V. S. Stepanov

Bio: V. S. Stepanov is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Craton & Mafic. The author has an hindex of 6, co-authored 11 publications receiving 218 citations.

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

Abstract: 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

Short-lived mantle generated magmatic events and their dyke swarms: The key unlocking Earth's paleogeographic record back to 2.6 Ga

Abstract: The continents preserve a rich record of short-lived mantle-generated magmatic events through time and space. Many of these events can now be dated routinely and precisely, with a resolution of a couple of million years or better. The spatial and temporal association of such events with rifting and continental break-up leads to remnants being preserved on originally adjacent (conjugate) margins and their respective hinterlands. Originally adjacent but now distant pieces of crust are thus likely to share remnants of one, if not several, short-lived magmatic events. The overall record of short-lived magmatic events (“magma bursts”) in a particular fragment of continental crust defines, in essence, a high-resolution “barcode” that characterizes the ancestry of that piece of crust. Originally adjacent pieces of crust (“nearest neighbours”) are thus likely to share part of their barcodes. Even though break-up margins may be severely modified and reworked during subsequent events, and many of the break-up related volcanic rocks may have long been eroded, associated dyke swarms have high preservation potential and are likely to preserve within them the high-resolution spatial and temporal information needed to allow successful paleogeographic reconstructions. Other independent, but generally more fuzzy data can then be used to test specific reconstructions based on the precise “piercing points” provided by coeval dyke swarms. In this paper we illustrate the general methodology and propose a new and detailed Superior-Hearne-Karelia reconstruction forming the core of 2.7-2.1 Ga supercraton Superia. In general, a complete characterization of all fragments of continental crust in terms of their magmatic event barcodes would be the most efficient way to solve Earth’s pre-Pangaea paleogeographic evolution, as far back as 2.6 Ga. High-resolution ages are the most efficient early filter to focus further work (e.g. paleomagnetism, geochemistry) on globally significant events. Only several hundred new ages would be required to catalyze a quantum leap of progress in this overall field. To store and efficiently disseminate all relevant data on short-lived magmatic events, we urgently need a peer-reviewed global database, similar to other formal databases in related fields that deal with globally significant datasets. To stimulate the creation of such an international database we herein propose datasheets that list the kind of information required for each short-lived magmatic event. Corresponding author: Wouter Bleeker Geological Survey of Canada 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8 Email: wbleeker@nrcan.gc.ca; tel: +1-613-995-7277