Eocene volcanism

Eocene volcanism
Name	Eocene volcanism
Period	Eocene
Time start	56 Ma
Time end	33.9 Ma
Primary locations	Global
Notable provinces	North Atlantic Igneous Province, Columbia River Basalt Group, Deccan (note: later), Basin and Range (related)

Eocene volcanism Eocene volcanism produced widespread magmatism that reshaped continents, ocean basins, and climates during the Paleogene. Key episodes occurred across North America, Europe, Asia, and Africa and interacted with plate reorganizations involving the Iapetus Ocean successor systems, the opening of the North Atlantic Ocean, and the evolution of the Pacific Plate. Eocene volcanic fields influenced sedimentation in basins tied to the Rocky Mountains, Alps, Himalaya, and Andes orogenic systems.

Overview and geologic context

Eocene magmatism coincided with major tectonic events such as the continued rifting of the North Atlantic Ocean and the collision of the Indian Plate with the Eurasian Plate; it occurred during the Paleogene epoch within the Cenozoic Era. This interval followed the end of the Cretaceous and paralleled climatic episodes like the Paleogene-Eocene Thermal Maximum aftermath and the Eocene–Oligocene transition precursory changes. Regional uplift, basin development, and volcanic stratigraphy link to episodes documented in the Williston Basin, Paris Basin, and Tarim Basin.

Global distribution and major volcanic provinces

Major provinces active in the Eocene include the North Atlantic Igneous Province, segments of the Columbia River Basalt Group chronology, high-latitude activity in the West Siberian Basin, and volcanic arcs along the western margin of North America and the western Pacific Ring of Fire such as the Aleutian Arc and the Izu-Bonin-Mariana Arc segments. Other important occurrences include magmatism in the Ethiopian Highlands region, fragmented episodes in the Carpathian Basin, and intraplate provinces in China and Kazakhstan.

Causes and tectonic settings

Eocene volcanism arose from diverse tectonic settings: continental rifting tied to the expansion of the North Atlantic Ocean, subduction-related arcs along the western margins of North America and South America, intraplate hotspot and plume activity associated with mantle upwelling as inferred for parts of the Iceland plume and Afro-Arabian Shield, and back-arc basin volcanism related to processes in the Western Pacific and Mediterranean realms. Plate reorganization events recorded at the Azores Triple Junction and plate boundary evolution near the Farallon Plate/Phoenix Plate influenced magmatic flux.

Volcanic products and eruption styles

Eocene volcanic products ranged from extensive flood basalts and tholeiitic lava sheets in provinces akin to the North Atlantic Igneous Province to calc-alkaline stratovolcanoes and andesitic deposits along arcs comparable to the Cascades precursor terranes. Pyroclastic deposits, ignimbrites, and welded tuffs intercalated with marine and continental sediments in basins such as the Baja California margin successions. Hydrothermal alteration and mineralization events produced ore deposits comparable in setting to those at Comstock Lode-style epithermal systems or porphyry clusters analogous to Chuquicamata-type occurrences.

Climatic and environmental impacts

Large-volume eruptions and flood basalt outpourings affected atmospheric chemistry, with sulfur and carbon dioxide emissions comparable in process to those invoked for the Deccan Traps and earlier Siberian Traps events, and likely influenced Paleogene greenhouse conditions prior to the Eocene–Oligocene transition. Volcanogenic aerosols and ashfall impacted marine productivity in regions linked to the North Atlantic Ocean circulation and affected terrestrial ecosystems recorded in the fossil assemblages of the Green River Formation, Messel Pit, and Fayum Depression faunas and floras.

Evidence and dating methods

Chronology of Eocene magmatism relies on radiometric techniques such as U–Pb dating on zircon, 40Ar/39Ar dating on volcanic sanidine and biotite, and paleomagnetic stratigraphy tied to the geomagnetic polarity time scale used in studies of the North Atlantic Igneous Province and continental sections like the Columbia Plateau. Geochemical fingerprinting using isotope systems including Sr-Nd-Pb isotopes distinguishes mantle sources, while seismic tomography and mantle tomography investigations anchored by results from institutions such as the USGS and university research consortia map deep mantle anomalies.

Regional case studies and notable events

- North Atlantic: The ramp-up of magmatism associated with the early opening of the North Atlantic Ocean produced volcanic centers linked to the Iceland hotspot and flood basalts emplaced near the British Isles and Greenland. - North America: Eocene arc magmatism affected the Cordilleran orogeny with volcanic fields in the Rocky Mountains and the Cascadia margin; basaltic to rhyolitic centers on the Columbia Plateau record phased eruptions. - Eurasia: Volcanic episodes in the West Siberian Plain and Central Asian basins interacted with basin evolution in the Tarim Basin and the Ural orogen hinterland. - Africa and Arabia: Highland volcanism in the Ethiopian Plateau and the Afar Depression relates to plume-rift interaction contemporaneous with Red Sea rifting near the Gulf of Aden.

Category:Volcanism