TECTONIC TRACERS: TRANSFERRED CONTINENTAL FRAGMENTS THAT LINK CRATONS WITHIN RODINIA

Ian Dalziel, one of the original proponents of the Meso-Neoproterozoic supercontinent, Rodina (Dalziel, 1991, Geology), recognized Laurentia was surrounded by Neoproterozoic rifted margins (Dalziel, 1992, GSA Today), and devoted much research to identifying cratons that rifted away. I have been fortunate to work with Ian to test proposed Rodinian conjugate margins of Laurentia using “tectonic tracers”, allocthonous continental fragments left behind on the conjugate margin following continent rifting (Dalziel, 1993, XII Congreso Geologico Argentino). We compared unique rock units, lithologic sequences, precise timing of events, and isotopic signatures of tectonic tracers and potential “parent” continents to identify piercing points where continents may have been juxtaposed in Rodinia.

My PhD work tested one of Ian’s favorite hypotheses which juxtaposed the Labrador-Scotland-Greenland Promontory (LSGP) of northeastern Laurentia with the Arica Embayment western South America. Dalziel (1994, Geology) proposed that the Arequipa-Antofalla Basement (AAB) of South America was a tectonic tracer from the LSGP transferred to Amazonia following Grenville-Sunsas collision. Rock types, rock sequences and ages from the AAB were strikingly similar to those in Scotland; however, comparison of more precisely dated sequences and Pb and Nd isotope signatures did not corroborate this link. Data supported two new correlations, the AAB was a tectonic tracer from Kalahari and the Blue Ridge Province of eastern Laurentia was a tectonic tracer from Amazonia transferred during juxtaposition of southeastern Laurentian and Amazonia (Loewy et al, 2003, Tectonophysics).

More recent work addressed the southern margin of Laurentia. Granites in the Coats Land Province of East Antarctica have similar ages and Pb isotope signatures to those of the Red Bluff granite suite in the Franklin Mountains of West Texas (Gose et al, 1997, JGR; Loewy et al 2011, Geology). This correlation places the Coats Land tectonic tracer within Laurentia prior to ca. 1000 Ma juxtaposition of southwestern Laurentia and Kalahari.

After three decades of work, the configuration of Rodinia is far from settled, but correlations from tectonic tracers have stood the test of time. Resulting continental links remain components of recent Rodinia reconstructions.