Kalaymyo Peridotite Massif in the Indo-Myanmar Ranges(Western Myanmar): Its Mineralogy and Petrology

Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar,and represent the remnants of the Neotethyan oceanic lithosphere(Sengupta et al.,1990;Mitchell,1993).These ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone(YZSZ)in southern Tibet farther northwest(Mitchell,1993;Fareeduddin and Dilek,2015),as indicated by their coeval crystallization ages and geochemical compositions(Yang et al.,2012;Liu et al.,2016).The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges(Fig.1).composition of these ophiolites from the central Tibetan Plateau(CTP)is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs,which is inconsistent with most ophiolites worldwide(Robinson and Zhou,2008;Zhang et al.,2008).But the generation and tectonic nature of these ophiolites are still controversial.*The Kalaymyo peridotites consist mainly of harzburgites,which show typical porphyroclastic or coarse-grained equigranular textures.They are composed ofolivine(Fo=89.8–90.5),orthopyroxene(En86-91Wo1-4Fs8-10;Mg#=89.6–91.9),clinopyroxene(En46-49Wo47-50Fs3-5;Mg#=90.9–93.6)and spinel(Mg#=67.1–78.9;Cr#=13.5–31.5),and have relatively homogeneous whole-rock compositions with Mg#s of90.1–90.8 and Si O2(41.5–43.65 wt.%),Al2O3(1.66–2.66wt.%)and Ca O(1.45–2.67 wt.%)contents.TheydisplayLightRareEarthElement(LREE)-depleted chondrite-normalized REE patterns with(La/Yb)CN=0.04–0.21 and(Gd/Yb)CN=0.40–0.84,and show a slight enrichment from Pr to La with(La/Pr)CN in the range of 0.98–2.36.The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic(Pd/Ir)CN ratios(1.15–2.36).Their calculated oxygen fugacities range between QFM–0.57 and QFM+0.90.These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees(5–15%)of partial melting at a mid-ocean-ridge(MOR)environment.The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts,percolating through these already depleted,residual peridotites.The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges hence represent mid-ocean ridge(MOR)–type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction–accretion system along the eastern margin of India.

Mineralogy and Petrology of A New Lunar Meteorite M16005

1 Introduction M16005 is a lunar meteorite found recently.Optical and microprobe examinations reveal that it is a well consolidated,polymict regolith breccia.M16005 is composed of abundant mineral fragments and a few

Petromagnetic Properties of Granulite-Facies Rocks from the Northern North China Craton: Implications for Magnetic and Evolution of the Continental Lower Crust

This paper studies magnetic properties and composition of granulite-facies rocks of both the Neogene and Archean continental lower crust in the Neogene xenolith-bearing Hannuoba （汉诺坝） alkaline basalt and the exposed lower crustal section in the Archean Huai＇an （淮安） terrain （Wayaokou （瓦窑口）-Manjinggou （蔓菁沟） profile）, the northern North China Craton. It provides a unique oppor-tunity for a comparative study of magnetic properties and composition of both the Archean and Neogene continental lower crust. We measure magnetic parameters （susceptibility x and magnetic hysteresis parameters, such as saturation magnetization Js, saturation isothermal remanent magnetization Jrs, and intrinsic coercivity He） of eleven Hannuoba lower crustal xenoliths and nine terrain granulites from the Archean Huai＇an terrain. Results indicate that the average values of K,Js and Jrs of Archean granu- lites are 4 122×10^-6 SI, 523.1 A/m and 74.9 A/m, respectively, which are generally higher than those of granulite-facies xenoliths （1 657×10^-6 SI, 163.9 A/m and 41.9 A/m, respectively）. These two types of granulites contain ilmenite, （titano） magnetite, minor hematite and some ＂magnetic silicates＂ （clinopyroxene, plagioclase and biotite）. The Mg-rich ilmenite in granulite-facies xenolith is relatively higher than that in terrain granulites. We observe a more evolved character as higher magnetic as well as lower Sr/Nd, Cr/Nd, Ni/Nd, Co/Nd and V/Nd ratios in terrain granulites. These differences in magnetic characteristics reflect their different origins and evolutions. The high magnetization of granulites in the Huai＇an terrain represents magnetic properties of the Archean continental lower crust, and low magnetization of granufite-facies xenoliths represents mag- netic properties of the Cenozoic lower crusts in the northern North China Craton.