The tectonic background of the early to middle Neoproterozoic (835~720 Ma) magmatic rocks in the northwestern margin of the Yangtze block is still in debate. We report the zircon LA- ICP- MS U- Pb ages, petrological and geochemical data of the gabbro, gabbro- diorite, and meta- andesitic basalt from the Heimulin- Xiakouyi suprasubduction zone (SSZ) ophiolitic mélange in Bikou Terrane, Mianxian- Lueyang- Ningqiang area, southern Shaanxi Province. The results show that the Muguayuan gabbro and meta- andesitic basalts belong to tholeiitic basalt series with right- dipping chondrite- normalized REE patterns, weak negative Eu anomalies. The primitive mantle normalized incompatible element patterns show the enrichment of LILE and LREE and depletion of HFSE (such as Nb, Ta, etc.), which is similar to island arc magmatic rocks. The Heimulin and the Xiakouyi gabbro- diorite belong to calc- alkaline series. The Heimulin gabbro- diorite displays similar geochemical characteristics to the Bonin fore- arc boninite, with relatively high SiO2 content (54.27%~56.79%), MgO content (11.10%~17.04%), and low TiO2 content (0.08%~0.19%). The trace elements of the whole rock have the characteristics of enrichment of LILE (Rb, Th, U and Pb), depletion of HFSE (Nb, Ti), and weak Zr- Hf positive anomalies. The Xiakouyi gabbro- diorite also shares similar geochemical signatures to boninite, with relatively lower MgO content (4.24%~8.91%). In addition, the N- MORB (normal mid- ocean- ridge basalt) - normalized trace element spider diagrams are similar to Bonin fore- arc boninitic rocks, which is enriched in LILEs and depleted in HFSEs, and show low Ti/Zr ratios, indicating that it could belong to transitional type of boninite- like rocks. Zircon LA- ICP- MS U- Pb dating results show that the age of Heimulin- Xiakouyi SSZ ophiolitic mélange is about 835~830 Ma. The crystallization age of Muguayuan gabbro, Heimulin and Xiakouyi gabbro- diorite are 835±4 Ma, 830±2 Ma and 830±11 Ma, respectively. Combined with previous research on the tectonic evolution of the early to middle Neoproterozoic in the northwestern margin of the Yangtze block, we suggest that the northwestern margin of the Yangtze block may be an active continental margin environment of long- term southeastward subduction of oceanic crust in the early to middle Neoproterozoic (950~720 Ma), and may develop subduction- accretion orogeny. In the early Neoproterozoic (835~830 Ma), intra- oceanic subduction occurred on the northwestern margin of the Yangtze block, forming the Heimulin- Xiakouyi SSZ ophiolitic mélange, and the final accretion collage was located in the Bikou Terrane.