Abstract: The metamorphosed basic body in the middle reaches of Lalingzaohuo intruded into the gneiss of Baishahe formation of the Paleoproterozoic Jinshuikou group. The petrography, chronology and geochemistry of basic metamorphic rocks are investigated in this study. The protolith, nature of source region, tectonic environment, ages and geological significance of these rocks are discussed. The results show that the basic metamorphic rocks are plagioclase amphibolite, metamorphosed diabases and amphibolite. The protolith belongs to subalkalic series, including tholeiite series, calc-alkaline series and shoshonitic series rocks. The contents of silica and alkali are 44.04%-54.39%, 1.97%-6.53%, and Na₂O are more than K₂O. The contents of MgO, Fe₂O₃,

and TiO₂ are 5.01%-9.58%, 7.71%-13.46%, and 0.56%-1.49%, respectively. The average values of ΣREE is 83.60×10-6 and δEu values range from 0.89 to 1.55 with an average value of 1.14, showing slightly positive Eu anomaly. The chondrite-normalized REE distribution patterns show a relatively smooth slightly right inclined curve, which has the features of slightly enriched LREE and
slightly differentiated HREE. The rocks are clearly enriched in LILEs (e. g., Cs, Rb, Ba, K, Sr, U, Pb) and significantly depleted in HFSE (e. g., Nb, Ta, Zr), slightly depleted in P and Ti. Combining SIMS zircon U-Pb dating with rock geochemical and regional geological background, it is believed that the magmatic-metamorphic events in early Neoproterozoic (928±25 Ma), the end of early Cambrian (514±11 Ma), middle-late Ordovician (451±11 Ma), and early-middle Devonian (392±12 Ma) have been recorded in the amphibolite. The zircon ages of 928±25 Ma and 514±11 Ma represent the ages of captured zircons, the crystallization age of the protolith is 451±11 Ma, the metamorphism of the amphibolites occurred at 392±12 Ma. The protolith of basic metamorphic rocks in the middle reaches of Lalingzaohuo was product result of partial melting in lithosphere mantle ever dehydrating by subduction slab and should be formed in an island-arc environment.

Key words: basic metamorphic rock, zircon U-Pb ages, geological and geochemical characteristics, East Kunlun mountains, Qimantage