FIA trends along the Precambrian Rocky Mountains: a new approach to timing continental docking

A similar succession of Foliation Inflection/Intersection Axis (FIAs) trends preserved within porphyroblasts is present in two areas separated by 200 km along the Rocky Mountains. The Precambrian rocks in Central Colorado and Northern New Mexico were affected by deformation and metamorphism from ～1506 to 1366 Ma. A succession of five FIAs trending W–E, SSW–NNE, NNW–SSE, NW–SE and WSW–ENE is distinguished in Central Colorado and dated at 1506 ± 15 Ma, 1467 ± 23 Ma, 1425 ± 18 Ma, not dated and 1366 ± 20 Ma respectively. To the south in Northern New Mexico, a succession of five FIAs trending SSW–NNE, WNW–ESE, NNW–SSE, NW–SE and WSW–ENE is distinguished and dated at 1482 ± 48 Ma, 1448 ± 12 Ma, 1422 ± 35 Ma, not dated and 1394 ± 22 Ma. The excellent correlation of the sequence of FIA trends and their ages between regions reveals a sixfold‐FIA succession across the region with the first developed FIA set in Central Colorado not present in Northern New Mexico and the third FIA set in the region not present in Central Colorado. Preferential partitioning of W–E trending deformation into the Central Colorado region ～1506 ± 15 Ma was followed by SSW–NNE trending deformation that affected both regions at 1470 ± 20 Ma. However, preferential partitioning of WNW–ESE trending deformation into Northern New Mexico at 1448 ± 12 Ma left Central Colorado unaffected. Both regions were then affected by the three remaining periods of orogenesis, the first trending NNW–SSE at 1424 ± 15 Ma followed by one trending NW–SE that has not yet been dated, and then one trending WSW–ENE at 1390 ± 19 Ma. This suggests that the Yavapai terrane was tectonized at ～1506 Ma, prior to amalgamation with the Mazatzal terrane ～1470 Ma. Subsequent orogenesis was initially partitioned preferentially into the Mazatzal terrane, but the following three periods of tectonism affected both terranes in a similar manner.