Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: Wolfgang Frank x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

A triangulation of a manifold (or pseudomanifold) is called a tight triangulation if any simplexwise linear embedding into any Euclidean space is tight. Tightness of an embedding means that the inclusion of any sublevel selected by a linear functional is injective in homology and, therefore, topologically essential. Tightness is a generalization of convexity, and the tightness of a triangulation is a fairly restrictive property. We give a review on all known examples of tight triangulations and formulate a (computer-aided) enumeration theorem for the case of at most 15 vertices and the presence of a vertex-transitive automorphism group. Altogether, six new examples of tight triangulations are presented, a vertex-transitive triangulation of the simply connected homogeneous 5-manifold SU(3)/SO(3) with vertex-transitive action, two non-symmetric 12-vertex triangulations of S 3 × S 2, and two non-symmetric triangulations of S 3 × S 3 on 13 vertices.

Restricted access

The results of seven new 40 Ar/ 39 Ar analyses and two K/Ar analyses of mineral separates of metamorphic rocks from the Transdanubian part (west of the Danube River) of the Tisza Mega-Unit is presented, and a review of the geochronological data available in the literature is given. Investigated rocks come from boreholes and include amphibolite facies rocks, mainly containing garnet, staurolite, kyanite, andalusite and sillimanite as index minerals. The investigated area covers 120 × 85 km in Transdanubia, including all tectonic units distinguished by previous authors. The 40 Ar/ 39 Ar spectra of the muscovites yielded fairly well-established plateau ages ranging from 307 Ma-312 Ma in all units. Similar muscovite Ar/Ar cooling ages of ca 310 Ma were obtained from other parts of Tisza Mega-unit east of the Danube, e.g. from the kyanite-sillimanite-bearing metapelites of the Villány-Bihar Subunit (Great Plain; Lelkes-Felvári et al. 2003).

Restricted access

Ultramylonites and margarite-bearing quartz-feldspar S-C mylonites, containing amphibolite lenses with symplectitic texture, were encountered in a borehole (Bajánsenye-B-M-I) close to the west of the Transdanubian Central Range Unit. These rocks demonstrate a ductile, horizontal extensional shear zone attaining a thickness of 300 m. Microstructural data, mineral parageneses and mineral chemistry of these rocks indicate a multistage metamorphic evolution, which is consistent with that of the Koralm-Pohorje basement. The youngest mylonitic event (Early Tertiary) took place in the Bajánsenye mylonites at 430-450oC (greenschist-facies); it rejuvenated coarse-grained muscovite crystals of eo-Alpine age (Early-Middle Cretaceous). The radiometric data presented in this paper demonstrate for the first time an important Early Tertiary tectonic zone in this area.

Restricted access

The Dorozsma Complex (DC) is defined and its main lithologies are described. The complex makes up the bulk of the Algyõ basement high, representing an outlier of a Cretaceous nappe system in the southernmost part of the Tisza Mega-unit (Great Hungarian Plain). The DC exhibits a polymetamorphic history characterized by a Permian, low-pressure amphibolite facies metamorphism, overprinted by a pressure-dominated eo-Alpine, amphibolite facies metamorphism, accompanied by penetrative mylonitization. "Carboniferous breccias" described by earlier authors and covering the metamorphic rocks sporadically are redefined as tectonized, mostly cataclastic rocks. The uppermost unit of the basement below the Neogene sediments is a nappe composed of Triassic clastic and carbonate sediments. Petrographic similarities of the DC with several units of the Koralpe-Wölz nappe system in the Eastern Alps indicate that both units were formed within a continuous belt in the Cretaceous.

Restricted access