https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:36062 Wed 29 Jun 2022 16:31:10 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:39964 Thu 30 Jun 2022 16:35:31 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:17778 Sat 24 Mar 2018 07:57:41 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:26786 18O=6.8⁰/₀₀-9.4⁰/₀₀) suggest that the Jiufeng pluton was mainly derived from melting of a common metasedimentary source, possibly with a minor basaltic contribution. We consider the geochemical variations of the Jiufeng pluton are primarily a result of incremental assembly of magma batches produced from rapid step-like transition from fluid-saturated to fluid-absent melting of the source. The muscovite granodiorite, with high Na₂O (>3.80wt.%; K₂O/Na₂O=~1), is interpreted to have been produced by fluid-saturated melting at low temperature (~650°C). High P₂O₅ (0.09-0.17wt.%), zircon saturation temperature (T_Zr=769-816°C) and La/Yb ratios (8.4-55.8) of the stage II two-mica granite support its formation from high-temperature (>800°C) biotite-dehydration melting, whereas lower P₂O₅ (<0.02wt.%), T_Zr (685-742°C) and La/Yb (<3) of the stage I two-mica granite suggest its generation at lower temperature, likely by muscovite-dehydration melting. We propose that extensive emplacement of basaltic melts in the lower crust most likely drove the rapid increase of mid-crustal (~20km) temperature (~50°C/m.y.) and widespread crustal melting for the formation of the Jurassic South China LGP. Therefore, formation of the LGP signifies prominent crustal growth as well as crustal reworking in an intraplate setting and was likely a response to flat-slab delamination and foundering.]]> Sat 24 Mar 2018 07:36:22 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:28212 15 kbar). Zircons show four main age groupings: 1.0–0.5 Ga, 50–45, 35–20, and 16–13 Ma. The oldest group is similar to common inherited zircons in the Gangdese belt, whereas the 50–45 Ma zircons match the crystallization age and juvenile character (εHf_i +0.5 to +6.5) of Eocene Gangdese arc magmas. Together these two age groups indicate that a component of the xenolith was sourced from Gangdese arc rocks. The 35–20 Ma Miocene ages are derived from zircons with similar Hf–O isotopic composition as the Eocene Gangdese magmatic zircons. They also have similar steep REE curves, suggesting they grew in the absence of garnet. These zircons mark a period of early Miocene remelting of the Eocene Gangdese arc. By contrast, the youngest zircons (13.0 ± 4.9 Ma, MSWD = 1.3) are not zoned, have much lower HREE contents than the previous group, and flat HREE patterns. They also have distinctive high Th/U ratios, high zircon δ¹⁸O (+8.73–8.97 ‰) values, and extremely low εHf_i (−12.7 to −9.4) values. Such evolved Hf–O isotopic compositions are similar to values of zircons from the UPV lavas that host the xenolith, and the flat REE pattern suggests that the 13 Ma zircons formed in equilibrium with garnet. Garnets from a strongly peraluminous meta-tonalite xenolith are weakly zoned or unzoned and fall into four groups, three of which are almandine-pyrope solid solutions and have low δ¹⁸O (+6 to 7.5 ‰), intermediate (δ¹⁸O +8.5 to 9.0 ‰), and high δ¹⁸O (+11.0 to 12.0 ‰). The fourth is almost pure andradite with δ¹⁸O 10–12 ‰. Both the low and intermediate δ¹⁸O groups show significant variation in Fe content, whereas the two high δ¹⁸O groups are compositionally homogeneous. We interpret these features to indicate that the low and intermediate δ¹⁸O group garnets grew in separate fractionating magmas that were brought together through magma mixing, whereas the high δ¹⁸O groups formed under high-grade metamorphic conditions accompanied by metasomatic exchange. The garnets record complex, open-system magmatic and metamorphic processes in a single rock. Based on these features, we consider that ultrapotassic magmas interacted with juvenile 35–20 Ma crust after they intruded in the deep crust (>50 km) at ~13 Ma to form hybridized Miocene granitoid magmas, leaving a refractory residue. The ~13 Ma zircons retain the original, evolved isotopic character of the ultrapotassic magmas, and the garnets record successive stages of the melting and mixing process, along with subsequent high-grade metamorphism followed by low-temperature alteration and brecciation during entrainment and ascent in a late UPV dyke. This is an excellent example of in situ crust–mantle hybridization in the deep Tibetan crust.]]> Sat 24 Mar 2018 07:23:51 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:24719 Sat 24 Mar 2018 07:11:04 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:37240 Mon 19 Feb 2024 15:52:57 AEDT ]]>