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Studia Geophysica et Geodaetica

, Volume 53, Issue 3, pp 295–314 | Cite as

Geological interpretation of gravity profiles through the Karlovy Vary granite massif (Czech Republic)

  • Vratislav Blecha
  • Miroslav Štemprok
  • Tomáš Fischer
Article

Abstract

We examined the shape of the Late Variscan Karlovy Vary granite massif located south of the Ohre/Eger graben in Northern Bohemia by reinterpretation of existing gravity data on two perpendicular profiles. The granite body of about 360 km2 total outcrop size has the elongation ratio 0.35 with the major axis trending NE-SW. The SW part of the body was crossed in the nineties by the seismic profile 9HR which localized the bottom of granites in a depth of about 10 km. We used this value as a reference datum in our gravity profiles. We positioned one of our profiles along the seismic profile 9HR and the other one perpendicularly, i.e. parallel with the elongation of the outcrop surface. We interpret the shape of the main granite body in the vicinity of Karlovy Vary as a continuous desk whose floor is horizontal (or subhorizontal) and varies along its whole extension about a depth of 10 km. This thickness is approximately identical with that of the Saxothuringian nappes imaged by seismic reflection. The near surface upper contact of the granite body is mildly inclined, and outward dipping. It changes to steep sides or inward inclined contacts in deeper levels. The Lesný-Lysina (Kynžvart) massif is a separate granite body about 324 km thick, not continuously connected with the main Karlovy Vary massif. The gravity curve suggests that granites often enclose in their endocontact large blocks of country metasediments or metabasites the existence of which is partly evidenced by their outcrops outside the line of the profile. The granite body is found density-homogenous. Minor density differences between granite varieties are caused mainly by more intense hydrothermal alterations in younger suite granites. We interpret vertical conduits for the ascent of granitic magmas to be parallel to the Jáchymov-Gera and Ohře (Eger) lineaments or the Mariánské Lázně fault zone as indicated by the elongation of some outcrops. However, they are not clearly imaged from the gravity data. The effect of the depression of the Sokolov basin along the faults parallel with the Ohře (Eger) lineament is shallow and it is not indicated by any change in the floor depth of the granite body. Comparison of the seismicity distribution suggests that the hypocenters occur mostly outside of the granite bodies or near their contact with the country rock.

Key words

Variscan granites gravity modeling Karlovy Vary Massif Western Bohemia Saxothuringian zone Ohře/Eger graben 

List of abbreviations

EGG

Ohře/Eger graben

Ka

intrusion of YIC granite in Karlovy Vary

Kr

Krudum massif

KVP

Karlovy Vary pluton

KVM

Karlovy Vary massif

Ls

Lesný-Lysina massif

MLC

Mariánské Lázně complex

MLF

Mariánské Lázně fault

NEM

Nejdek-Eibenstock massif

OIC

Older Intrusive Complex

WKEP

Western Krušné hory (Erzgebirge) pluton

TWT

Two-ways travel time

YIC

Younger Intrusive Complex

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Copyright information

© Institute of Geophysics of the ASCR, v.v.i 2009

Authors and Affiliations

  • Vratislav Blecha
    • 1
  • Miroslav Štemprok
    • 2
  • Tomáš Fischer
    • 1
    • 3
  1. 1.Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Faculty of ScienceCharles University in PraguePraha 2Czech Republic
  2. 2.Institute of Petrology and Structural Geology, Faculty of ScienceCharles University in PraguePraha 2Czech Republic
  3. 3.Institute of GeophysicsAcad. Sci. Czech RepublicPraha 4Czech Republic

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