“Hot” subduction initiation and the origin of the Yarlung-Tsangbo ophiolites, southern Tibet: New insights from ultrahigh temperature metamorphic soles

Formation of the Xigaze Metamorphic Sole under the Tibetan continental margin reveals generic characteristics of the subduction initiation process

“…As prograde garnet growth in supracrustal mafic protoliths requires an increase in both P and T, we interpret those growth ages as a minimum age for formation of the Xigaze metamorphic sole at an incipient plate contact, as is the case in other soles (Guilmette et al, 2018;Mulcahy et al, 2018;Pourteau et al, 2019). Other studies have reported zircon ages 133-119 Ma for the same locality (Duan et al, 2022) and an adjacent one . These authors interpreted the zircon grains as igneous, implying that the 133-119 Ma dates would be protolith ages.…”

“…The maximum metamorphic conditions recorded in the grt-cpx amphibolite of the XO sole are ~14 kbar and over 850 °C (Duan et al, 2022;Guilmette et al, 2008;Zhang et al, 2019), consistent with other soles worldwide (Agard et al, 2016). They returned 133-119 Ma U-Pb zircon dates that are interpreted either as post-peak metamorphism or igneous protolith ages (Duan et al, 2022;Zhang et al, 2019), and 40 Ar/ 39 Ar hornblende cooling ages of 130-119 Ma (Guilmette et al, 2012;Guilmette et al, 2009), all overlapping with the age of overlying ophiolitic crust (Chan et al, 2015;Wang et al, 2016). Such a dismembered sole sharing the same geochronological and petrological characteristics has also been described under the Saga ophiolite, farther west along the central segment of the YZSZ (Guilmette et al, 2012).…”

Apatite MAP-3: a new homogeneous and low common lead natural reference for laser in situ U–Pb dating and Nd isotope analysis

“…Each analysis comprises 20 s background measurement with the laser switched off, 40 s ablation, and 20 s washout. The following masses were detected, including 42 Ca, 88 Sr, 89 42 Ca concentrations of MAP-3 from EPMA results were used as internal reference values.…”

“…Laser Sr isotopic analyses were conducted using a Neptune Plus MC-ICPMS instrument (Thermo Fisher Scientic, Germany), coupled to a RESOLution S155 LR 193 nm excimer ArF laser-ablation system at the CUGB Milma Lab, with a beam size of 90 mm, laser pulse frequency of 5 Hz, and energy density of 6 J cm −2 . L4 to H3 Faraday cups were used to collect 83 Kr, 167 Er ++ , 84 Sr, 85 Rb, 86 Sr, 173 Yb ++ , 87 Sr and 88 Sr, respectively, at an integration time of 0.254 s. Durango was analyzed as a monitor standard in our experiments. For each analysis, 25 s integration for the gas blank and 45 s integration for the signal collection were set up with 150 cycles of raw data.…”

“…35,63,[65][66][67][68][69] We ignored isobaric interferences of Ca dimers and argides, polyatomic oxide, and 40 Ca 37 Cl, as described in more detail elsewhere. 12,26,61,70 Finally, using the exponential law, the isotope mass fractionation of Sr isotopes was normalized from the interference-corrected 86 Sr/ 88 Sr ratios.…”