Sr, Nd, Pb and Os Isotope Systematics of CAMP Tholeiites from Eastern North America (ENA): Evidence of a Subduction-enriched Mantle Source

Abstract

The Central Atlantic Magmatic Province (CAMP) is one of the largest igneous provinces on Earth, with an areal extent exceeding 10 7 km 2 . Here we document the geochemical characteristics of CAMP basalts fromTriassic^Jurassic basins in northeastern USA and Nova Scotia (Canada). The CAMP rocks occur as lava flows, sills and dykes. All of our analysed samples show chemical characteristics typical of CAMP basalts with low titanium content, which include enrichment in the most incompatible elements and negative Nb anomalies. All the basalts also show enriched Sr^Nd^Pb initial201 Ma) isotopic compositions ( 206 Pb/ 204 Pb ini. ¼ 18•1551 8•691, 207 Pb/ 204 Pb ini. ¼ 15•616^15•668, 208 Pb/ 204 Pb ini. ¼ 38•160^38•616, 143 Nd/ 144 Nd ini. ¼ 0•512169^0•512499). On the basis of stratigraphy, rare earth element (REE) chemistry and SrN d^Pb isotope composition, three chemical groups are defined. The Hook Mountain group, with the lowest La/Yb ratios, initial 206 Pb/ 204 Pb ini. 418•5 and 143 Nd/ 144 Nd ini. 40•51238, comprises all the lastest and upper stratigraphic units. The Preakness group, with intermediate La/Yb ratios, 206 Pb/ 204 Pb ini. 418•5 and

Continental flood basalts derived from the hydrous mantle transition zone

“…This is based on water partitioning in the Earth's mantle 18 , behaviour of slab-triggered wet upwelling and upward percolation 23,40 , hydrous mantle melting 51 , the mantle wedge model 21 , and upwelling from the hydrated mantle transition zone 24 . rocks from the Siberia 9 and Karoo 7 LIPs show that crustal contamination cannot be the controlling factor. Detailed geochemical and isotopic analyses of basaltic rocks from the Siberia 9 , Karoo 7 and Central Atlantic 6 LIPs demonstrate that their generations involved water and possibly other fluid phases released from subducted slabs and that their source reservoirs were both isolated and hydrated over a considerable period of time. Because the hydration processes would result in instability of subcontinental lithospheric mantle 56 , hydrated subcontinental lithospheric mantle cannot remain isolated from the convective upper mantle.…”

“…All the samples show prominent positive spikes for Ba, K, Pb and Sr in the primitive mantle normalized diagram ( Supplementary Fig. 5), a typical characteristic of hydrated mantle melts 6,20,27,28 .…”

“…However, the chemical compositions of most CFBs are dissimilar to ocean island basalts (OIBs) 4 that are associated with hot spots-the surface expressions of mantle plumes 5 . Furthermore, although CFBs are generally several hundred kilometres from plate boundaries (subduction zones), some exhibit subduction-like geochemical signatures 4,6 . Petrological and geochemical evidence from the Karoo 7 , Etendeka 8 , Siberian 9 and Central Atlantic LIPs 6 suggests that generation of CFBs is ultimately related to fluid/melt derived from subducted slabs.…”

“…Furthermore, although CFBs are generally several hundred kilometres from plate boundaries (subduction zones), some exhibit subduction-like geochemical signatures 4,6 . Petrological and geochemical evidence from the Karoo 7 , Etendeka 8 , Siberian 9 and Central Atlantic LIPs 6 suggests that generation of CFBs is ultimately related to fluid/melt derived from subducted slabs. However, the question of how fluid is released from deep subducted oceanic slabs and effects or controls partial melting of the mantle in an intracontinental setting is unclear.…”

Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O‐ and CO2‐ Rich Fluids

“…Therefore, we selected representative samples of these two continental basalt provinces. For the CAMP, basaltic lava flows and shallow intrusions (sills) were collected in Morocco (Marzoli et al, 2004), eastern North America (Merle et al, 2014), and Portugal (Callegaro et al, 2014). The selected samples have an average grain size of 100–300 μm and a maximum grain size <2 mm.…”