Tectonic evolution Southern Oklahoma Aulacogen
an illustration of formation history of southern oklahoma aulacogen. in a, volcanoes form along continental plate boundary. b shows triple junction s basic appearance following formation. c shows 1 of 3 arms has not split while other 2 do, continuing d, in iapetus ocean forms. the southern oklahoma aulacogen formed sometime in late proterozoic eon, between 525 , 550 million years ago, during rifting of laurentia supercontinent or north american craton, geological core of north america. formation , bimodal igneous activity occurred simultaneously, 2 definite episodes of magma activity, mafic , felsic, former of being chiefly composed of gabbro-heavy magma , latter phase being composed of rhyolitic magma. hypothesized between mafic , felsic stages of magmatic activity substantial uplift occurred, correlates lack of coarse-grained massif anorthosites presented previously. remaining 2 arms of original triple-junction became spreading zones nascent iapetus ocean. aulacogen penetrated crat...