Search Results

Upper Carboniferous (Westphalian) coal-bearing fluvial sediments (Téseny Sandstone Formation) of the Slavonian-Drava Unit and their reworked pebbles and cobbles occurring in the western part of the Mecsek Mountains in Miocene conglomerate sequences (Szászvár Formation) were studied.  Based on the petrographic and geochemical characteristics, the sandstone studied consists of arkose, subarkose, litharenite and sublitharenite. The main clastic source was a recycled orogenic area (collision suture and fold-thrust belt) dominated by metamorphic rocks. It was associated with a probably Variscan magmatic arc as indicated by the volcanic rock fragments. The original source area of these clastic sediments was felsic and the analyzed sandstone could correspond to a continental arc/active margin tectonic suite.  The pebble and cobble-sized clasts of the conglomerate were predominantly derived from acidic and intermediate volcanic rocks, low-grade regional metamorphic rocks (different types of schist, metasandstone, mylonite, metagranitoid, gneiss, quartzite, and metaquartzite) and siliceous sedimentary rocks. Among the sedimentary clasts, reworked black siltstone and fine-grained sandstone from older (possibly Carboniferous) deposits are common. Chert and contact metamorphic rocks are present in minor quantity. The extracted volcanic clasts consist of andesite, trachyandesite, dacite and rhyolite. Their geochemistry suggests convergent, active continental margin affinity. Upper Carboniferous siliciclastic successions are widely known at the southeastern margin of the European Variscides. In the area of the Upper Silesian Coal Basin, the Cracow Sandstone Series (Westphalian C and D) shows a similar petrographic composition to that of the Téseny Sandstone Formation. Additionally, volcanic clasts of the Upper Carboniferous conglomerate from southern Transdanubia and the calc-alkaline volcanites from the Intra-Sudetic Basin can be characterized by similar geochemical patterns.

Abstract

Ringwoodite, produced by shock metamorphism, is common in and adjacent to melt veins in highly shocked chondrites. Although ringwoodite can be crystallized from the silicate melt in the shock-veins or pockets, a major part of the easily observed ringwoodite in shock veins is formed by the transformation of olivine in host-rock fragments entrained in the melt or olivine along shock-vein margins. In this paper we examine the microstructures and textures of ringwoodites from NWA 5011 L-chondrite in order to better understanding the transformation mechanisms of ringwoodite by optical microscope. Finally, we attempt to locate the source region of L-type chondrites in three different impact scenarios of the L parent body.

Abstract

The Mesozoic complex of Darnó Hill area in NE Hungary, according to well core documentation, is made up of two units. The upper unit, the Darnó Unit s.s., consists predominantly of blocks of ophiolitic rocks (pillow and massive basalt, gabbro) and subordinate abyssal sediments (red radiolarite and red pelagic mudstone of either Ladinian-Carnian or Bathonian-Callovian age, as well as bluish-grey, sometimes blackish siliceous shale of the latter age). The basalt is geochemically of MOR type, based on earlier evaluations. However, it comes in two types: reddish or greenish amygdaloidal pillow basalts with peperitic facies containing reddish micritic limestone inclusions, and green basalts without any sedimentary carbonate inclusion. The former type is probably Middle- Triassic, advanced rifting stage-related basalt, whereas the latter is probably of Jurassic age, corresponding to the Szarvaskõ-type basalt of the western Bükk Mountains. Pre-Miocene presence of an ultramafic sheet above the complex is indicated by serpentinite pebbles in the Lower Miocene Darnó Conglomerate.

The lower unit, corresponding to the Mónosbél Unit of the western Bükk Mountains, consists of lower slope and toe-of-slope type sediments: dark grey shale and bluish-grey siliceous shale of Jurassic age, both showing distal turbiditic character, with frequently interbedded carbonate turbidites and debris flow deposits containing cm- to dm-sized limestone and micaceous sandstone clasts. One to ten m-sized slide blocks of reddish, siliceous Triassic Bódvalenke-type limestone associated with the above-mentioned reddish, amygdaloidal basalt also occur. In one of the studied cores a block comprising evaporitic siliciclastics akin to those of the Middle Permian Szentlélek Formation and black, fossiliferous limestone similar to the Upper Permian Nagyvisnyó Limestone Formation of the Bükk Mountains, was also encountered.

A preliminary comparison with similar Triassic advanced rifting-type basalt and limestone/radiolarite of the western ophiolite zone of the Balkan Peninsula is presented (Fig. 1): the Zagorje region of NW Croatia, the Zlatibor-Zlatar Mountains of SW Serbia, and the North Pindos and Othrys Mountains, as well as Euboea Island, of Northern Greece. We propose the terms “Loggitsi Basalt” for such Triassic basalt containing peperitic facies, after the village of Loggitsion located in the central part of the Othrys Mts, and “Bódvalenke Limestone” for the transitional facies between Hallstatt Limestone and Triassic red radiolarite, after the village of Bódvalenke located in the Rudabánya Hills. The northwesternmost occurrence of both of these typical Neotethyan formations can be found in NE Hungary (Darnó Hill and Bódva Unit of Rudabánya Hills, respectively).

Abstract

We studied optical microscopic and micro-Raman spectroscopic signatures of shocked olivine from the ALH 77005 Martian meteorite sample. The purpose of this study is to document pressure and temperature-related effects in olivine over the entire sample, which can aid in understanding structural changes due to shock metamorphism and the post-shock thermal annealing processes of lherzolitic Martian meteorites. According to the optical microscope observations, three areas may be discernible in olivine of the ALH 77005 in the vicinity of the melt pocket. The first area is the thermally undisturbed part of a grain, which contains a high density of shock-induced planar microdeformations such as Planar Deformation Features (PDFs) and Planar Fractures (PFs). Compared to the first area, the second area shows less shock-induced microstructures, while the third area is a strongly recrystallized region, but not formed from a melt.

A common Raman spectral feature of these olivines is a regular doublet peak centered at 823 and 852 cm⁻¹; additionally, two new peaks at 535 and 755 cm⁻¹ appear in the weakly annealed transition zones.

The 1,200-m-deep Budaörs-1 borehole provided important data for our understanding of the stratigraphy and tectonic setting of the southern part of the Buda Hills. Although previous reports contained valid observations and interpretations, a number of open questions remained. The importance of this borehole and the unsolved problems motivated us to revisit the archived core. The new studies confirmed the existing stratigraphic assignment for the upper dolomite unit (Budaörs Dolomite Formation) as the dasycladalean alga flora proved its late Anisian to Ladinian age assignment. An andesite dike was intersected within the Budaörs Dolomite. U–Pb age determination performed on zircon crystals revealed a Carnian age (~233 Ma), and settled the long-lasting dispute on the age of this dike, proving the existence of a Carnian volcanic activity in this area after the deposition of the Budaörs Dolomite. Palynostratigraphic studies provided evidence for a late Carnian to early Norian age of the upper part of the lower unit (Mátyáshegy Formation). This result verified an earlier assumption and reinforced the significance of the tectonic contact between the upper unit (Budaörs Formation) and the lower unit (Mátyáshegy Formation). Based on structural observations and construction of cross sections, two alternative models are presented for the structural style and kinematics of the contact zone between the Budaörs and Mátyáshegy Formations. Model A suggests a Cretaceous age for the juxtaposition, along an E–W striking sinistral transpressional fault. In contrast, model B postulates dextral transpression and an Eocene age for the deformation. The latter one is better supported by the scattered dip data; however, both scenarios are considered in this paper as possible models.