Many geological and geochemical changes are recorded on Earth between 3 and 2 Ga. Among the more important of these are the following: (1) increasing proportion of basalts with “arc-like” mantle sources; (2) an increasing abundance of basalts derived from enriched (EM) and depleted (DM) mantle sources; (3) onset of a Great Thermal Divergence in the mantle; (4) a decrease in degree of melting of the mantle; (5) beginning of large lateral plate motions; (6) appearance of eclogite inclusions in diamonds; (7) appearance and rapid increase in frequency of collisional orogens; (8) rapid increase in the production rate of continental crust as recorded by zircon age peaks; (9) appearance of ophiolites in the geologic record, and (10) appearance of global LIP (large igneous province) events some of which correlate with global zircon age peaks. All of these changes may be tied directly or indirectly to cooling of Earth's mantle and corresponding changes in convective style and the strength of the lithosphere, and they may record the gradual onset and propagation of plate tectonics around the planet. To further understand the changes that occurred between 3 and 2 Ga, it is necessary to compare rocks, rock associations, tectonics and geochemistry during and between zircon age peaks. Geochemistry of peak and inter-peak basalts and TTGs needs to be evaluated in terms of geodynamic models that predict the existence of an episodic thermal regime between stagnant-lid and plate tectonic regimes in early planetary evolution.

A planet in transition: The onset of plate tectonics on Earth between 3 and 2 Ga?

The North Atlantic craton in southern West Greenland mainly consists of a tectonic collage of Mesoarchean continental crustal terranes, which were amalgamated at c. 2.7 Ga and are currently exposed at mid-crustal amphibolite to granulite facies levels. Tonalitic orthogneisses predominate, intercalated with slightly older tholeiitic to andesitic metavolcanic rocks and associated gabbro-anorthosite intrusive complexes. The North Atlantic craton also contains enclaves of Eoarchean, c. 3.86-3.6 Ga orthogneisses and supracrustal rocks including the Isua greenstone (or supracrustal) belt. This is the oldest known assemblage of rocks deposited at the surface of the Earth, comprising mafic pillow lavas, banded iron formations and metasedimentary schists with local disseminated graphite of possible biogenic origin. Eoarchean rocks have not been found in Kola and Karelia in Fennoscandia where most rocks are 2.9-2.7 Ga tonalitic-trondhjemitic- granodioritic orthogneisses with intercalated coeval greenstone belts and amphibolites. Mesoarchean 3.0-3.2 Ga rocks are found in the eastern and western parts of the Karelian province. Subduction-related rocks like the Iringora supra-subduction type ophiolite and basalt-andesite-dacite-rhyolite series volcanic rocks in many greenstone belts, as well as eclogites are found in the Archean of Fennoscandia. A clear distinction between Greenland and Fennoscandia is the abundance of 2.75-2.65 Ga igneous rocks in Fennoscandia which indicates that these two cratons had a separate evolution during the Neoarchean.

Archean of Greenland and Fennoscandia

Petrogenesis of the 2115 Ma Haicheng mafic sills from the Eastern North China Craton: Implications for an intra-continental rifting

The 2.31 Ga mafic dykes in the Karelian Craton, eastern Fennoscandian shield: U–Pb age, source characteristics and implications for continental break-up processes

Nature of three Proterozoic (1680Ma, 1230Ma and 775Ma) mafic dyke swarms in North China: Implications for tectonic evolution and paleogeographic reconstruction

Major-element, lithophile trace element, and Sm^Nd and U^Pb zircon isotopic data are presented for Palaeoproterozoic mid-ocean ridge basalt (MORB)-type tholeiitic dikes ranging in age from 2140 3 to 2126 5 Ma studied at six localities within three terranes in the Karelian Craton, eastern Fennoscandian Shield. All the studied dikes have remarkably uniform geochemical and isotope characteristics.They are tholeiitic basalts with low contents of large ion lithophile elements, high field strength elements, and rare earth elements (REE), nearly flat chondrite-normalized REE patterns [(La/Sm)n1⁄4 0·9^1·2, (Gd/Yb)n1⁄41·0^1·2], and positive Ti, Nb, and Zr anomalies in the primitive mantle-normalized diagrams. The dikes also show relatively uniform initial Nd isotope compositions, with eNd values ranging fromþ1·4 toþ3·0, despite the occurrence of these dikes within Archaean terranes with different crustal history. According to the results of U^Pb (zircon) and Sm^Nd internal isochron dating the crystallization age of the dikes is constrained to be c. 2·14 Ga. The studied MORB-type tholeiitic dikes are probably comagmatic with Palaeoproterozoic MORB-type basalts that have previously been recognized in the Karelian Craton, and might represent relicts of their magma feeder system.The uniformity of ages and geochemical and isotope characteristics of the MORB-type dikes and volcanic rocks suggest that they are probably related to a common magmatic event.This event was nearcontemporaneous with the eruption of high-Ti plume-related basalts and intrusion of dikes in the c. 2·1 Ga Jatulian continental flood basalt province. Geochemical modelling indicates that the chemical and isotopic compositions of the dikes are best explained by derivation of their parental magmas by partial melting of a uniformly depleted mantle source in the spinel peridotite stability field, followed by fractional crystallization and minor (56%) assimilation of continental crustal material. This suggests that magma-storage processes in upper crustal chambers were very short-lived; this could be the

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Palaeoproterozoic Continental MORB-type Tholeiites in the Karelian Craton: Petrology, Geochronology, and Tectonic Setting

Introduction. Modern housing construction requires (1) a single digital platform that has a common data environment, (2) workflow digitization, involving all stakeholders of an investment and construction project. The authors demonstrate that the implementation of this approach will ensure not only the monitoring and control of financial values of construction, including disbursement schedules and a single consolidated database for all documents on each construction project showing access rights to information, but it will also ensure the integrity and reliability of information required for the implementation of day-to-day urban planning activities, as well as quick and flexible integration with state information systems. 
 
Materials and methods. Optimization methods were used to find rational engineering and economic solutions for investment and residential housing construction projects. Multivariance was employed to substantiate the applicability of solutions in the process of introducing digital BIM technologies aimed at identifying the most effective project options. 
 
Results. The main result of the presented research is the application of the G. Taguchi loss function to devise a model for assessing the economic efficiency of options of an investment and construction project, that take into account the total loss of economic efficiency in the course of implementing various technologies of an investment and housing construction project. 
 
Conclusions. The results enable the co-authors to use the proposed model to evaluate the economic efficiency and to identify (1) options of an investment and housing construction project, (2) the range of acceptable options of project implementation that are economically feasible, as well as (3) ranges of unacceptable project implementation options that are “too bad for the consumer” and “too expensive for the producer”; (4) the best project option; (5) the way to improve the generalized algorithm of BIM technology application in practical housing construction.

A. N. Larionov

Papers

Palaeoproterozoic Continental MORB-type Tholeiites in the Karelian Craton: Petrology, Geochronology, and Tectonic Setting

Further introduction of information modelling technologies in the course of implementation of investment projects in the field of housing construction