Abstract
Object . The results of geochronological and isotope-geochemical studies of the Arsentyevsky titaniferous gabbro-syenite massif of the Western Transbaikalia, which previously referred to the gabbro-syenite series of a two-phase structure are presented. The rocks of the massif contain an increased concentration of titanomagnetite, ilmenite, magnetite and in some cases apatite and are considered as complex iron-titanium ores. Methods. The studies were performed by silicate analysis methods, XRF and ICP-MS; age determination for zircons was carried out by LA-ICP-MS and SHRIMP-II methods. The composition of minerals on the X-ray microarray analyzer MAP-3 and electron microscope LEO-1430 was studied. Results. In the basites, a standard trend is observed for the evolution of compositions from melanocratic to terminal leucocratic differences with an increase in the content of silica, alumina, and sodium, and a decrease in magnesium and calcium. Syenites differ from anorthosites in the content of impurity elements including rubidium, niobium, strontium and REE The geochronological studies of rocks of Arsent’evsky gabbro-syenite massif, showed a significant time gap in the formation of gabbroids relative to syenites. The U-Pb age of the gabbroids was 279.5 ± 2.0 Ma, alkali feldspar syenites have age 229.4 ± 2.8 Ma, and biotite syenites - 226 ± 2.4 Ma. Conclusion. The obtained results by age and data on the geochemical features of the rocks made it possible to conclude that there was no genetic relationship between basites and syenites. Petrochemical and geochemical features of biotite and alkali-feldspar syenites proved to be close to the rocks of the Mesozoic Kunaleisky complex.
Highlights
The results of geochronological and isotope-geochemical studies of the Arsentyevsky titaniferous gabbro-syenite massif of the Western Transbaikalia, which previously referred to the gabbro-syenite series of a two-phase structure are presented
The studies were performed by silicate analysis methods, XRF and ICP-MS; age determination for zircons was carried out by LA-ICP-MS and SHRIMP-II methods
Syenites differ from anorthosites in the content of impurity elements including rubidium, niobium, strontium and REE The geochronological studies of rocks of Arsent’evsky gabbro-syenite massif, showed a significant time gap in the formation of gabbroids relative to syenites
Summary
Состоящий из базитовых и сиенитовых пород, имеет овальную форму, слегка удлиненную в меридиональном направлении, занимает площадь около 20 км. Уран-свинцовый возраст методом лазерной абляции определен на приборе LA-ICP-MS [Хубанов и др., 2016] на масс-спектрометре высокого разрешения Element XR (Thermo Fisher Scientific) с системой пробоотбора UP-213 (New Wave Research) в ГИН СО РАН 1 – оливиновое габбро, пироксениты, габбро, габбронориты; 2 – лейкогаббро и анортозиты; 3 – биотитовые сиениты; 4 – щелочно-полевошпатовые сиениты; 5 – гранитогнейсы; 6 – титаномагнетитовые рудные тела; 7 – элементы залегания трахитоидности; 8 – места отбора проб на геохронологические и геохимические исследования. Биотитовые сиениты сложены калиевым полевым шпатом и плагиоклазом (An16–25), включают амфибол и биотит. Щелочно-полевошпатовые сиениты состоят из щелочных полевых шпатов, представлены в основном микропертитами, альбитом (An5–10) и акцессорными магнетитом, апатитом. Сингенетический тип рассеянно-вкрапленных руд характерен для оливиновых габбро и габброидов с содержанием до 10% Fe-Ti минералов (магнетита, ильменита). К эпигенетическому типу относятся жилообразные тела массивных руд, сложенные на 70–90% магнетитом, титаномагнетитом и ильменитом, содержащие небольшое количество сульфидов и шпинели
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