In situ study of calcite-Ⅲ dimorphism using dynamic diamond anvil cell

The phase transitions among the high-pressure polymorphic forms of CaCO_(3)(cc-Ⅰ,cc-Ⅱ,cc-Ⅲ,and cc-Ⅲb)are investigated by dynamic diamond anvil cell(dDAC)and in situ Raman spectroscopy.Experiments are carried out at room temperature and high pressures up to 12.8 GPa with the pressurizing rate varying from 0.006 GPa/s to 0.056 GPa/s.In situ observation shows that with the increase of pressure,calcite transforms from cc-Ⅰto cc-Ⅱat~1.5 GPa and from cc-Ⅱto cc-Ⅲat~2.5 GPa,and transitions are independent of the pressurizing rate.Further,as the pressure continues to increase,the cc-Ⅲb begins to appear and coexists with cc-Ⅲwithin a pressure range that is inversely proportional to the pressurizing rate.At the pressurizing rates of 0.006,0.012,0.021,and 0.056 GPa/s,the coexistence pressure ranges of cc-Ⅲand cc-Ⅲb are 2.8 GPa-9.8 GPa,3.1 GPa-6.9 GPa,2.7 GPa-6.0 GPa,and 2.8 GPa-4.5 GPa,respectively.The dependence of the coexistence on the pressurizing rate may result from the influence of pressurizing rate on the activation process of transition by reducing the energy barrier.The higher the pressurizing rate,the lower the energy barrier is,and the easier it is to pull the system out of the coexistence state.The results of this in situ study provide new insights into the understanding of the phase transition of calcite.

Contribution of trimethylamine N-oxide on the growth and pressure tolerance of deep-sea bacteria

Trimethylamine N-oxide(TMAO) is widely dispersed in marine environments and plays an important role in the biogeochemical cycle of nitrogen. Diverse marine bacteria utilize TMAO as carbon and nitrogen sources or as electron acceptor in anaerobic respiration. Alteration of respiratory component according to the pressure is a common trait of deep-sea bacteria. Deep-sea bacteria from dif ferent genera harbor high hydrostatic pressure(HHP) inducible TMAO reductases that are assumed to be constitutively expressed in the deep-sea piezosphere and facilitating quick reaction to TMAO released from ?sh which is a potential nutrient for bacterial growth. However, whether deep-sea bacteria universally employ this strategy remains unknown. In this study, 237 bacterial strains affliated to 23 genera of Proteobacteria,Bacteroidetes, Firmicutes and Actinobacteria were isolated from seawater, sediment or amphipods collected at dif ferent depths. The pressure tolerance and the utilization of TMAO were examined in 74 strains. The results demonstrated no apparent correlation between the depth where the bacteria inhabit and their pressure tolerance, regarding to our samples. Several deep-sea strains from the genera of Alteromonas, Halomonas,Marinobacter, Photobacterium, and Vibrio showed capacity of TMAO utilization, but none of the isolated Acinebacter, Bacillus, Brevundimonas, Muricauda, Novosphingobium, Rheinheimera, Sphingobium and Stenotrophomonas did, indicating the utilization of TMAO is a species-speci?c feature. Furthermore, we noticed that the ability of TMAO utilization varied among strains of the same species. TMAO has greater impact on the growth of deep-sea isolates of Vibrio neocaledonicus than shallow-water isolates. Taken together, the results describe for the ?rst time the TMAO utilization in deep-sea bacterial strains, and expand our understanding of the physiological characteristic of marine bacteria.

Petrogenesis of volcanic rocks from Eastern Manus Basin: indications in mineralogy and geochemistry

To understand the petrogenesis and magma evolution history in the Eastern Manus Basin(EMB),geochemistry of pyroxene and plagioclase mineral phenocrysts in basaltic andesites and dacites were reported.The plagioclase-melt thermometry showed that,plagioclase in dacites crystalized in 1027.2–1028.5°C under 3.37–5.08 kbar,whereas in basaltic andesite was 1181.4–1187.0°C under 1.79–4.46 kbar.Pyroxene compositions and invariable La/Sm vs La values of whole rock powders indicate that lavas were erupted in rapid cooling rate and mainly controlled by fractional crystallization(FC).In addition,oscillatory zonings in plagioclase and pyroxene phenocrysts indicated small local perturbations and degassing episodes in the magma chamber.Some high Mg#clinopyroxene antecrysts were found in EMB lavas.The highest Mg#of parental EMB melts is 69,which falls into the range of initial partial melts from upper mantle peridotite source(68–75).In terms of isotopic compositions,the EMB lavas most likely originated from Indian-type MORB mantle which was infl uenced by subduction components.In details,the subduction components are mainly derived from the dehydration of a subducted altered oceanic crust,and the contribution of sediment infl uence is minor.The Pb isotopic compositions and end member modeling further suggest that the source of subduction components is more likely from the Pacifi c Plate instead of the Solomon Plate.

Synthesis of Polycrystalline Diamond Compact with Selenium:Discovery of a New Se–C Compound

Sintering of polycrystalline diamond with selenium was investigated under pressure of 6.5-10.5 GPa at a constant temperature of 1850℃.A new carbon-selenium compound with a most plausible chemical formula of SeC and a WC-type hexagonal structure(space group P6m2)has been discovered in the recovered samples sintered at 10.5 GPa and 1850℃.Refined lattice parameters are as follows:a=2.9277(4)A,c=2.8620(4)A,V=21.245(4)A^3.The diamond compacts hot-pressed at 10.5 GPa have excellent mechanical properties with a Vickers hardness of about 68 GPa at a loading force of 19.6 N.Diamond intergrowths observed in these samples may have benefited from the catalytic effects of Se/SeC on the nucleation and crystal growth of diamond.