Petrology of Ortsog-Uul peridotite-gabbro massif in Western Mongolia

9th All Russian petrographic conference with international participation: Petrology of magmatic and metamorphic complexes

Shapovalova, M.^1,2 ; Tolstykh, N.^1 ; Shelepaev, R.^1,2 ; Cherdantseva, M.^1,2

V.S. Sobolev Institute of Geology and Mineralogy SB RAS, 3 Koptug avenu, Novosibirsk

630090, Russia^1

Novosibirsk State University, 1 Pirogova, Novosibirsk

630090, Russia^2

关键词: Elements distribution;    Fractionation process;    Incompatible element;    Isotopic data;    Magmatic rock;    Model calculations;    Tectonic blocks;    Ultramafic massifs;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/110/1/012020/pdf
DOI  :  10.1088/1755-1315/110/1/012020

来源: IOP

【 摘 要 】

The Ortsog-Uul mafic-ultramafic massif of Western Mongolia is located in a tectonic block with overturned bedding. The massif hosts two intrusions: a rhythmically-layered peridotite-gabbro association (Intrusion 1) and massive Bt-bearing amphibole-olivine gabbro (Intrusion 2). Intrusions 1 and 2 have different petrology features. Early Intrusion 1 (278±2.5Ma) is characterized by lower concentrations of alkalis, titanium and phosphorus than late Intrusion 2 (272±2Ma). The chondrite-normalized REE and primitive mantle-normalized rare elements patterns of Ortsog-Uul intrusions have similar curves of elements distribution. However, Intrusion 2 is characterized higher contents of REE and rare elements. High concentrations of incompatible elements are indicative of strong fractionation process. It has been suggested that Intrusions 1 and 2 derived from compositionally different parental melts. Model calculations (COMAGMAT-3.57) show that parental melts of two intrusions were close to high-Mg picrobasaltic magmas. The concentration of MgO in melt is 16.21 (Intrusion 1) and 16.17 (Intrusion 2). Isotopic data of Ortsog-Uul magmatic rocks exhibit different values of Nd (positive and negative) for Intrusion 1 and 2, respectively.