Proterozoic Kivakka layered mafic-ultramafic intrusion, Northern Karelia, Russia: Implications for the origin of granophyres of the upper boundary group

Layered Intrusions of Paleoproterozoic Age in the Kola and Karelian Regions

“…Maximum SiO 2 , CaO, and (Na 2 O + K 2 O) concentrations in Kivakka intrusion rocks and komatiitic basalts are similar (Figures 7 and 9). Al 2 O 3 concentration in intrusive rocks is 5 wt% higher, which seems to be due to higher pressure in the intrusive chamber [27]. The Burakovsky Pluton is more complex in structure and composition than the Kivakka intrusion, as indicated by the diagrams (Figure 10).…”

“…The Layered Series, in turn, is divided into a dunite zone (400 m), a harzburgite-melanonorite interlayering zone (400 m), a norite zone (300 m), a gabbronorite zone (320 m), and a gabbronorite zone with pigeonite (320 m). According to [26,27], the Lower Marginal, Layered, and Upper Marginal Series (Figure 3) of 100, 1700, and 50 m in average thickness, respectively, are distinguished from the base upwards. The Layered Series, in turn, is divided into a dunite zone (400 m), a harzburgite-melanonorite interlayering zone (400 m), a norite zone (300 m), a gabbronorite zone (320 m), and a gabbronorite zone with pigeonite (320 m).…”

“…Pyroxene and plagioclase are partially replaced by amphibole and saussurite, respectively. According to [27,29], the granophyre bodies were produced by crystallization of fluid-enriched residual melts, suggesting magma differentiation under closed-system conditions.…”

“…To focus on the REE abundance of intrusive rocks, the results of REE analysis in the main mineral phases of the Kivakka intrusion are used [27]. Maximum normalized concentrations were shown for augite with equal amounts of LREE and HREE and a positive Sm anomaly, as well as medium concentrations for orthopyroxene with an excess of HREE over LREE (La n /Lu n = 22) and poorly defined Ce and Eu anomalies.…”

“…To focus on the REE abundance of intrusive rocks, the results of REE analysis in the main mineral phases of the Kivakka intrusion are used [27]. Maximum normalized con- The trace elements of komatiitic basalts display the same type of poorly differentiated chondrite-normalized REE pattern with a slight excess of LREE over HREE (Lan/Lun = 1.5), as well as a poorly defined negative Eu anomaly (Figure 15a).…”