We appreciate the opportunity to discuss our paper on the Cenozoic mafic magmatism of eastern Australia and potential relationships to plate motion and are thankful to Musgrave and Schmidt (2019) for bringing the uncertainties and inconsistencies of Jones et al. (2017) to our attention. The comments from Musgrave and Schmidt (2019) focus on the paleomagnetic record of Australian plate motion, so, to begin, we note that Jones et al. (2017) did not include new paleomagnetic data. Instead, the paper presented new 40Ar/39Ar results from east Australian mafic rocks and evaluated them in light of tectonic reconstruction circuits compiled by Seton et al. (2012). To reiterate the original motivation behind our paper, we created animations from previous tectonic reconstructions to examine spatial-temporal relationships between east Australian magmatism and tectonic processes such as the opening of the Tasman and Coral Seas and collision of the Ontong Java Plateau (OJP) with the Solomon Islands. In particular, we examined (1) the age and location of mafic magmatism in eastern Australia with respect to tectonic reshuffling in the southwest pacific; (2) possible formation mechanisms of magmatic provinces in eastern Australia; and (3) the relationship between the latitude of the Australian plate according to a global moving hotspot reference frame (GMHRF; Doubrovine et al., 2012) and different apparent polar wander paths (APWPs) for Australia using previously published paleomagnetic data from Idnurm (1985), Embleton (1981), and Embleton and McElhinny (1982).
Below we clarify our methodology in compiling these previous results, which, as shown by Musgrave and Schmidt (2019), was poorly explained. Some confusion may have arisen from references to “linear and longitudinal apparent polar wander paths (APWPs)” (Jones et al., 2017, p. 474) versus “linear and longitudinal reconstructions” (Jones et al., 2017, p. 466, 477–478). The latter refers only to the animations, which are either based on a modified rotation file of Seton et al. (2012) or on the same reconstruction tree rearranged around paleomagnetic data from Embleton (1981) and Embleton and McElhinny (1982), as described in the methodology section of our paper. Inferences between plate motion and the timing of magmatism or collisions were based solely on the first animation, which used a base reconstruction file, digitized spreading ridges, and plate boundaries compiled by Seton et al. (2012), modified to include an approximate reconstruction of collisional terrains in Papuan New Guinea (PNG), the docking of the OJP, continent polygons, and several digitized features (i.e., east Australian volcanoes, OJP, and the PNG terrains) linked to the base rotation of their respective plate IDs. The Australia-Antarctica plate circuit was selected to represent models that reflect “linear” motion, as it produces motion paths similar to those of Musgrave (1989), Idnurm (1985), and Torsvik et al. (2008) with well-defined longitudinal constraints. In the case of references to the linear and longitudinal APWPs, they are only compared directly to each other, or to the GMHRF. The comparison was made between the paths to determine which data, if any, in either path was more representative of Australian Cenozoic plate motion.