Fourier transform infrared spectroscopy data and carbon isotope characteristics of the ophiolite-hosted diamonds from the Luobusa ophiolite, Tibet, and Ray-Iz ophiolite, Polar Urals

Abstract

We report new δ 13 C data and N content and aggregation state values for microdiamonds recovered from peridotites and chromitites of the Luobusa ophiolite (Tibet) and chromitites of the Ray-Iz ophiolite in the Polar Urals (Russia). All analyzed microdiamonds contain significant nitrogen contents (from 108 to 589 atomic ppm ± 20%) with a consistently low aggregation state and show identical infrared spectra dominated by strong absorption between 1130 cm -1 and 1344 cm -1 , and therefore characterize type Ib diamond. Microdiamonds from the Luobusa peridotites have δ 13 C (PDB) values ranging from −28.7‰ to −16.9‰, and N contents from 151 to 589 atomic ppm. The δ 13 C and N content values for diamonds from the Luobusa chromitites are −29‰ to −15.5‰ and 152-428 atomic ppm, respectively. Microdiamonds from the Ray-Iz chromitites show δ 13 C values varying from −27.6‰ to −21.6‰ and N contents from 108 to 499 atomic ppm. The carbon isotopes values have features similar to previously analyzed metamorphic diamonds from other worldwide localities, but the samples are characterized by lower N contents. In every respect, they are different from diamonds occurring in kimberlites and impact craters. Our samples also differ from the few synthetic diamonds we analyzed, in that they show enhanced δ 13 C variability and less advanced aggregation state than synthetic diamonds. Our newly obtained N aggregation state and N content data are consistent with diamond formation over a narrow and rather cold temperature range (i.e., <950 °C), and in a short residence time (i.e., within several million years) at high temperatures in the deep mantle.

Factors Controlling the Chromium Isotope Compositions in Podiform Chromitites

“…The presence of harmful Cr(VI) in soils and in turn in groundwater may be related to natural processes or/and human activities, such as transfer of weathered material from rocks and primary raw materials, wastes and/or application of large amounts of fertilizers and pesticides for a long time in cultivated areas. The European Soil Data Centre has established a link between the effects of metal bio-availability and metal bio-accumulation, and human health and negative impacts on ecosystems [25][26][27][28][29][30][87][88][89][90][91][92][93][94][95][96]. Dose-dependent differences in toxicities of elements, the particle size, and the oxidation state require serious consideration in health-risk assessments [90].…”

“…The salinization of shallow aquifers may have a major effect on plant/crop growth and toxicity. The use of multidisciplinary methods in the study of ecosystem processes in response to groundwater and soil system has great potentials for sustainable developments [87][88][89][90][91][92][93][94][95][96].…”

“…In summary, the original geochemical compositions of chromitites may have been modified by subsequent, post-magmatic processes taking place at shallow mantle depths [35][36][37][38]56,57,68,69,[72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89]97]. The wide range of δ 53 Cr values, from positive, slightly negative to the most negatively fractionated signatures, even present in individual relatively large chromitite deposits, together with negative trends observed between δ 53 Cr values and Cr/(Cr + Al) ratios in chromitites, may reflect a control of Cr isotope compositions in chromitites by degrees of partial melting and by magma fractionation.…”

Ophiolites, diamonds, and ultrahigh-pressure minerals: New discoveries and concepts on upper mantle petrogenesis

“…The widespread occurrence in the Dingqing peridotites of quartz, rutile, titanite, corundum, almandine garnet, kyanite, and andalusite also shows deep, subduction-driven recycling of crustal material in the mantle. Xu et al (2018) report new δ 13 C data and nitrogen content and aggregation state values for microdiamonds obtained from peridotites and chromitites of the Cretaceous Luobusa ophiolite in southern Tibet and from chromitites of the Early Devonian Ray-Iz ophiolite in the Polar Urals of Russia (Yang et al, 2015b). The authors chose to do this work because nitrogen is the most abundant impurity in natural diamonds and nitrogen aggregation characteristics in diamonds help to constrain diamond residence time and mantle temperatures during their formation.…”

“…Diamond, stishovite, qingsongite, and Ca-silicate perovskite that form from melts and recycled material become mixed with other UHP phases and highly reduced minerals, derived from zones with extremely low fO 2 within the MTZ, as required for the formation of moissanite and other numerous native elements (Bai et al, 1993;Xu et al, 2018). Near the top of the MTZ (>300 km depth) (Fig.…”