TY - JOUR

T1 - Geochemistry, Sm-Nd, Rb-Sr, and lu-Hf isotopes, sources, and conditions of formation of early Paleozoic plagiogranitoids in the south of the lake zone in Western Mongolia

AU - Rudnev, S. N.

AU - Mal'kovets, V. G.

AU - Belousova, E. A.

AU - Tret'yakova, I. G.

AU - Serov, P. A.

AU - Kiseleva, V. Yu

AU - Gibsher, A. A.

AU - Nikolaeva, I. V.

PY - 2020/2/1

Y1 - 2020/2/1

N2 - We present results of geochemical and isotope (Rb-Sr, Sm-Nd, and Lu-Hf) studies of the early Paleozoic plagiogranitoid associations in the south of the Lake Zone in Western Mongolia, which formed at the island-arc and accretion-collision stages of the regional evolution. According to the petrogeochemical composition, the early Paleozoic plagiogranitoid associations of the island-arc (Tugrug, Hatan-Hunga, Udzur-Hunga, and Bayasgalant plutons, 531-517 Ma) and accretion-collision (Tugrug, Mandalt, and Dut Uul plutons, 504-481 Ma) stages are high- and low-alumina rocks. The recognized types of plagiogranitoids, with regard to their trace-element composition, indicate that their parental melts were generated from MORB-type metabasites at ≥10-12 kbar, in equilibrium with garnet-containing restite, and at ≤8 kbar, in equilibrium with plagioclase-containing restite. The Sr-Nd isotope data on the rocks and the Lu-Hf isotope parameters of their magmatic zircons show two groups of plagiogranitoids, with different sources of melts. The first group includes plagiogranitoid associations of most plutons (Tugrug, Udzur-Hunga, Hatan-Hunga, Bayasgalant, and Dut Uul) with isotope parameters (εNd = 8.5-4.6, (87Sr/86Sr)0 = 0.7034-0.7036, and εHf = 14.7-11.9) indicating the juvenile nature of their sources. The second group includes plagiogranitoids of the Mandalt pluton; their isotope parameters (εNd = 1.4-0.2, (87Sr/86Sr)0 = 0.7053, and εHf = 7.2-5.4) indicate that the parental melts were generated mostly from enriched-mantle metabasites. The Hf isotope data on inherited and xenogenic zircons (664-519 Ma) from the early Paleozoic plagiogranitoid associations of the southern Lake Zone permit us to separate these rocks into three groups according to their εHf values (14.5-12.8, 2.9, and 10.6-6.7). The Hf isotope parameters of magmatic and inherited zircons, with regard to their age, indicate that the source of the parental melts lacked rocks with a long crustal history, such as the early Precambrian associations of the Dzavhan microcontinent.

AB - We present results of geochemical and isotope (Rb-Sr, Sm-Nd, and Lu-Hf) studies of the early Paleozoic plagiogranitoid associations in the south of the Lake Zone in Western Mongolia, which formed at the island-arc and accretion-collision stages of the regional evolution. According to the petrogeochemical composition, the early Paleozoic plagiogranitoid associations of the island-arc (Tugrug, Hatan-Hunga, Udzur-Hunga, and Bayasgalant plutons, 531-517 Ma) and accretion-collision (Tugrug, Mandalt, and Dut Uul plutons, 504-481 Ma) stages are high- and low-alumina rocks. The recognized types of plagiogranitoids, with regard to their trace-element composition, indicate that their parental melts were generated from MORB-type metabasites at ≥10-12 kbar, in equilibrium with garnet-containing restite, and at ≤8 kbar, in equilibrium with plagioclase-containing restite. The Sr-Nd isotope data on the rocks and the Lu-Hf isotope parameters of their magmatic zircons show two groups of plagiogranitoids, with different sources of melts. The first group includes plagiogranitoid associations of most plutons (Tugrug, Udzur-Hunga, Hatan-Hunga, Bayasgalant, and Dut Uul) with isotope parameters (εNd = 8.5-4.6, (87Sr/86Sr)0 = 0.7034-0.7036, and εHf = 14.7-11.9) indicating the juvenile nature of their sources. The second group includes plagiogranitoids of the Mandalt pluton; their isotope parameters (εNd = 1.4-0.2, (87Sr/86Sr)0 = 0.7053, and εHf = 7.2-5.4) indicate that the parental melts were generated mostly from enriched-mantle metabasites. The Hf isotope data on inherited and xenogenic zircons (664-519 Ma) from the early Paleozoic plagiogranitoid associations of the southern Lake Zone permit us to separate these rocks into three groups according to their εHf values (14.5-12.8, 2.9, and 10.6-6.7). The Hf isotope parameters of magmatic and inherited zircons, with regard to their age, indicate that the source of the parental melts lacked rocks with a long crustal history, such as the early Precambrian associations of the Dzavhan microcontinent.

KW - Central Asian Orogenic Belt

KW - Geochemistry

KW - Granitoid magmatism

KW - Lake Zone in Western Mongolia

KW - Nd-Sr-Hf isotopy

KW - geochemistry

KW - CONTINENTAL GROWTH

KW - MAGMATISM

KW - MECHANISMS

KW - GEOCHRONOLOGY

KW - CRUST

KW - EVOLUTION

KW - CALEDONIDES

KW - ADAKITE

KW - granitoid magmatism

KW - ASIAN OROGENIC BELT

KW - GRANITOIDS

UR - http://www.scopus.com/inward/record.url?scp=85089037131&partnerID=8YFLogxK

U2 - 10.15372/RGG2019087

DO - 10.15372/RGG2019087

M3 - Article

AN - SCOPUS:85089037131

VL - 61

SP - 119

EP - 138

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 2

ER -