Late Paleozoic granitoids of western Transbaikalia: magma sources and stages of formation

Abstract

Geochemical and geochronological studies of the main types of granitoids of the Angara-Vitim batholith (AVB) and granites of the Zaza complex in western Transbaikalia were carried out. U-Pb (SHRIMP-II) and Rb-Sr dating yielded the age of autochthonous gneiss-granites of the Zelenaya Griva massif (325.3±2.8 Ma), quartz syenites of the Khangintui pluton (302.3±3.7 Ma) and intruding leucogranites of the Zaza complex (294.4±1 Ma), monzonites of the Khasurta massif (283.7±5.3 Ma), and quartz monzonites of the Romanovka massif (278.5±2.4 Ma). The U-Pb and Rb-Sr dates show that the Late Paleozoic magmatism in western Transbaikalia proceeded in two stages: (1) 340–320 Ma, when predominantly mesocratic granites of the Barguzin complex, including autochthonous ones, formed, and (2) 310–270 Ma, when most AVB granitoids formed. We suggest that at the early stage, crustal peraluminous granites formed in collision geodynamic setting. At the late (main) stage, magmatism occurred in postorogenic-extension setting and was accompanied by the formation of several geochemical types of granitoids: (1) typical intrusive mesocratic granites of the Barguzin complex, similar to those produced at the first stage; (2) melanocratic granitoids (monzonitoids, quartz syenites), which were earlier dated to the early stage of the AVB evolution; (3) leucocratic medium-alkali (peraluminous) granites of the Zaza intrusive complex; and (4) some alkali-granite and syenite intrusions accompanied by alkaline mafic rocks. The diversity of granitoids that formed at the late stage of magmatism was due to the heterogeneous composition of crust protoliths and different degrees of mantle-magma participation in their formation.

Growth rate of the preserved continental crust: II. Constraints from Hf and O isotopes in detrital zircons from Greater Russian Rivers

“…Transbaikalia region, to the south of Lake Baikal, is a region of intense and prolonged granitic magmatism (Kuzmichev et al, 2001;Tsygankov et al, 2007;Zorin et al, 2009). The oldest granites in the region are dated at 800 Ma (Kuzmichev et al, 2001).…”

“…The largest granite complex is the Angara-Vitim batholith with an area of more than 150,000 km 2 . The batholith formed in two stages, 340-320 Ma and 310-270 Ma, on a heterogeneous basement with a variable isotopic signature (Tsygankov et al, 2007).…”

“…2f) and most of these grains were sourced from the Caledonian terranes of the Sayan Mountains. Grains of 400-250 Ma may have originated from Hercynian collisional complexes, which include the vast 340-270 Ma Angara-Vitim granite batholith (Tsygankov et al, 2007). Eight grains with a Mesozoic age could have originated from alkaline granites (Kovalenko et al,1999) or core complexes in the Transbaikalia region .…”

Silurian age of major folding in Riphean deposits of the Baikal-patom zone

“…According to the geochronological studies conducted in the most studied field of Sukhoi Log, these types of gold mineralization occurred in significantly distant time intervals dated 447±5 and 321±14 Ma, respectively [Laverov et al, 2007]. The first dating is consistent with the occurrence of granitoids in the Mama formation (421±15 Ma, U-Pb dating, SHRIMP-II) [Zorin et al, 2008], and the second dating corresponds to the age of the Barguzin formation composing the Angara-Vitim batholith (330-310 Ma) [Tsygankov et al, 2007;.…”

U‐pb La‐icp‐ms Dating of Zircons From Subvolcanics of the Bimodal Dyke Series of the Western Transbaikalia: Technique, and Evidence of the Late Paleozoic Extension of the Crust

“…Возможно, завышение Rb-Sr изохронной даты обусловлено некоторой контаминацией кислых дайковых магм коровым субстратом с высоким содержанием ра-диогенного стронция. Тем не менее пермские воз-расты дайковых пород, полученные U-Pb LA-ICP-MS методом, соответствуют геологическим наблюде-ниям: во-первых, дайки секут известково-щелоч-ные граниты баргузинского комплекса (330-300 млн лет) и граниты зазинского комплекса (305-285 млн лет) [Tsygankov et al, 2007[Tsygankov et al, , 2010; во-вторых, они пространственно сопряжены с пермскими гра-нитоидами повышенной щелочности (Брянский и Хоринский массивы) и бимодальными вулканита-ми с возрастом 285-280 млн лет Litvinovsky et al, 2002;Riechow et al, 2010], а также близки к ним по своим вещественным ха-рактеристикам [Khubanov, 2009].…”