A DETAILED COMPARISON BETWEEN MID-PALEOZOIC NEW ENGLAND AND LATE CENOZOIC COASTAL CALIFORNIA: SUBDUCTION OF AN OCEANIC RIDGE-TRANSFORM FAULT SYSTEM

The mid-Paleozoic Norumbega fault system (NFS) in Maine may have formed in the same way as the San Andreas fault system (SAFS) of coastal California, by subduction of an oceanic ridge-transform system (Kuiper, 2016, Geology). The model explains why convergent tectonics was ongoing until the latest Devonian or earliest Carboniferous in eastern Massachusetts, while to the northeast, in Maine, a progressive southwestward transition from mainly convergent tectonics to mainly strike-slip movement along the NFS occurred. This is similar to the current northward transition associated with the progression of the SAFS, while the Cascadia subduction zone is convergent. Fault systems such as the SAFS and NFS are rare. We present a detailed comparison between the two systems, where mid-Paleozoic New England is a mid-crustal equivalent for late Cenozoic California.

Similarities between the two systems in the model include: (1) both the SAFS and NFS formed through subduction of a ridge-transform fault system; (2) the Norumbega triple junction migrated SW in the same way as the Mendocino triple junction migrates north; (3) both the NFS and SAFS migrated land-inward; (4) the slab window region had a triangular shape; and (5) splay shaped faults developed along the northern end of the SAFS and SW end of the NFS as the triple junctions migrated.

Differences include: (1) the Cascades are experiencing dextral transpression, while eastern Massachusetts experienced sinistral transpression; (2) eastern New England does not have a mid-Paleozoic equivalent of the Basin and Range, probably because the Rheic ocean plate had a stronger convergent component with respect to North America than the Pacific plate; (3) while slab window magmatism generally is younger towards the north along the SAFS, similar younging cannot be recognized to the SW in New England, because of other coeval tectonic processes and associated magmatism in mid-Paleozoic New England; (4) the offset along the NFS is probably much smaller than along the SAFS, due to lower rates of relative plate motion; and (5) the NFS does not have an equivalent to the Transverse Ranges.