The classic failed continental rift or aulacogen is one that intersects a rifted continental margin at a high angle. Based on recent geological and geophysical studies, we have revisited a classic analogy that was drawn between two major intracratonic rifts, the Southern Oklahoma aulacogen in the southern portion of Laurentia and the Dniepr-Donets aulacogen in the southern portion of Baltica. The Southern Oklahoma aulacogen, also known as the Wichita aulacogen, consists of a linear alignment of extensively inverted rift structures that begins at the rifted margin of Laurentia in northeast Texas and extends northwestward at least to southern Colorado. Deep seismic profiles have revealed the upper crustal structure of this feature, and gravity data provide a regional context for interpreting these results. Velocities low enough to indicate the presence of sedimentary rocks extend to a depth of ∼15 km, and the deepest of these sedimentary layers has been interpreted as rift fill. In addition, the main inversion structure of the Southern Oklahoma aulacogen (Wichita uplift) is underlain by very high-velocity and dense mafic material even at upper crustal depths of ∼5 km. The Dniepr-Donets aulacogen has been cited as a type example of an aulacogen and is clearly a “failed rift” in the sense that it did not itself lead to continental breakup and ocean crust formation. The main feature of the aulacogen is a Late Devonian rift basin overlain by a substantial (but variable) postrift sedimentary sequence that records several extensional or transtensional events and at least one moderate compressional reactivation. Recent deep seismic reflection and refraction surveys resolve the geometry of the sedimentary succession in the Donets segment of the basin, indicating an asymmetric form with a steeper basement surface in the south than in the north and a total sedimentary thickness of ∼20 km. A thick (>10 km) high-velocity (>6.9 km/s) lower crustal body lies beneath the rift basin itself and is offset slightly to the north compared to the main basin depocenter. The Moho displays only slight topography around a depth of 40 km although, based on older deep seismic data, it shallows somewhat under the rift axis in the Dniepr segment to the northwest. Thus, major differences between these two major rifts are the nature of the magmatic modification of the crust and degree of inversion. Both the age of initial rifting and subsequent inversion in the Dniepr-Donets aulacogen are redefined compared to what was thought at the time the original analogy was made with the Southern Oklahoma aulacogen.

Abstract Europe provides on outstanding field laboratory for studying lithospheric processes through time: for tracing the results of plate movements from the present back into the early Precambrian. This book has been designed to focus on tectonic processes in the European lithosphere through these three billion years and how they may have changed during this time. Two things are particularly striking: the importance of plate tectonics far back through the Proterozoic into the Archaean, and the significance of tectonic inheritance, older structures and rheologies guiding, even defining, the younger evolution. Basement structure has a profound influence on subsequent basin evolution and the distribution of geo-resources. The economic importance of understanding these processes cannot be overestimated.

Abstract Vendian-Early Palaeozoic sedimentation on the East European Craton (EEC) was confined to the cratonic margins with limited intracratonic subsidence. Generally, there are two geodynamic stages involved: in stage 1, basins formed in response to continental break-up processes; in stage 2, basins formed in response to the reassembly of continental lithosphere fragments and associated continental accretionary processes. The establishment of the Peri-Tornquist passive margin was a polyphase process that commenced in the Early Vendian in the SW and ended in the Cambrian in the NW. Neoproterozoic rifting along the Scandinavian margin was essentially a long process (250 Ma), whereas the fragmentation of the continent along the earlier Timanian orogen in the east and establishment of Peri-Uralian basins took place in a rather short time span. A similar scenario is suggested for the basement of the Peri-Caspian Basin. The rift-to-drift transition is expressed differently on the various EEC margins and this could be a reflection of the relative strengths of the underlying lithosphere. The change to a convergent margin setting is recorded in Peri-Tornquist basins in the Late Ordovician, climaxing with high rates of subsidence during Late Silurian time. Subsidence rates on the cratonic margins were governed by the emplacement of orogenic loads. Where there was a short time span between Stages 1 and 2, continuing thermal subsidence from the former was superimposed onto the flexural subsidence of the latter, such as on the Dnestr margin. Other processes, such as dynamic loading related to mantle flow, are implied for the anomalously broad Stage 2 Baltic Basin. Peri-Uralian basins developed as passive continental margin basins throughout the Early Palaeozoic. Stress regime changes generated at the craton margins are reflected in the structure and subsidence patterns recorded in the intracratonic Moscow Basin.

Abstract The southern part of the Eastern European continental landmass consists mainly of a thick platform of Vendian and younger sediments overlying Precambrian basement, referred to as the East European and Scythian platforms (EEP and SP). Some specific geological features, such as the Late Devonian Pripyat–Dniepr–Donets rift basin, the Karpinsky Swell, the Permo(?)-Triassic troughs of the SP, and the deformed belt running from Dobrogea to Crimea and the Greater Caucasus, in which rocks as old as Palaeozoic crop out, form a record of the geodynamic processes affecting this part of the European lithosphere. Hard constraints on the Palaeozoic history of the SP are very sparse. The conventional view has been that the SP is a Late Palaeozoic orogenic belt. However, it is shown that the few available data are also consistent with an alternative interpretation in which it is the thinned margin of the Precambrian continent, reworked by Late Palaeozoic–Early Mesozoic rifting events. The geodynamic setting of the margin is classically reported as one of active convergence throughout the Late Palaeozoic and Early Mesozoic, with subduction of the Palaeotethys Ocean beneath Europe. Actually, there are no direct observations constraining the polarity of Palaeotethys subduction in this area although indirect evidence is not inconsistent with the conventional model. In such a case, the sedimentary–tectonic record of the SP suggests that convergence during the Permo-Triassic(?) and certainly during the Early and Mid-Jurassic was oblique. An Eo-Cimmerian (Late Triassic–Early Jurassic) event is widespread and implies a tectonic compressional regime with systematic inversion of most sedimentary basins. There is also a widespread unconformity at the end of the Mid-Jurassic and in the Late Jurassic. These can be interpreted as indicators of compressional tectonics; however, nowhere is there evidence of intense shortening or other orogenic processes. A revised tectonic model is proposed for the area but, given the degree of uncertainty characterizing the geology of this area, it is best considered as a basis for further discussion.