Constraining the Cambrian drift of Gondwana with new paleomagnetic data from post-collisional plutons of the Araçuaí orogen, SE Brazil

Abstract

Despite their importance in constraining the dynamics of Gondwana’s final phase of assembly, Cambrian paleomagnetic data from Gondwana are sparse. The Cambrian paleomagnetic dataset of Western Gondwana is especially poor, being defined by only a handful of poles. Here we contribute new Furongian paleomagnetic data from the ~500 Ma post-collisional, Santa Angelica and Venda Nova plutons from the southern portion of the Araçuaí orogen in SE Brazil. The characteristic magnetization isolated from both plutons reveals two groups of directions that are demonstrated to be antipodal. On the basis of a thermal diffusion model, we attribute these antipodal directions to primary thermoremanent magnetizations acquired by cooling of the plutons in the presence of a reversing field. Together, paleomagnetic results from 35 sites distributed between the two plutons allows computation of a new ~500 Ma paleopole: 4.7° N, 332.2° E, A95 = 4.06 and K = 68.82. This pole does not resemble any younger paleomagnetic poles either from Gondwana or the independent South American plate after the demise of Pangea, but instead closely corresponds to the Miaolingian and Furongian sector of reference apparent polar wander paths for Gondwana. It also agrees well with the limited existing individual early Paleozoic poles from Western Gondwana. Our new result may thus be regarded as a reference pole for Western Gondwana in Furongian time. Considerations of the Cambrian paleomagnetic data from Eastern and Western Gondwana suggest that while the supercontinent was amalgamated by ~500 Ma, there was likely significant motion between Eastern and Western Gondwana in earlier Cambrian time.