Granitoid magmatism and metallogeny of the Lake Zone in Western Mongolia (by the example of the Bumbat-Hairhan area)

Abstract

We present the results of a study of the geologic structure and age sequence of formation of the Late Neoproterozoic–Early Paleozoic plagiogranitoid and gabbroid associations in the Bumbat-Hairhan intrusive area of the Lake Zone in Western Mongolia. The petrogeochemical characteristics of the plagiogranitoids provide information about the conditions of formation of their parental melts at the island-arc and accretion–collision stages of the regional evolution. They also help to establish the main magma-generating sources as well as the major mechanisms of large-scale formation of granitoid melts and their relationship with ore generation processes. According to the trace-element and REE patterns and indicative ratios of these elements, the plagiogranitoids are subdivided into high- and low-alumina ones. Among the island-arc plagiogranitoids (551–524 Ma) of the Bumbat-Hairhan area, high-alumina varieties are the most widespread. They resulted from the partial melting of metabasites in equilibrium with garnet-containing restite at ≥ 15 kbar during their subsidence into the subduction zone. In geochemical features these plagiogranitoids are similar to high-Si adakites of different world regions. Island-arc low-alumina plagiogranitoids are scarcer. Their geochemical characteristics indicate that the parental melts were generated through the partial melting of metabasites in the lower part and/or in the basement of the island-arc system in equilibrium with amphibole-containing restite at ≤ 8 kbar. Plagiogranitoid associations of the accretion–collision stage (511–468 Ma) are the most widespread in the Bumbat-Hairhan area. They are subdivided into high- and low-alumina ones. According to the contents of trace elements and their indicative ratios, the low-alumina plagiogranitoids resulted from the partial melting of metabasites in equilibrium with plagioclase-containing restite at ≤ 8 kbar in the upper part of the collisional structure, and the high-alumina ones were generated through the melting of metabasites in the basement of thick crust in equilibrium with garnet-containing restite at ≥ 15 kbar. Geochronological studies in the Bumbat-Hairhan area revealed two stages of ore-generating processes spatially and temporally related to the formation of low-alumina plagiogranitoids. The early stage (518 ± 5 Ma), development of vein Cu (Au) mineralization, coincided in time with the formation of island-arc low-alumina plagiogranitoids of the Darbi massif (~ 524 Ma). The late stage (456 ± 4 Ma), formation of porphyry Cu-Mo (Au) mineralization, was synchronous with the formation of the low-alumina plagiogranites at the accretion-collision stage (~ 468 Ma).

The Early Palaeozoic mega‐thrusting of the Gondwana‐derived Altay–Lake zone in western Mongolia: Implications for the development of the Central Asian Orogenic Belt and Paleo‐Asian Ocean evolution

“…The Lake zone of Mongolia (Figure ) is a major zone of ophiolite and arc complexes within the CAOB (Byamba, ; Kovach et al, ; Kovalenko et al, ; Kröner et al, ; Rudnev et al, ; Rudnev, Izokh, Borisenko, & Gas'kov, ; Rudnev, Izokh, Kovach, Shelepaev, & Terent'eva, ; Ruzhentsev & Burashnikov, ; Tomurtogoo, ; Yarmolyuk et al, ). The Lake zone consists mainly of Cambrian volcano‐sedimentary rocks and ophiolites (Byamba, ; Dergunov, Luvsandanzan, & Pavlenko, ; Kovalenko et al, ; Ruzhentsev & Burashnikov, ; Tomurtogoo, ; Zonenshain & Kuzmin, ).…”

“…The granitoid complexes of the Lake zone formed over a wide time interval from the early Cambrian to the beginning of the Silurian (540–440 Ma) (Fig. ), and their intrusion was associated with a change from island arc and accretion to post‐accretion geodynamic settings (Kovach et al, ; Kovalenko et al, ; Rudnev et al, ; Rudnev et al, ; Rudnev et al, ; Soejono et al, ; Yarmolyuk et al, ). U–Pb geochronological data on zircons from rocks of various magmatic associations indicate ages of 535 ± 6 Ma for a plagiogranite (Bumbat Khairkhan massif, Rudnev et al, ), 529 ± 6 Ma of the diorite, 531 ± 10 Ma and 519 ± 8 Ma for tonalite–plagiogranite (Khar Tolgoy and Shar Tolgoy plutons, respectively; Rudnev et al, ), 514 ± 8 Ma for a tonalite, 449 ± 1 Ma–alkaline granite, and 511 ± 2 Ma (Bayan Khairkhan and Bor Khar massifs; Yarmolyuk et al, ) and 459 ± 2 Ma for a granite (Togtokhinshil complex, Soejono et al, ).…”

“…Inset B shows the zones of the Mongolian Altay. 1-Tsagaanshuvuut, 2-Khovd, 3-Ulegey, 4-Tavan Bogd, 5-Bodonch-Tseel [Color figure can be viewed at wileyonlinelibrary.com] Kovalenko et al, 1996;Kröner et al, 2010;Rudnev et al, 2012;Rudnev, Izokh, Borisenko, & Gas'kov, 2016;Rudnev, Izokh, Kovach, Shelepaev, & Terent'eva, 2009;Ruzhentsev & Burashnikov, 1996;Tomurtogoo, 2012;Yarmolyuk et al, 2011). The Lake zone consists mainly of Cambrian volcano-sedimentary rocks and ophiolites (Byamba, 2009;Dergunov, Luvsandanzan, & Pavlenko, 1980;Kovalenko et al, 1996;Ruzhentsev & Burashnikov, 1996;Tomurtogoo, 2012;Zonenshain & Kuzmin, 1978).…”

“…The granitoid complexes of the Lake zone formed over a wide time interval from the early Cambrian to the beginning of the Silurian (540--440 Ma) ( Fig. 3), and their intrusion was associated with a change from island arc and accretion to post-accretion geodynamic settings Kovalenko et al, 1996;Rudnev et al, 2009;Rudnev et al, 2012;Rudnev et al, 2016;Soejono et al, 2016;Yarmolyuk et al, 2011 (Dergunov et al, 1980;Dergunov, 1989;Byamba & Dejidmaa, 1999;Tomurtogoo, 2014).…”

Modern Dryland Source-to-Sink System Segments and Coupling Relationships from Digital Elevation Model Analysis: A Case Study from the Mongolian Altai

“…The Jargalant Nuruu S2S system is influenced by the NW-SE-trending Har-Us-Nuur strike-slip fault (Figure 3) in northwestern Mongolia. Most catchment drainage units along the NW-SE trend are covered by Vendian-lower Cambrian andesite (V-Є 1 ) in the central and northernmost parts, lower Cambrian marine carbonate rocks (Є 1 ) and middle-upper Cambrian calc-alkaline tonalite and anorthosite assemblages (Є 2-3 ) in the mid-northern part, and small areas of lower Cambrian marine carbonate rocks (Є 1 ) and lower-middle Jurassic clastic rocks (J 1-2 ) in the southern part [58,59].…”