THE EARLY-MIDDLE PALEOZOIC VOLCANISM AND GEODYNAMIC EVOLUTION OF THE HERLEN MASSIF, CENTRAL PART OF THE CAOB: CONSTRAINS FROM GEOCHEMISTRY, U-PB GEOCHRONOLOGY, LU-HF AND RB-SR ISOTOPES OF VOLCANIC ROCKS

Mongolia lies in the central part of the Central Asian Orogenic Belt [Mossakovsky et al., 1994; Zorin, 1999; Jahn, 2004; Khain et al., 2003; Badarch et al., 2002; Windley et al., 2007; Zhang et al, 2008], or Altaids [Şengör et al., 1993; Şengör, Natal’in, 1996; Wilhem et al., 2012], which is fringed by the Siberian craton in the north and by the Tarim and Sino-Korean Cratons in the south. According to the recent tectonic subdivision, the territory of Mongolia is subdivided into Northern and Southern domains which are separated by the so called Mid Mongolian Tectonic Line [Tomurtogoo, 2012]. The Herlen Massif is one of the important tectonic units of the South Mongolian domain in the Argun-Idermeg super terrane extending through the territories of Russia and China [Parfenov et al., 2009; Tomurtogoo, 2014b]. The Herlen massif, also known as Herlen superterrane [Tomurtogoo, 2012] or Idermeg terrane [Tomurtogoo, 2014a] is composed of Ereendavaa, Undur-Khaan, Idermeg and Gobian Altay-Baruun Urt terranes converged at the end of the Cambrianbeginning of the Ordovician [Badarch et al., 2002; Tomurtogoo, 2014b].Mongolia lies in the central part of the Central Asian Orogenic Belt [Mossakovsky et al., 1994; Zorin, 1999; Jahn, 2004; Khain et al., 2003; Badarch et al., 2002; Windley et al., 2007; Zhang et al, 2008], or Altaids [Şengör et al., 1993; Şengör, Natal’in, 1996; Wilhem et al., 2012], which is fringed by the Siberian craton in the north and by the Tarim and Sino-Korean Cratons in the south. According to the recent tectonic subdivision, the territory of Mongolia is subdivided into Northern and Southern domains which are separated by the so called Mid Mongolian Tectonic Line [Tomurtogoo, 2012]. The Herlen Massif is one of the important tectonic units of the South Mongolian domain in the Argun-Idermeg super terrane extending through the territories of Russia and China [Parfenov et al., 2009; Tomurtogoo, 2014b]. The Herlen massif, also known as Herlen superterrane [Tomurtogoo, 2012] or Idermeg terrane [Tomurtogoo, 2014a] is composed of Ereendavaa, Undur-Khaan, Idermeg and Gobian Altay-Baruun Urt terranes converged at the end of the Cambrianbeginning of the Ordovician [Badarch et al., 2002; Tomurtogoo, 2014b]

Geochemistry and geochronology of the Paleozoic sedimentary rocks in the Shar Khutul area, Central Mongolia

The study area is located in the central part of Tsetserleg terrane in the southwestern margin of the Khangai-Khentey orogenic system. The paper presents new data on geochemistry and geochronology of sedimentary rocks from the Shar Khutul area, where the Tsetserleg terrane consists of Silurian-Devonian oceanic plate stratigraphic unit and Carboniferous shallow water sediment. The Upper Silurian to Middle Devonian Erdenetsogt Formation (S3-D2er), which is an oceanic plate stratigraphic unit, is mainly composed of siliceous siltstone, volcanites, tuffs, quartzite, and cherts. The shallow water sediments are divided into Upper Devonian to Lower Carboniferous Tsetserleg Formation (D3-C1cc) and Lower–Middle Carboniferous Dzargalant Formation (C1-2dz). The Tsetserleg Formation (D3-C1cc) consists of only sedimentary rocks such as bluish-grey sandstones and siltstones, and Lower–Middle Carboniferous Dzargalant Formation (C1-2dz) is principally composed of medium- to coarse-grained, brown-greenish grey sandstones with thin-layers of dark siltstones and gravelites. The SiO2 content of the Shar Khutul area sandstones ranges from 63.85 to 67.95 wt.% and the average content of TiO2 is 0.72 wt.% and Al2O3 content is 14.38 wt.%. The Chemical Index of Alteration (CIA) value ranges from 48.71 to 56.94 and the range of Index of compositional variations (ICV) is from 0.98 to 1.24. Moreover, the samples studied show that most of the sandstones are generally immature and were derived from weakly weathered source rocks. The ratios of Eu/Eu* (0.83), La/Sc (3.81), La/Co (5.30), and Cr/Th (13.81) indicate that the derivation of the Shar Khutul area sandstones from felsic rock sources and confirm the signatures of a felsic igneous provenance and suggest an active continental margin tectonic setting of the source area. The clastic zircons from the medium grained sandstone (Erdenetsogt formation) yield ages between 2.5 Ga and 236 Ma and the detrital zircons exhibit four peak ages at 1.7-2.5 Ga (n = 13), 455-499 Ma (n = 6), 337-382 Ma (n = 13) and 236–250 Ma (n = 5)

THE EARLY-MIDDLE PALEOZOIC VOLCANISM AND GEODYNAMIC EVOLUTION OF THE HERLEN MASSIF, CENTRAL PART OF THE CAOB: CONSTRAINS FROM GEOCHEMISTRY, U-PB GEOCHRONOLOGY, LU-HF AND RB-SR ISOTOPES OF VOLCANIC ROCKS

Mongolia lies in the central part of the Central Asian Orogenic Belt [Mossakovsky et al., 1994; Zorin, 1999; Jahn, 2004; Khain et al., 2003; Badarch et al., 2002; Windley et al., 2007; Zhang et al, 2008], or Altaids [Şengör et al., 1993; Şengör, Natal’in, 1996; Wilhem et al., 2012], which is fringed by the Siberian craton in the north and by the Tarim and Sino-Korean Cratons in the south. According to the recent tectonic subdivision, the territory of Mongolia is subdivided into Northern and Southern domains which are separated by the so called Mid Mongolian Tectonic Line [Tomurtogoo, 2012]. The Herlen Massif is one of the important tectonic units of the South Mongolian domain in the Argun-Idermeg super terrane extending through the territories of Russia and China [Parfenov et al., 2009; Tomurtogoo, 2014b]. The Herlen massif, also known as Herlen superterrane [Tomurtogoo, 2012] or Idermeg terrane [Tomurtogoo, 2014a] is composed of Ereendavaa, Undur-Khaan, Idermeg and Gobian Altay-Baruun Urt terranes converged at the end of the Cambrianbeginning of the Ordovician [Badarch et al., 2002; Tomurtogoo, 2014b]