Early Proterozoic Orogen Research Articles

THE PHENOMENON OF RAPID ACCUMULATION OF SEDIMENTS BELONGING TO THE UDOKAN GROUP AND THE FORMATION OF THE UNIQUE UDOKAN COPPER DEPOSIT (ALDAN SHIELD, SIBERIAN CRATON)

We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.

Early Proterozoic Central Plains orogen: A major buried structure in the north-central United States

A major early Proterozoic orogen (Central Plains) more than 1000 km long and at least 500 km wide has been delineated in the subsurface of Nebraska, Kansas, and Missouri as a result of a new compilation of Precambrian basement drill data in the northern midcontinent. The orogen is composed of metamorphic and granitoid rocks in the ringe 1.63–1.80 Ga, and it is interpreted on the basis of isotopic ages, rock types, and structure—as reflected by magnetic and gravity anomalies—as being the eastward extension of the early Proterozoic foldbelt exposed in basement uplifts in Colorado and southeastern Wyoming. It truncates the southern margin of the Superior Archean craton and its marginal early Proterozoic orogens, the Penokean (1.83–1.90 Ga) and the Trans-Hudson (1.85–1.95 Ga). The pattern of intersecting Proterozoic mobile belts marginal to Archean cratons is comparable to that in other continents, such as Western Australia and southern Africa.