THE 1501 MA KUONAMKA LARGE IGNEOUS PROVINCE OF NORTHERN SIBERIA: U-Pb GEOCHRONOLOGY, GEOCHEMISTRY, AND LINKS WITH COEVAL MAGMATISM ON OTHER CRUSTAL BLOCKS
R.E. Ernst1,2, A.V. Okrugin3, R.V. Veselovskiy4, S.L. Kamo5, M.A. Hamilton5, V.E. Pavlov4, U. Söderlund6, K.R. Chamberlain7, C. Rogers8
1Department of Earth Sciences, Carleton University, pr. Lenina 36, Tomsk, 634050, Russia
2Faculty of Geology and Geography, Tomsk State University
3Diamond & Precious Metal Geology Institute, Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677000, Russia
4Institute of Physics of the Earth, Russian Academy of Sciences, ul. Bol'shaya Gruzinskaya 10, build. 1, 123995, Moscow, Russia
5Jack Satterly Geochronology Laboratory, University of Toronto, Toronto, ON, M5S 3B1, Canada
6Department of Geology, Lund University, Lund, 223 62, Sweden
7Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, 82071, USA
8Department of Earth Sciences, Carleton University, Ottawa, ON, K1S 5B6, Canada
Keywords: Магматизм, дайки, силлы, крупная изверженная провинция, север Сибири, Magmatism, dikes, sill, igneous province, northern Siberia
Abstract
A new large igneous province (LIP), the 1501 ± 3 Ma Kuonamka LIP, extends across 700 km of northern Siberia and is linked with coeval dykes and sills in the formerly attached São Francisco craton (SFC)-Congo craton to yield a short-duration LIP event 2000 km across. The age of the Kuonamka LIP can be summarized as 1501 ± 3 Ma (95% confidence), based on 7 U-Pb ID-TIMS ages (six new herein) from dolerite dikes and sills extending across the Anabar shield and within western Riphean cover rocks for a distance of 270 km. An additional sill yielded a SIMS (CAMECA) age of 1483 ± 17 Ma and sill in the Olenek uplift several hundred kilometers farther east, a previous SIMS (SHRIMP) age of ca. 1473 Ma was obtained on a sill; both SIMS ages are within the age uncertainty of the ID-TIMS ages. Geochemical data indicate a tholeiitic basalt composition with low MgO (4-7 wt.%) within-plate character based on trace element classification diagrams and source between E-MORB and OIB with only minor contamination from crust or metasomatized lithospheric mantle. Two subgroups are distinguished: Group 1 has gently sloping LREE ((La/Sm)PM = 1.9) and HREE ((Gd/Yb)PM = 1.8) patterns, slightly negative Sr and moderate TiO2 anomalies (2.2 wt.%), and Group 2 has steeper LREE ((La/Sm)PM = 2.3) and HREE ((Gd/Yb)PM = 2.3), strong negative Sr anomaly, is higher in TiO2 (2.7 wt.%), and is transitional from tholeiitic to weakly alkaline in composition. The slight differences in REE slopes are consistent with Group 2 on average melting at deeper levels. Proposed reconstructions of the Kuonamka LIP with 1500 Ma magmatism of the SFC-Congo craton are supported by a geochemical comparison. Specifically, the chemistry of the Chapada Diamantina and Curaça dikes of the SFC can be linked to that of Groups 1 and 2, respectively, of the Kuonamka LIP and are consistent with a common mantle source between EMORB and OIB and subsequent differentiation history. However, the coeval Humpata sills and dikes of the Angola block of the Congo craton represent a different magma batch.
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