Melting of subduction modified mantle and continental crustal assimilation recorded by end-Triassic tholeiites from southern Eastern North America
Abstract
The driving processes responsible for producing the Central Atlantic Magmatic Province (CAMP), the Large Igneous Province (LIP) associated with end-Triassic rifting of Pangea, remain largely debated. In particular, the geochemical signature and geodynamic origin of the voluminous tholeiitic magmas have been contested. Here we present new 176Hf/177Hf isotope measurements for southern Eastern North America (ENA) CAMP basalts and diabases, which seem to record a notably localized petrogenetic history. Tholeiites from southern ENA span a particularly diverse range of geochemical compositions within the CAMP series and thus have been a key focus area for identifying possible CAMP magma origins. ɛHf ratios for ENA CAMP, corrected to an emplacement age of 201 Ma, range from -7.85 to +5.86 and mostly lie along a trend that is shallower than the terrestrial array on a ɛHf vs. ɛNd diagram.
Comparison of our 176Hf/177Hf results to other isotope ratios and trace element data rule out a number of petrogenetic scenarios for the origins of southern ENA CAMP, particularly mixing of partial melts from a variety of isotopic reservoirs, including depleted MORB mantle (DMM), enriched mantle reservoirs (EM-1 and EM-2), recycled continental crustal rocks, and subducted terrigenous sediments. In contrast, partial melting of depleted mantle peridotite metasomatized by subduction-derived fluids can reasonably explain the parental magma composition for southern ENA. Such metasomatism likely occurred during Paleozoic subduction around Pangea and may have been dominated by sediment-derived aqueous fluid reactions in the mantle underlying the southern ENA region. Following generation of these parent magmas, the observed 176Hf/177Hf vs. 143Nd/144Nd data array could be explained by subsequent assimilation of lower continental crust with relatively low ɛNd, high Lu/Hf for a given Sm/Nd leading to comparatively radiogenic ɛHf, and low Pb isotope ratios. This proposed melting and assimilation scenario does not specifically support or preclude a mantle plume origin for the CAMP LIP, but instead shows that distinct local mantle sources and crustal assimilation can play a significant role in controlling the erupted magma compositions, making identification and characterization of a plume source difficult.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V31C0111E
- Keywords:
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- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY;
- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism;
- TECTONOPHYSICS;
- 8408 Volcano/climate interactions;
- VOLCANOLOGY