|
Vitaly Kalinin, Institute of Geochemistry, Mineralogy and Ore Formation N.P. Semenenko (Ukraine)
Olexandr Ponomarenko, Institute of Geochemistry, Mineralogy and Ore Formation N.P. Semenenko (Ukraine)
Konstantin Esipchuk, Institute of Geochemistry, Mineralogy and Ore Formation N.P. Semenenko (Ukraine)
|
|
There are two well-known large plutons of gabbro-anorthosite-rapakivi-granite composition on the Ukrainian Shield, Korostensky (12000 km2) and Korsun'-Novomyrgorodsky (5000 km2). The former one is located within the limits of Northwest (Volynsk), and the latter is within Ingulsky (Kirovograd) megablocks. Azov Block includes Octiabrsky massif (100 km2) of alkaline rocks and Yuzhnokalchinsky massif of gabbro-sienite-garnet composition (330 km2).All of the massifs listed have the age of 1820-1740Ma.
At small (20-50 km) distance from the Korosten pluton, to northwest, west and southwest of it some massifs that comprise gabbroes, diorites, quartz diorites, monzonites, quartz monzonites and monzodiorites, granodiorites and granites such as Osnitsky (more than 1000 km2), Bukinsky (300 km2) and a number of small ones (Novograd-Volynsk, Barashevsky, Smoldyrevsky, Shepetovsky, Mucharevsky, Tokaresky, etc.) are located.
Novoukrainsky massif (3500 km2), that directly flanks Korsun-Novomyrgorodsky pluton to the south, is comprised of norites, gabbronorites, gabbroes, diorites, monzodiorites, quartz monzodiorites, monzonites and quartz monzonites, syenites and quartz syenites, garnet- pyroxene granites (intrusive charnockitoides), garnet-biotite and biotite granites. It is typical, that garnet - biotite and biotite trachytoid granites quite often show the presence of rapakivi structure so they can be considered as rapakivi-like granites.
Similar rocks also comprise some smaller massifs (Bokoviansky, Verbliuzhsky, Mitrophanivky, some parts of Chigirinsky and Dolinsky) that are allocated to the east and west of Novoukrainsky massif.
There are also some massifs (total area is about 2000 km2) to the west and southeast from the Oktiabrsky massif. These massifs (Chlebodarovsky, Dubovsky, Talakovsky, Greko-Aleksandrovsky, Kumachevsky) are comprised by gabbroes, gabbroes - monzonites and monzodiorites, hyperstene and bi-pyroxene quartz syenites (intrusive charnockitoides), biotite - amphibolite granites.
Rocks of all three groups of massifs that flank to gabbro - anorthosite - rapakivi-granite and Octiabrsky alkaline massifs show the age of 2050-2000 Ma, that is they are more older than the former one of about 230-260Ma, and form with them certain pairs. Some common features of geological structure, petrographic composition and structure make it possible to suppose their genetic relation and to consider, that in geological history of the Ukrainian Shield, at Paleo-Mesoproterozoic boundary two stages of tectonic-magmatic activization with break in time of a little bit more than 200 Ma have occurred. Their regular spatial location allows to relate formation of these massifs with tectonics of lithospheric plates, namely - with subduction of Middle Dnieper plate under Near Azovian as well as Dniester-Bugsk plate under Ingulsk and Volynsk ones.
It is obviously possible to estimate on this basis the speed of subduction (moving) of one plate under another as about 1 mm per year.
|
