Emplacement Phases And Potential Environmental Effect Of The Ca.1.32 Ga Large Volumes Of Diabase Sills In The Yanliao Area

Emplacement mechanism and intrusive phases of large scale diabase sills is one of the recent frontier topics of Earth community.Although many models,such as ring-dike emplacement model,cap emplacement model,etc.,have been proposed,the emplacement mechanism and intrusive phases of large scale diabase sills has not been well resolved so far.In addition,when large-scale diabase sills intrude into sedimentary basin and contact with black shale,carbonate and evaporate,they will produce a lot of CO₂ and other greenhouse and harmful gases,which will have an important impact on the Earth surface environments and biological extinctions.This paper focuses on two aspects:1)the emplacement phases the ca.1.32 Ga large igneous province(LIP)recently discovered in Yanliao area in northern North China Craton;2)the volumes of CO₂ released during its emplacement and its potential influence on paleoenvironment.Two representative diabase sill sections including Chengde and Kuancheng were selected for petrographic and geochemical analyses to study the magmatic intrusion times and emplacement mechanism of the large-scale diabase sills in Yanliao area.Both Chengde and Kuancheng diabase sills exhibit composition discontinuity,suggesting that these two sills were not formed by single magma injection.The petrographic and geochemical results show that the diabase sill in Chengde was formed by two pulses of magma injection;while the diabase sill in Kuancheng was formed by two or more pulses of magma injection.It can be inferred that there were at least two magma injections during the formation of the ca.1.32 Ga large-scale diabase sills in Yanliao area.On the other hand,the contacts between black shales of the Xiamaling Formation and the ca.1.32 Ga diabase sills were investigated.Two key sections were selected for total organic carbon content(TOC)analysis with an aim to estimate the volumes of CO₂ released during emplacement of the ca.1.32 Ga diabase sills into the black shales of the Xiamaling Formation.The potential effects of emplacement of large-scale diabase sills in Yanliao area on paleoenvironment are also discussed.The preliminary estimation results show that the amount of CO₂ released from the large scale diabase sill emplaced into the black shale of Xiamaling formation in Yanliao area is about 2.76×10¹¹ ton to 1.56×10¹² ton.If the ca.1.32 Ga Derim Derim large scale diabase sills emplaced into the black shales within the Velkerri formation in Mac Arthur basin in North Australia craton were considered,the CO₂ and other gases released during emplacement of the ca.1.32 Ga diabase sills in Yanliao and northern Australian cratons may have a significant impact on the global atmosphere and marine environments.The results show that the element and isotopic anomalies and the difference of biomass indexes may exist in the ca.1.32 Ga sedimentary strata of other cratons(such as Siberia,Baltic,etc.).