Soft Giant Dipole Modes in Ca Isotopes in the Relativistic RPA

The isovector giant dipole resonance in Ca isotopes is investigated in the framework of the fully consistent relativistic random phase approximation. The calculations are performed in an effective Lagrangian with a parameter set , which was proposed for satisfactorily describing nuclear ground state properties. It is found that a soft isovector dipole mode for Ca isotopes near drip lines exists at energy around . The soft dipole states are mainly due to the excitation of the weakly bound and pure neutron (proton) states near Fermi surface as well as the correlation of isoscalar and isovector operators. For nuclei with the extreme value of , the contributions of isoscalar mesons in the isovector mode play a non-negligible role.

The potential of Ca isotopes to trace subducted marine carbonates in deep mantle

Marine carbonates,the major carrier of carbon upon the upper crust,can be subducted into the Earth’s interior along with oceanic crust,and then returned to the surface through magmatism,which constitute the deep carbon cycle.This process plays an important role in modulating the CO_(2) concentrations in the atmosphere over geologic time,and thus the forming of the habitable earth.Therefore,identifying recycled marine carbonates in the mantle is critical to well understand the global deep carbon cycle.Calcium is one of the major constituent cations in marine carbonates and its isotopes may be a potential tracer for recycled marine carbonates in the mantle.To further evaluate the capability and challenges of Ca isotopes as such a geochemical tracer,we reviewed the Ca isotopic compositions in important reservoirs and the behavior of Ca isotopes during high-temperature geological processes that are related to the deep carbon cycle,including plate subduction,mantle metasomatism,mantle partial melting,magma differentiation,etc.Available studies show that carbonate-rich marine sediments have significantly lowerδ^(44/40) Ca than the Earth mantle,and metasomatism by such recycled materials can cause lighter Ca isotopic compositions in deep mantle-derived rocks than those of the depleted mantle and mid ocean ridge basalts.However,the Ca isotopic fractionation during partial melting of mantle peridotites is small(~0.10‰)and the Ca isotopic fractionation during plate subduction and intermediate-mafic magma evolution is indistinguishable.These investigations suggest that Ca isotopes have great advances in tracing such recycled materials in the mantle.However,other processes(such as the influence by partial melts of eclogites)may induce similar effects on mantle-derived rocks as subducted marine carbonates but still remains debated,and thus further investigations are strongly needed in the future.

Tensor force effect on proton shell structure in neutron-rich Ca isotopes

In the framework of the Skyrme-Hartree-Fock approach with 36 sets of the TI J parameterizations,the tensor force effect on the evolution of the single-proton states in the calcium isotopes is systematically investigated.It is shown that the single-proton states with higher angular momenta are influenced significantly by the tensor force and the trend in the evolution of somesingle-particle energy differences with the mass number of the isotopes depends sensitively on a parameter βT associated with the intensity of the tensor force.To understand this phenomenon,we analyze the spin-orbit potentials and the radial wave functions of relevant single-proton orbits in detail.In addition,it is found that some TI J interactions could cause the 2s1/21d3/2 energy level inversion in 48Ca.

Calcium isotopic signatures of depleted mid-ocean ridge basalts from the northeastern Pacific

A number of high-temperature processes(e.g.,melt-rock reactions,metasomatism,partial melting)can produce signifi cant Ca isotopic fractionation and heterogeneity in the mantle,but the mechanism for such fractionation remains obscure.To investigate the eff ect of mantle partial melting on Ca isotopic fractionation,we reported high-precision Ca isotopic compositions of depleted mid-ocean ridge basalts(MORBs)from the East Pacifi c Rise and Ecuador Rift in the northeastern Pacifi c.Theδ44/40 Ca of these MORB samples exhibit a narrow variation from 0.84‰to 0.88‰with an average of 0.85‰±0.03‰,which are similar to those of reported MORBs(0.83‰±0.11‰)and back-arc basin basalts(BABBs,0.80‰±0.08‰)in literature,but are lower than the estimate value for the bulk silicate Earth(BSE,0.94‰±0.05‰).The lowδ44/40 Ca signatures of MORB samples in this study cannot be caused by fractional crystallization,since intermediate-mafi c diff erentiation has been demonstrated having only limited eff ects on Ca isotopic fractionation.Instead,the off set ofδ44/40 Ca between MORBs and the BSE is most likely produced by mantle partial melting.During this process,the light Ca isotopes are preferentially transferred to the melt,while the heavy ones tend to stay in the residue,which is consistent with the fact thatδ44/40 Ca of melt-depleted peridotites increases with partial melting in literature.The behavior of Ca isotopes during mantle partial melting is closely related to the inter-mineral(Cpx and Opx)Ca isotopic fractionation and melting mineral modes.Mantle partial melting is one of the common processes that can induce lowerδ44/40 Ca values in basalts and Ca isotopic heterogeneity in Earth’s mantle.

Deep carbon recycling and isotope tracing:Review and prospect

Deep carbon recycling is an essential part of the global carbon cycle.The carbonates at the bottom of the ocean are brought to the mantle by subduction.Subsequently, deep carbon is released to the atmosphere in the form of CO2 through volcanism.At present, research on deep carbon recycling is still at its early stage.The proportion of subduction-related carbon and primary mantle-derived carbon in CO2 released by volcano is an important issue.Carbon isotopes can easily distinguish organic carbon from inorganic carbon.However, ～95% of subduction-related and primary mantle-derived carbon released by volcano is inorganic, which carbon isotopes find difficult to distinguish.Recently, Ca and Mg isotope geochemistry has provided important tools for tracing crust-derived material recycling.Here we focus on this topic by introducing the principles of C, Ca, and Mg isotopes in tracing deep carbon recycling and previous research results.We also summarize the research progress on the total storage and phases of deep carbon, CO2 fluxes which depend on the release via volcanism, the partial melting of the carbon-bearing mantle, and carbon behaviour during oceanic subduction.