Important role of intra-transform spreading centers in shaping thermal structure along the Blanco transform fault

The thermal structures of oceanic transform faults (OTFs) affect the earthquake distribution， surface heat flow， and magmatic evolution in the ridge-transform systems. However， the thermal structures of OTFs are not well constrained due to limited observations. Especially， the thermal structures of segmented OTFs and their relationship with earthquake behavior are still unclear. The Blanco transform fault (BTF)， divided into eastern and western segments by the Cascadia Depression， exhibits relatively shallower earthquake focal depths in the western segment， which cannot be interpreted by the existing thermal models. Whether this asymmetry is caused by the distribution of intra-transform spreading centers (ITSCs)， the Cobb thermal anomaly beneath the western Juan de Fuca Ridge (JdFR)， or other mechanisms remains unclear. In this study， we employed three-dimensional numerical models to investigate the mantle flow and thermal structure of the BTF， taking into account the influences of ITSCs and the Cobb thermal anomaly. Our study encompassed two scenarios: (1) models with 0，1， and 4 ITSCs which account for increasing complexity of segmentation patterns at the BTF; (2) models with 4 ITSCs and a thermal anomaly beneath the JdFR. Our results indicate that the presence and distribution of ITSCs significantly uplift the thermal structure beneath the BTF by localized mantle upwelling， while the Cobb thermal anomaly has a minor warming effect on the western BTF due to the obstructing effect of axial thermal convection from the BTF. Particularly， the model associated with 4 ITSCs， which treats two additional extensional basins in the western BTF as ITSCs， leads to substantial mantle upwelling beneath the whole western portion of the BTF， generating an asymmetric thermal structure that closest to the seismicity-derived one.