Polygenesis of mafic-ultramafic complexes: Isotope-geochronological and geochemical evidence from zircons of the Berezovka massif rocks (Sakhalin Island) |
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| Affiliation: | 1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;3. Sakhalin Geological-Prospecting Expedition, ul. A. Matrosova 28, Yuzhno-Sakhalinsk, 693005, Russia;4. A.P. Karpinsky Russian Geological Research Institute, Srednii prosp. 74, St. Petersburg, 199106, Russia;5. St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia;1. Department of Earth Sciences, Faculty of Sciences, Shiraz University, Shiraz, Iran;2. Department of Geology, Bowling Green State University, USA;1. Environmental Microbiology Laboratory (EML), École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland;2. Petrology and Geochemistry Area, Earth Sciences Department, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain;3. School of Geographical and Earth Sciences, University of Glasgow, United Kingdom;4. Instituto Andaluz de Ciencias de la Tierra (IACT) (CSIC-UGR), Avda. de las Palmeras, 4, 18100 Armilla, Granada, Spain;1. Department of Applied Sciences, Punjab Technical University, Kapurthala 144601, India;2. Department of Physics, D.A.V. College, Bathinda 151001, Punjab, India;3. Department of Physics, Kanya Maha Vidyalaya, Jalandhar 144001, India;4. Department of Applied Sciences, Ferozpur College of Engineering and Technology, Ferozshah, Ferozpur 142052, India;1. School of Geology, Faculty of Science, University of Tehran, 141556455, Iran;2. Department of Earth Sciences, Kanazawa University, Kanazawa 920-1192, Japan;3. School of Mining Engineering, College of Engineering, University of Tehran, Iran |
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| Abstract: | Results of comprehensive isotope-geochronological (U-Pb dating; SHRIMP II) and geochemical (LA-ICP-MS) studies of zircons from different rocks of the Berezovka polygenetic mafic-ultramafic massif of the East Sakhalin ophiolite association are presented. The massif includes three proximal but genetically autonomous structure-lithologic complexes of different ages: protrusion of ultramafic rocks of restite nature, gabbroid intrusion breaking through it, and contact reaction zone located along their boundaries. The isotopic age of zircons in the massif as a whole and in its individual rocks varies over a broad range of values. The zircons belong to several populations according to their age (Ma) and other features: relict and xenogenous (~ 3100-990, 70–410, and ~ 395-210) and syngenetic (~ 200-100, ~ 90-65, and ~ 30-20). They differ in grain size and morphology, optical and cathodoluminescence images, and trace-element patterns. By morphology, the grains are divided into short-prismatic crystals with well-developed faces and edges, long-prismatic crystals with well-developed faces and edges, prismatic crystals with slightly resorbed faces and edges, prismatic crystals with strongly resorbed faces and edges, and intensely resorbed grains totally or partly lacking faceting. The ages of zircons depend inversely on the contents of La, Ce, and Yb, total contents of REE, (Ce/Ce*)n, and (Eu/Eu*)n. Some grains are characterized by abnormal REE and trace-element patterns due to their epigenetic redistribution. The wide scatter of the intermediate ages of relict and xenogenous zircon grains, their resorption and disturbed optical and geochemical features are probably due to the nonuniform rejuvenation of their isotope systems and variations in other parameters, caused by the effect of younger mafic melt and its fluids, whose crystallization gave rise to a gabbroid intrusion dated at 170–150 Ma. The obtained data on the isotopic age and other properties of zircons from the rocks of the Berezovka massif agree with the geological model of its polygenesis. |
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