Chemistry and metamorphic evolution of Kulet eclogite from the Kokchetav Massif, Kazakhstan

The Kulet eclogites occur as lenses in Grt-Phn quartz schist. Two types of eclogite body were identified: A, dark-green and B, pale grayish green. Type A consists of Grt + Omp + Qtz + Rt + Phn with fine-grained granoblastic texture. Type B is composed of normal and transitional coronitic eclogites. The coronitic eclogite shows three stages of recrystallization: (1) pre-eclogite (Zo + Mg-Hbl or Brs + Qtz + Ms), (2) eclogite (Grt + Omp + Qtz + Rt ± Phn) and (3) retrograde (Mg-Ktp ± Pl ± Bt + Ttn). In the coronitic eclogite, fine-grained garnet replaced coarse-grained pale magnesiohornblende, barroisite and zoisite along grain boundaries. Eclogitic garnet has higher almandine component (Alm56-63Spe1Grs19-31Prp12-18) than that of coronitic garnet (Alm42-56). Omphacite in both rocks has similar composition (Jd30-37). Grt-Cpx-Phn thermobarometer yielded a peak P-T condition of 30 kbar and 758 oC. For Phn-free samples, the temperature estimates at 30 kbar are 640-710 oC for normal eclogite, and 720-840 oC for coronitic eclogite. All eclogites have basaltic composition; most are low in FeO (< 11 wt%) - TiO2 (< 1 wt%) and high in MgO (8-10 wt%), and remainders are relatively high in FeO (~15 wt%)-TiO2 (~2.5 wt%) and low in MgO (< 8 wt%). Eclogites show flat REE pattern or slightly LREE-enriched pattern [(La)N = 9-27, (La/Lu)N = 1.1-3.4]; they are similar to those of either E-MORB or arc tholeiite. Most eclogites exhibit Ba, Sr negative anomalies and Ti positive anomaly. Based on chemical compositions of whole rock and discrimination diagrams of 2Nb-Zr/4-Y, Zr/Y-Zr and FeOtotal/MgO-TiO2, The Kulet eclogites are chemically comparable to arc tholeiite.