Petrology, geochemistry and tectonic setting of the Panan intrusion in Mamen, Sangri,Tibet

The Panan intrusion is mainly composed of monzogranite and monzonite. It is calc-alkaline potassic basanite rock. The zircon LA-ICP-MS U-Pb dating of the Panan intrusive rocks yields a crystallization age of 80.91±0.48Ma, indicating the Panan intrusion was formed in Late Cretaceous. Geochemically, Panan intrusive rocks are rich in large ion lithophile elements and poor in high field-strength elements. The REEs of the rocks are obviously fractionated, with a (La/Yb)_N=8.88~11.86 value and a negative Eu anomaly. The Sr-Nd isotopic compositions indicate that the Panan intrusion is characterized by high Pb, Sr, Sm and Nd contents, a low I_Sr value (0.70442~0.70486), and a positive ε_Nd(t) value (+1.99~+2.73).Based on petrological, geochemical and chronological characteristics, the Panan intrusion may be formed from the normal island arc magma by the partial melting of continental crusts in an island background during the northward subduction of Neo-Tethys oceanic plate. With the development of the subduction angle of the Neo-Tethys ocean slowed down into almost zero degree in the Late Cretaceous, the large-scale magmatic activities in 109-80 Ma ended in the studied areas soon.