Detrital Chromian Spinels Research Articles

A Better Picture of the Mantle Section of the Nain Ophiolite Inferred from Detrital Chromian Spinels

AbstractDetrital chromian spinels from adjacent sediment (recent sands and a Tertiary sandstone) were used to obtain a general view of the lithological and petrological characteristics of the Nain ophiolitic melange, Iran. They display a wide chemical range in terms of Cr# (= atomic ratio), from 0.10 to 0.92. Except for some grains (11% of the total), the spinels show low TiO2 contents ( 0.25 wt%, up to 1.26 wt%) are relatively low in Mg# (= atomic ratio), from 0.15 to 0.65, and were possibly derived from mantle peridotite that reacted with impregnating melt (e.g., dunite or plagioclase-bearing peridotites). The high-Cr# (0.55–0.92) spinels, which are dominant in the Tertiary sandstone, are chemically homogenous and clearly different from high-Cr# altered spinels (ferritchromite and Cr-magnetite), which are formed by low-T alteration, and are low in Mg# and high in Fe3+. The higher abundance of the high-Cr#...

Detrital chromian spinels from Miocene and Holocene sediments of northern Iraq: provenance implications

*Corresponding author The study integrates mineralogical and chemical characteristics of the chromian spinels from northern Iraq using standard petrographic and scanning microscope techniques as well as electron microprobe analyses in order to better understand their provenance, and the implications thereof. Detrital chromian spinels are found as one of the predominant accessory heavy minerals within fluviatile Miocene and Holocene sediments. In addition, such spinels are also present in the Palaeogene–Neogene and Cretaceous alluvial, deltaic and turbiditic sandstones. The results indicate that most of the chromian spinels have interrelated ranges of Cr/(Cr+Al) at rather low contents of Fe and Ti suggesting that the sandstones which host the chromian spinels were derived from a source area dominated by ultramafic rocks. Mineralogical and chemical data suggest that Alpine-type peridotites were the main source rocks for the studied chromian spinels. All available evidence supports the idea that the sandstones originated from the ophiolite-radiolarite belt of the Taurus Range in northeastern Turkey, as well as from recycling of the uplifted Cretaceous strata of northern Iraq.

Detrital chromian spinels from beach placers of Andaman Islands, India: A perspective view of petrological characteristics and variations of the Andaman ophiolite

AbstractAlong the east coast of the Andaman Islands, abundant detrital chromian spinels frequently occur in black sands at the confluence of streams meeting the Andaman Sea. The mineral chemistry of these detrital chromian spinels has been used in reconstructing the evolutionary history of the Andaman ophiolite. The chromian spinels show wide variation in compositional parameters such as Cr# [= Cr/(Cr + A1) atomic ratio] (0.13–0.91), Mg# [= Mg/(Mg + Fe2+) atomic ratio] (0.23–0.76), and TiO2 (<0.05–3.9 wt%). The YFe3+[= 100Fe3+/(Cr + A1 + Fe3+) atomic ratio] is remarkably low (usually <10 except for south Andaman). The ranges of chemical composition of chromian spinels are different in each locality. The spinel compositions show very depleted signatures over the entire island, which suggests that all massifs in the Andaman ophiolite were affected under island‐arc conditions. Although the degree of depletion varies in different parts of the island, a directional change in composition of the detrital chromian spinels from south to north is evident. Towards the north the detrital chromian spinels point to less‐depleted source rocks in contrast to relatively more depleted towards the south. The possibilities to explain this directional change are critically discussed in the context of the evolution of Andaman ophiolite.

東北日本，上部白亜系久慈層群の砕屑性重鉱物.-特に砕屑性クロムスピネルの化学組成ついて－

東北日本，上部白亜系久慈層群の砕屑性重鉱物.-特に砕屑性クロムスピネルの化学組成ついて－

Geochemistry and biostratigraphy of Eocene sediments from Samothraki Island, NE Greece

Elevated whole-rock concentrations in Cr, Ni and V as well as the occurrence of detrital chrome spinel suggest an input of (ultra)mafic detritus into the Eocene elastic sediments of Samothraki Island. Detrital chrome spinel chemistry indicates a mixed source of MOR-type peridotites and supra-subduction zone (SSZ) peridotites, and minor volcanic rocks, supposedly island-arc basalts and MORB-type rocks, most likely derived from Vardarian ophiolites. Wackestones from the southwest of Samothraki contain a moderately well-preserved calcareous microfossil assemblage, comprising Nummulites fabianii (PREVER), Nummulites striatus (BRUGUIERE), Pellatispim sp., and Operculina sp., indicating an early Priabonian age (Late Eocene). The sedimentation of the Eocene succession was influenced by regional tectonic and volcanic activity. The rocks have been deposited contemporaneous with the extensional exhumation of the eastern Rhodope Massif.

Detrital chromian spinels from Upper Ordovician deposits in the Precordillera terrane, Argentina: A mafic crust input

The study of heavy minerals from the Caradocian Pavón Formation (central Argentina) suggests that MORB and continental intraplate flood basalts were among the source rocks for the detrital record. The Pavón Formation was deposited on the disputed exotic Precordillera terrane. Provenance studies on this formation revealed sedimentary rocks characterized by an upper continental crustal component mixed with a mafic source, where the latter could not be described. The detrital chromian spinels provide more information about this component. The detrital spinels were chemically separated into two groups. Group 1 shows characteristics typical for host rocks related to MORB (Cr# values are between 0.4 and 0.6, Fe 2+# range from 0.2 to 0.4, and they have low TiO 2 and low Fe 3+# contents). Conversely, Group 2 has Cr# of 0.7, Fe 2+# ranging from 0.5 to 0.8, higher Fe 3+# and TiO 2 contents up to 4.7%, and they are related to continental flood basalts. The detrital spinels are chemically and texturally compared to those hosted in probable source rocks. Although the mafic source still remains unknown, the presence of detrital chromian spinels within the Pavón Formation implies the existence of an oceanic crustal component closely related to the Precordillera terrane.

Geochemistry, provenance and stratigraphic age of metasedimentary rocks from the eastern Vardar suture zone, northern Greece

Uppermost Palaeozoic and Mesozoic sediments from the Vardar suture zone in northern Greece record a cycle of Neotethyan oceanic basin opening and closure and their analysis places tight constraints on the geotectonic evolution of the area. The oldest post-Carboniferous sedimentary unit in the study area is the Examili Formation, which comprises mainly metaarkoses and metaquartzites, and was deposited in an intracontinental rift-related sedimentary basin in proximity to the Vertiskos Terrane during the Permian–Triassic. The Melissochori Formation (former Svoula flysch) comprises predominantly metasandstones with significant carbonate content and was deposited in front of a Carboniferous–Permian basement unit of volcanic-arc origin with minor input from older basement rocks, probably at the slope of a carbonate platform in the Early–Middle Jurassic. By contrast, the petrography and whole-rock geochemistry of sedimentary rocks of the Prinochori Formation point to a source area dominated by mafic–ultramafic but also intermediate rocks, presumably ophiolites and granodiorites or equivalents. This is reinforced by the presence of detrital chrome spinel, which is the first find of this mineral in sedimentary successions from the eastern Vardar Zone of northern Greece. Microprobe analyses suggest that most of the detrital chrome spinels were derived from MOR-type peridotites and supra-subduction zone (SSZ) peridotites, whereas only a small fraction comes from volcanic rocks, presumably mid-ocean ridge and island-arc basalts. The Prinochori Formation was probably deposited in front of a nappe complex in the Early Cretaceous, comprising ophiolitic rocks and basement slivers from the Vertiskos Terrane or equivalent rocks. Furthermore, a microfauna assemblage of Ovalveolina sp., Pseudonummuloculina sp. and dasycladacea algae of genus Thaumatoporella sp. was found in a calcareous clastic succession cropping out in the Oreokastro area, which was so far thought to be of Late Triassic–Middle Jurassic age. These data clearly indicate an Albian–Cenomanian age of deposition for this sedimentary succession. In conclusion, the rocks of the eastern Vardar suture zone record Mesozoic rifting, related to the opening of a Neotethyan Ocean, Middle Jurassic intraoceanic subduction, attendant volcanic-arc magmatism, ophiolite emplacement, and finally oceanic basin closure. Polyphase tectonics and metamorphism complicate palinspastic reconstructions.

Early Cretaceous paleogeography of Korea and Southwest Japan inferred from occurrence of detrital chromian spinels

AbstractThe Sindong Group was deposited in the north–south trending half‐graben Nakdong Trough, southern Korean peninsula. The occurrence of detrital chromian spinels from the Jinju Formation of the Sindong Group in the Gyeongsang Basin means that the mafic to ultramafic rocks were exposed in its provenance. The chromian spinels from the Jinju Formation are characterized by extremely low TiO2 and Fe3+. Moreover, their range of Cr# is from 0.45 to 0.80 and makes a single trend with Mg#. The chemistry of chromian spinels implies that the source rocks for chromian spinels were peridotites or serpentinites, which originated in the mantle wedge. To more narrowly constrain their source rocks, the Ulsan and Andong serpentinites exposed in the Gyeongsang Basin were examined petrographically. Chromian spinels in the Andong serpentinite differ from those of the Jinju Formation and those in the Ulsan serpentinite partly resemble them. Furthermore, the Jinju chromian spinel suite is similar to the detrital chromian spinels from the Mesozoic sediments in the Circum‐Hida Tectonic zone, which includes the Nagato Tectonic zone in Southwest Japan and the Joetsu Belt in Northeast Japan. This suggests that the basement rocks, which were located along the main fault bounding the eastern edge of the Nakdong Trough, had exposures of peridotite or serpentinite. It is possible that the Nakdong Trough was directly adjacent to the Circum‐Hida Tectonic zone before the opening of the Sea of Japan (East Sea).

Thematic Section: Geological anatomy of East and South Asia: Paleogeography and paleoenvironments in Eastern Tethys (IGCP 516) Part 1

Thematic Section: Geological anatomy of East and South Asia: Paleogeography and paleoenvironments in Eastern Tethys (IGCP 516) Part 1

Geochemical constraints on the provenance and depositional setting of sedimentary rocks from the islands of Chios, Inousses and Psara, Aegean Sea, Greece: implications for the evolution of Palaeotethys

The provenance and depositional setting of Late Palaeozoic and Early Mesozoic clastic sediments from the eastern Aegean archipelago are examined here for the first time using whole-rock geochemistry and composition of detrital chrome spinel. Major- and trace-element data for Late Palaeozoic and Permo-Triassic clastic sediments from the Lower and Upper Units of Chios are compatible with an acidic to intermediate source, minor input of (ultra)mafic detritus and recycling of older sedimentary components. Chondrite-normalized REE profiles are uniform with light REE enrichments (La N /Yb N c . 7.7), negative Eu anomalies (Eu/Eu* c . 0.67) and flat heavy REE patterns (Gd N /Yb N c . 1.5), indicating an upper continental crustal source and/or young differentiated arc material. Detrital chrome spinel from the clastic sediments of Chios has Cr-number (Cr/(Cr + Al)) values between 0.29 and 0.89 and Mg-number (Mg/(Mg + Fe 2+ )) values between 0.24 and 0.70, suggesting a probably mixed (ultra)mafic source involving ridge peridotites (mid-ocean ridge type), fore-arc peridotites and island-arc basalts. The metasediments from the islands of Inousses and Psara have similar whole-rock chemical signatures to those of Chios, although no evidence was found for an (ultra)mafic source. We conclude that both the Late Palaeozoic sediments from the Lower and Upper Units of Chios and the metasediments from Inousses and Psara were deposited in a continental island-arc setting until at least Late Permian times, probably at a single Palaeotethyan margin. They are interpreted to be allochthonous, tectonically transported to their present position by Late Mesozoic to Cenozoic orogenic processes.

Chemical variability in chrome spinel grains from magnetically fractionated ilmenite concentrates: implications for processing

Detrital chrome spinels are contaminant grains within ilmenite rich heavy mineral concentrates found along the southeast coastline of Africa and in the Murray Basin region of southeastern Australia. Separation is often difficult because of overlaps of physical properties between the chrome spinels and ilmenite. The presence of even minor levels of chromia in the concentrates will downgrade their market value as potential feedstocks for the production of titania pigment. In the present paper, the chemistry and distribution of chrome spinels in magnetically fractionated ilmenite concentrates from both regions are characterised using electron microprobe imaging and analysis techniques to establish the chemical and mineralogical factors that impact on their separation behaviour. Results show that the South African sample contains two chemically and magnetically distinct chrome spinel groups. The first group is dominated by a strong trend that reflects the mutual substitution between Al3+ and Cr3+ while the second group is characterised by compositions containing abundant Fe3O4 magnetite component. The presence of these two spinel groups means that physical separation from the ilmenite is relatively straightforward using simple roasting and magnetic separation procedures. In comparison, the Murray Basin chrome spinels exhibit broad chemical variation that results in no clear separation based on magnetic response. The broad spread in composition and magnetic susceptibility of the chrome spinels is responsible for the previously observed difficulties in developing successful separation methods.

Widespread arc-related melting in the mantle section of the northern Oman ophiolite as inferred from detrital chromian spinels

We examined detrital chromian spinels, in recent river beds, derived from the mantle section to deterrmine whether the mantle peridotite of the northern Oman ophiolite is of oceanic or arc origin. The Cr-number (= Cr/(Cr + Al) atomic ratio) of the detrital chromian spinels mostly ranges from 0.4 to 0.8, and more than 60% of them have Cr-numbers higher than 0.6. This indicates a significant extent of island-arc nature because chromian spinels seldom have Cr-numbers higher than 0.6 in ocean-floor rocks. The high-Cr-number (>0.6) spinels, which are also low in TiO 2 (<0.3 wt%), are probably derived from an arc setting. Lherzolite with spinel Cr-numbers <0.2 is absent except near the base of the section. The high-Cr-number detrital chromian spinels are more abundant from the mantle section with more frequent discordant dunite pods. Post-deformational discordant dunite and adjacent harzburgite include the high-Cr-number spinels in outcrops. The upper mantle of the northern Oman ophiolite was formed at a fast-spreading ridge and was later modified by island-arc magmatism in a subduction-zone environment. This switch of tectonic setting from a mid-oceanic ridge to an island arc is essential in the explanation of obduction of a slice of oceanic lithosphere onto a continental margin as an ophiolite.

On the provenance of mid-Cretaceous turbidites of the Pindos zone (Greece): implications from heavy mineral distribution, detrital zircon ages and chrome spinel chemistry

Two heavy mineral populations characterize the siliciclastic material of the mid-Cretaceous turbidites of the Katafito Formation (‘First Flysch’) of the Pindos zone: a stable, zircon-rich group and an ophiolite-derived, chrome spinel-rich one. U/Pb and Pb/Pb dating on magmatic zircons from the stable heavy mineral group clearly illustrate the existence of Variscan magmatic complexes in the source terrain, but also provide evidence for magmatism as old as Precambrian. Based on microprobe analyses, the chrome spinel detritus was predominantly supplied from peridotites of mid-ocean ridge as well as suprasubduction zone origin. A small volcanic spinel population was mainly derived from MORB and back-arc basin basalts. The lithological variability of the mid-Cretaceous ophiolite bodies, based on spinel chemistry, is much broader than that of ophiolite complexes presently exposed in the Hellenides. The chrome spinel detritus compares closely with that from the Outer and Inner Dinarides. The source terrain of the ophiolite-derived heavy minerals was situated in a more internal palaeogeographic position than that of the Pindos zone. The zircon-rich heavy mineral group could have had either an external and/or an internal source, but the chrome spinel constantly accompanying the stable mineral detritus seems to be more indicative of an internal source terrain.

Detrital chrome-spinel grains in heavy-mineral sand deposits from southeast Africa

AbstractDetrital chrome-spinels are contaminant grains within ilmenite concentrates produced from heavy-mineral deposits along the coast of southeast Africa. The presence of even minor levels of chromia in the predominantly ilmenite-rich concentrates, downgrades their market value as potential feedstocks for the production of titania pigment. An understanding of their composition can assist in their removal from the ilmenite concentrates.Compositions from a database of close to 900 chrome-spinel analyses shows the major element components and their ranges (in wt.%) are: Cr: 0.4-45.3, Al: 0.0-31.0, Fe: 8.5-69.6 and Mg: 0.0-12.2. Minor components include Ti: 0.1-11.4 and Zn: 0.0-13.7.The chrome-spinel data fall into two compositionally distinct groups. The first group of spinels is dominated by a strong trend reflecting the mutual substitution between Al3+ and Cr3+ in the spinel structure. The second group of spinels is characterized by compositions containing abundant Fe3O4magnetite component. The clear division between chrome-spinel compositional types indicates the grains are derived from at least two chemically dissimilar provenances.The compositional differences between the chrome-spinel groups has a positive impact on subsequent ilmenite upgrading treatments as the spinels which contain the highest magnetite component are easily removed via low-intensity magnetic separation procedures.

Compositional and textural variation in detrital chrome-spinels from the Murray Basin, southeastern Australia

AbstractDetrital chrome-spinels are contaminant grains within heavy-mineral concentrates found in the Murray Basin of southeastern Australia. The presence of even minor levels of chromia in the predominantly ilmenite-rich concentrates downgrades their market value as potential feedstocks for the production of titania pigment.Compositions from a database of close to 5000 chrome-spinel analyses show a broad range in chemistry. The major element components and their ranges (wt.%) are Cr: 3.10–52.06, Al: 0.46–32.50, Fe: 3.50–44.48 and Mg: 0.03–15.79. Minor components include; Ti: 0.01–6.41, Zn: 0.00–23.00 and Mn: 0.00–5.82. The broad variation in composition suggests multiple source areas for the chrome-spinels although detailed textural examination indicates that variation has also been introduced through pre- and post-deposition alteration processes.The Murray Basin chrome-spinel database has the potential to be used in interpreting and predicting the effects of various processing conditions used to separate the chrome-spinels from the ilmenite.

Missing ophiolitic rocks along the Mae Yuam Fault as the Gondwana–Tethys divide in north‐west Thailand

Abstract Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north‐west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean‐floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion.

Petrography and chemistry of sandstones from the Swiss Molasse Basin: an archive of the Oligocene to Miocene evolution of the Central Alps

Abstract Oligocene to Miocene fluvial sandstones from the Swiss Molasse Basin were analysed for sandstone framework composition, heavy minerals, whole‐rock geochemistry and detrital chrome spinel chemistry. Samples were taken from the proximal part of the basin close to the Alpine main thrust and are chronostratigraphically calibrated between 31 and 13 Ma. Sandstone composition allows the identification of different source rocks, and their variation in time and space place constraints on the Oligocene to Miocene evolution of the Central Alps. In the eastern part of the basin, sandstones document a normal unroofing sequence with the downcutting from Austroalpine sedimentary cover into Austroalpine crystalline rocks and, slightly later at ≈ 21 Ma, into Penninic ophiolites. In the central part, downcutting into crystalline basement rocks occurred at ≈ 25 Ma, and the removal of the sedimentary cover was much more advanced than in the east. This may be interpreted as a first signal from the doming of the Lepontine area. At ≈ 20 Ma, extensional tectonics in the hinterland led to the first exposure of low‐grade metamorphic rocks from the footwall of the Simplon Fault in the Central Alps. Erosion of these rocks persisted up to the youngest sediments at ≈ 13 Ma. In the western part of the basin, a contribution from granitoid and (ultra)mafic rocks is documented as early as ≈ 28 Ma. The source for the (ultra)mafic detritus is Penninic ophiolites from the Piemonte zone of the western Alps, which were already exposed at the surface at that time.

Provenance of the Peloponnese (Greece) flysch based on heavy minerals

The heavy mineral distribution of the Palaeogene flysch deposits of the Ionian, Gavrovo–Tripolitza and Pindos zones of the Peloponnese has been systematically investigated. The Ionian zone is distinguished from the Gavrovo–Tripolitza zone by higher amounts of detrital chrome spinel. The Ionian and the western occurrences of the Gavrovo–Tripolitza flysch are comparable with the successions of the Greek mainland, whereas samples of the Gavrovo–Tripolitza flysch from central and eastern locations of the Peloponnese, which crop out in tectonic windows, are clearly distinct. On the basis of heavy mineral distribution, the Gavrovo–Tripolitza flysch of the central and eastern Peloponnese shows clear relationships to the metaflysch sediments exposed in the tectonic windows of Olympos and Ossa, in Thessaly, which have no relation to the Gavrovo flysch of the mainland. The Pindos flysch from the Peloponnese contains the same heavy mineral assemblages as the pre-Middle Eocene deposits of the mainland. Younger Pindos flysch sediments are not observed on the Peloponnese. The differences in heavy mineral distribution within the Gavrovo–Tripolitza flysch, between the western and eastern localities, can be explained by an intensive reworking of Pindos flysch during the tectonic progradation of the Pindos nappe onto its foreland basin.

Geodynamic Evolution of Loei and Phetchabun Regions — Does the Discovery of Detrital Chromian Spinels from the Nam Duk Formation (Permian, North-Central Thailand) Provide New Constraint?

The discovery of the chromian spinel detritus in sandstones from the Permian Nam Duk Formation (Phetchabun region) confirms that the siliciclastic part of this formation is related to the erosion of a mountain belt caused by compressional deformation. The question discussed is whether this detritus is derived from an older orogen exposed today in the region of Loei east of the Nam Duk Basin, or it is from a mountain belt which evolved during Permian times in the west (Nan-Uttaradit region). In the first case the Nam Duk Formation would represent the passive continental margin sequence of the “Indochina craton”, and in the second case it would be part of the sedimentary wedge associated with the compressional deformation and subsequent uplift to the erosional level during Middle to Upper Permian of a rising mountain belt further in the west. In this contribution, arguments in favour of the second scenario are discussed. The region close to the Nan-Uttaradit suture zone shows evidence of compressional deformation and subsequent uplift to an erosional level in the Permian when the chromian spinel detritus was deposited in the Nam Duk Formation.

Tectonic significance of detrital chromian spinels in the Permian Nam Duk Formation, central Thailand

Detrital chromian spinels in the Permian Nam Duk Formation, Thailand are examined to determine the petrological characteristics of eroded mafic-ultramafic rocks in the Phetchabun area. Detrital chromian spinels are found as one of accessory heavy minerals from turbiditic sandstones of the Nam Duk Formation. The detrital chromian spinels are generally deep brown to almost opaque in thin section due to their wide compositional variation, and are relatively small, about 20–190 microns across. They sometimes exhibit subhedral to euhedral shapes and rarely have inclusions. Thirty–five grains were chosen for microprobe analysis. They have relatively high Cr contents, the Cr#(=Cr/[Cr+Al] atomic ratio), being mostly higher than 0.50, and up to 0.83. TiO2 contents are generally low but variable from 0.02 to 1.16 wt%, and Fe3+ ratios are consistently low. The relatively high Cr# and low TiO2 contents of the Nam Duk detrital chromian spinels in the Permian sediments indicate their derivation from mafic-ultramafic rocks of are origin. The relatively small and euhedral to subhedral spinels with inclusions especially suggest their provenance from volcanic rocks. It is strongly inferred that igneous rocks, namely volcanics and peridotites, of arc origin were exposed in this region at the Permian at least. The Loei-Phetchabun-Ko Chang volcanic belt, interpreted to have been constructed by several magmatic episodes (Devonian, Permian, Triassic, and Late Tertiary), could be a good candidate for the source of detrital chromian spinels in the Nam Duk Formation.