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Skały ultrazasadowe i zasadowe z otoczenia mariupolitów występujących w alkalicznym Masywie Oktiabrskim (SE Ukraina) – badania wstępne

Dumańska-Słowik M., Heflik W.

Gospodarka Surowcami Mineralnymi

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2016

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T. 32, z. 2

63--77

PL

Treścią pracy są wyniki badań mineralogiczno-geochemicznych próbek skał ultrazasadowych (perydotyt, piroksenit) i zasadowych (gabra oliwinowe) pobranych z bezpośredniego kontaktu z utworami alkalicznymi pochodzącymi z Pola Mazurowskiego Masywu Oktiabrskiego położonego nad morzem Azowskim (południowo-wschodnia Ukraina). Na podstawie składu mineralnego perydotyt został zaklasyfikowany jako wehrlit, a piroksenit jako klinopiroksenit oliwinowy. Omawiane skały odznaczają się znaczną zawartością, Fe, Mg, Ca, Ti oraz zubożeniem w P, alkalia (przewaga Na nad K) i REE. Spośród badanych skał gabro oliwinowe charakteryzuje się największym udziałem REE , w tym La, Ce, Nd, Y, Sm i Th oraz najwyższymi zawartościami alkaliów. Ten typ gabra wykazuje bliskie genetyczne spowinowacenie ze skałami alkalicznymi, występującymi w ich otoczeniu.

EN

The preliminary results of the mineralogical and geochemical investigations of ultramafic (peridotite and pyroxenite) and mafic (olivine gabbro) rocks from the Mazurovski Field of the Oktiabrski Massif in South-eastern Ukraine are presented in this paper. Peridotite is mainly composed of olivine (forsterite), pyroxene (diallage), plagioclase (labradorite) and ore minerals such as magnetite, ilmenite and pyrite. Antigorite and talk are secondary components. Diallage with subordinate plagioclase, olivine and Fe compounds (oxides/sulphides) are found in pyroxenite. Gabro is made of two generations of plagioclase, diallage, olivine, biotite and amphiboles (hornblende and actinolite). Chlorite, talk and ore minerals (ilmenite, pyrite, Fe oxides/hydroxides) occur as its subordinate components. On the basis of their mineral composition peridotite was classified as wehrlite, pyroxenite as clinopyroxenite, whereas the mafic rocks are represented by olivine gabbro. The mafic rocks are most likely products orginating from calc-alkaline magma. Owing to the fact that chromite was not identified in periodite, it is very probable that this rock is loco-temperature differentation product of ultramorfic rocks. The ultrabasic rocks and enriched with Al2O3, CaO and Fe and complethy impoverished of REES and alkalis. Only one olivine gabbro shows some amounts of REE s (0.096 wt.% REE s with the distinct predominance of LREE over HREE ) and alkalis (2.89–4.0 wt.% Na2O + K2O), which are surely genetically associated with alkaline rocks occurring in the near vicinity of the ultramafic and mafic rocks of the Oktiabrski Massif. The enrichment of gabbro in REEs and alkalis most probably proceeded post-magmatic activity.

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Mantle rock exposures at oceanic core complexes along mid-ocean ridges

Ciazela J., Koepke J., Dick H. J. B., Muszynski A.

Geologos

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2015

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Vol. 21, No. 4

207--231

EN

The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.

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The origin of the Popiel peridotite (Western Sudetes, SW Poland) : metamorphism of the island arc tholeiitic cumulate

Kukuła A., Puziewicz J., Ntaflos T.

Geological Quarterly

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2015

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Vol. 59, No. 2

239--247

EN

A small (280 x 140 m) outcrop of peridotite occurs on Popiel Hill (Sudetes, SW Poland) within the low-grade metabasic rocks of the Rudawy Janowickie Complex, which form the eastern and north-eastern cover of the Variscan Karkonosze granite. The peridotite is situated on the Intra-Sudetic Fault, one of the major Variscan dislocations in the region. The rock consists of strongly tectonised olivine (Fo84-88) and orthopyroxene (Mg# 0.84–0.88) aggregates, overgrown by tremolite-magnesiohornblende, locally forming large crystals, embedded in serpentine. Spinel and magnetite are subordinate; ilmenite, Fe-sulfide, and apatite are accessories. The bulk-rock chemical composition suggests a lherzolitic composition and the occurrence of primary clinopyroxene, now completely replaced by tremolite and magnesiohornblende. Rare Earth Element patterns are flat, slightly enriched relatively to primitive mantle, as is typical of island arc tholeiites. Olivine, orthopyroxene, and spinel were the first to crystallize, and they represent relics of a primary igneous assemblage. They were followed by tremolite and serpentine, formed during uplift and related metamorphism. The last mineral to crystallize was magnesiohornblende, which originated due to contact metamorphism by the Karkonosze granite magma. The Popiel peridotite probably represents a small slice of lherzolitic cumulate, which originated in a tholeiitic magma chamber at the roots of a supra-subduction volcanic arc.