The Experts below are selected from a list of 25812 Experts worldwide ranked by ideXlab platform

Andrew C Morton - One of the best experts on this subject based on the ideXlab platform.

  • integrated Heavy Mineral study of jurassic to paleogene sandstones in the mandawa basin tanzania sediment provenance and source to sink relations
    Journal of African Earth Sciences, 2019
    Co-Authors: Katrine Fossum, Andrew C Morton, Henning Dypvik, W Hudson
    Abstract:

    Abstract This paper concerns the Heavy Mineral composition of Jurassic, Cretaceous and Paleogene sedimentary successions in the Mandawa Basin. The nature of the Heavy Mineral assemblages in 38 samples was investigated to assess changes in sediment provenance through time. Further, the geochemistry of detrital amphiboles and garnets and the detrital zircon populations were used to determine possible sediment source terranes. Based on the Heavy Mineral compositions the sandstones were grouped into four Heavy Mineral assemblages: garnet-dominated, amphibole-dominated, epidote-dominated and zircon-dominated. Garnet-dominated sandstones are abundant in most Middle Jurassic to Middle Eocene samples and represent the main sediment input into the Mandawa Basin. Amphibole-dominated sandstones occur in a few Lower Cretaceous samples deposited in close proximity to their sediment source in the Masasi Spur area. A change in provenance is observed in the epidote-dominated sandstones of Middle Eocene and Early Oligocene age. This change coincides with a climatic shift towards a wetter and cooler climate associated with an uplift phase in East Africa. The detrital zircon population in the investigated samples share the same age fractions and are indistinguishable within analytical error. Mineral chemistries and zircon ages imply that the sediments deposited in the Mandawa Basin were mainly derived from several high-grade sources within the Neoproterozoic Mozambique Belt to the west of the basin.

  • Heavy Mineral assemblages in sandstone intrusions panoche giant injection complex california u s a
    Journal of Sedimentary Research, 2017
    Co-Authors: Andrew Hurst, Andrew C Morton, Dirk Frei, Anthony Scott, Mario Vigorito
    Abstract:

    Excellent exposure from part of the Panoche Giant Injection Complex in the San Joaquin Valley is used to examine provenance characteristics of sandstone intrusions with respect to two parent sandstone units that are known to feed the sand-injection complex. The succession is part of the upper Mesozoic to lower Tertiary Great Valley Group, and was deposited in a deepwater part of an evolving deep-water forearc basin. The section examined is mudstone-dominated, and the sand injection is constrained to have occurred in the Danian. Sandstones in the Dosados Member (Moreno Fm) are identified as the main parent unit on the basis of total Heavy-Mineral-assemblage compositions and varietal studies of selected Minerals (tourmaline, garnet, titanite, apatite, and zircon). Fluidized sand is emplaced in turbulent flow conditions creating high-velocity inter-grain collisions. Evidence of comminution and diminution of Minerals that are less hard than quartz is documented using indices for the relative hardness (TAH) and durability (TAD) of Heavy Minerals. Preferential settling of high-density zircon relative to lower-density tourmaline produces density-controlled variations of zircon:tourmaline upward through the injection complex. Heavy-Mineral dissolution occurred in the most permeable sandstone intrusions and is believed to record the effects of mid-Eocene deep weathering, when subtropical climate prevailed in the study area. Detrital Heavy-Mineral assemblages, which are dominated by titanite and garnet, record erosion of the Sierran metamorphic terrane with mafic and alkaline plutonic rocks. Zircon with U/Pb ages of c. 140–160 Ma and c. 90–110 Ma, consistent with earlier independent analyses, record erosion of Sierran granitoids. On the paleo-seafloor, enrichment of Ca-amphibole and epidote is indicative of Sierran provenance concurrent with sand extrusion. The presence of Na-amphibole in the Uhalde Sandstone supports earlier work that suggested sediment input from obducted seafloor to the west.

  • Heavy Mineral and zircon age constraints on provenance of the sherwood sandstone group triassic in the eastern wessex basin uk
    Proceedings of the Geologists' Association, 2016
    Co-Authors: Andrew C Morton, Robert Knox, Dirk Frei
    Abstract:

    Abstract Heavy Mineral and zircon age data demonstrate that in the Sherwood Sandstone Group of the Marchwood-1 and Southampton-1 boreholes, on the eastern margin of the Wessex Basin, sediment was supplied from both the south (Variscan highlands) and the east (recycled Old Red Sandstone). Interplay of these two sources led to a well-defined Heavy Mineral stratigraphy in the area. However, the Sherwood Sandstone Group in the Wytch Farm oilfield, towards the centre of the Wessex Basin, contains only sandstones derived from the Variscan highlands to the south and lacks significant amounts of recycled Old Red Sandstone detritus. The equivalent sandstones (Otter Sandstone Formation) on the western margin of the Wessex Basin have a different provenance to both the central and eastern parts of the basin, since they almost entirely lack input from Variscan granitoids. Heavy Mineral and zircon provenance data therefore demonstrate sediment input from a number of discrete source areas into the Wessex Basin during the Early and Middle Triassic, and that the ‘Budleighensis River’ system may not have been a single river, at least in the southern Wessex Basin area. It is also evident that provenance-based correlation schemes such as Heavy Mineral analysis or whole-rock geochemistry should be used with caution over long distances and require careful evaluation of lateral changes in provenance.

  • constraining the origin of reservoirs formed by sandstone intrusions insights from Heavy Mineral studies of the eocene in the forties area united kingdom central north sea
    AAPG Bulletin, 2014
    Co-Authors: Andrew C Morton, Andrew Hurst, Sean Mcfadyen, Jeff Pyle, Philip Rose
    Abstract:

    The presence of hydrocarbon-bearing sandstones within the Eocene of the Forties area was first documented in 1985, when a Forties field (Paleocene) development well discovered the Brimmond field. Further hydrocarbons in the Eocene were discovered in the adjacent Maule field in 2009. Reservoir geometry derived from three-dimensional seismic data has provided evidence for both a depositional and a sand injectite origin for the Eocene sandstones. The Brimmond field is located in a deep-water channel complex that extends to the southeast, whereas the Maule field sandstones have the geometry of an injection sheet on the updip margin of the Brimmond channel system with a cone-shape feature emanating from the top of the Forties Sandstone Member (Paleocene). The geometry of the Eocene sandstones in the Maule field indicates that they are intrusive and originated by the fluidization and injection of sand during burial. From seismic and borehole data, it is unclear whether the sand that was injected to form the Maule reservoir was derived from depositional Eocene sandstones or from the underlying Forties Sandstone Member. These two alternatives are tested by comparing the Heavy Mineral and garnet geochemical characteristics of the injectite sandstones in the Maule field with the depositional sandstones of the Brimmond field and the Forties sandstones of the Forties field. The study revealed significant differences between the sandstones in the Forties field and those of the Maule and Brimmond fields), both in terms of Heavy Mineral and garnet geochemical data. The Brimmond-Maule and Forties sandstones therefore have different provenances and are genetically unrelated, indicating that the sandstones in the Maule field did not originate by the fluidization of Forties sandstones. By contrast, the provenance characteristics of the depositional Brimmond sandstones are closely comparable with sandstone intrusions in the Maule field. We conclude that the injectites in the Maule field formed by the fluidization of depositional Brimmond sandstones but do not exclude the important function of water from the huge underlying Forties Sandstone Member aquifer as the agent for developing the fluid supply and elevating pore pressure to fluidize and inject the Eocene sand. The study has demonstrated that Heavy Mineral provenance studies are an effective method of tracing the origin of injected sandstones, which are increasingly being recognized as an important hydrocarbon play.

  • Heavy Mineral stratigraphic analysis on the clair field uk west of shetlands a unique real time solution for red bed correlation while drilling
    Petroleum Geoscience, 2012
    Co-Authors: Andrew C Morton, Alex Milne
    Abstract:

    Hydrocarbons in the Clair Field, west of the Shetland Islands, are hosted by Devonian–Carboniferous clastic red beds deposited in a non-marine fluviolacustrine setting. The succession is almost entirely biostratigraphically barren and, hence, alternative approaches to reservoir correlation are required. Heavy Mineral analysis (HMA), which subdivides clastic successions on the basis of changes in provenance and sediment transport history, has proven successful in establishing a high-resolution correlation framework for the Clair Field. Since the technique offers a reliable and rapid method for monitoring the stratigraphy of the Clair reservoir succession, HMA has been undertaken on a real-time basis at well site for virtually all development wells during Phase 1 of the Clair Field development, and for all Phase 2 appraisal wells. Heavy Mineral data can be acquired in less than 2 hours from receipt of sample. Consequently, owing to the relatively slow penetration rates frequently associated with Clair drilling, stratigraphic information is usually acquired ahead of logging while drilling. Heavy Mineral data are used in the decision-making process in a variety of situations, including picking of casing and coring points, whether to maintain or alter well trajectory, and when to terminate drilling. In the Clair Field, formation tops can be subtle and, since HMA can establish trends and predict formation changes before they are encountered, they are critical in aiding geosteering decisions. HMA has also been used to monitor stratigraphy and to pick formation tops when logging tools have failed, allowing drilling to continue and avoiding tripping to change the bottom-hole assembly. The application of HMA to the Clair Field development is illustrated by reference to a number of wells drilled on the field since 2005.

Eduardo Garzanti - One of the best experts on this subject based on the ideXlab platform.

  • Removing the “Heavy Mineral effect” to obtain a new Pb isotopic value for the upper crust
    Geochemistry Geophysics Geosystems, 2013
    Co-Authors: Marion Garçon, Catherine Chauvel, Christian France-lanord, Mara Limonta, Eduardo Garzanti
    Abstract:

    Based on the concept that sedimentary processes average large areas of exposed crust, sediment data have been widely used to estimate the average Pb isotopic composition of the upper continental crust. However, the possible effects of Mineral sorting processes on sediment Pb isotopes have never been fully investigated. Here, we report Pb isotopic compositions of Himalayan river sediments as well as those of several grain‐size fractions and Mineral separates. We demonstrate that Pb isotopes of both bed loads and suspended loads are biased toward more radiogenic values than their source rocks due to a “Heavy Mineral effect” caused by Mineral sorting during fluvial transport on continents. The sparse zircons, monazites and allanites present in all samples (

  • removing the Heavy Mineral effect to obtain a new pb isotopic value for the upper crust
    Geochemistry Geophysics Geosystems, 2013
    Co-Authors: Marion Garçon, Catherine Chauvel, Mara Limonta, Christian Francelanord, Eduardo Garzanti
    Abstract:

    [1] Based on the concept that sedimentary processes average large areas of exposed crust, sediment data have been widely used to estimate the average Pb isotopic composition of the upper continental crust. However, the possible effects of Mineral sorting processes on sediment Pb isotopes have never been fully investigated. Here, we report Pb isotopic compositions of Himalayan river sediments as well as those of several grain-size fractions and Mineral separates. We demonstrate that Pb isotopes of both bed loads and suspended loads are biased toward more radiogenic values than their source rocks due to a “Heavy Mineral effect” caused by Mineral sorting during fluvial transport on continents. The sparse zircons, monazites and allanites present in all samples (<1 wt%), including suspended loads, generate a Pb isotopic variability as large as that observed in the Earth's mantle. After correction of this effect, we propose an average value for the composition of the upper Himalayan crust together with a new Pb isotopic value for the Earth's upper continental crust. We conclude that Mineralogical effects must be evaluated carefully before using Pb isotopes of sediments as provenance and anthropogenic tracers.

  • controlling factors on Heavy Mineral assemblages in chinese loess and red clay
    Palaeogeography Palaeoclimatology Palaeoecology, 2013
    Co-Authors: Junsheng Nie, Eduardo Garzanti, Sergio Ando, Wenbin Peng, Katharina Pfaff, Andreas Moller, Thomas Stevens, Anna Bird, Hong Chang, Yougui Song
    Abstract:

    Abstract Heavy-Mineral analysis is a sensitive technique in constraining provenance of sandstone, but has rarely been applied to loess. Here we report a Heavy-Mineral study of selected samples from the Luochuan, Xifeng and Caoxian loess-Red Clay sections on the Chinese Loess Plateau, based on the novel QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) technique. We found that Heavy Mineral assemblages of loess deposited through the past 500 kyr are similar and unchanged by post-depositional chemical dissolution. In contrast, in samples deposited from 900 ka to 3 Ma, the relative proportion of stable Minerals tends to increase down section. In addition, the Xifeng samples consistently display higher contents of unstable ferromagnesian Minerals than the Luochuan samples. Detailed analysis of surface textures displayed by different Minerals by optical methods indicates that such a compositional difference can be ascribed to more effective diagenetic dissolution for the Luochuan section, explained by more extensive percolation of interstitial waters in wetter climatic conditions. Interestingly, Heavy-Mineral assemblages in the underlying upper Miocene Red Clay from Xifeng (deposition age ~ 7 Ma) are similar to those of recent loess deposited since 500 ka. This similarity indicates that climate and/or local preservation conditions hampered dissolution reactions, thus helping to preserve an original provenance signal that remained largely unchanged throughout the considered time period. Our study demonstrates that climatically- and time-controlled diagenesis plays a key role in determining the composition of Heavy-Mineral assemblages contained in loess deposited several hundreds of thousands years ago. We also show that by using both QEMSCAN and traditional optical techniques on the same samples we can obtain fundamental complementary information for a correct interpretation of the Heavy-Mineral assemblage.

  • Raman spectroscopy in Heavy-Mineral studies
    Geological Society London Special Publications, 2013
    Co-Authors: Sergio Ando, Eduardo Garzanti
    Abstract:

    Abstract: Raman spectroscopy is an innovative tool with tremendous potential, serving as a fun-damental complement to a variety of provenance methods including Heavy-Mineral analysis anddetrital geochronology. Because of its accuracy, efficiency and versatility, the results of theRaman technique are indispensable for fully reliable identification of Heavy Minerals in grainmounts or thin sections. Thorny long-standing problems that cannot be solved confidently witha polarizing microscope alone, such as the determination of opaque and altered Heavy Minerals,of detrital grains as small as a few microns, or of colourless crystals with uncertain orientationand rounded morphology, can finally be addressed. Although the method can be highly automa-tized, the full ability and experience of the operator is required to combine Raman data with theoptical information obtained under the microscope on the same grains, which is essential for theefficient application of the method in provenance studies. This article provides exemplaryRamanspectrausefulforthecomparisonand determinationof over70 differentopaqueandtrans-parent Heavy-Mineral species commonly found in sediments, conveying specific information onthe genesis of their source rocks, and thus is particularly useful in provenance diagnoses andpalaeotectonic reconstructions.Supplementary material: Detailed information on the lasers used and the origin of the analysedMinerals is available at http://www.geolsoc.org.uk/SUP18615It is the scattering of light by atoms and moleculesthat gives us the light of the sky, the blue colour ofthe deep sea and the delicate opalescence of largemasses of clear ice. (Raman 1928, pp. 368–369)

  • chapter 20 Heavy Mineral concentration in modern sands implications for provenance interpretation
    Developments in sedimentology, 2007
    Co-Authors: Eduardo Garzanti, Sergio Ando
    Abstract:

    Abstract Heavy Mineral concentration in sediments depends primarily on the chemistry and tectono-stratigraphic level of rocks eroded within continental-block, arc, or orogenic source terranes. Detritus derived from mantle peridotites and lower crustal gabbros, as well as from high-pressure (oceanic or continental eclogite) and high-temperature (amphibolite, granulite) metamorphic rocks contains one to two orders of magnitude more Heavy Minerals than detritus derived from upper crustal rocks including granites and sedimentary successions. Concentrated Heavy Mineral assemblages, however, may result from density-sorting during erosion, transport, or deposition by tractive currents, which can very effectively segregate Minerals with even small differences in density within distinct grain-size fractions and sedimentary environments (e.g., fluvial channel versus overbank, beach versus shelf). Conversely, depleted Heavy Mineral assemblages may result from severe diagenetic dissolution in ancient sandstones, a process that in Alpine and Himalayan foreland basins very extensively affected clastic wedges older than the Pleistocene. Through a series of key modern examples from various geodynamic settings in arid to semi-arid climate, we stress the importance of giving full consideration to Heavy Mineral concentration while interpreting provenance of terrigenous sediments and sedimentary rocks. The concentration parameters introduced herein (Heavy Mineral Concentration index, Source Rock Density index), coupled with parameters based on Heavy Mineral species with either contrasting density (% opaque, % ultradense, % ZR) or chemical stability, allow us to reveal and quantify also the effects of hydraulic sorting in the depositional environment and of diagenetic dissolution in ancient terrigenous rocks. We document that in most modern sands, the relative abundance of chemically stable species (e.g., zircon, tourmaline, rutile, apatite, chrome spinel) is considerably less than the experience on ancient sandstones generally induces to believe, and show that the actualistic approach provides crucial insight for a correct interpretation of Heavy Mineral suites.

Shuhong Wang - One of the best experts on this subject based on the ideXlab platform.

  • provenance of Heavy Mineral deposits on the northwestern shelf of the south china sea evidence from single Mineral chemistry
    Marine Geology, 2015
    Co-Authors: Wen Yan, Lifeng Zhong, Zhen Xia, Shuhong Wang
    Abstract:

    Abstract A study of Heavy Mineral geochemistry has been carried out in order to examine the potential sources of Heavy Mineral deposits within surficial sediment on the northwestern shelf of the South China Sea. Tourmaline, amphibole and garnet from six samples near the coast and eleven samples on the shelf were analyzed by an electron microprobe. Chemical varieties of tourmaline and amphibole indicate that the Pearl River is the main supplier of sandy sediments on the eastern shelf within a 100 km radius west of the paleo-deltas. Sandy sediments on the western shelf are mainly sourced from the Jian River and the Wanquan River. Heavy Mineral placers on the middle and outer shelves are mainly derived from reworking of the paleo Pearl River deltas. Heavy Mineral placers in the west are mainly sourced from the small rivers and are distributed in the sandy deposits near the coasts. This study demonstrates that the occurrence of Heavy Mineral placers on wide continental shelf is mainly determined by the sediment supply and marine processes during transgressions.

Christopher Fanning - One of the best experts on this subject based on the ideXlab platform.

  • correlation of triassic sandstones in the strathmore field west of shetland using Heavy Mineral provenance signatures
    Developments in sedimentology, 2007
    Co-Authors: Andrew C Morton, Robert H Herries, Christopher Fanning
    Abstract:

    Abstract Integrated Heavy Mineral, Mineral–chemical and zircon age data show that Triassic sandstones in the Strathmore Field result from the interplay of sediment derived from eastern and western sources. The Early Triassic Otter Bank Formation is interpreted as having a source on the British margin of the Faeroe-Shetland rift. Two main provenance components (recycled Devonian-Carboniferous Upper Clair Group in conjunction with Lewisian orthogneiss) were involved. The overlying Foula Formation (Middle-Late Triassic) was derived from high-grade metasedimentary/charnockitic basement rocks, interpreted as lying in the Nagssuqtoqidian belt of southern East Greenland on the opposite side of the rift. Zircon age data from the Foula Formation also provide evidence for an important Permian igneous event along the proto-northeast Atlantic rift. The switch in sediment supply from easterly-sourced to westerly-sourced detritus is the most clearly defined correlative event in the Triassic succession of the Strathmore Field. Variable supply from a subordinate zircon-rich component (probably of granitic origin) provides a basis for intra-Foula subdivision and correlation. The upper part of the Otter Bank Formation is characterised by a relatively high apatite/tourmaline ratio, believed to indicate the initial appearance of sediment from East Greenland. The construction of the correlation framework for the Triassic succession in the Strathmore Field depends crucially on identification and quantification of parameters that are sensitive to changes in provenance and insensitive to other processes that operate during the sedimentation cycle. This study demonstrates that ditch cuttings and core samples yield closely comparable Heavy Mineral data, indicating that construction of correlation frameworks can be readily achieved using ditch cuttings samples, although ideally cuttings data would benefit from calibration with core material.

  • provenance of late cretaceous to paleocene submarine fan sandstones in the norwegian sea integration of Heavy Mineral Mineral chemical and zircon age data
    Sedimentary Geology, 2005
    Co-Authors: Andrew C Morton, Andrew G Whitham, Christopher Fanning
    Abstract:

    Abstract This paper describes a strategy for effective discrimination and provenance evaluation of sandstones transported by different sediment dispersal systems using an integrated programme of Heavy Mineral analysis, Mineral chemistry and zircon age dating. Sandstones derived from different source regions are initially discriminated using provenance–sensitive Heavy Mineral parameters (ratios of abundances of stable, hydraulically equivalent Minerals). Differences between the Heavy Mineral populations are reinforced by single-grain Mineral chemical analysis, which also provides further information on the nature of the source terrains. Zircon age dating of representative samples places further constraints on the location of the source areas, by identifying the main crust-forming events. In addition, the validity of the Mineralogical discrimination can be tested by the zircon age data. The value of this integrated approach is illustrated by a case study of deep marine Late Cretaceous–Paleocene sandstones in the Norwegian Sea. Potential sources of coarse clastic sediment lie both to the east, in mid-Norway, and the west, in East Greenland. Three main sand types (MN1, MN2 and MN3) have been identified, each of which has a unique combination of Heavy Mineral ratios (rutile/zircon, monazite/zircon, chrome spinel/zircon and apatite/tourmaline) and Mineral chemistry (garnet and tourmaline). Sand type MN1 has a simple zircon age spectrum, with a large Early–Middle Proterozoic group and a small Early Paleozoic group, indicating derivation from northern mid-Norway. Sand type MN2 has a complex age structure including Archaean and early Proterozoic zircons. It can be divided into two subtypes, MN2a and MN2b, and can be ascribed to a source in East Greenland. Sand type MN3 has a simple age structure dominated by Middle Proterozoic zircons, and it was sourced from southern mid-Norway. Since reservoir presence is a major area of uncertainty in the deep water Norwegian Sea, the use of Heavy Mineral, Mineral chemical and zircon age data to discriminate sandstones of eastern and western origin is crucial to hydrocarbon exploration of the area.

Inga Sevastjanova - One of the best experts on this subject based on the ideXlab platform.

  • provenance of the cretaceous eocene rajang group submarine fan sarawak malaysia from light and Heavy Mineral assemblages and u pb zircon geochronology
    Gondwana Research, 2017
    Co-Authors: Thomson Galin, Tim H Breitfeld, Robert Hall, Inga Sevastjanova
    Abstract:

    Abstract The Rajang Group sediments in central Borneo form a very thick deep-water sequence which was deposited in one of the world's largest ancient submarine fans. In Sarawak, the Lupar and Belaga Formations form the Rajang Group, characterised by turbidites and large debris flows, deposited in an interval of at least 30 Ma between the Late Cretaceous (Maastrichtian) and late Middle Eocene. Borneo is one of the few places in SE Asia where sediments of this age are preserved. Heavy Mineral assemblages and detrital zircon U-Pb dating permit the Rajang Group to be divided into three units. The Schwaner Mountains area in SW Borneo, and West Borneo and the Malay Tin Belt were the main source regions and the contribution from these source areas varied with time. Unit 1, of Late Cretaceous to Early Eocene age, is characterised by zircon-tourmaline-dominated Heavy Mineral assemblages derived from both source areas. Unit 2, of Early to Middle Eocene age, has zircon-dominated Heavy Mineral assemblages, abundant Cretaceous zircons and few Precambrian zircons derived primarily from the Schwaner Mountains. Unit 3, of Middle Eocene age, has zircon-tourmaline-dominated Heavy Mineral assemblages derived from both sources and reworked sedimentary rocks. There was limited contemporaneous magmatism during deposition of the Rajang Group inconsistent with a subduction arc setting. We suggest the Rajang Group was deposited north of the shelf edge formed by the Lupar Line which was a significant strike-slip fault.

  • a detrital Heavy Mineral viewpoint on sediment provenance and tropical weathering in se asia
    Sedimentary Geology, 2012
    Co-Authors: Inga Sevastjanova, Robert Hall, D H M Alderton
    Abstract:

    Abstract Understanding Heavy Mineral preservation is important for interpreting generation, pathways, provenance and geochemistry of sediments. Despite this, many assumptions about Heavy Mineral stability are based on ancient strata and few studies consider modern sediments, particularly those in tectonically active tropical areas such as SE Asia. We report new Heavy Mineral data on 69 river sand samples from the Malay Peninsula and Sumatra, in which one aim was to find provenance indicators specific to these areas. Identifications were performed using optical microscopy and confirmed with SEM-EDS. In the Malay Peninsula Heavy Minerals record granitic and contact metamorphic provenance. Variable amounts of zircon, tourmaline, hornblende, andalusite, epidote, monazite, rutile and titanite, and minor amounts of pyroxene, apatite, anatase, garnet, diaspore, colourless spinel, cassiterite and allanite are typical of this source area. The composition of assemblages from Sumatra indicates contributions from two major sources: the modern volcanic arc (I) and the basement (II). Abundant pyroxene, particularly hypersthene (up to 70%), is diagnostic of the volcanic arc source. Vesuvianite, garnet, andalusite, tourmaline, chrome spinel, rutile, anatase and corundum, are present only in small amounts (