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Procesy wielokrotnego brekcjonowania deformacyjnego i powstawania stopów impaktowych w chondrytach na przykładzie meteorytów z kolekcji Jacka Siemiątkowskiego

Krzesińska A., Siemiątkowski J.

Przegląd Geologiczny

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2011

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Vol. 59, nr 8

576-588

EN

Chondrites NWA-869 (L3.9-6 S2), Tsarev (L5 S5), Ghubara (L5 S4), Zag (H3-6 S3) from the Jacek Siemiatkowski Collection show evidence of multiple brecciation. Petrographic and microprobe analyses of thin sections allowed to identify and distinguish syn- and postaccretion impact and thermal transformations which took place on the chondrite parent bodies. The studied meteorites contain clasts of chemically equilibrated and unequilibrated rocks as well as many unusual achondritic-like clasts. The latter are cognate impact-melt rocks. All the clasts provide records of complex metamorphic and deformational histories of the parent bodies. Chondrites displayed numerous metamorphic transformations and deformations caused by many shock or shock-related processes under conditions ranging from impact-related shearing to HP shock-induced shattering and melting. These processes led to the formation of quenched impact melts, metal veins and nodules, darkened clasts and locally cataclasis.

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High resolution x-ray tomography as a tool for analysis of internal textures in meteorites

Krzesińska A.

Meteorites

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2011

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Vol. 1, No. 1

3-12

EN

A comparison of internal textures of the NWA-5929, Ghubara and Pułtusk chondrites has been carried out using high resolution X-ray tomography. This is a powerful, non-destructive technique that allows on to determine textural and compositional dierences that occur between ordinary chondrites of various groups by means of grey-levels calehistograms, first-order statistics, and 3D imaging. Deformational structures in the Pułtusk meteorite such as cataclastic zones, impact melt clasts, melt veins, and melt pockets are observed and studied. Measurements of metal particle size are achieved, giving even deeper insight into textural features of meteorite. My approach shows that as shock deformation occurred, numerous small metal grains became progressively dispersed within the volume of the deformed Pułtusk meteorite rock. Simultaneously, metal was mobilized via frictional or direct impact melting to form scarce large metal nodules or grains arranged along the margins of relict chondritic clasts or as components of irregular injection veining. The possibility of tracing of these impact related processes by using tomography micrograms (without breaking the sample) is very useful for distinguishing which parts of each meteorite were deformed in diferent ways in order to make first order observations regarding the deformational history of these meteorites.

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Struktury hydratacyjne i deformacyjne w skałach czapy gipsowej wysadu solnego Dębiny w rowie Kleszczowa

Krzesińska A., Redlińska-Marczyńska A., Wilkosz P., Żelaźniewicz A.

Przegląd Geologiczny

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2010

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Vol. 58, nr 6

522-530

EN

The Dębina salt dome is situated in central part of the Tertiary Kleszczów Graben, central Poland. Cap rocks of the dome were characterized on the basis of analysis of core material from a well drilled in the northern part of that structure. The cap rock sequence may be subdivided into two parts. Its lower part with breciated structure represents residuum from dissolution of saline series whereas the upper comprises rocks developed by coalescence of shale cover with gypsum. Gypsum rocks of the cap form 6 lithotypes. In these lithotypes it is possible to distinguish: 1) recrystallizational structures developed during diagenesis and multiple hydration transformations, 2) structures developed in a local stress field related to displacements evoked by dissolution of the cap rocks and fluid circulation. Structures of the first type include microcrystalline gypsum with anhydrite relics and carbonate nodules, lenticular and acicular gypsum, porphyroblastic and even-grained gypsum as well as vein gypsum and first generation of stylolites. The other type of structures is represented by: gypsum showing shape fabrics and associated gypsum nodules, gypsum grains with geometry of -clasts, fibrous gypsum in pressure shadows, structures of the core-and-mantle type, subgrains developing in bigger crystals and second generation of stylolites and slickolites. Five sets of fractures were recorded. These fractures developed in the cape rocks under stress field with the vertical maximum stress axis and active shear planes. The normal faults of B, C and D sets could be formed during upward motion of the dome, its stagnation, or during gravitational collapse triggered by karst processes. Oblique striations on microfault B surfaces point to later reactivation under local normal-slip regime caused by ongoing subsidence of the cap rocks, or alternatively - a reactivation that occurred in response to external stress field which controlled evolution of the extensional Kleszczów Graben.