Flood basalt (trap) provinces: formation, characteristics, and global significance

Characteristics and deposits

Flood basalt provinces are characterized by vast, relatively flat accumulations of basaltic rock, sometimes hundreds of metres thick and extending over hundreds of thousands to millions of square kilometres. Individual flows are typically thin and extensive, stacking to create step-like topography (the word "trap" derives from a Scandinavian word for stairs). The lava involved is mafic — rich in iron and magnesium — and its low viscosity permits it to travel long distances.

Formation and mechanisms

Scientists explain flood basalts through combinations of mantle processes. One common model invokes a mantle plume or hotspot that delivers a high heat flux from deep in the mantle, producing large volumes of basaltic melt. Continental rifting or lithospheric thinning can facilitate decompression melting and allow this melt to reach the surface. Partial melting commonly occurs in the upper mantle and asthenosphere at depths that may range from tens to a few hundred kilometres, although precise depths vary by province.

History and notable examples

Flood basalt events have punctuated Earth history and are associated with some of the planet's largest igneous provinces. Well-known continental examples include the Deccan Traps (India), the Siberian Traps (Russia) and the Columbia River Basalt Group (northwestern United States). Oceanic examples include large plateaus such as the Ontong Java Plateau. These provinces formed in different geological eras and have been studied for their timing, duration and links to other global changes.

Impacts, importance and distinctions

Flood basalt eruptions can have major environmental consequences because they release large volumes of gases — including carbon dioxide and sulfur species — and inject aerosols and particulates into the atmosphere. Some large igneous provinces are temporally associated with dramatic climate shifts and, in several cases, with mass extinction intervals; scientists view these associations cautiously, seeking evidence of timing and causal mechanisms. Geologically, flood basalts differ from stratovolcanoes and smaller basaltic shield volcanoes mainly by their scale, eruption rates, and the way lava is emplaced.

Further reading and resources

• Overview of large volcanic eruptions
• Flood basalts on ocean floors
• Basalt composition and properties
• Lava flow dynamics
• Scale and extent of igneous provinces
• Flood basalt events in Earth history
• Plateau formation and morphology
• Relationship to mountain building
• Implications for Earth's thermal history
• Continental rifting and volcanism
• Partial melting processes
• Magma generation in the mantle
• Viscosity and flow behaviour of basalt
• Why flood basalts produce plateaus, not tall cones
• Asthenosphere and melting depth
• Heat sources for large igneous provinces
• Hotspots, plumes and surface volcanism