Abstract
Geological and paleomagnetic data support the hypothesis that a Paleo-Mesoproterozoic supercontinent, referred to as Columbia, existed before the formation of Rodinia. This pre-Rodinia supercontinent was assembled along global-scale 2.1–1.8 Ga collisional orogens and contained almost all of Earth's continental blocks. Following its final assembly at ∼1.8 Ga, the supercontinent Columbia underwent long-lived (1.8–1.3 Ga), subduction-related growth via accretion at key continental margins, forming a 1.8–1.3 Ga large magmatic accretionary belt along the present-day southern margin of North America, Greenland and Baltica. It includes the 1.8–1.7 Ga Yavapai, Central Plains and Makkovikian Belts, 1.7–1.6 Ga Mazatzal and Labradorian Belts, 1.5–1.3 Ga St. Francois and Spavinaw Belts and 1.3–1.2 Ga Elzevirian Belt in North America; the 1.8–1.7 Ga Ketilidian Belt in Greenland; and the 1.8–1.7-Transscandinavian Igneous Belt, 1.7–1.6 Ga Kongsberggian–Gothian Belt, and 1.5–1.3 Ga Southwest Sweden Granitoid Belt in Baltica. Other cratonic blocks also underwent marginal outgrowth at about the same time. In South America, a 1.8–1.3 Ga accretionary zone occurs along the western margin of the Amazonia Craton, represented by the Rio Negro, Juruena and Rondonian Belts. In Australia, 1.8–1.5 Ga accretionary magmatic belts, including the Arunta, Mt. Isa, Georgetown, Coen and Broken Hill Belts, occur surrounding the southern and eastern margins of the North Australia Craton and the eastern margin of the Gawler Craton. In China, a 1.8–1.4 Ga accretionary magmatic zone, called the Xiong'er belt (Group), extends along the southern margin of the North China Craton. Fragmentation of this supercontinent began about 1.6 Ga ago, associated with continental rifting along the western margin of Laurentia (Belt–Purcell Supergroup), southern margin of Baltica (Telemark Supergroup), southeastern margin of Siberia (Riphean aulacogens), northwestern margin of South Africa (Kalahari Copper Belt), and northern margin of North China (Zhaertai–Bayan Obo Belt). The fragmentation corresponded with widespread anorogenic magmatic activity, forming anorthosite–mangerite–charnockite–granite (AMCG) suites in North America, Baltica, Amazonia and North China, and continued until the final breakup of the supercontinent at about 1.3–1.2 Ga, marked by the emplacement of the 1.27 Ga MacKenzie and 1.24 Ga Sudbury mafic dike swarms in North America.
Highlights
Rocks accumulated within the Navysh graben and formed the Navysh suite
In the final stage of rifting, already at the initial stages of the development of the Kama‐Belaya aulacogen (Chudin suite), the erosion products from the paleo‐aquifers occupying vast areas began to be transported into the rift
By that time, significant areas of the Archaean basement of the Volga‐Ural region might have become hidden underneath a proto‐cover and not eroded, so the Archean detritus in the Chudin suite is poorly represented in comparison with the Navysh suite, considering both the amounts and ages of detrital zircons
Summary
На юге Западного Урала расположен обширный выход докембрийских пород (рис. 1), описываемый обычно как Башкирский антиклинорий [Puchkov, 2010; Maslov, 2004]. Geological scheme (б): 1 – Late Paleozoic complexes of the Pre‐Ural marginal trough; 2–6 – Precambrian and Paleozoic complexes of the West Ural megazone: 2 – fauna‐characterized Paleozoic strata, 3–8 – Lower Paleozoic and Precambrian complexes of the Bashkir Uplift: 3 – Upper Vendian – Cambrian Asha group, 4–8 – Riphean strata of the stratotype area: 4 – Upper Riphean (Karatau group), 5 – Middle Riphean (Jurmat group); 6–8 – Lower Riphean (Burzyan group): 6 – Bakal formation, 7 – Satka formation, 8 – Ai formation; 9 – Early Precambrian metamorphic rocks (Taratash complex); – unevenly metamorphosed Paleozoic and pre‐Palaeozoic complexes in the uplift located at the eastern side of the Bashkir anticlinorium and Uraltau; – Early and Middle Paleozoic complexes of the East Ural megazone and mar‐ ginal allochthons (Kraki and Tirlyian); – faults: a – disturbing the internal structure of the regional tectonic elements; б – bordering the tectonic units within the Uraltau zone; – large thrusts and overthrusts; – structural lines: a – boundaries of the rock groups, for‐ mations, suites and strata within the complexes; б –positions of the Kukkarauk conglomerates within the field of development of the Asha rocks; – sampling sites and their numbers This scheme uses the data from V.I. Kozlov’s small‐scale geological map (Ufa sheet) and figures in [Puchkov, 2010; Keller, Chumakov, 1983; Kuznetsov et al, 2013, 2014a].
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