Mesozoic–Cenozoic Volcanic Cycle and Volcanic Reservoirs in East China

There are widespread Mesozoic–Cenozoic terrestrial volcanic activities in East China,and they produced favorable geologic factors for the volcanic reservoirs.To reveal the spatio-temporal evolution of regional volcanisms and their tectonic setting,we subdivide Mesozoic–Cenozoic volcanic activities into 6 volcanic cycles(Ⅰ–Ⅵ),and summarize the temporal-spatial distribution,rock association and tectonic setting of each cycle.The Cycle I forms a post-orogenic intraplate bimodal volcanic association.The cyclesⅡandⅢinclude arc volcanic associations formed in compressional and extensional subduction environments,respectively.The CycleⅣcontains a post-orogenic arc bimodal association.The CycleⅤis a basaltic association of tholeiite series under initial rift setting,and the CycleⅥis basaltic association of alkaline series under typical rift setting.The volcanic strata between each cycle are bounded by regional unconformity.The above 6 volcanic cycles correspond to 6 sequential stages of tectonic evolutions from the Early Jurassic post-orogeny,the Mid-Jurassic–Cretaceous subduction of the paleo-Pacific Plate to the Cenozoic marginal rifting.According to the geological characteristics of volcanic reservoirs in different volcanic cycles,it is put forward that the CycleⅤis the major formation period of volcanic reservoirs in East China and should be the focus of exploration,and that the volcanic reservoirs of the CycleⅣare also worthy of attention.

Geopulsation,Volcanism and Astronomical Periods

Volcanism is mainly controlled by the intermittent release of energy in the earth. As far as the differential rotation of the earth’s inner core is concerned, the Galactic Year may change the gravitational constant G, the solar radiative quantity and the moving speed of the solar system and affect the exchange of angular momentum between core and mantle as well as the energy exchange between crust and mantle. As a result, this leads to eruptions of superplumes and magma, and controls the energy flow from core-mantle boundary (CMB) to crust. When the earth’s speed decreases, it will release a huge amount of energy. They are the reason of the correspondence of the volcanic cycles one by one with the astronomical periods one by one. According to the astronomical periods, volcanic eruptions may possibly be predicted in the future.

Formation mechanism of in-situ volcanic reservoirs in eastern China:A case study from Xushen gasfield in Songliao Basin

A large number of in-situ volcanic reservoirs have been discovered from the Meso-Cenozoic rift basin group in eastern China.Based on drilling results in combination with geological and geophysical analysis,a case study from the Early Cretaceous Xujiaweizi fault-depression shows that the formation mechanism of in-situ volcanic reservoirs is characterized by"fault-controlled body,body-controlled facies,facies-controlled reservoir,and reservoir-controlled accumulation".In other words,deep faults control the volcanic eruption type,volcanic body,and gas reservoir distribution;the volcanic body determines the spatial distribution of volcanic facies and volcanic gas reservoir size;the volcanic facies control reservoir physical properties and effective thickness of gas formation;the volcanic reservoir properties control gas reservoir type and gas productivity.The result is useful to guiding the discovery of in-situ volcanic gas reservoirs in faulted basins in both theory and practice.