The Big Picture

  • This is an outline of the tectonic events that shaped the Great Lakes region.
  • From this window you can access a description of each individual event.

      • 1) ASSEMBLY OF THE SUPERIOR PROVINCE

        Assembly of the first pieces of continental crust in North America from roughly 3.5 to 2.6 billion years ago, acted as a nucleus for further continental development.


      2)CONTINENTAL COLLISION 2.6 BILLION YEARS AGO

        The first large scale orogeny in the Great Lakes region involved a micro continent collision with the now southern edge of the Superior province approximately 2.6 billion years ago.


      3) A RIFTING SEQUENCE IN THE PREVIOUSLY ACCRETED TERRANE

        The Penokean Orogeny began with rifting starting as early as 2.4 bya, until 1.9 bya. As rifting matured, sediments including the famous Iron Formations filled into the ocean. These sediments are important biologically as well as economically.

      4) TWO CRUSTAL COLLISIONS COMPLETE THE PENOKEAN OROGENY

        The first compacted and twisted the previously laid sediments when an island arc collided into the southern edge of the continental craton around 1.87 bya.
        The second collision soon behind it was caused by a mature micro continent which accreted around 1.86 bya. The bulk of the Great Lakes continental crust was developed by this time.

      5)RHYOLITIC VOLCANIC ACTIVITY

        in southern Wisconsin, believe it or not. When the volcanoes cooled and eroded down, sandstones were deposited and were later deformed into quartzites.


      6)THE WOLF RIVER BATHOLITH

        was emplaced into the solid continental crust around 1.47 billion years ago as multiple blurps of "granitic" magma. It was part of a continent wide magmatic event.

      7)THE MID-CONTINENTAL RIFT

        last scar left on the Great Lakes Region occurred when another rifting sequence began to rip apart the continent a billion years ago.

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