The Paleoproterozoic Kandalaksha-Kolvitsa Gabbro-Anorthosite Complex (Fennoscandian Shield): New U–Pb, Sm–Nd, and Nd–Sr (ID-TIMS) Isotope Data on the Age of Formation, Metamorphism, and Geochemical Features of Zircon (LA-ICP-MS)

Abstract

The paper provides new U–Pb, Sm–Nd, and Nd–Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex. Rare earth element (REE) contents in zircons from basic rock varieties of the Kandalaksha-Kolvitsa area were analyzed in situ using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Plots of REE distribution were constructed, confirming the magmatic origin of zircon. Temperatures of zircon crystallization were estimated using a Ti-in-zircon geochronometer. The U–Pb method with a 205Pb artificial tracer was first applied to date single zircon grains (2448 ± 5 Ma) from metagabbro of the Kolvitsa massif. The U–Pb analysis of zircon from anorthosites of the Kandalaksha massif dated the early stage of the granulite metamorphism at 2230 ± 10 Ma. The Sm–Nd isotope age was estimated on metamorphic minerals (apatite, garnet, sulfides) and whole rock at 1985 ± 17 Ma (granulite metamorphism) for the Kolvitsa massif and at 1887 ± 37 Ma (high-temperature metasomatic transformations) and 1692 ± 71 Ma (regional fluid reworking) for the Kandalaksha massif. The Sm–Nd model age of metagabbro was 3.3 Ga with a negative value of εNd = 4.6, which corresponds with either processes of crustal contamination or primary enriched mantle reservoir of primary magmas.

Late Ordovician Mafic Magmatic Event, Southeast Siberia: Tectonic Implications, LIP Interpretation, and Potential Link with a Mass Extinction

“…Nd isotope analyses for samples AS18-17, SM18-20, and SM18-24 were performed on a Finnigan MAT 262 mass spectrometer at the Geological Institute of the Kola Science Center RAS (Apatity, Russia), using the method described in [37]. During the course of this study, the mean value of the 143 Nd/ 144 Nd ratio in the JNdi-1 standard was 0.512075 ± 31 (N = 5).…”

“…For the 147 Sm/ 144 Nd and 143 Nd/ 144 Nd ratios, the analytical errors (2σ) were 0.3% and 0.005%, respectively. Sample X04-14-1 was analyzed on a TRITON TI mass spectrometer (at the Institute of Precambrian Geology and Geochronology of the Russian Academy of Sciences, St. Petersburg, Russia) using a method, similar to that of [37] and described in [39]. Total blank measurements were 0.03-0.2 ng for Sm and 0.1-0.5 ng for Nd.…”