Search

The orogenic process and crustal growth of the Changning–Menglian Palaeo-Tethys orogenic belt in the southeastern Tibetan Plateau is not fully understood. Triassic Caojian rhyolites and granites occur extensively in this orogenic belt and represent important constraints for this issue. This study aims to examine the relationships between the Triassic Caojian rhyolites and granites and to gain a better understanding of their possible petrogenesis. The study used zircon U–Pb geochronology, trace element analyses and Sr–Nd–Hf isotope data to better understand the relationships and possible origin of the rhyolites and granites. Recent zircon U–Pb ages indicated that the Caojian rhyolites were emplaced at 227.2 Ma, whereas age estimates for Caojian granites were slightly older (233.4–236.9 Ma). The Caojian rhyolites are enriched in large-ion lithophile elements and high-field-strength elements, with elevated FeOtot/MgO and Ga/Al ratios. However, they are significantly depleted in Ba, Sr, Eu, P and Ti. These geochemical characteristics indicate that they have an A-type affinity. Furthermore, the Caojian granites comprise biotite monzogranites and granodiorites and show unfractionated composition. Mineralogically, the Caojian granites were found to contain diagnostic I-type minerals such as hornblende. Geochemical data suggest that the petrogenesis of the Triassic Caojian rhyolites is characterized by rejuvenation of crystal mush represented by the Triassic Caojian granites. The necessary thermal input was supplied by mafic magma. This magmatic evolution was likely related to lithospheric delamination and upwelling of the asthenosphere during the Mid- to Late Triassic, forming post-collisional I-type granites and A-type volcanics in the Changning–Menglian Palaeo-Tethys orogenic belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Mengku dacites, Lincang granites and diorites are spatially and temporally related. • The Triassic Mengku dacites is characterized by rejuvenation of the Lincang crystal mush. • The thermal input was supplied by mafic magma represented by the Lincang diorites. • Magmatic evolution was related to mantle upwelling in the post-collisional setting. The tectono-magmatic event of the Changning-Menglian Paleo-Tethys orogen is an important process for understanding the tectonic evolution of the SE Tibetan Plateau. This orogen is composed of Changning-Menglian suture, Lancang group, Lincang batholith, and Yunxian volcanics. The Lincang batholith and its volcanic counterparts are part of Triassic magmatism in this orogen. The botholith is composed of biotite monzogranite, granodiorite and diorite. The Middle to Late Triassic volcanics include Manghuai rhyolite, Xiaodingxi basalt and Mengku dacite. The Mengku dacite is volcanic dome in west of the batholith. Lincang biotite monzogranite and Mengku dacite have similar geochemistry and are characterized by negative ε Hf (t) values (–13.2 to –5.2) and ε Nd (t) values (–14.7 to –8.8), whereas diorite dikes within the Lincang batholith have slightly high ε Hf (t) values (–8.3 to –4.9) and ε Nd (t) values (–6.9 to –6.7). Manifestations of resorption textures in quartz and reverse compositional zoning in feldspars are recognized from Mengku dacite. We consider that Mengku dacites resemble the erupted Lincang biotite monzogranite as they occur in the same tectonic settings and have similar geochemical features and mineral assemblages dominated by plagioclase, alkali-feldspar, quartz, and biotite. The evolution of the Mengku dacite magma is characterized by the rejuvenation of crystal mush represented by the Lincang batholith. The required thermal input was supplied by mafic magma, represented by diorite dikes and enclaves within the Lincang batholith. The Middle to Late Triassic magmatic event in this orogen likely resulted from lithospheric delamination and upwelling of the asthenosphere in a post-collisional environment. [ABSTRACT FROM AUTHOR]