The Cape Porcupine Complex, northern mainland Nova Scotia - no longer a geological orphan

The Cape Porcupine Complex west of the Strait of Canso in northern mainland Nova Scotia consists of mainly fault-bounded units of metasedimentary, metavolcanic, and granitoid rocks. A previously reported U-Pb (zircon) age of 610 +/- 3 Ma from syenogranite combined with petrological characteristics indicates that some of the granitic rocks and possibly an associated body of leucodiorite are Late Neoproterozoic. In contrast, alkali-feldspar granite from a more extensive suite of quartz alkali-feldspar syenite/alkali-feldspar syenite, alkali-feldspar granite/syenogranite, and quartz alkali-feldspar leucosyenite with A-type characteristics yielded an early Ordovician age of 478 +/- 3 Ma. Similar A-type chemical characteristics suggest that the metavolcanic unit may be the extrusive equivalent of the Ordovician suite. Similarities in age and petrological characteristics indicate that the Cape Porcupine Complex is linked to rock units in the Antigonish Highlands. The ca. 610 Ma granitic rocks are likely related to plutonic and volcanic rocks of similar age in the Antigonish Highlands interpreted to have formed at a continental margin subduction zone. In contrast the A-type syenitic and metavolcanic rocks are probably related to the compositionally similar West Barneys River plutonic suite and younger volcanic rocks formed in an extensional regime. Such rocks do not occur in adjacent Ganderia or Avalonia in Cape Breton Island or southern New Brunswick, further demonstrating the regional significance of the Canso Fault in tectonic reconstructions.