Grenville orogeny
Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland.
The timescale outlined by Toby Rivers in 2002 is derived from the well-preserved Grenville Province and represents one of the most detailed records of the orogeny.
Due to the great size of the area affected by Grenville events, there is some variance in timing across the orogenic belt.
[3][4] Rivers' 2008 paper examines the timing of the different periods of the orogeny and reconstructs the timeline based on the spatial and temporal metamorphism of the rocks present.
[8][9] Timing of these events is constrained by cross-cutting relations observed in the field as well as SHRIMP (sensitive high-resolution ion microprobe) and TIMS (thermal ionization mass spectrometry) uranium-lead dating.
Slab pull and far-field drivers such as ridge push were aiding in closing the distance between the island arc and the continent.
Today, the Grenville orogen is marked by northwest verging fold-and-thrust belts and high pressure metamorphic regimes, as well as distinctive AMCG suite magmatism.
Eclogitized metagabbros (very high pressure ultramafic metamorphic rocks) are found in some localities and likely represent areas of deepest burial and/or most intense collision.
[11] Throughout the orogen, these sequences of high pressure metamorphic rocks are cut by intrusive AMCG suite plutons, generally interpreted as syn- or post-tectonic.
[1][12] This is derived from the theory that AMCG plutonism is driven by ponding of olivine tholeiite basalt at the base of the continental crust during tectonic extension.
Subdivisions of this belt include the Bancroft, Elzevir, Sharbot Lake, and Frontenac Domains and the Adirondack Lowlands.
[4][7] It is important to separate local from large-scale tectonic history of the orogenic belt in order to understand the orogeny.
[1][13] Texas and Mexico represent the southern margin of Laurentia and likely collided with a different continent than that involved in the eastern collision.
Rocks of the former group bear geochemical signatures implying island arc and back-arc basin provenance.
[14] It is suggested that the regime of subduction under the Laurentian margin (currently in Texas, north of the accreted Mexican terrane) ended around 1230 Ma, and that subduction polarity reversed to bring the colliding continent north, since the Llano Uplift, which records the history of the Grenville in Texas, bears no evidence of arc magmatism after this time.
Other exposures include the Shenandoah and French Broad massifs, which comprise the Blue Ridge province of Virginia.
