Yaojiazai complex massif is located at the northeastern margin of Indochina block and lower grade metamorphic belt for southwestern side of Ailaoshan tectonic zone, made up of hornblende-gabbro and granodiorite. The hornblende-gabbro contains abundance hydrous mineral-hornblende and has 70km(2) outcroup, show that intruded in compressed regional tectonic setting. The high-alumina mafic rock (Al2O3 >= 16%) features,and the fact that distribution of strongly enrichment of large-ion lithophile elements (K, Rh, Ba and Sr) and light rare earth elements, such as La and Ce, relative to those in the primitive mantle, negative anomaly of Nd and Ta in the primitive mantle-normalized trace elemental spider diagram, Mg-# (52.14 similar to 65.35) are close to the compositions of primitive arc magmas, and all samples plotted in the field of intraoceanic island arc in the diagram of Ta/Yb vs. Th/Yb, show the hornblende-gabbro is related with subduction of slab, and intruded in arc type tectonic setting. The granodiorite is strongly close to the compositions of adakite with high Sr and low Y, and high Na2O and low K2O contents. The positive anomaly of K, La and Tb, and negative anomaly of Nd, Ta, P and Ti in the primitive mantle-normalized trace elemental spider diagram, suggest that the granodiorite formed and emplaced in arc type tectonic setting as the same as the hornblende-gabbro. The results of zircon U-Pb LA-ICP-MS dating indicate the hornblende-gabbro and granodiorite intruded in 763 +/- 10Ma (MSWD = 4.1), and 761 +/- 11Ma (MSWD = 5.9), respectively. The fact of the granodiorite intruded in hornblende-gabbro, and the same intrusive ages show they formed and emplaced in the same time, but not the same stage. The intrusive rocks with arc feature in Yaojiazai complex massif in northeastern margin of Indochina block are the same with that in the western margin of Yangtz block, their ages are the same in the rough, and the evolution features of the Lower Paleozoic sedimentary rock, paleospecies and delta O-18/delta C-13 ratios in the Upper Paleozoic sedimentary rocks and paleomagnetic latitude in two blocks are similar, and the Sinian sedimentary rock is widely in Yangtz block, but is omitted in Indochina block. Our study show the ocean crust between the two blocks began to subduct in right-about in Neoproterozoic, and amalgated together each other in Late Neoproterozoic, and formed different size arc magmatic rock zones in the west margin of the Yangtz block and northeastern margin of the Indochina block respectively.
