Petrogenesis and tectonic implication of the Late Mesozoic volcanic rocks in East Mongolia

Abstract

This paper presents new geochemical and geochronological data of the Late Mesozoic volcanic rocks in East Mongolia. These volcanic rocks belong to high‐K calc‐alkaline and shoshonitic series and exhibit features of bimodal rocks. The mafic rocks have elevated incompatible trace element concentrations and significantly negative Nb, Ta, and Ti anomalies, with 87Sr/86Sr(i) and ƐNd(t) values of 0.70502–0.70572 and −1.72459 to +1.720736, respectively, which suggest that the mafic magma was derived from a lithospheric mantle source that might have been metasomatized by subduction‐derived fluids, experienced fractional crystallization, and was contaminated by crustal materials. The felsic rocks have similar rare earth element patterns to the mafic rocks but show much more significantly negative Eu and Sr anomalies. The felsic rocks have higher 87Sr/86Sr(i) values of 0.706496–0.71104 than the mafic rocks but similar ƐNd(t) values (−0.28003 to +2.928506) to the mafic ones. These data indicate that the felsic rocks originated from partial melting of a crustal source that is dominated by juvenile mafic rocks. Our new K‐Ar dating, together with previous data, shows that the Late Mesozoic volcanism in East Mongolia took place during the Late Jurassic‐Early Cretaceous between ca. 155 and 99 Ma. The model of back‐arc extension, possibly induced by slab rollback of the westward subducted Pacific Plate and the subduction zone retreat, can explain the geodynamic setting and the eastward younging trend of the Late Mesozoic volcanism in East Mongolia and in adjacent NE China.

Detrital Zircon Provenance Analysis in the Central Asian Orogenic Belt of Central and Southeastern Mongolia—A Palaeotectonic Model for the Mongolian Collage

“…The εHf (t) results from the discordantly overlying, post-collisional continental red beds document that moderate juvenile and juvenile volcano-plutonic sources continued activity during Mesozoic until Early Cretaceous [70,71]. The~160-120 Ma detrital zircon age data we obtained match the regionally occurring surficial volcanic activity, which was sourced in a metasomatized depleted lithospheric mantle with minor crustal contamination [70,71].…”

Geochemical comparison of late Mesozoic and early Cenozoic volcanic rocks in South Mongolia

“…Mesozoic volcanic rocks in East Mongolia erupted during late Jurassic-Early Cretaceous (ages ranging from ca. 155 to 99 Ma), essentially coeval with those of the adjacent Great Xing'an Range of NE China continent (e.g., Pei et al, 2008;Dash et al, 2013;Bars et al, 2018), whereas other basalts were formed in South Mongolia during 114 to 90 Ma. In contrast to the Mesozoic basalts of East Mongolian, the late Cretaceous volcanism in south Mongolia relatively are scattered over large area, where the early Cenozoic volcanic complex of 60-50 Ma were also distributed (Enkhtuvshin et al, 1995;Barry et al, 2003;Yarmolyuk et al, 2015).…”

“…Mongolia, demonstrated that bimodal series arc type volcanic rocks migrates from west to east with time. Their origin was linked to the backarc extension induced by slab rollback of the westward-subducted Pacific Plate (Dash et al, 2013;Bars et al, 2018). In contrast, South Mongolian volcanic rocks are isolated in space and have relatively smaller outcrop which is erupted both late Cretaceous and Early Cenozoic.…”

“…As a matter of fact, the Late Mesozoic volcanic rocks in South and East Mongolia, and NE China are discontinuously distributed, and individual volcanic belts generally extend in a NNE direction, parallel to the Mesozoic volcanic sedimentary basins (e.g., the Hailar and the Song Liao basins), both of which are conformable to the Pacific subduction zone (e.g., Li, 2000;Wu et al, 2005) which all implies that the volcanism is likely related to the Pacific subduction. Therefore, we prefer the model of the back-arc extension induced by the westward Pacific-subduction, as suggested by Bars et al (2018) to interpret the geodynamic settings Late Cretaceous volcanic rocks in South Mongolia. Model emphasizes that the slab rollback of the subduction retreat of the Pacific Plate might have caused the upwelling of the asthenosphere, which in turn caused the extension and melting of the overriding lithospheric mantle, to generate the Late Mesozoic volcanic rocks.…”

Late stages in the evolution of the late Mesozoic East Mongolian volcanic areal: rock age and composition

“…В полном объёме такая история прослеживается для Гоби-Алтайской и Западно-Забайкальской областей [2,4,5]. В отличие от них, развитие Восточно-Монгольской области не прослеживалось за границы раннего мела [6,7], что ставило под сомнение применимость к ней представлений о её принадлежности к вулканической провинции. В сообщении приводятся геохимические и геохронологические данные, которые свидетельствуют, во-первых, о продолжении магматической активности в пределах Восточно-Монгольской области в позднем мелу и кайнозое и, во-вторых, о соответствии тенденций в изменении состава её магматических продуктов тем же закономерностям, которые были установлены для других вулканических областей.…”