Mafic Dikes of NE Kaapvaal craton, geochemistry and cross cutting relationship ages
Swarms in the dykes may be further defined as the large geological feature that consists of major groups of linear and parallel dikes creates an overlying intrusion within the continental crust with a radial orientation. Several to about hundreds of dikes are emplaced marginally during the intrusive event that occurs once, and they are magmatic and stratigraphic. When such dike, swarms form a large igneous state they might be at one time the cause or origin of a volcanic state. In some areas such as the Archean and paleoproterozoic terrains, mafic dike swarm occurrence is referenced often as pure evidence. This is because of the activity in the mantle plume, which is associated with abnormal temperatures in the mantle.
Dike swarms may have a wide extension of over 400 km (249 mi) in both width and length. The Mackenzie dike swarm located halfly in the Canadian shields in the west is well known as the largest dike swarm in the whole world. It is more than 500 km (311 mi) wide and 3,000 km (1,864 mi) long. However the numbers of huge dike swarms on earth are at a lower level of about 25 only, yet the primary bisection of the most huge swarms is at a poor recognition all over the world. The reasons for this being the age factor and varioust activities of the tectonic (Vel\’Azquez and Riccomini et al. 18). Different swarms were established and developed at different times, and on different reasons and current trends of the world. The evidences viable in this sect show the differences.
Swarm is collectively referring to a certain behavior shown by different animals, insects, people or any other group of the same kind that puts them together, for example, migrating together or milling about a very same point (O’loan and Evans 99). In this text, we deal with the trends or patterns of different swarms of dikes in different countries relating them to age, cross cutting relationships, and geochemistry.
Specifically we narrow down to the Mafic Dikes of NE Kaapvaal craton in South Africa.
Field evidence is one of the methods used in determining the age approximations of the complex array of the mafic dykes across the Eastern Kaapvaal craton in the South Africa while the analysis of these trends in the dikes and also the character of petrology of some dyke samples forming the other (Klausen and S\”Oderlund et al. 501–522).
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Facts deploy that xenoliths at the basement of the dikes are contained in the dikes with some elements of calc-alkaline, andesitic and quartz-oversaturated character. On the other side of it, Proterozoic dykes are aero magnetically prominent tholeiitic basalts which have high modal oxide elements. A positive indication states that geochemical there is a clear distinction observed between the two swarms that is Archean high and Proterozoic low and La/Yb dyke swarms, and the calc-alkaline nature of the swarms is expanded by LILE-enhanced spider-element designs as contrasted to the Proterozoic swarm (Klausen and S\”Oderlund et al. 501–522).
Roughly the geochemical similarities may be consistent with the dykes with values ∼2.95 and ∼2.65 Ga with the coeval lava being the feeders to the system. These lavas are located within the Nsuze Group and Allan ridge Formation, respectively. The coeval sills found mostly in Zimbabwe and the Kaapvaal cratons have a close relationship to each other. These sills are however the feeders to the south pans berg group of lavas at presumable facts (Olsson and S\”Oderlund et al. 490–500). The dated feeder dyke systems are the source of the new information thus being the source code to the cause of petronic setting re-evaluation, where the range is from the state back-arc to either radiating swarms or vice versa originating from igneous centers.
When we organize an over view towards the Kaapvaal craton origin eliminating some form of the plate tectonics to have been operative, the Kaapvaal craton nucleus formation formed by approximately 3.1 Ga can be related to the first value of thin-skin thrusting in within the ocean and arc settings and subsequent merging of the displaced oceanic and arc terrains, in conjunction with the significant granitoid magmatism suggestions states that the bulk of the terrain accretion which formed the Kaapvaal craton, occurred along two prominent ENE-WSW suture zones, the Barberton lineament (BL) and the Thabazimbi-Murchison lineament (TML) between 3.23 and 2.9 Ga (Anhaeusser 193–210).
Kaapvaal craton is composed of a minimum of four terranes that are clearly distinct (Barberton-North [BN] and Barberton-South [BS] either side of the BL; Murchison-Northern Kaapvaal [MNK] north of the TML, and Limpopo Central Zone [LCZ] Recent U-Pb and Lu-Hf isotope which underwent several crustal evolutions and they had success accretion at c.3.23 (BN and BS), 2.9 (assembled BN-BS and MNK) and 2.65-2.7 Ga (three existing terranes and LCZ) (Zeh and Gerdes et al. 215–223).
The Murchison greenstone belt, is another feature that accreted from approximately N to S through the set margin on the north east of the Kaapvaal nucleus hence was characterized by c. 3.1 – 2.9 Ga mafic and granitic magmatism that was in within an arc-subduction system; thus, it formed part of the MNK composite terrane, non-exclusive of the Pietersburg greenstone belt. Between c. with value 2.7Ga and value 2.6 Ga, this where further accretion took place from the opposite side of the north, with an exotic terrane placed at a juxtaposition, the Central layer of the Limpopo mobile belt (LMB), along a ENE-WSW trending, inward dipping, strike-slip shear zone, the Palala-Zoetfontain shear zone (Zeh and Gerdes et al. 215–223). Rocks of the Southern Marginal zone (SMZ) of this mobile belt, which represent high-grade equivalents of the granite-greenstone cratonic successions, were thrust onto the Kaapvaal craton along the Hout River shear zone at 2691-2620 Ma (Van Reenen).
The accretion that occurred western side onto the Kaapvaal nucleus took place at c. 2-8-2.72 Ga and along a suture point presently preserved as the Coles burg magnetic lineament (De Wit and Tinker 185–206).
The contents of some elements were experimented and a vertical analysis put across for several shale elements that is about 100 from the ten formations mostly in the eastern central and some parts of the craton in South Africa. The shale found in the Kaapvaal have characters of components which are at a low value, atomic ratios in kerogens from the shales created an indication that the loss of the Kaapvaal shales at considerable amounts of the elements during diagenesis and regional metamorphism (Watanabe and Naraoka et al. 3441–3459).
From relationships between the H/C ratios of kerogen contents of shales formed theoretically, the actual contents of the shales from the Kaapvaal Craton (Archean and Proterozoic) are approximated to be on an average of ˜2 wt.%. These values and the average organic of the modern marine sediments are similar.
This is a suggestion to mean that the organic elements preserved and the organic productivity in an ocean during a specified duration were same as to those in the earlier era, so long as there was a close relationship in the elasticity of the sediments. Additionally, this will implicate that the rate of oxygen accumulation in the system of atmosphere-ocean, which has an equal value to the burial rate of sediments containing organic matter, has been at the same level since ˜3.0 Ga (Watanabe and Naraoka et al. 3441–3459).
There are values that are very consistent In that the higher amount of the crystals coming from pyrite in the shales of the archean were formed due to the bacterial activity on seawater sulfate where 34S component has values between +2% and +10‰ and this seawater was sulfate rich (Watanabe and Naraoka et al. 3441–3459).
Changes spotted in values related to the 13Corg during the process of kerogen development underwent evaluation with non-practical examinations from the experimental facts on natural samples. The 13Corg levels rise depicted are more of less than values of estimation. These facts creates an awareness that some of the elements decrease only if other factors are present(Peters and Rohrback et al.).
Recent geophysical and mantle-xenoliths geochemistry studies of the Kaapvaal Craton most results, which appear, at times, to provide disparate views of the physical structure, chemical and thermal structure of the lithosphere. However the models from our recent SAMTEX magneto telluric (MT) research across the Kaapvaal Craton of South Africa pose a resistive, 220-240 km thick lithosphere that the central core has within the craton.
One published S-wave receiver function (SRF) study amongst other surface-wave studies suggests that a smaller lithosphere characterized by a ~160 km solid high-velocity “top” underlain by a low-velocity stripe (LVZ) of range 65-150 km in width. Additional seismic research implies that the lithosphere is dense, in the margin of 220 km. Mantle xenolith pressure-temperature patterns from Mesozoic kimberlites expect that the foundation of the “thermal” lithosphere (i.e., the deepness above which a conductive geotherm is stated – the t LAB) is at minimal 220 km under, to consider for mantle geotherms in the series 35-38 mWm-2 (Jones and Evans et al. 03).
A short description on the geology and evolution of the cover sequences on the Kaapvaal craton from c. 3.1 – 2.05 Ga presented in this paper gives a suggestion that mantle thermal
Processes, which are mainly in plumes and super plume form events, might have predominantly resided over plate tectonics, however, influencing this period, and there is an exception of unequivocal support for Kaapvaal that formed part of any super continental merging prior to c. 2.0 Ga.
The deformation of the Godwan protobasinal fill, that related to the Black Reef Formation, or removal of chemical sediments along the Southern TB being one of the evidences among others, all appear to have been local events, and concomitantly all in the general area of the paleo-Rand anticline, a long-lived feature subject to repeated uplifts (Eriksson et al.107-119).
None of the above tectonic shortening events gives in either intensity or scale to an interpretation. Due to this fact or reason, a question is raised above the eye brow stating the possible geodynamic properties for the craton whilst the long period of over a billion years, and yet here we have a recourse to the available and possible conditions at the transition in Earth history from a thermally-dominated planet to a layered mantle and where plate tectonics rest at the pre-eminent structure. However, due to the processes and evidences viable in the text, they prove that the bush veld complex has a close relationship with the mafic dyke formation that is the formation of the dyke’s extents its processes to the complex.
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