Paleoproterozoic ca. 2.2 Ga high-Cl metagabbro in the Belomorian province, Eastern Fennoscandian Shield: Origin and tectonic implications

Tectonic and fluid reworking of deep-seated mafic intrusions in the orogenic belts often erase primary magmatic characteristics, and crystallization parameters of mafic melts enriched in volatiles remain an issue. This study presents new U-Pb geochronological data for zircons, mineral composition, whole-rock geochemistry and Sr-Nd isotopic data for Pechnoy ca. 2.2 Ga mafic layered sill in the central Belomorian province, Eastern Fennoscandian Shield. The Pechnoy intrusion comprises low-alumina, silica-undersaturated, Cl enriched mafic rocks depleted in HREE and HFSE with εNd values of -0.1–+1.5 and (87Sr/86Sr)2200 = 0.7024–0.7039. Field and petrological studies indicate that studied rocks preserved relicts of primary magmatic characteristics because it was encapsulated in host gabbronorite intrusion and avoided intensive fluid reworking during 1.8-2.0 Ga Lapland-Kola orogeny. Variations of mineral composition, major, and trace elements within intrusion originated via in situ fractional crystallization with dominated settling of clinopyroxene and plagioclase. Chlorine distribution within intrusion and in the host rocks inferred a magmatic origin Cl enrichment. High-Na scapolite is the main concentrator of the Cl in the rocks. The inclusions of scapolite in the relict magmatic plagioclase and higher Ca content relative to adjacent Na-rich plagioclase likely indicate early crystallization of high-Na scapolite. Trace element and isotopic characteristics of rocks indicate OIB and subduction modified SCLM signatures of their primary melts. A comparison of the available data for Pechnoy sill and coeval mafic sills in the Karelian Craton reveals a common mantle source for ca. 2.2. Ga igneous rocks in the Fennoscandian Shield although intrusions in the Belomorian province represent deeper levels of 2.2 Ga large igneous province plumbing system. •High-Cl mafic sill in the Belomorian province is 2.2 Ga old•Petrographical and geochemical features suggest in situ fractional crystallization•SrNd isotopes indicate OIB and enriched SCLM signatures of primary melts•Studied sill represent deep-seated levels of the 2.2 Ga LIP plumbing system