Carbon isotope anomaly in marbles associated with eclogites from the Dabie Mountains

This is a report of carbon isotope anomaly in marbles associated with the UHP eclogites from the Dabie Mountains. The results place constraints on the degree of crust-mantle interaction during the UHP metamorphism.     

Coupled isomorphic substitution and exsolution of pyroxene,rutile, apatite and quartz in supersilicic garnet

Dissolution of pyroxene in garnet at ultrahigh pressures produces supersilicie garnet with the coupled substitutions of Si^Ⅵ M^Ⅵ= A^Ⅵ A^Ⅵ and Si^Ⅵ Na^Ⅷ=A^Ⅵ M^Ⅷ,which are enhanced by rising pressure. The supersilicic garnet and exsolution of pyroxene, rutile, apatite and quartz in garnet during decompression were found in natural rocks,pointing to the importance in studying mantle-derived rocks and ultrahigh pressure metamorphism related to plate deep subduction. Ti, P, K and H2O enters garnet via the substitutions of Ti = Si, P^Ⅵ Na^Ⅷ = Si^Ⅵ CaⅧ, Si^Ⅵ K^Ⅷ = AI^Ⅵ M^Ⅷ, and [(OH)4]^4- = [SiO4]^4- or [4H]^4 = Si^4 respectively. The possible entering of Eskola pyroxene component M0.5AlSi2O6 in clinopyroxene, together with the common pyroxene component M2Si2O6, into garnet can lead to the presence of the substitution of Si^Ⅵ 0.5□^Ⅷ= A^Ⅵ 0.5M^Ⅷ in garnet structure, which plays a key role in the exsolution of rntile, apatite and quartz in garnet. Two new breakdown reactions are thus proposed on the basis of the new coupled substitution, which can be regarded as a theoretical model for the exsolntion of the 3 minerals in garnet. The real exsolution may be a combination of several breakdown reactions.     

超高压技术在菜用大豆和番茄汁保鲜贮藏中的应用研究

对经过超高压处理的菜用大豆和番茄汁进行了微生物指标分析,并优化出最适宜它们保鲜贮藏的参数组合。     

超高压处理对大肠杆菌DH5α质粒DNA的影响

文章研究了超高压处理对大肠杆菌DH5α菌株质粒pMD-18DNA的影响.大肠杆菌DH5α在不同的压力下于25 ℃处理15 min后,提取其质粒pMD-18DNA,检测质粒在260 nm和280 nm处的吸光度得到其纯度,并进行了琼脂糖凝胶电泳.实验发现:大肠杆菌DH5α质粒pMD-18DNA经100 MPa、200 MPa处理后其A260、A280与未经高压处理样相比吸光度下降;而经300 MPa、400 MPa和500 MPa处理后其吸光度与未经高压处理样相比吸光度上升.通过琼脂糖凝胶电泳分析,大肠杆菌DH5α质粒DNA经高压(300 MPa、400 MPa和500 MPa)后条带增多.实验结果表明超高压处理影响了质粒DNA的结构.     

Seismic tomography showing subduction and slab breakoff of the Yangtze block beneath the Dabie-Sulu orogenic belt

Seismic tomography reveals that a subducted ancient block has been preserved beneath the Moho of the Dabie-Sulu orogenic belt. Taking into account of geological and geochronological data, we inferred from the tomographic images that the Yangtze block was subducted northward beneath the Sino-Korean block and broken off at the depth <200 km during 200—190 Ma. The slab breakoff of the Yangtze block is the most important dynamic mechanism to control the exhumation of UHP rocks.     

First occurrence of preiswerkite in the Dabie UHP metamorphic belt

This note reports the preiswerkite that was found as the first occurrence in the UHP metamorphic belt of the Dabie Mountain. It occurs in the quartz jadeitite, and coexists with plagioclase, taramite and magnetite as retrograde symplectite. The calculated temperature of formation for preiswerkite is about 600 – 620 °C (at P=1.0 – 1.5GPa), suggesting that the preiswerkite is an indicator mineral of high-grade greenschist facies retrograded from eclogitefacies rocks.     

Coesite in the eclogite and schist of the Atantayi Valley,southwestern Tianshan,China

Coesite is an indicator mineral of ultra-high-pressure metamorphism. Since coesite was reported in the Habutengsu Valley, we have also found it in eclogite and schist from the Atantayi Valley in the southwestern Tianshan, China. Petrographic and micro-Raman analyses were carried out for the Atantayi metamorphic rocks and coesite was recognized in the predominant rock types, i.e. schist and eclogite, from three sections. The coesite-bearing schist consists mainly of garnet, Na-Ca amphibole, quartz, white mica and albite; the coesite-bearing eclogite is mainly composed of omphacite, garnet, glaucophane and zoisite. The coesite occurs as various mineral inclusions within porphyroblastic garnet. Findings of coesite in eclogite and associated schist indicate not only the regional in situ formation of the Atantayi ultra-high-pressure eclogite, but also the large areal extent of ultra-high-pressure metamorphism in southwestern Tianshan, extending up to 10 km north-south and 60-80 km east-west.     

Heterogeneity of water in UHP eclogites from Bixiling in Dabieshan： Evidence fromgarnet

Garnets in ultrahigh pressure (UHP) eclogites from Bixiling in Dabieshan were investigated by Fourier transform infrared spectrometer (FTIR). The results demonstrate that all garnets contain structural water which occurs as hydroxyl (OH), with contents ranging from 164 to 2034 ppm (H2O wt.) and mostly higher than 500 ppm. Like omphacite which is another major OH-rich mineral in eclogites, garnet is an important carrier that can recycle the surface water into deep mantles. Heterogeneity of water in garnets exists not only among different samples of the same outcrop (～150 m), but also among different crystals of the same sample (～1 cm). This indicates that the mobility of fluids during UHP metamorphism is very limited (possibly on centimeter scales), and that both subduction and exhumation processes of UHP rocks are very fast.     

Evidence for UHP metamorphism of eclogites from the Altun Mountains

Ultrahigh pressure (UHP) metamorphism refers to metamorphism that has occurred at pressures for the stability of coesite. The polycrystalline quartz inclusions showing the characteristic texture within garnets of eclogites indicates the pre-existence of coesites under the peak metamorphic condition. The unusual exsolution textures in ompacites and apatites, and the pressure estimations of phengite-bearing eciogites have been taken to provide further proof of eclogite formation under the UHP conditions.Combined with the fact that coesites have been observed in country rocks of eclogites in North Qaidam Mountains, another UHP metamorphic belt cut by the large-scale strikeslip fault in the AItun-North Qaidam area of China is confirmed.``     

Discovery of ultrahighpressure magnesite-bearing garnet lherzolite (>3.8 GPa) in the Altyn Tagh,Northwest China

Magnesite-bearing garnet lherzolite from the Altyn Tagh, associated with garnet pyroxenite, and garnet-bearing felsic gneiss, crops out as lenses in Proterozoic gneiss about 100 km east of the Jianggelasayi River. The garnet lherzolite, together with the eclogite in western Jianggelasayi, composes a high-pressure to ultrahigh- pressure metamorphic belt in the southern margin of the Altyn Tagh. Parageneses of minerals from magnesite-bearing garnet lherzolite indicate that the rock evolved a multi-stage metamorphism. The peak-stage metamorphism produces an assemblage of Grt+Ol+Opx+Cpx±Mgs, in which Al₂O₃ content of Opx is very low (0.30 — 0.66wt%). The calculated P-T condition of the peak stage is 3.8—5.1GPa and 880—970℃, some exsolution rods of clinopyroxene and rutile occur in the Grt and magnesite is rimed by dolomite and orthopyroxene, all implying that the peak stage was a UHP metamorphic process. Together with regional geological studies, isotopic dating and the discovery of coesite inclusions in zircon separates from felsic gneiss from the northern margin of the Qaidam Basin, the presence of a very long UHP metamorphic belt in northwest China is suggested.