摘要
Granitoids are widespread in the Songpan-Garze （松潘-甘孜） fold belt, western China. These granitoids provide insight into regional tectono-magmatic events, basement nature and tectonic evolution. However, previous studies mainly focused on the eastern Songpan-Garze fold belt. In this article, five granitoid intrusions from the western Songpan-Garze fold belt have been studied. These intrusions are composed of quartz-diorite and granodiorite. Using LA-ICP-MS zircon dating method, the obtained magma crystallization ages are 219±2 Ma for the quartz-diorite and 216±5 Ma for the granodiorite. The ages, combined with regional geological analyses, show that they formed in a post-coilisional tectonic setting. The quartz-diorite and granodiorite display co-linear variation in their chemical compositions. REE compositions for both the quartz-diorite and granodiorite show strongly fractionated patterns with （La/Yb）N=5.02-18.34 and Eu/Eu^＊=0.44-0.89. The quartz-diorites have initial ^87Sr/^86Sr ratios （Isr） of 0.70929-0.71197 and εNd（t） values of -8.6 to -6.1 and the granodiorites have Isr values of 0.70549-0.70997 and εNd（t） values of -8.3 to -4.3. Zircon Hf isotopic data show εHr（t） values of -3.8 to ＋1.6 for the quartz-diorites and -1.2 to ＋3.0 for the granodiorites. Geochemical and Sr-Nd-Hf isotopic compositions indicate that the quartz-diorites and granodiorites have similar petrogenesis. We suggest that the magmas for the quartz-diorites and granodiorites were derived from partial melting of lower crustal mafic source, resulting from amphibole dehydration melting reaction. The probing of the magma source reveals that the western Songpan-Garze fold belt contains an unexposed continental basement, which is similar to the eastern Songpan-Garze fold belt. Geodynamically, it is proposed that a lithospheric delamination model can account for the magma generation for the quartz-diorites and granodiorites in the western Songpan-Garze fold belt.
Granitoids are widespread in the Songpan-Garze （松潘-甘孜） fold belt, western China. These granitoids provide insight into regional tectono-magmatic events, basement nature and tectonic evolution. However, previous studies mainly focused on the eastern Songpan-Garze fold belt. In this article, five granitoid intrusions from the western Songpan-Garze fold belt have been studied. These intrusions are composed of quartz-diorite and granodiorite. Using LA-ICP-MS zircon dating method, the obtained magma crystallization ages are 219±2 Ma for the quartz-diorite and 216±5 Ma for the granodiorite. The ages, combined with regional geological analyses, show that they formed in a post-coilisional tectonic setting. The quartz-diorite and granodiorite display co-linear variation in their chemical compositions. REE compositions for both the quartz-diorite and granodiorite show strongly fractionated patterns with （La/Yb）N=5.02-18.34 and Eu/Eu^＊=0.44-0.89. The quartz-diorites have initial ^87Sr/^86Sr ratios （Isr） of 0.70929-0.71197 and εNd（t） values of -8.6 to -6.1 and the granodiorites have Isr values of 0.70549-0.70997 and εNd（t） values of -8.3 to -4.3. Zircon Hf isotopic data show εHr（t） values of -3.8 to ＋1.6 for the quartz-diorites and -1.2 to ＋3.0 for the granodiorites. Geochemical and Sr-Nd-Hf isotopic compositions indicate that the quartz-diorites and granodiorites have similar petrogenesis. We suggest that the magmas for the quartz-diorites and granodiorites were derived from partial melting of lower crustal mafic source, resulting from amphibole dehydration melting reaction. The probing of the magma source reveals that the western Songpan-Garze fold belt contains an unexposed continental basement, which is similar to the eastern Songpan-Garze fold belt. Geodynamically, it is proposed that a lithospheric delamination model can account for the magma generation for the quartz-diorites and granodiorites in the western Songpan-Garze fold belt.
基金
supported by the National Natural Science Foundation of China (Nos. 40773019 and 40821061)
the Ministry of Education of China and the State Administration of Foreign Expert Affairs of China (No. B07039)
