Impact of the body waves on the serpentine structure

A rare case of rhythmic banded eclogitization on serpentinites in crustal condition (3 km south of Avren village, Krumovgrad district), is interpreted as an effect of seismic impact. Bands of garnet lherzolites (2–5 cm) alternate with strips of unchanged serpentinite. The bands consist of pyrope, diopside, enstatite, olivine, spinel, crystallized at Т 560–820 oC and P 8–15 kbar. The longitudinal P-waves create zones of dilatation in the serpentine structure where the bonds were broken. After crystallization of mobilized particles a stripped texture was formed.

40Ar/39Ar Geochronology and New Mineralogical and Geochemical Data from Lamprophyres of Chompolo Field (South Yakutia, Russia)

The alkaline igneous rocks of the Chompolo field (Aldan shield, Siberian craton), previously defined as kimberlites or lamproites, are more correctly classified as low-Ti lamprophyres. The emplacement age of the Ogonek pipe (137.8 ± 1.2 Ma) and the Aldanskaya dike (157.0 ± 1.6 Ma) was obtained using 40Ar/39Ar K-richterite dating. The Chompolo rocks contain abundant xenocrysts of mantle minerals (chromium-rich pyropic garnets, Cr-diopsides, spinels, etc.). The composition of the mantle xenocrysts indicates the predominance of spinel and garnet–spinel lherzolites, while the presence of garnet lherzolites, dunites, harzburgites, and eclogites is minor. The Chompolo rocks are characterized by large-ion lithophile element (LILE) and Light Rare Earth Element (LREE) enrichments, and high field strength element (HFSE) depletions. The rocks of the Ogonek pipe have radiogenic Sr (87Sr/86Sr (t) = 0.70775 and 0.70954), and highly unradiogenic εNd(t) (−20.03 and −20.44) isotopic composition. The trace element and isotopic characteristics of the Chompolo rocks are indicative of the involvement of subducted materials in their ancient enriched lithospheric mantle source. The Chompolo rocks were formed at the stage when the Mesozoic igneous activity was triggered by global tectonic events. The Chompolo field of alkaline magmatism is one of the few available geological objects, which provides the opportunity to investigate the subcontinental lithospheric mantle beneath the south part of the Siberian craton.

PETROLOGY AND GEOCHEMISTRY OF INTRUSIVE ROCKS OF THE SINYUKHINSKOYE DEPOSIT (GORNY ALTAI)

New data on phase relationships, petrology and geochemistry of the Sinyukhinskoye rocks and dikes of the same deposit are presented. Five phases of rock intrusions formed in a homodromic-antidromic sequence are found. The Sinyukhinskoye rocks fall in the oxidized type. In the depth, a source of melting was garnet lherzolites, and, to a lesser extent, spinel lherzolites of an enriched mantle source of the lithospheric slab with a degree of partial melting from 0.2 to 0.4 and low pressure. The formation of intrusive rocks of the deposit took place in the post-collisional environment. The magmatite fluids of the massif and dikes were characterized by high partial pressures of such volatile components as H2O, Cl, F, CO2, which were the main carriers of metals. The rocks exhibit the tetrad effect of the W-type REE fractionation. The dependences of the values of the latter and the concentrations of copper and gold in igneous rocks and fluids were determined by different regimes of acidity and alkalinity of the medium. The deposit belongs to a complex family of ores of the copper-gold-skarn-porphyry type. In the Cheryomukhovaya Sopka and Chir areas, this is also confirmed by the presence of the copper-gold-porphyry type in the ore field, in addition to the gold-copperskarn mineralization.