Detrital Spinels Research Articles

Primary petrological characteristics of peridotites in the Sangun zone of northern Kyushu: a preliminary note from detrital chromain spinels.

Detrital chromian spinel grains in recent river beds in the Sangun zone of northern Kyushu are examined to infer primary characteristics of the peridotite, which has not been studied in detail. The use of the detrital chromian spinel is of great advantage to understand a general character of peridotite complexes. The peridotites were metamorphosed and serpentinized to various extent but their protoliths are possibly dunite and wehrlite. Their chromian spinel sometimes preserves almost intact cores, which are expected to be an indicator of their primary petrological characteristics. The primary spinel is high in Cr# (= Cr/[Cr+Al] atomic ratio), frequently around 0.7 to 0.9, low in Fe3+/(Cr+Al+Fe3+) atomic ratio, around 0.1, and is low in TiO2, containing 0.15 wt% on average. Some detrital spinels, especially those from Sasaguri, have high Mg#s (=Mg/[Mg+Fe2+] atomic ratios) at given Cr#s, being derived from rocks with high Mg#s or high spinel concentrations. Spinels in selected metaperidotite samples are within the compositional range of the detrital spinels. These spinels from northern Kyushu are notably different from those in ultramafic rocks, mainly dunite and harzburgite, exposed in the Sangun zone of the central Chugoku district, of which Cr# is around 0.5. The dunite and wehrlite with high-Cr#, low-Ti spinel are possibly of supra-subduction zone, especially of fore-arc, origin. This type of dunite and wehrlite have not been known from the Sangun zone, and this study highlights a high lithological variety of peridotite distributed in the Sangun zone. The variety can be inherited from petrological heterogeneity of the upper mantle to Moho transition zone of a supra-subduction zone setting.

Compositions of detrital spinels from Lower Cretaceous Sasayama Group, Hyogo Prefecture, Japan: Constraints on source lithology and tectonic setting.

Compositions of detrital spinels from Lower Cretaceous Sasayama Group, Hyogo Prefecture, Japan: Constraints on source lithology and tectonic setting.

Chemistry of detrital chromian spinels as an insight into petrological characteristics of their source peridotites: an example from the Ilocos Norte ophiolite, northern Luzon, Philippines.

Chemistry of detrital chromian spinels provides us useful information on the petrological characteristics of their source ultramafic and related rocks. This method is applied to the Ilocos Norte ophiolite, north of Laoag City, northern Luzon, Philippines, of which petrological characteristics have not been well known. Cr# (=Cr/[Cr+Al] atomic ratio) of the detrital spinels from one of the rivers running through the Ilocos Norte ophiolite ranges from 0.4 to 0.8, possibly indicating moderately to highly depleted harzburgites for their source rocks. This further indicates a supra-subduction zone origin for the Ilocos Norte ophiolite. The spinel chemistry demonstrates that the Ilocos Norte peridotites are different from the Coto and Acoje peridotites of the Zambales ophiolite, western Luzon.

Detrital Chromian Spinel Compositions Used to Reconstruct the Tectonic Setting of Provenance: Implications for Orogeny in the Canadian Cordillera

ABSTRACT Detrital chromian spinel is an important accessory mineral in chert and volcanic lithic sandstones from the northern Bowser Basin. Microprobe analyses show that Bowser Basin detrital chromian spinels have Cr/(Cr + Al) between 0.21 and 0. 89, Mg/(Mg + Fe2+) between 0.24 and 0.70, and Fe3+/(Fe3+ + Al + Cr) values below 0.12. Comparison with spinels from literature on ultramafic rocks indicates that the compositional range of the detrital spinels closely matches that of spinels from Alpine-type peridotites emplaced by obduction of marginal-basin crust and island-arc complexes. Furthermore, Bowser Basin spinels are compositionally distinct from spinels derived from either mid-ocean ridge, stratiform ultramafic complex, or Alaskan-type peridotite. The composition of the detrital spinel demonstrates that the source for Bowser Basin sediments included extensive Alpine-type peridotite, which probably originated as marginal-sea lithosphere. In addition, there is no evidence for material derived from mid-ocean ridge, Alaskan-type peridotites, or stratiform complexes. This provenance interpretation is in agreement with earlier interpretations that related chert pebbles in the Bowser Basin to chert-rich strata of the Cache Creek terrane and is consistent with the detrital modal analysis of sandstones, which calls for a source terrane consisting of obducted oceanic crust and island arc. The chemistry of the detrital spinels further suggests the source area was eroded prior to emplacement of Alaskan-type peridotites or any regional gree schist or higher-grade metamorphic events. Thus, microprobe compositional analysis of detrital spinels adds important detail to the provenance interpretation that is not available through analysis of detrital modes alone. The inference that marginal-basin lithosphere rather than material derived from mid-ocean ridges was the sediment source suggests that the obducted source terranes were closely associated with North America.

Chemistry of chromian spinel in volcanic rocks as a potential guide to magma chemistry

AbstractChromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO2 content of spinel, compared at similar Fe3+/(Cr + Al + Fe3+) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiO2 level at comparable Fe3+ ratios. Spinels from back-arc basin basalts, although similar in TiO2/Fe3+ ratio, are more enriched in Fe3+ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO2 than other intraplate basalt spinels and even slightly lower in TiO2 than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinelbearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.

Detrital spinels from alpinotype source rocks in middle Devonian sediments of the Rhenish Massif

Middle Devonian sandy siltstones of the Gummersbach area (Rhenish Massif) show increased Cr contents (up to 675 ppm). The chromium is mainly associated with detrital Cr-Al spinels. The spinels are characterized by a wide spectrum of chemical composition. In more than 50% of 134 analyzed spinel grains the Cr2O3 content exceeds 50 wt %. The A12O3 content which is negatively correlated to Cr2O3 reaches 40 wt %. The MgO contents are, with few exceptions, lower than the FeO contents; both elements are negatively correlated. The Fe2O3 contents which were calculated from a quarter of the grains rarely exceed 5 wt %. Besides Cr, Al, Fe, Mg TiO2 contents were determined. The chemical composition of the detrital spinels indicates provenance from peridotites of an ophiolite suite. Provenance analysis shows that the source area of the Middle Devonian clastic sediments was situated in the north.