Penrose, June Did Plate Tectonics begin in Paleoproterozoic time? …well before, but scale & style become more modern during the Paleoproterozoic Wouter Bleeker, Richard Ernst & Ken Buchan Geological Survey of Canada, Ottawa Evidence for plate behaviour at Ga: break-up, dispersal & suturing of Archean cratons Evidence for plate behaviour at Ga: break-up, dispersal & suturing of Archean cratons

Penrose, June No data Bleeker & Enst, in prep. Significant secular change?...Yes, of course! Higher heat productionHigher heat production Weaker lower crustWeaker lower crust Always more basalt in the system …more significant density inversionsAlways more basalt in the system …more significant density inversions Smaller plate scalesSmaller plate scales Faster recyclingFaster recycling “The 2.7 Event”

Penrose, June Precambrian geology of North America Modified after Hoffman, 1989 ; based on a century of geological research A Paleoproterzoic collage of micro- plates and inter- vening arcs terranes

Penrose, June 20064

5 Great Slave Lake Shear Zone 7. Large strike-slip faults?…Yes. The ~1.8 Ga collage: plate tectonics? L ITHOPROBE’S SNORCLE Transect Relevant questions: 1.Was there significant lateral movement?...Yes. 2.Are now adjacent blocks unrelated (exotic)?...Yes, commonly. 3.Plate behaviour: rifting, break-up, convergence?...Yes. 4.Did blocks behave (quasi) rigid?...Yes, some. 5.Strong asymmetry across suturing orogens?...Yes. 6.Are time spans and rates similar?…Yes, comparable. Relevant questions: 1.Was there significant lateral movement?...Yes. 2.Are now adjacent blocks unrelated (exotic)?...Yes, commonly. 3.Plate behaviour: rifting, break-up, convergence?...Yes. 4.Did blocks behave (quasi) rigid?...Yes, some. 5.Strong asymmetry across suturing orogens?...Yes. 6.Are time spans and rates similar?…Yes, comparable.

Penrose, June Bleeker, 2002 Cook et al., 1999

Penrose, June Accretionary structure along western margin of Slave craton, Ga: Cook et al., 1999

Penrose, June Successive sutures:

Penrose, June Suture geometries: e.g., White et al., 2002

Penrose, June Baltica Siberia? Australia- Antarctica? ??? Laurentia within ~1.8 Ga “Nuna”: e.g., Buchan et al., 2000 Long-lived active margin

Penrose, June Nuna to Rodinia:

Penrose, June ~1 Ga Rodinia (conceptual only): Rifted Nuna fragments Intact core of ~1.8 Ga Nuna Stray fragments

Penrose, June Bleeker, 2005 Further back in time: before Nuna

Penrose, June Ancestral landmass “Superia” “Break-out” of the Superior craton, out of ancestral landmass Superia: Karelia Hearne Wyoming Kola Others

Penrose, June Superia WyomingSuperia:Superia: Bleeker & Ernst, 2006

Penrose, June Correlating multiple events: Bleeker & Ernst, 2006

Penrose, June From late Archean supercratons to Nuna: break-up & independent drift of cratonic fragments Not to scale!

Penrose, June Did things move? ~5 cm/yr

Penrose, June Ophiolites? Sparse but present!! Kontinen, Peltonen et al.

Penrose, June Diagnostic rock associations: -Plume-assisted extension & break-up?…Yes, definitely. -Rift & passive margin sequences?…Yes. -Plume-assisted extension & break-up?…Yes, definitely. -Rift & passive margin sequences?…Yes. Slave basement Passive margin sequence Rift sequence Foredeep sequence Arc

Penrose, June Diagnostic rock associations: -Plume-assisted extension & break-up?…Yes, definitely. -Rift & passive margin sequences?…Yes. -Arcs? Arc batholiths (at plate scale)?…Yes. -Ophiolites?…Yes. -Elevated P/T metamorphic facies series?…Yes,…but UHP?? -Blueschists…No…or? -Plume-assisted extension & break-up?…Yes, definitely. -Rift & passive margin sequences?…Yes. -Arcs? Arc batholiths (at plate scale)?…Yes. -Ophiolites?…Yes. -Elevated P/T metamorphic facies series?…Yes,…but UHP?? -Blueschists…No…or?

Penrose, June Conclusions: The Paleoproterozoic preserves a clear record of (small) plate tectonics, resulting in Earth’s first “modern” supercontinent Nuna Not to scale!

Penrose, June

Penrose, June Matachewan dykes 2446 Ma ( Ga) Hearne – southern Superior link: 2446 Ma dykes Ma ( Ga) Kaminak dykes Dates by Heaman

Penrose, June Bleeker, 2002, Ma Solution allowed by current paleomagnetic data:

Penrose, June Bleeker & Ernst, 2006 Barcodes:Barcodes:

Penrose, June KaapvaalSlaveSuperiorLew. Nain Labr. Karelia Hearne Superia Sclavia Vaalbara “Fragmentation tree” of Archean fragments The Archean family tree

Penrose, June “Evidence for plate behaviour at Ga: break-up, dispersal, and suturing of Archean cratons” Wouter Bleeker & Richard Ernst Presentation style: oral is preferred. I will trace the origin of Archean cratons within the context of much larger supercratons in the late Archean. These may or may not have been connected in a ca. 2.6 Ga supercontinent. The mininum length scale of supercratonic landmasses was many thousands of kilometres. Whatever the details, fundamental heterogeneity of Archean cratons demands that horizontal movements and terrane juxtaposition must have played a major role in building supercratonic aggregations. Following emplacement of numerous LIPs, and their plumbing systems, the supercratonic landmasses broke up diachronously between ca. 2.2 Ga and 1.9 Ga, spawning most of the ca. 35 known Archean cratons (s.s.). After a dispersal phase, these cratonic fragments and intervening juvenile terranes aggregated and collided between 1.9 and 1.8 Ga to form Earth’s first “modern” supercontinent Nuna (a.k.a. Columbia). I call Nuna the fist “modern” supercontinent because its geodynamics and tectonics show mostly familiar aspects (e.g., incorporation of sediment-rich passive margins, the first bonafide ophiolites, large coherent arcs, and undisputed sutures). Also, it was large enough to start dominating, for the first time, geochemical cycles with continental signatures (e.g., the seawater Sr isotopic record). The only major “tectonic innovation” yet to come were blueschists. From 1.8 Ga to ca. 1.0 Ga, Nuna evolved into Rodinia. Details remain murky but general systematics suggest themselves. Going back in time, component Archean cratons within 1.8 Ga Nuna can be restored into their ancestral supercratonic aggregations. We show that there is enough information in the system to do so for many of the ca. 35 cratons. In fact, a concerted international effort could accomplish this in less than a decade. Only then will we be able to test whether late Archean supercratons were ever connected in a pre-Nuna supercontinent and make general statements about the early part of the supercontinent cycle.