Objectives：The Pamir syntax at the central part of the Tethys tectonic domain records the whole Tethys evolution process. However, some key issues such as the subduction orientation and process of the Proto-Tethys Ocean, and the transition from the Proto-Tethys to Paleo-Tethys transition in the region, are still hotlly debated. This study attempts to address the genesis and tectonic background of Ordovician pyroxene diorites in Tashkorgan，and to shed new light for our better understanding the Early Paleozoic tectonic evolution in the Proto-Tethys Ocean. Methods：In this paper，we present field observations, petrography, new zircon U-Pb ages，whole-rock as well as mineral geochemistry，bulk-rock Sr-Nd isotopic and zircon Hf isotopic data of the Early Paleozoic Tashkorgan pyroxene diorites in the Pamir syntax． Results：The Ordovician Tashkorgan pyroxene diorites were emplaced at the southern part of the Bulukuole Group as sheets and extended several kilometers in length. They are mainly composed of hornblende (40%-45%), plagioclase (35%-40%), biotite (6%-10%), and altered pyroxene (15%-20%). The LA-MC-ICP-MS zircon U-Pb dating yields concordant age of 457.6±2.6Ma (MSWD=0.68，n=20).The rocks have variable Al2O3 (13.17-18.79 wt.%), SiO2 (49.85-55.85 wt.%), MgO (3.52-9.12 wt.%), and alkali (Na2O+K2O=2.93-4.92 wt.%) contents，and they are enriched in large ion philanthropists elements(LILEs) and LREE(LaN/YbN=2.47-5.87), and are depleted in high-field-strength elements(HFSEs) (Nb/La=0.31-0.81), sharing the features of island arc basalts. The samples exhibit decoupled Nd-Hf isotopic compositions, with enriched bulk-rock Nd isotopic compositions (εNd(t)= -8.79~-2.46,) but depleted zircon Lu-Hf composition (εHf(t)= -2.1~+4.5). All these characteristics demonstrated that the Tashkorgan pyroxene diorites most likely originated from partial melting of the enriched lithospheric mantle metasomatized by subduction slab fluids but with variable involvement of melts from depleted asenthospheric mantle. Conclusions：The data presented in this contribution, in combination with previous works, unambiguously argue for the southward subduction of the Proto-Tethys oceanic slab.