The Belomorian Mobile Belt (BMB) in northern Karelia mostly consists of gently sloping shear zones, whose gneisses and migmatized amphibolites and blastomylonites are typically thinly banded, with their banding consistently dipping north- and northeastward. These gently sloping shear zones were not affected by folding after they were produced and are not cut by Paleoproterozoic metabasite dikes. Intrusive metabasites in the gently sloping shear zones make up relatively small (usually <5 m) equant or elongate bodies and occur as fragments of larger bodies. These fragments are often concentrated in stripes. Metabasites in the gently sloping shear zone are sometimes also found as lenses and tabular bodies of relatively small thickness, which are conformable with the foliation of the host rocks. The gently sloping shear zones cut across older domains of more complicated structure, which suggests that these zones are gently sloping ductile shear zones. Along these zones, the nappes were thrust south- and southwestward, and this process was the last in the origin of major structural features of BMB when the Paleoproterozoic Lapland–Kola orogen was formed. Practically identical age values were obtained for the gently sloping shear zone in the two widely separated Engonozero and Chupa segments of BMB: 1879 ± 21 Ma ( 40 Ar/ 39 Ar amphibole age of amphibolite whose protolith was mafic rock) and 1857 ± 13 Ma (Sm–Nd mineral isochron age of garnet amphibolites after gabbronorite). The P – T metamorphic parameters in these gently sloping shear zones are remarkably different from the metamorphic parameters outside these zones: the pressure is 3–4 kbar lower and the temperature is 60–100°C lower. Thrusting-related decompression triggered the transition from the older high-pressure episode of Paleoproterozoic metamorphism to a younger syn-thrusting higher temperature metamorphic episode. The peak metamorphic parameters corresponding to the boundary between the amphibolite and granulite facies were reached only in the central portions of the shear zones: T = 680–760°C, P = 8.0–11.9 kbar. In areas of the most intense migmatization, temperature estimates in the central portions of the shear are as high as 810–830°C. The marginal portions of the shear zones were formed at lower temperatures of 610–630°C. The temperature heterogeneous and rock heating in the gently sloping shear zones may have resulted from flows of high-temperature metamorphic fluid that were focused to the central portions of the zones.

U-Pb zircon isotopic data on rocks from the Kandalaksha-Umba zone of the Lapland granulite belt in the Por’ya Bay area constrain the age of the protolith of the apodacite (apotonalite) Opx-Bt granulite gneisses at 2799 ± 4 Ma, and the age of the apogabbronorite Grt-Opx-Cpx-Hbl crystalline schists at 2315 ± 23 Ma. The U-Pb sphene age of the magmatic crystallization of the postmetamorphic granodiorites is 1901 ± 5 Ma. The zircon yields the U-Pb age of the contamination of xenogenic zircons, which were captured during the dissolution of xenoliths of the host Grt-Opx-Cpx-Hbl crystalline schists in granodiorite melt. The comparison of the most important attributes of the endogenic histories of the adjacent Lapland Granulite and Belomorian Mobile belts testifies to their similar evolutionary histories: (1) the protolith age of the acid Opx-Bt granulites of the Lapland Belt (2799 ± 4 Ma) coincides with the protolith age of acid gneisses in the Belomorian Belt (2890-2690 Ma); (2) the ages of the gabbronorite protolith of Grt-Opx-Cpx-Hbl granulites in the Lapland Belt (2315 ± 23 Ma) and gabbro-anorthosite in the Kolvitsa Massif (2462-2423 Ma) are close to the protolith age of eclogitized gabbronorites in the Belomorian coronite suite (2.46–2.36 Ga); (3) the age of granulite metamorphism of acid and mafic rocks in the Lapland Belt is 1912–1925 Ma, and the age of eclogite metamorphism of gneisses and metabasites in the Belomorian Belt is approximately 1.9 Ga, i.e., their metamorphism took place in Svecofennian time; (4) the peak pressure of granulite metamorphism in the Lapland Belt was 9–11 kbar at a temperature of 800–850°C, whereas the peak metamorphic parameters of eclogite metamorphism in the Belomorian Belt were 10–12 kbar and 640–700°C. This means that the metamorphic complexes of the Lapland and Belomorian belts had the same Mezo- and Neoarchean protoliths hosting bodies of Paleoproterozoic gabbroids and were completely formed largely by a single cycle of Svecofennian high-pressure zonal metamorphism within a temperature range from the lowest grade of the eclogite to the granulite facies.

В Кандалакшско-Умбинской зоне Лапландского гранулитового пояса (район Порьей Губы) на основе U-Pb геохронологических исследований цирконов был определен возраст протолита аподацитовых (апотоналитовых) Opx-Bt гранулитовых гнейсов – 2799 ± 4 млн лет и апогабброноритовых гранат-двупироксен-роговообманковых кристаллосланцев – 2315 ± 23 млн лет. Этим же методом по сфену определен возраст магматической кристаллизации постметаморфических гранодиоритов – 1901 ±5 млн лет, а также возраст ксеногенных цирконов, захваченных при растворении ксенолитов окружающих Grt-Opx-Cpx-Hbl кристаллосланцев гранодиоритовым расплавом. Сравнение граничащих друг с другом Лапландского гранулитового и Беломорского подвижного поясов по важнейшим атрибутам эндогенной истории обнаружило явные признаки их единства: 1) возраст протолита кислых Opx-Bt гранулитов Лапландского пояса (2799 ± 4 млн лет) совпадает с таковым протолита кислых гнейсов Беломорского пояса (2890–2690 млн лет); 2) возраст габбро-норитового протолита Grt-Opx-Cpx-Hbl гранулитов Лапландского пояса (2315 ± 23 млн лет), и габбро-анортозитов Колвицкого массива (2462–2423 млн лет) близок к таковому протолитов эклогитизированных габбро-норитов друзитовой серии Беломорья (2.46–2.36 млрд лет); 3) возраст гранулитового метаморфизма кислых и основных пород Лапландского пояса составляет 1912–1925 млн лет, а эклогитового метаморфизма гнейсов и метабазитов Беломорского пояса – около 1.9 млн лет, т.е. их метаморфизм является одновозрастным свекофеннским; 4) пиковое давление при гранулитовом метаморфизме в Лапландском поясе составляет 9–11 кбар с температурным максимумом 800–850°С, а эклогитовый метаморфизм Беломорского подвижного пояса протекал при близком давлении 10–12 кбар и температуре 640–700°С. Это означает, что окончательное формирование метаморфических комплексов Лапландского и Беломорского поясов, имеющих одинаковый мезо-неоархейский протолит с телами палеопротерозойских габброидов, обусловлено проявлением единого цикла свекофеннского высокобарического зонального метаморфизма в температурном интервале от начальной ступени эклогитовой до гранулитовой фации в условиях коллизии.

New data are obtained on the major-component and minor- and trace-element composition of metamorphosed gabbronorites and Fe-Ti gabbro in the Krasnaya Guba area, Belomorian Mobile Belt. These two magmatic complexes, which are spatially combined but are of different age and were produced in different geodynamic environments, were simultaneously metamorphosed in the Paleoproterozoic to parameters transitional between the amphibolite and eclogite facies. Eclogite metamorphism was associated with perceivable changes in the concentrations of alkalis and alkali earth elements, and the metamorphic transformation of the plagioclase eclogite (which can be metamorphosed gabbronorite and/or gabbro) into amphibolite and biotite amphibolite was associated with changes in the concentrations of practically all trace elements. This implies that the metamorphic processes were not isochemical and were accompanied by significant removal and introduction of incompatible elements. However, some trace-element ratios (such as Ti/Y, Ti/Zr, Zr/Y, La/Sm, and Nb/Th) remained unmodified in the course of metamorphism and remained the same as in the pristine gabbronorite or gabbro and likely can be employed as indicators of the composition of the probable protolith and the conditions under which it was produced.

In most alkaline-ultrabasic-carbonatite ring complexes, the distribution of trace elements in the successive derivatives of mantle magmas is usually controlled by the Rayleigh equation of fractional crystallization in accordance with their partition coefficients, whereas, that of late derivatives, nepheline syenites and carbonatites, is usually consistent with trends characteristic of silicate-carbonate liquid immiscibility. In contrast to the carbonatites of ring complexes, carbonatites from deep-seated linear zones have no genetic relation with alkaline-ultrabasic magmatism, and the associated alkaline rocks are represented only by the nepheline syenite eutectic association. The geochemical study of magmatic rocks from the Vishnevye Gory nepheline syenite-carbonatite complex (Urals), which is assigned to the association of deep-seated linear zones, showed that neither differentiation of a parental melt nor liquid immiscibility could produce the observed trace element distribution (Sr, Rb, REE, and Nb) in miaskites and carbonatites. Judging from the available fragmentary experimental data, the distribution patterns can be regarded as possible indicators of element fractionation between alkaline carbonate fluid and alkaline melt. Such trace element distribution is presumably controlled by a fluid melt interaction; it was also observed in carbonatites and alkaline rocks of some ring complexes, and its scarcity can be explained by the lower density of aqueous fluid released from magma at shallower depths.

Four intermediate collectors of minerals of the kimberlitic association (MKA) are identified in the Latvian territory. They are confined to Upper Devonian (Gauya, Ogre, and Ketleri formations) and Quaternary sediments. Each intermediate collector is characterized by a certain assemblage of minerals. The present communication considers specific features of the MKA distribution within each collector, as well as chemical composition and grain surface character of separate MKAs. Based on the study of typomorphism of minerals and peculiarities of sedimentation in different geological epochs, scheme of the localization of bedrock KMA sources is proposed. It is supposed that the Latvian territory incorporates three bedrock (kimberlite-type) sources with different prospects for diamond potential. The diamond potential of one source located in northeastern Latvia is rather high.