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In this work, we investigate the formation of a magnetic flux rope (MFR)above the central polarity inversion line (PIL) of NOAA Active Region 12673during its early emergence phase. Through analyzing the photospheric vectormagnetic field, extreme ultraviolet (EUV) and ultraviolet (UV) images,extrapolated three-dimensional (3D) non-linear force-free fields (NLFFFs), aswell as the photospheric motions, we find that with the successive emergence ofdifferent bipoles in the central region, the conjugate polarities separate,resulting in collision between the non-conjugated opposite polarities.Nearly-potential loops appear above the PIL at first, then get sheared andmerge at the collision locations as evidenced by the appearance of a continuousEUV sigmoid on 2017 September 4, which also indicates the formation of an MFR.The 3D NLFFFs further reveal the gradual buildup of the MFR, accompanied by theappearance of two elongated bald patches (BPs) at the collision locations and avery low-lying hyperbolic flux tube configuration between the BPs. The finalMFR has relatively steady axial flux and average twist number of around$2.1\times 10^{20}$~Mx and -1.5, respective. Shearing motions are founddeveloping near the BPs when the collision occurs, with flux cancellation andUV brightenings being observed simultaneously, indicating the development of aprocess named as "collisional shearing" (firstly identified by Chintzoglou etal. 2019). The results clearly show that the MFR is formed by "collisionalshearing", i.e., through shearing and flux cancellation driven by the collisionbetween non-conjugated opposite polarities during their emergence.

Formation of a Magnetic Flux Rope in the Early Emergence Phase of NOAA Active Region 12673