Craton

0. Abstract                               1
1. Introduction                               2
2. Paleomagnetic constraints on the Neoproterozoic supercontinent  3
2.1 1100–900 Ma: Laurentia and Baltica               3
2.2 1100–900 Ma: Amazonian craton (AC) and Baltica       3
2.3 1100–900 Ma: Kalahari craton               5
2.4 1100–900 Ma: Congo–Sao Francisco (CSF) craton       5
2.5 1075–990 Ma Siberian craton                       5
2.6 India 1100–1000 Ma                               5
3. True polar wander?                       5
4. The breakup of Rodinia: 800–700 Ma               5
5. 580 Ma and younger reconstructions               7
6. Conclusions                             7

Mesoarchean magmatism is widespread on the eastern margin of the Kaapvaal Craton, but its origin is still poorly understood, mainly because geochemical data is rare. To shed some light on the source of this Mesoarchean magmatism and to relate different Mesoarchean volcanic sequences to each other, we provide major and trace element data as well as Hf-Nd isotope compositions of amphibolites sampled close to the Kubuta Ranch in south-central Eswatini. These amphibolites, so far, were of unknown correlation to any volcanic sequence in Eswatini or South Africa. Hence, the aim of our study is to characterize the mantle source composition of these volcanic rocks and, furthermore, to constrain their genetic relation to other volcanic sequences in Eswatini and South Africa. Our findings reveal that, based on coherent trace element patterns and similar Nd isotope characteristics, the Kubuta volcanic rocks can be genetically linked to the ca. 3.0 Ga Usushwana Igneous Complex in West-Central E...

Major element and Re–Os isotope analysis of single sulfide inclusions in diamonds from the 240 Ma Jwaneng kimberlite has revealed the presence of at least two generations of eclogitic diamonds at this locality, one Proterozoic (ca. 1.5 Ga) and the other late Archean (ca. 2.9 Ga). The former generation is considered to be the same as that of eclogitic garnet

Quantitative analysis of geoscientific data to determine areas most likely to contain mineral deposits is becoming increasingly common in the mining industry. The approach is based on characterising areas known to contain deposits and seeking similar areas elsewhere. This paper presents an automatic image processing technique for the prospectivity analysis of Archaean lode-gold deposits, which differs from previous methods in that it is based solely on aeromagnetic data and does not require knowledge of the location of existing deposits. Instead, the aeromagnetic expressions of what are perceived to be geologically significant characteristics are sought within the aeromagnetic data.Gold mineralisation is known to occur near major crustal breaks manifesting as large-scale shear zones, which act as conduits for mineralising fluids. Mineralisation occurs in regions of structural complexity adjacent to the shear zones. Progressing towards the automatic detection of such regions, the proposed system finds firstly regions of magnetic discontinuity that correspond to both lithological boundaries and shear zones using a combination of texture analysis and symmetry feature detection techniques. Secondly, it examines the data using fractal analysis to find areas nearby with a complex magnetic expression (zones of structural complexity). The most prospective areas are those where inferred structural complexity occurs adjacent to the regions of magnetic discontinuity.A preliminary experiment was conducted using aeromagnetic data from the Yilgarn Craton in Western Australia and the regions selected by the proposed system contained over 76% of all known deposit locations and 82% of the greater than 1 tonne deposit locations.

A new mechanism for Paleozoic subsidence of the Russian, or East European, platform is suggested, since a model of lithosphere tilting during the Uralian subduction does not explain the post-Uralian sedimentation record. Alternatively, I propose that the Proterozoic and Paleozoic rifting (when a platform-scale Central Russia rift system and a set of Paleozoic rifts were formed) modified the structure and composition of cratonic lithosphere, and these tectono-magmatic events are responsible for the post-Uralian subsidence of the Russian platform. To support this
hypothesis, (a) the thermal regime and the thickness of the lithosphere are analyzed, and (b) lithospheric density variations of non-thermal origin are calculated from free-board constraints.

The results indicate that Proterozoic and Paleozoic rifting had different effects on the lithospheric structure and composition.
(1) Proterozoic rifting is not reflected in the present thermal regime and did not cause significant lithosphere thinning (most of the Russian platform has lithospheric thickness of 150-180 km and the lithosphere of the NE Baltic Shield is 250-300 km thick). Paleozoic rifting resulted in pronounced lithospheric thinning (to 120-140 km) in the southern parts of the Russian platform.
(2) Lithospheric density anomalies suggest that Proterozoic^Paleozoic rifting played an important role in the platform subsidence. The lithospheric mantle of the Archean^early Proterozoic part of the Baltic Shield is ca 1.4+/-0.2% less dense than the typical Phanerozoic upper mantle. However, the density deficit in the subcrustal
lithosphere of most of the Russian platform is only about (0.4-0.8)+/-0.2% and decreases southwards to ca 0%.
Increased densities (likely associated with low depletion values) in the Russian platform suggest strong metasomatism of the cratonic lithosphere during rifting events, which led to its subsidence. It is proposed that only the lower part of
the cratonic lithosphere was metasomatized as a result of Proterozoic rifting; the boundary between a depleted upper and more fertile lower layers can be at ca. 90-150 km depth and can produce a seismic pattern similar to the top of a seismic low-velocity zone. Paleozoic rifting has modified the entire lithospheric column and the regions affected are still subsiding.

The Palaeoproterozoic collision of Archaean Fennoscandia, Volgo-Uralia and Sarmatia, viewed as a large composite of terranes, each with an independent history during Archaean and Early Proterozoic time, formed the East European Craton. This paper summarizes the results of deep seismic sounding investigations of the lithospheric structure of the southwestern part of the East European Craton. On the basis of the modern EUROBRIDGE'94-97, POLONAISE'97 and CELEBRATION 2000 projects, as well as of data from the Coast Profile and from reinterpreted profiles VIII and XXIV, the main tectonic units of Fennoscandia and Sarmatia are characterized. The crustal thickness in the whole area investigated is relatively uniform, being between 40 and 50 km (maximum about 55 km). For Fennoscandia, the crystalline crust of the craton can be generally divided into three parts, while in Sarmatia the transition between the middle and lower crust is smooth. For both areas, relatively high P-wave velo...

The basement of the Moesian Platform is extremely heterogeneous, including rocks ascribed to the Archean, Palaeoproterozoic and Neoproterozoic. Largely concealed by the Palaeozoic to Cenozoic platform cover, the basement exposed in the tectonic block of Central Dobrogea contains mainly Neoproterozoic-Eocambrian turbidites (the Histria Formation), deformed under very low grade metamorphic conditions at the end of the Neoproterozoic, in the "Cadomian" or "Baikalian" events. The Histria Formation includes channelized, midfan turbidites and distal, outer fan turbidites, forming two sandstone dominated, upward coarsening and thickening sequences, separated by a much thinner, upward fi ning and thinning sequence. Sedimentological, mineralogical and petrological studies are consistent with the model that the turbiditic basin was sourced by a continental margin dominated by an active volcanic arc. From various lines of evidence, a foreland basin as the tectonic setting f...

Thermobarometric data for mantle xenoliths from a kimberlite pipe in the NWT, Canada are used to constrain the thermal properties of the lithospheric mantle underlying the Slave craton. We derive an analytical expression for a steady-state conductive mantle geotherm that is independent of the geometry and thermal properties of the crust. The model has an upper boundary coincident with the MOHO at a depth Zm and has temperature Tm and heat flow qm. The mantle is assumed to have constant radiogenic heat production (A) and we allow for a temperature-dependent thermal conductivity [K.T / D Ko.1 C B.T − T m//]. Inverting the thermobarometric data through the model geotherm gives limiting values for mantle heat production (A) and bounds on the temperature dependence of K (e.g. B) that are consistent with the mantle P–T array. We characterize the Slave lithospheric mantle in terms of three critical parameters qm (mW m−2), A (mW m−3), Tm (C). The optimal solution has values [15.1, 0.012, 45...

... Xenolith data from (Ackerman et al., 2007), (Bianchini et al., 2007), (Bjerg et al., 2005), (Ionov, 2004), (Ionov et al., 1993), (Ionov et al., 2002), (Ionov et al., 2005), (Peltonen et al., 1999), (Rudnick et al., 2004) and (Wiechert et al., 1997), and Xu et al. (1998). View Within Article. ...