Compositional and geochronological signatures of metamafic dykes from the Sangsang peridotites, South Tibet:Evidence for magma-starved forearc rifting during Neo-Tethyan subduction re-initiation

摘要: Abstract In this study we present new mineral chemistry, whole-rock geochemical and zircon U–Pb geochronological data for 12 metamafic dykes in the mantle sequence of Sangsang ophiolite South Tibet (China). Modal analyses these gave averages ~40%–65% plagioclase ~35%–60% amphibole small amounts (igneous) clinopyroxene, epidote opaque minerals. This assemblage resembles that typical orthoamphibolites. Nevertheless, due to absence foliation investigated rocks are described as lithologies. These have primitive (PM)-normalized multi-element patterns with negative Nb Ta anomalies well weak, Ti anomalies. addition, they initial 87Sr/86Sr ratios [(87Sr/86Sr)i] 0.702844–0.703581, 143Nd/144Nd [(143Nd/144Nd)i] 0.512891–0.512959 high eNd(t) values (+7.9 +9.3). Uranium-Pb ages magmatic zircons separated from indicate parental melts their protoliths intruded at ~119.0–118.5 ​Ma. The metamorphic assemblages recognized suggestive a retrograde process, (epidote-)amphibolite facies (~470–610 ​°C, ~1.9–4.3 ​kbar) prehnite-pumpellyite (≤280 ​°C, ≤ 3 ​kbar), active within rift-produced oceanic lithosphere. Microtextural suggest were most likely massive gabbros. Compositional show magmas gabbroic generated by melting depleted (DM) source had been weakly modified fluids emanating subducted lithospheric slab. age is slightly younger than existing ophiolites central Yarlung-Zangbo Suture Zone (YZSZ) literature (~129–123 ​Ma). We, therefore, formed an incipient forearc setting during Neo-Tethyan subduction re-initiation (Aptian). Our tectonomagmatic model provides insights into igneous accretion post-solidification evolution lithosphere Tibet.