Abstract
The Wudalianchi monogenetic volcanic field (WMVF) is located in the Songliao basin within a major continental rift system in NE China. Bubbling springs and diffuse degassing from soils are typical features of the WMVF. Chemical compositions and C-He isotope analyses revealed that the cold spring gases might originate from the enriched upper mantle (EM), which resulted from the mixing between slab materials (subducted organic sediments and carbonates) in the mantle transition zone (MTZ) and the ambient depleted mantle. These EM-derived volatiles experienced variable degrees of crustal input, including both continental organic metasediments and crustal carbonates during their ascending path to the surface. The estimated results of the degassing CO2 fluxes, combined with previous geophysical evidence, suggest that the CO2 degassing activities become weaker from early to late in Quaternary.
Highlights
Continental rift systems, together with the related intraplate volcanism, have been regarded as a possible trigger of deepderived CO2 degassing into the atmosphere and long-term climate change [1,2,3,4,5,6]
Cenozoic volcanic activity has formed 800 km2 of lava flows, which includes the middle Pleistocene to Holocene volcanic activity in Wudalianchi monogenetic volcanic field (WMVF) (Figure 1(b)) [23, 24]. These fissure-central-type eruptions are controlled by NE- to NNW-striking fractures or deep faults [23, 29], which are linked to the continental rift systems in East Asia [30, 31]
Considering the dispersed cold springs, and the decoupling of soil temperatures and CO2 fluxes in WMVF, we suggest that the resulting weak degassing is due to the solidification and/or cooling down of the underlying magma body beneath the Laoheishan in about 300 years
Summary
Continental rift systems, together with the related intraplate volcanism, have been regarded as a possible trigger of deepderived CO2 degassing into the atmosphere and long-term climate change [1,2,3,4,5,6]. The Songliao basin in NE China has experienced long-term extension-induced continental rifting since the Late Mesozoic as indicated by many intraplate volcanoes (Figure 1(a)) [10]. Based on both petrogenesis and geophysical evidences, these Cenozoic volcanic activities have been considered to be linked to the stagnant Pacific slab materials in the mantle transition zone (MTZ) [11,12,13,14,15]. New data on the chemical and C-He isotopic composition of gases associated with four cold springs located in the area are presented and used to gain insights into the mechanisms responsible for CO2 formation at depth
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