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Various tectonic models have been proposed to account for the widely distributed igneous activities in the southeastern part of the South China Block (SCB) during the Triassic–Jurassic period. One of the major contending debates is on the timing of initiation of the palaeo-Pacific plate subduction under the SCB, due to lack of unequivocal evidence for arc magmatism during the period in this region.The 191 ± 10 Ma (N = 5, MSWD = 12) calc-alkalic high-K I-type Talun metagranite occurs in the southern Tailuko belt of the Tananao metamorphic complex, Taiwan. In terms of age, this metagranite belongs to the Early Yanshanian igneous activity in the southeastern part of the SCB. However, its geographic position does not accord with the well-known general oceanward younging trend of the Yansnanian igneous rocks. In view of the large age uncertainty reported, this metagranite is redated in this study. Some zircons of this metagranite are high in U content and are metamict. Zircons with low U contents are a...

Major and trace elements and whole rock Sr–Nd isotope data of Late Permian silicic plutonic and volcanic rocks from the Phan Si Pan–Tu Le region in NW Vietnam were collected in order to establish their petrogenetic relationship with the magmatic rocks of the Song Da zone (NW Vietnam) and the alkaline silicic rocks of the Panxi area of the Emeishan large igneous province (ELIP) in SW China. The granites and rhyolites have geochemical characteristics of anorogenic granites (e.g. high Fe# and high Ga/Al) and are further subdivided based on mineralogy. The Phu Sa Phin and Muong Hum granites contain sodic to sodic–calcic amphiboles and sodic pyroxene, while the Phan Si Pan granite does not. The Phu Sa Phin and Muong Hum granites occasionally show peralkaline to metaluminous compositions, while the Phan Si Pan granites and the Tu Le rhyolites have metaluminous to peraluminous compositions. The chondrite-normalized REE patterns [(La/Yb)N = 3.6–51.3, (Gd/Yb)N = 1.4–3.4] and the primitive mantle-normalized spidergrams (enrichment in high field strength elements) are similar to those of the Song Da silicic rocks and the Panzhihua and Taihe granites in the Panxi area. Rhyolite-MELTS modeling suggest that the silicic magmas were likely generated by fractionation of the Song Da high-Ti basalts. The eNd(t) values range from weakly negative to moderately positive values (−2.2 to +2.2), suggesting the silicic rocks may be assimilated by basement rocks during magma emplacement. Permian magmatic rocks in the Phan Si Pan–Tu Le region are petrologically, geochemically and geochronologically comparable to those of the inner zone of ELIP. Although Permian lithospheric mantle and lower crustal structure of the Phan Si Pan–Tu Le region may be destroyed by a lithospheric removal in response to Cenozoic India–Eurasia collision, our results along with recent geophysical analyses in NW Vietnam suggest that the upper to middle crust of Phan Si Pan–Tu Le region represent a remnant upper to middle crust of inner zone of ELIP.

In-situ zircon U–Pb and Hf isotope analyses were carried out for alkaline silicic magmatic rocks from the Phan Si Pan-Tu Le region in northern Vietnam to constrain their possible sources and to determine their petrogenetic relationship with the Emeishan Large Igneous Province (ELIP), SW China. Nine granites and nine rhyolites yield zircon 206Pb/238U ages from 262 Ma to 249 Ma, coinciding with the timing of silicic magmatism in the Panxi area of the ELIP. The zircon eHf(t) values (+14 to +3) of these granites and rhyolites suggest a moderately depleted mantle source and overlap with those of peralkaline and metaluminous granites in the Panxi area [i.e. eHf(t) = +14 to +4]. The zircon Hf isotope ratios show that the zircons probably record the original source characteristics whereas whole-rock Nd isotope data indicate an evidence for crustal contamination that may have occurred at lower temperatures during magma emplacement. The synchroneity, coupled with petrological and geochemical similarities, indicate that silicic rocks from the Phan Si Pan-Tu Le region are cogenetic with the Panxi silicic plutonic rocks and that they are likely derived by similar petrogenetic processes (i.e. fractionation of mafic magmas or partial melting of mafic rocks). Therefore, we propose that the Phan Si Pan-Tu Le region represents a displaced portion of the ELIP inner zone.