Development peculiarities of the magmatism synchronous to the formation of the North Atlantic passive margins

Development of passive volcanic margins of the Central Atlantic and initial opening of ocean

“…The rocks are olivine and pigeonit porfiric containing also augite, plagioclase, Cr spinel, titano magnetite, and ilmenite phenocrysts. [1,2,12,18,25,35,40,44,45,57,58]. (1) Fragments of Pangea supercontinent in Africa, North and South America; (2) Central Atlantic plume; (3-7) passive volcanic mar gins: (3,4) igneous rocks at proximal margins: (3) dikes, (4) sills and lava flows; (5-7) elements of distal margins: (5) igneous rocks of SDRs; (6, 7) magnetic anomalies: (6) ECMA, (7) WACMA; (8) Rocks varying in compositions from almost primary to markedly evolved varieties (14.8-4.7 wt % MgO) with a predominance of moderately enriched low Ti tholeiites (0.40-1.35 wt % TiO 2 ) are characteristic of volcanic complex and dikes in the proximal zone.…”

“…The trigger mechanism for the partial melting related to the for mation of large igneous provinces (LIPs), e.g., CAMP, is a matter of debate. The following hypo theses are being discussed: (1) heating of the mantle beneath the Pangea supercontinent [3,7,13,15,19,48,54,52]; (2) adiabatic melting at the plate margin in the process of lithosphere extension and ocean opening [7,64]; (3) the activity of an anomalous thermal plume beneath the West African Craton, which controlled magmatism and breakup of the continent [12,17,33,42,50,63]. This plum was defined as the Central Atlantic plume [12,50].…”

“…The viewpoint of Pegram [51] and other authors [11,12,42] who connect magmas enrichment with melting of the ancient subcontinental lithospheric mantle under thermal effect of plume is the best grounded for the comprehension of the source of tholeiite dikes in the eastern United States and their analogs at the African margin. 2 The enrichment of the mantle source is presumably explained by suprasubduc tion metasomatism during creation of the Rodinia [51] or, more likely, Pangea [11] supercontinents. The model of Callegaro et al [11] suppose that the subducting upper continental upper crustal material and oceanic sediments, as well as portions of the obducted lower continental crust could have been incorporated into the lithosphere and underlying mantle wedge due to the Paleozoic continental collision.…”

“…More likely the melt was formed in the lithosphere due to its conductive heating above the mantle plume under conditions of decompression and partial melting of the metasomat ically enriched and readily fusible ancient rock com 2 In [54], this melt is explained by the heating of the mantle beneath the Pangea supercontinent. plexes at the stage of evolved rifting.…”

“…To the north, the breakup of Newfoundland and Iberia started in the Early Cretaceous; in the Labrador Sea the breakup took place in the Late Cretaceous or Paleocene; and between Greenland and Norway in the early Eocene. The latter region, pertaining to the North Atlantic Igneous Province (NAIP), is considered to be a tec tonotype of volcanic passive margins [1,2].…”