An insight on occurrence of Fe-rich spherules from the Central Indian Ocean Basin(CIOB)provides an understanding of their distribution at a water depth of>5,000 m.In the present study,Fe-rich spherules are identifi...An insight on occurrence of Fe-rich spherules from the Central Indian Ocean Basin(CIOB)provides an understanding of their distribution at a water depth of>5,000 m.In the present study,Fe-rich spherules are identified to occur in two different sediment types(i.e.,siliceous and pelagic)and tectonic settings(i.e.near seamounts and fracture zones).These are single spheres or aggregates,of different sizes(63 to 390μm)and show textural variability(smooth/quenched,brickwork,corkscrew,interlocking and dendritic).A comparative study based on physical morphology and chemical composition suggests a common mechanism of formation.The association of spherules with fracture zones(FZ)and seamounts signifies that morpho-tectonic features play an important role in fluid-driven hydrovolcanism.Based on the evidence and geologic conditions existing in the basin,we conclude that molten fuel-coolant interaction(MFCI)coupled with submarine hydrothermal exhalations could be an ideal mechanism for the formation of spherules and Fe-particles.The accretion of the spherules on the surface sediments could be a result of recent volcanic phenomena,while those occurring at different depths(280-355,and 460-475 cm-bsf)within the sediment core indicate two different episodes.The study provides a global implication in understanding fluid-driven magmatism in a deep-sea intraplate environment.展开更多
Investigations of modern volcanic eruptions have demonstrated that ancient volcanic eruptions widely involved water,which was thus named as hydrovolcanic eruptions. Hydrovolcanisms are distinctive in many aspects, suc...Investigations of modern volcanic eruptions have demonstrated that ancient volcanic eruptions widely involved water,which was thus named as hydrovolcanic eruptions. Hydrovolcanisms are distinctive in many aspects, such as dynamics,eruptive pattern, texture and structure of rock, and vesicularity. First, normal sediments covered directly by volcanic rocks are the indicators of eruption environments. In addition, microfeatures, special structures, lithofacies or facies associations,and geochemical index of volcanic rocks can also provide significant evidences. Moreover, perlitic texture, quenching fragmentation, surface feature, cementation type, vesicularity, and pillow structure, parallel bedding, large-scale low-angle cross-bedding, antidune cross-bedding of pyroclast are keys to indicating hydrovolcanisms. Clearly,these marks are not equally reliable for identifying eruption environments, and most of them are effective and convincible in limited applications only. For explosive eruptions, the most dependable identification marks include quenching textures, vesicularity in pyroclasts and special large-scale cross-bedding. However, for effusive eruptions,useful indicators mainly include pillow structure, peperite and facies associations. Condensation rate of magma,exsolution of volatile affected by eruptive settings and magma—water interaction, and quenching in hydrovolcanisms have an influence on formation and scale of primary pores, fractures and their evolution during diagenetic stage.Therefore, this review provides systematic identification marks for ancient hydrovolcanisms, and promotes understanding of the influence of eruptive environments on hydrocarbon reservoirs of volcanic rocks in oil-gas bearing sedimentary basins.展开更多
基金The sediment samples were collected during several cruises(AAS-22,AAS-38 and SSD-48)under the auspices of the project“Surveys for Polymetallic Nodules”(GAP 2175)funded by the Ministry of Earth Sciences,New Delhi,India。
文摘An insight on occurrence of Fe-rich spherules from the Central Indian Ocean Basin(CIOB)provides an understanding of their distribution at a water depth of>5,000 m.In the present study,Fe-rich spherules are identified to occur in two different sediment types(i.e.,siliceous and pelagic)and tectonic settings(i.e.near seamounts and fracture zones).These are single spheres or aggregates,of different sizes(63 to 390μm)and show textural variability(smooth/quenched,brickwork,corkscrew,interlocking and dendritic).A comparative study based on physical morphology and chemical composition suggests a common mechanism of formation.The association of spherules with fracture zones(FZ)and seamounts signifies that morpho-tectonic features play an important role in fluid-driven hydrovolcanism.Based on the evidence and geologic conditions existing in the basin,we conclude that molten fuel-coolant interaction(MFCI)coupled with submarine hydrothermal exhalations could be an ideal mechanism for the formation of spherules and Fe-particles.The accretion of the spherules on the surface sediments could be a result of recent volcanic phenomena,while those occurring at different depths(280-355,and 460-475 cm-bsf)within the sediment core indicate two different episodes.The study provides a global implication in understanding fluid-driven magmatism in a deep-sea intraplate environment.
基金supported by the National Natural Science Foundation of China (Grants No. 41172104 and No. 41372117)the National Science and Technology Major Project (Grants No. 2017ZX05009-002 and No. 2016ZX05026-007)
文摘Investigations of modern volcanic eruptions have demonstrated that ancient volcanic eruptions widely involved water,which was thus named as hydrovolcanic eruptions. Hydrovolcanisms are distinctive in many aspects, such as dynamics,eruptive pattern, texture and structure of rock, and vesicularity. First, normal sediments covered directly by volcanic rocks are the indicators of eruption environments. In addition, microfeatures, special structures, lithofacies or facies associations,and geochemical index of volcanic rocks can also provide significant evidences. Moreover, perlitic texture, quenching fragmentation, surface feature, cementation type, vesicularity, and pillow structure, parallel bedding, large-scale low-angle cross-bedding, antidune cross-bedding of pyroclast are keys to indicating hydrovolcanisms. Clearly,these marks are not equally reliable for identifying eruption environments, and most of them are effective and convincible in limited applications only. For explosive eruptions, the most dependable identification marks include quenching textures, vesicularity in pyroclasts and special large-scale cross-bedding. However, for effusive eruptions,useful indicators mainly include pillow structure, peperite and facies associations. Condensation rate of magma,exsolution of volatile affected by eruptive settings and magma—water interaction, and quenching in hydrovolcanisms have an influence on formation and scale of primary pores, fractures and their evolution during diagenetic stage.Therefore, this review provides systematic identification marks for ancient hydrovolcanisms, and promotes understanding of the influence of eruptive environments on hydrocarbon reservoirs of volcanic rocks in oil-gas bearing sedimentary basins.
