Abstract

The Grenville orogenic belt along the southern margin of Laurentia records more than 300 m.y. of orogenic activity culminating in arc-continent and continent-continent collision ca. 1150–1120 Ma. Exposures in Texas provide a unique profile across the Grenville orogen from the orogen core to the cratonal margin. In the Llano uplift of central Texas, ca. 1360–1232 Ma upper amphibolite–lower granulite facies, polydeformed supracrustal and plutonic rocks represent the core of the collisional orogen. This exposure contains a suture between a 1326–1275 Ma exotic island-arc terrane and probable Laurentian crust and records A-type subduction. In west Texas, 1380–1327 Ma amphibolite to greenschist facies, polydeformed supracrustal rocks are thrust over ca. 1250 Ma carbonate and volcanic rocks along the cratonal margin. The carbonate and volcanic rocks form a narrow thrust belt with post–1123 Ma synorogenic sedimentary rocks, which grade into undeformed sedimentary rocks northward on the Laurentian craton.

The Texas basement reveals a consistent but evolving tectonic setting for the southern margin of Laurentia during Mesoproterozoic time. This paper summarizes recent advances in our knowledge of the Texas basement and proposes plate models to explain the tectonic evolution of this margin during Mesoproterozoic time. The orogenic history is strikingly similar to that of the Canadian Grenville orogen and requires a colliding continent off the southern Laurentian margin during the assembly of Rodinia.

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