Geochemistry and geochronology of mafic rocks from the Luobusa ophiolite, South Tibet

摘要: Abstract This study presents geochemical compositions of mafic rocks outcropped in the Luobusa ophiolite that locates at eastern part Yarlung Zangbo Suture Zone (YZSZ). The studied include gabbroic/diabase dykes cutting peridotites and foliated amphibolites embedded within subophiolitic melange. diabases have low K 2 O contents display N-MORB-like characteristics, i.e., with flat REE patterns weak enrichment LILE (e.g., Rb, Ba, Th U). gabbros show LREE-depleted variable Rb Ba. Foliated mainly consist hornblendes plagioclases, minor titanites. They commonly patterns, strong LILE. Three depleted Sr–Nd–Hf isotope compositions, initial 87 Sr/ 86 Sr ratios 0.703009–0.703502, e Nd ( t ) + 5.0 to + 8.5 Hf ca + 14. Two similar Nd–Hf isotopes diabases, but slightly higher (i.e., 0.704820 0.704550). Compared both gabbros, 0.705131–0.705825), more + 9.1 + 11.6 + 18.2 + 21.9. Geochemical diabase indicate they were formed a mid-ocean ridge setting. Zircon SIMS U–Pb dating gabbroic dyke serpentinites yields an age 128.4 ± 0.9 Ma, which is identical uncertainty zircon amphibolite 131.0 ± 1.2 Ma). Low U zircons support their metamorphic origin. Titanites been dated by LA-ICPMS give ages ~ 131–134 Ma, are gabbro amphibolite. Therefore, we suggest was generated Early Cretaceous underwent intra-oceanic emplacement immediately after its formation. implies ophiolites segment YZSZ roughly synchronously those central western segments YZSZ.