ljubljana‐type’ axes (Lt). The raw materials show a common OIB‐like signature and metamorphic and spilitization features that recall oceanic conditions. The typological and geochemical characteristics and the very high percentage of Lt axes among the polished stone axe assemblages of Ljubljansko barje suggest that the raw material was probably gathered from one or more relatively small outcrops close to Ljubljansko barje. Similar igneous rock types outcrop in the presumably Palaeozoic diabase/shale complex (Eisenkappler Diabaszug), intruded by the northern Karawanken plutonic belt. A probable provenance from this area, particularly rich in copper ore deposit, would confirm the important role of Ljubljansko barje as a metallurgical district, as well as a strong relation between lithic raw materials and Cu cultivation districts during the Copper age.

Structural interpretation of gravity anomalies from the Kribi–Edea zone, South Cameroon: a case study

The analyses of established gravimetric anomaly maps, the multi-scale evaluation of the maxima of gradients and the quantitative interpretation of residual anomalies by spectral analysis, by the ideal body solution and by 2.5D modelling suggest the presence of contacts between rocks of different densities at different depths and a dense intrusive igneous body in the upper crust of the Kribi?Edea zone. The model obtained along our study profile shows two blocks of the same type of igneous rock with a density contrast of 0.167?g cm?3?in comparison with the density of the surrounding metamorphic rocks. The upper surfaces of these igneous blocks locally lie at depths between 0.9 and 1?km, but generally lie between depths of 3.5 and 4?km. Their lower surfaces, which are flat, lie between depths of 9 and 9.3?km. The multi-scale evaluation of the maxima of gradients reveals three contacts oriented SSW?NNE, one contact oriented N?S and one contact oriented SSE?NNW. We have given, after the analysis of the results of the multi-scale evaluation of maxima of gradients, the limit values that estimate the depth interval over which the depth to the bottom of each contact is found.

Petrology, geochemistry, and tectonic significance of Mesozoic shoshonitic volcanic rocks, Luzong volcanic basin, eastern China

We studied the geochemical characteristics of three types of Mesozoic igneous rocks from the Luzong volcanic basin: basaltic trachyandesite at Shuangmiao, pyroxene monzonite at Bajiatan, and quartz-syenite (A-type granite) at Huangmeijian. Based on analyses of whole-rock major elements, all investigated rocks are enriched in K, Na, Ti, Al, but depleted in Ca, representing a shoshonitic series. Trace element analyses show that these rocks are characterized by enrichments of large-ion lithophile elements and high field strength elements. Positive Nb and Ta anomalies in the chondrite-normalized spider diagram indicate that the shoshonitic volcanic rocks share similar features with Nb-enriched basalts, which are different from normal island-arc volcanical rocks (they are typically strongly depleted in Nb and Ta). Bulk-rock chemical compositions and Sr–Nd isotopes indicate that the three types of igneous rocks are geochemically comagmatic, suggesting that the melts were derived from an enriched mantle reservoir. We postulate an extensional tectonic setting for the formation of Luzong volcanic basin, possibly related to subduction of a palaeo-Pacific plate beneath the east Chinese continent during the Yanshanian period (Cretaceous). Therefore, the petrogenetic features of those volcanic rocks as well as A-type granites in the Luzong basin indicate that the regional large-scale Fe–Cu–Au mineralization was associated with oceanic slab melting, but not delamination or recycling of the ancient lower continental crust, as previously proposed.

U-Pb zircon age of Ordovician magmatism in the Albera Massif (Eastern Pyrenees)

New geochronological data from the Albera Massif confirm the presence of an Early – Mid Ordovician igneous event (472 - 465Ma) recorded in the pre-Variscan rocks of the Pyrenees. This event resulted in the emplacement of a large granitic body in the lower part of the pre-Upper Ordovician metasedimentary succession and in the intrusion of a series of metric sized dykes in the middle and upper parts of it. The two types of igneous rocks were gneissified during subsequent Variscan deformation. The geochronological data confirm the occurrence of the gneiss as having derived from an Ordovician intrusive sheet, as in other Pyrenean massifs. The dykes are considered to be the subvolcanic equivalent of the intrusive sheet. The data also provide insight into the age of the metasedimentary series of the massif and enable us to correlate the dated rocks with other gneissic and subvolcanic bodies of the Variscan massifs of the Pyrenees and Iberia.

Development of a New Method for Estimating the Indirect Uniaxial Compressive Strength of Rock Using Schmidt Hammer

Uniaxial compressive strength as one the mechanical properties of rock has various applications in rock engineering. This parameter can be determined directly either in laboratory tests or estimated indirectly using a cheap and conventional method such as Schmidt hammer rebound test and unit weight. Schmidt hammer rebound, unit weight, porosity and uniaxial compressive strength were determined for 104 specimens of different types of sedimentary, igneous and metamorphic rocks. Relationships of Schmidt hammer rebound value, unit weight and porosity of different types of rock and uniaxial strength were analyzed statistically using test results. Present relationships of estimating the indirect uniaxial compressive strength of rock were evaluated on the basis of the test results. Statistic analysis of the results showed that estimating indirect uniaxial compressive strength using the present relationships yields different re- sults compared to measured uniaxial compressive strength. Various relationships of estimating uniaxial compressive strength (σc) as a function of combination of three properties of Schmidt hammer rebound (Hs), unit weight (γ) and porosity (P) were applied to find improved relationships. For the relationship between uniaxial compressive strength (σc) and (Hs-P)γ a correlation (R2 =0.9501) was achieved. When effect of porosity as one of the weakness points of rock on the relationship was applied to analyze the test results, a relationship with a better correlation was obtained to estimate uniaxial compressive strength.

A Reappraisal of Redox Melting in the Earth’s Mantle as a Function of Tectonic Setting and Time

Redox melting refers to any process by which melt is generated by the contact of a rock with a fluid or melt with a contrasting oxidation state. It was originally applied to melting owing to the oxidation of reduced CH4and H2-bearing fluids in contact with more oxidized blocks in the mantle, particularly recycled crustal blocks.This oxidation mechanism causes an increase in the activity of H2O by the reaction of CH4 with O2, and the increased aH2O causes a rapid drop in the solidus temperature, and is here termed hydrous redox melting (HRM). Recently, a second redox melting mechanism (carbonate redox melting; CRM) has been discovered that operates in more oxidized conditions, and may post-date the first mechanism in the same geographical area, explaining the sequence of igneous rock types from lamproites to ultramafic lamprophyres that occurs during the development of rifts through cratons. The CRM mechanism relies on the oxidation of solid carbon as graphite or diamond that has accumulated in the lithosphere over time. The solidus temperature for rocks with both CO2 and H2O is lower than in conditions with H2O alone; it does not occur at depths less than 65 km, but has recently been confirmed experimentally to depths of at least 200 km. Melts produced by HRM are not SiO2-undersaturated, even at depths of 200 km, and may often resemble lamproites or SiO2-rich picrites, whereas melts produced by CRM are always SiO2-undersaturated and range from carbonatitic to ultramafic lamprophyric or melilititic with increasing degree of melting.The operation of redox melting may be more common than has been recognized because the oxidation state of the upper mantle is not uniform as a function of depth, geodynamic setting or geological time.The general decrease of oxygen fugacity (fO2) of c. 0·7 log units per 1GPa pressure increase dictates that rapidly subducted oceanic lithosphere will be considerably more oxidized than ambient mantle peridotite at depths of 200^300 km. Hydrothermal alteration (serpentinization), addition of continental or carbonate sediments, and dehydration reactions during subduction all contribute to the heterogeneity of oxidation states in the subducted slab, which may vary over 6 log units; this raises the potential for redox reactions on local and regional scales. The oceanic lithosphere has a lower average fO2 than either continental or cratonic mantle lithosphere at a given depth, so that the HRM mechanism dominates in recycled blocks and at the base of the continental lithosphere. The higher thermal gradients dictate that HRM is more common in the modern Earth beneath ocean islands and in upwelling mantle currents than in subduction zones. The oxidation state of the mantle is often described as having been constant since 3·5 Ga, but this overlooks the bias towards continental samples. Redox melting of oxidized recycled blocks (at approximately the fayalite^magnetite^quartz buffer) in the mantle was not important in the Hadean and Archaean, as it had to await the gradual oxidation of the mantle and the establishment of the subduction process, as well as the stabilization of the continents. The lack of CRM explains the lack of carbonatites before 2·7 Ga. However, the lower fO2 of the Archaean asthenosphere and higher volatile contents caused more prevalent HRM in the Hadean and Archaean mantle. Degassing is controlled by solubility of volatile species in melts, which are H2O-rich but C-poor in reducing conditions. Silicate melts under reduced conditions contain much less carbon but more nitrogen than melts in the modern mantle, arguing for a nitrogen-rich, CO2-poor early atmosphere.

Historic Building Stones and Flooding: Changes of Physical Properties due to Water Saturation

Natural stone is a common material in historic constructions. Flood events may directly affect surfaces of historic stone buildings. Since ashlars and stone sculptures often carry valuable cultural information, a more detailed knowledge about changes in physical properties due to water saturation is crucial for the assessment of their surface stability in case of flooding. Water saturation of stones leads to loss of mechanical strength and to expansion of volume (hydric dilatation). On the basis of data from literature, a rough scheme of vulnerability is suggested for different kinds of building stones. The majority of igneous and metamorphic rock types with dense crystalline structure are not vulnerable to flooding, whereas some types of pyroclastic rocks (tuffs) as well as clay-bearing sandstones are highly vulnerable. Detailed laboratory investigations on Elbe sandstone demonstrate the influence of petrographic features on material behavior due to water saturation. Results of laboratory tests are in go...

A fundamental parameters approach to calibration of the Mars Exploration Rover Alpha Particle X‐ray Spectrometer: 2. Analysis of unknown samples

Our fundamental parameters method was recently applied to results from geochemical reference materials to provide a new calibration of the laboratory Alpha Particle X‐ray Spectrometer (APXS) instrument from the Mars Exploration Rovers mission. The method is now extended to provide an iterative approach for the treatment of unknown samples, based upon that initial calibration. It is tested by regarding small subsets of the reference materials and other materials as unknown samples; agreement of derived element concentrations with suppliers' recommended values is good with the exception of certain igneous rock types. In these exceptions, the deviations can be explained via the location of the elements concerned in minority or accessory mineral phases, and different calibration schemes can be developed empirically for specific rock types which are defined via a TAS diagram. The necessary reliance upon an iterative approach in normalizing the sum of oxide concentrations to 100% is investigated. It turns out that this can cause significant errors in derived element concentrations when a significant amount of mineralogically bound water (H2O+) is present, but our method has been extended to enable determination of this H2O+ concentration under known geometry. Various implications for calibration of the new APXS selected for the Mars Science Laboratory are discussed.

Correlating index properties of rocks with P-wave measurements

Abstract The determination of index properties of rock, such as Cerchar Abrasivity Index, Shore Hardness, Protodyakonov Index and Vickers Hardness in laboratory or insitu conditions is time-consuming and requires special equipment and expertise. However, the use of P-wave technology to measure the P-wave velocity of rock is a relatively simple task because the portable equipment can be used in the laboratory or in the field without tedious preparation of rock cores and it is non-destructive. This paper presents an experimental study of the measurement of P-waves of several types of igneous, sedimentary and metamorphic rock. The index properties were also determined in the laboratory to obtain correlations between P-waves and various index properties. Good linear relationships were found between all the index properties determined and the P-wave measurements.

Multilevel aeromagnetic response curves over selected iron deposits and igneous rock types

Editor's note: This paper summarizes a career of work measuring and analyzing magnetic susceptibility values at numerous iron deposits and igneous rock sites in Utah, California, Nevada, and Montana. Today, multilevel estimations using upward continuation have all but replaced old and expensive multiple measurement approaches. Fortunately, the author has made this very rare and valuable data set available for future generations of geomagnetic practitioners. In 1950–1975, U.S. Steel flew a number of aeromagnetic surveys in the western United States while exploring for iron deposits. The work was done by U.S. Steel's Western Division, Columbia Geneva Steel Company, and by the Raw Materials Exploration Group. S. G. Sargis, assistant manager of Raw Materials Exploration, and John K. Hayes, manager of the Raw Materials Exploration, organized one of the most aggressive and successful mineral exploration groups in the western United States during this period in their search for raw materials critical to making steel.

Apatite Composition: Tracing Petrogenetic Processes in Transhimalayan Granitoids

Apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements. In this study, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of theTranshimalayan igneous plutonic suite: S-type granites, the I-type Gangdese batholith and postcollisional adakites. F, Mn, Sr and rare earth elements (REE) in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers. More specifically, the F and Mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index. Combined with Sr and REE data, which show significant variations in apatite from different rock types, these elements are useful for constructing ‘discrimination diagrams’. This study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution. Systematic variations of Sr and REE in apatite with bulk-rock aluminosity are the results of partition competition with pre-existing and coexisting major and accessory minerals in silicate melts, and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing, which is signaled by inconsistent Eu anomalies, Sr abundances and REE patterns relative to bulkrock compositions.

English

Past open pit mining operations at the Chevron Mining Inc. (CMI) Questa Mine in Questa, New Mexico, resulted in several large overburden rock piles. The rock piles are generally steep, angle of repose (2:1 and steeper), acidic (pH 2.5 - 7.0) and composed of a variety of igneous rock types. Pre-mining and currently undisturbed vegetation in the area of the mine site is dominated by mixed conifer forests. Forestry is the approved post-mining land use for this mine. Since the early 1990's studies have been conducted examining the potential for establishing the forest vegetation directly on the overburden rock piles. In the fall of 1996 and spring of 1997 two operational scale plantings at two locations on the mine rock piles were conducted to examine both the logistics associated with planting trees and shrubs directly on angle of repose slopes and the subsequent survival and growth performance of the transplanted vegetation. Short-term (three year) overall survival averaged 81%. There were survival differences between the two planting sites and among the three types of plants being transplanted with crop trees (conifers) averaging 87%, nurse trees (deciduous) averaging 63% and shrubs averaging 92%. Long-term (twelve year) survival averaged 43% and differed between planting sites with the lower elevation (2,500 m) planting site averaging 45% and the higher elevation (3,000 m) site averaging 41% overall survival. The resulting vegetative communities differed between the two planting sites with the higher elevation site having a higher proportion of crop trees compared to the lower site that had comparatively a higher proportion of shrub species. Implications of the results relative to future reclamation plantings are discussed.

Calcium Isotopes (δ44/40Ca) in MPI‐DING Reference Glasses, USGS Rock Powders and Various Rocks: Evidence for Ca Isotope Fractionation in Terrestrial Silicates

We report δ44/40Ca(SRM 915a) values for eight fused MPI‐DING glasses and the respective original powders, six USGS igneous rock reference materials, the U‐Th disequilibria reference material TML, IAEA‐CO1 (Carrara marble) and several igneous rocks (komatiites and carbonatites). Sample selection was guided by three considerations: (1) to address the need for information values on reference materials that are widely available in support of interlaboratory comparison studies; (2) support the development of in situ laser ablation and ion microprobe techniques, which require isotopically homogenous reference samples for ablation; and (3) provide Ca isotope values on a wider range of igneous and metamorphic rock types than is currently available in the scientific literature. Calcium isotope ratios were measured by thermal ionisation mass spectrometry in two laboratories (IFM‐GEOMAR and Saskatchewan Isotope Laboratory) using 43Ca/48Ca‐ and 42Ca/43Ca‐double spike techniques and reported relative to the calcium carbonate reference material NIST SRM 915a. The measurement uncertainty in both laboratories was better than 0.2‰ at the 95% confidence level. The impact of different preparation methods on the δ44/40Ca(SRM 915a) values was found to be negligible. Except for ML3‐B, the original powders and the respective MPI‐DING glasses showed identical δ44/40Ca(SRM 915a) values; therefore, possible variations in the Ca isotope compositions resulting from the fusion process are excluded. Individual analyses of different glass fragments indicated that the glasses are well homogenised on the mm scale with respect to Ca. The range of δ44/40Ca(SRM 915a) values in the igneous rocks studied was larger than previously observed, mostly owing to the inclusion of ultramafic rocks from ophiolite sections. In particular, the dunite DTS‐1 (1.49 ± 0.06‰) and the peridotite PCC‐1 (1.14 ± 0.07‰) are enriched in 44Ca relative to volcanic rocks (0.8 ± 0.1‰). The Carrara marble (1.32 ± 0.06‰) was also found to be enriched in 44Ca relative to the values of assumed precursor carbonates (< 0.8‰). These findings suggest that the isotopes of Ca are susceptible to fractionation at high temperatures by, as yet, unidentified igneous and metamorphic processes.