The Mazicuo quartz diorites is located at southwest of the Xainshuihe fault, southern Songpan Ganzi Terrane. The quartz diorites demonstrate high potassium (3.53%~3.86%), Ca rich (4.91%~6.07%), low Al content (14.60%~15.24%, A/CNK=0.80~0.89) and total rare earth elements (REE). Light rare earth elements (LREEs) are enriched but slightly Eu depleted, with whole rock (87Sr/86Sr)i = 0.707407~0.707640 implying that the Mazicuo magma origined from crust mantle mixed melting or partial melting of lower crust. The Mazicuo quartz diorites belong to lower crust remelting I type high potassium calc alkaline granite series. The trace element diagrams for discriminating tectonic environments indicate that the Mazicuo quartz diorites resemble volcanic arc granites. The enrichment in Rb (60.1×10-6~85.9×10-6) and Cs (4.01×10-6~19.62×10-6), and high K2O/Na2O (1.31~1.82) ratio suggest that biotite rich sources are responsible for the Mazicuo magma. The zircon SHRIMP U Pb age of 221±2.0 Ma (MSWD=1.4) shows the intrusive age is Late Triassic, while the whole rock Rb Sr age of 207±2.0 Ma may indicate the quartz diorites uplifted at late Late Triassic. The Mazicuo quartz diorites might form in Late Triassic back arc tectonic background and derive from crust mantle mix melting resulting from diapiric uplifting of lithospheric mantle magma.