The formation of the Voldum salt pillow in the Danish Zechstein basin, Jutland (Denmark)

Bulletin of the Geological Society of Denmark

Thybo, H.:¹ 

[1] Crustal structure and tectonic evolution of the Tornquist Fan region as revealed by geophysical methods. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 145–160. Copenhagen.
Crustal structure derived primarily from geophysical investigations reveals features that may be related to the complex tectonic evolution of the Tornquist Fan region. This northwestwards widening splay of Late Carboniferous – Early Permian fault zones in the Danish region emanates from the Teisseyre-Tornquist Zone in northern Poland. Seismic reflections and velocity anomalies image collisional fault zones that formed during the Proterozoic and Palaeozoic amalgamation of the crust. Re-equilibration of Moho appears to have taken place before late Palaeozoic rifting and magmatism initiated the main phase of basin formation that continued into the Mesozoic. The resulting, strong Moho topography, with variation between depths of 26 and 48 km, has been practically “frozen in” since then, although the late Cretaceous – early Cenozoic inversion tectonics may have formed a crustal keel underneath part of the Sorgenfrei-Tornquist Zone which cuts across the Proterozoic crust of the Tornquist Fan region.

关键词: Crust;    Mantle;    Geophysics;    Seismic velocity;    Geological Institute;    University of Copenhagen;    Øster Voldgade 10;    DK-1350 Copenhagen K;    Denmark. 3 May 1999.;   

学科分类：地球科学(综合)

来源: Dansk Geologisk Forening

【 摘 要 】

On the basis of seismic and well data, supported by Bouguer gravity data, the sequence of events leading to the formation of a Zechstein salt pillow – called Voldum – in east central Jutland is discussed (the study area is delimited in Fig. 1). The initial salt movements, activated by faulting in the Triassic, resulted in the formation of a minor salt pillow on the edge of a graben within the Zechstein (Upper Permian) basin. During a renewed faulting (Voldum fault) of the base Zechstein in Late Jurassic and consequent deepening of the graben, a syncline developed above the salt where thick sediments of Late Jurassic age accumulated. In the process large quantities of salt, due to differential loading, withdrew from the graben and moved laterally up-dip across the older fault scarps. Thus a new and larger salt accumulation (Voldum pillow) formed above the southern flank of the graben. A relict Triassic thin, formed during the growth of the first pillow, remains, but no salt accumulation which could account for this thin is present. The Voldum pillow continued to grow during the Cretaceous and the Tertiary, but the speed of growth decreased considerably during post-Late Cretaceous times, although there are still large quantities of, virtually undisturbed, salt present south of the pillow in the part of the basin corresponding to the Silkeborg Gravity High. The graben area apparently underwent a mild inversion at the close of the Cretaceous. The reasons why the Voldum pillow did not develop into a diapir are considered to be a strong and thick overburden which existed at the beginning of the Voldum pillow formation, the deeply buried salt which probably acted as a deterrent to the rupture of the overburden, and the nature of the Voldum fault which, apparently, had an appreciable strike-slip component in dextral sense.

【 授权许可】

Unknown