Volcanic Rock Distribution Based on Characteristics of Pathway and Magma Chamber:An Example from Lower Cretaceous Yingcheng Formation in Changling Fault Depression of Songliao Basin
The distribution pattern of volcanic rocks in a scale of fault depression requires a unified analysis,starting from the deep magma chamber,to the transport system,and then to the eruption and distribution.However,the dominating of individual factor analyses in research process generally leads to an insufficient understanding.To fully understand the spatial distribution of the Lower Cretaceous Yingcheng Formation volcanic rocks in Changling faulted depression,the controlling effects of the magma chamber and ascending pathways are analyzed based on drilling data,seismic data and deep structures.The results are as follows:Laterally,the volcanic rocks of the Yingcheng Formation exhibit characteristics of east-west zonation and north-south blockiness,concentrating in the central depression zone.Horizontal fault throw is a sensitive parameter for determining the development of volcanic rocks,while vertical fault throw has a more significant impact on volcanic rock thickness.Faults are only a necessary condition for the development of volcanic rocks,not a sufficient one.The distribution of volcanic rocks is also constrained by up-doming of the asthenosphere and thinning zones in the crust due to extension.Volcanic material filling corresponds to the basin subsidence center in general.When the volume of volcanic rocks is limited,hydrocarbon source rocks can form a good source-reservoir combination with volcanic rocks.However,when the volume of volcanic rocks is large,it significantly reduces the deposition space for fine-grained sedimentary rocks and limits the spatial extension of hydrocarbon source rocks.
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