Jingbo Liu

Mineral Inclusions in Zircon from Gneisses in the Ultrahigh‐Pressure Zone of the Dabie Mountains, China

Mineral inclusions in zircon from gneisses in the ultrahigh‐pressure (UHP) zone of the Dabie Mountains, China, are studied by using laser Raman spectrophotometry. We identified numerous mineral inclusions including coesite, quartz, clinopyroxene, phengite, barite, anhydrite, and feldspar. Coesite is found to occur as zircon‐hosted inclusions in all types of gneisses, indicating that these gneisses had shared the ultrahigh‐pressure metamorphic history with the UHP eclogite blocks that reside in them. The occurrence of barite and anhydrite probably implies the existence of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Ultrahigh-pressure (UHP) low-Al titanites from carbonate-bearing rocks in Dabieshan-Sulu UHP terrane, eastern China

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Chlorine-rich amphibole in Yangkou eclogite, Sulu ultrahigh-pressure metamorphic terrane, China

\end{document} ‐bearing fluids during the UHP metamorphic stage. We also found no simple ways to correlate growth zones of zircon as shown by cathodoluminescence images with metamorphic conditions determined from inclusion in any specific zircon grains. Of particular interest is the discovery of coesite included in zircons from gneiss of the “cold” eclogite zone that was previously considered to have not experienced UHP conditions.

Coesite inclusions in zircon from gneisses identified by laser Raman microspectrometer in ultrahigh pressure zone of Dabie Mountains, China

Abstract A transitional eclogite- to high-pressure granulite-facies paragenesis (Omp+Pl+Qtz±Grt) after peak coesite–eclogite facies metamorphism and predating the later amphibolite-facies overprint is identified in coesite–eclogite from the Taohang area of the Sulu ultrahigh-pressure (UHP) terrane in eastern China. These minerals were equilibrated at 17 kbar and 820°C. This reveals that fluid infiltration might activate retrograde recrystallisation even at a deep level during the exhumation process of the UHP rocks. The tectono-metamorphic significance of the unusually high pressure overprint is also discussed.

Hydration and dehydration in the lower margin of a cold mantle wedge: implications for crust-mantle interactions and petrogeneses of arc magmas

Abstract Titanites previously reported from high-pressure rocks commonly contain high Al and F contents. This finding has led previous workers to conclude that high Al and F in titanite can expand its stability field to high-pressure and ultrahigh-pressure (UHP) conditions. In this study, a coesite inclusion was identified in titanite of aragonite- and jadeite-bearing gneiss from the Dabieshan UHP metamorphic terrane of eastern China. We also found UHP titanite in carbonate-bearing garnet clinopyroxenite from the Sulu UHP terrane. Interestingly, both types of the UHP titanite mentioned above contain low Al and F contents. Therefore, our data indicate that the high-Al and F contents are not necessary criteria for stabilizing titanite to UHP conditions. It is inferred that the UHP titanite formed via the reaction TiO2 + CaCO3 + SiO2 = CaTiSiO5 + CO2, and that the presence of the UHP assemblage aragonite + rutile + clinopyroxene + coesite in the host rock and a very low XCO₂ value in the coexisting fluid are crucial conditions for the formation of these UHP titanites

Multistage metamorphism of garnet orthopyroxenites from the Maowu mafic–ultramafic complex, Dabieshan UHP terrane, eastern China

The Yangkou gabbro-to-granite complex is a petrotectonic unit of the Su-Lu ultrahigh-pressure (UHP) metamorphic terrane in eastern China. It consists of lherzolites, metagabbro–eclogites, metagranodiorites and deformed granites. Whether or not the felsic members of the complex have undergone UHP metamorphism as is recorded in the metagabbro–eclogites is significant to understanding the relationship between eclogite and host rock. The metagabbro–eclogites have low εNd (220 Ma) values (−17 to −12) at the time of UHP metamorphism, indicating that their protoliths are old mafic intrusive rocks emplaced in a continental domain. Geochemical and isotopic studies for the Yangkou unit suggest that the protoliths of the unit (except eclogites) represent a cogenetic magmatic suite, produced by differentiation of a mafic parental magma. The parental magma was derived from melting of a long-term enriched mantle, and was emplaced into a crustal level during continental extension at c. 700–800 Ma. The cogenetic relationship for the protoliths of the unit suggests that the metagranodiorites and deformed granites were also subducted to extreme mantle depths along with the metagabbro–eclogites at c. 220 Ma. The lherzolites, however, are genetically not related to the mafic protoliths; they represent ‘mantle xenoliths’ of tectonic origin.

Could tectonic overpressure cause ultrahigh-pressure metamorphism?

Cl-rich amphiboles occur as corona surrounding garnet and omphacite grains, in symplectite after omphacite and in quartz-phengite vein in eclogites at Yangkou, in the Sulu ultrahigh-pressure (UH P ) metamorphic terrane. The veins formed during the high-pressure eclogite-facies stage, the symplectite developed during the transitional eclogite- to amphibolite-facies stage, and the coronas were produced during the two stages. Pargasite and hastingsite are predominant in all occurrences and characterised by high Cl and K 2 O contents, ranging from 0.05 to 3.00 wt% and 1.00 to 4.00 wt%, respectively. The significant Cl contents in amphiboles suggest that fluids of high chlorinity attended the vein, corona and symplectite formation. All types of amphiboles show large variations of chlorine contents and are zoned with decreasing Cl contents from core to rim. Combining with the compositional data of apatite coexisting with amphibole, it can be determined that the fluids were evolved along a decreasing chlorine content from early to late stages, which is considered to be related to the water release by phengite-consuming reactions and the breakdown of nominally anhydrous minerals in country gneisses during the exhumation process of UH P terrane.

Metamorphic P-T trajectory and multi-stage fluid events of vein-bearing UHP eclogites from the Dabie terrane: insights from compositional zonations of key minerals

The mineral inclusions in zircon from gneisses in ultra-high pressure (UHP) zone of the Dabie Mountains were identified by using a laser Raman microspectrometer. Coesite occurs as inclusions in zircons from all types of gneiss. Other important minerals, such as jadeite, omphacite, aragonite, barite, and anhydrite were also found as inclusion minerals. These discoveries indicate that (i) gneissic country rocks had metamorphosed at the same time as the enclosed eclogites; and (ii) SO4−2-bearing fluids were present in the UHP metamorphic process, which is manifested by occurrence of barite and anhydrite coexisting with coesite.