Deccan Traps

Deccan Traps. The Deccan Traps constitute one of the largest volcanic features on Earth, a vast province of flood basalt covering much of west-central India. This immense large igneous province formed from a series of extraordinarily voluminous eruptions during the transition from the Mesozoic to the Cenozoic era. Its formation is a pivotal event in Earth science, closely studied for its potential role in a major mass extinction and its profound influence on the geology of India.

Formation and geology

The formation of this province is attributed to a deep-seated mantle plume originating near the core–mantle boundary, often associated with the present-day Réunion hotspot. As the Indian Plate moved northward over this stationary plume during the Late Cretaceous, it generated massive quantities of mafic magma. This low-viscosity magma erupted through long fissures, producing extensive, fluid lava flows rather than tall stratovolcanoes. The primary rock type is tholeiitic basalt, characterized by minerals like plagioclase, clinopyroxene, and titanomagnetite. The sequence reveals thousands of individual flows, with intertrappean beds of sedimentary rock preserving crucial fossil evidence. Key geological studies of the province have been conducted by institutions like the Geological Survey of India and researchers at the Indian Institute of Technology Bombay.

Extent and structure

Originally covering an estimated area of 1.5 million square kilometers, the lava flows once spanned a region larger than modern-day France, Germany, and the United Kingdom combined. The main outcrop occupies the Deccan Plateau, with its thickest sequences, over 2,000 meters, found in the Western Ghats near cities like Mumbai and Pune. The structure is a large, gently dipping plateau, with escarpments like the Sahyadri range marking its eroded western edge. Significant sections are also present in regions such as Madhya Pradesh, Gujarat, and Maharashtra. Over millions of years, erosion has created distinctive mesa and butte landscapes, while the remaining basalt layers form major watersheds for rivers like the Godavari and the Krishna.

Age and duration

Precise dating using argon–argon dating and uranium–lead dating techniques has constrained the main eruptive phase to a window centered on the Cretaceous–Paleogene boundary, approximately 66 million years ago. The bulk of the eruptions occurred over a relatively short, intense period of less than one million years, with some models suggesting a peak pulse lasting only about 750,000 years. This timing places the most voluminous phase coincident with the Cretaceous–Paleogene extinction event. Earlier studies, including work by Walter Alvarez, helped establish this chronological link. The rapidity of this volcanism represents one of the most significant geologically instantaneous events in Phanerozoic history.

Connection to the Cretaceous–Paleogene extinction event

The temporal coincidence between the peak eruptions and the mass extinction that ended the reign of non-avian dinosaurs has led to extensive scientific debate. The eruptions would have released enormous volumes of volcanic gas, including sulfur dioxide and carbon dioxide, potentially triggering severe global warming followed by volcanic winter. This could have caused widespread ocean acidification and disrupted ecosystems globally. The debate often contrasts this volcanic hypothesis with the Alvarez hypothesis, which posits an asteroid impact at the Chicxulub crater as the primary cause. Many contemporary researchers, including teams from the University of California, Berkeley, support a scenario where both the Chicxulub impactor and Deccan volcanism acted in concert to create a catastrophic "double-punch" for Cretaceous life.

Flora and fossil record

The sedimentary layers sandwiched between lava flows, known as intertrappean beds, provide a remarkable snapshot of life before, during, and after the eruptions. These beds have yielded diverse fossils, including early mammals, frogs, snakes, and dinosaur remains. Plant fossils, such as pollen and leaf impressions, indicate a shift from lush gymnosperm and angiosperm forests to more arid-adapted flora as the eruptions progressed. Key fossil sites are found near Nagpur and in the Narmada valley. This record is crucial for understanding the pattern of the mass extinction on the Indian subcontinent and is studied by paleontologists at institutions like the Birbal Sahni Institute of Palaeosciences.

Economic and cultural significance

The weathered basalt soils of the region, known as regur or black cotton soil, are highly fertile and support major agricultural regions for crops like cotton and sugarcane. The hard basalt rock is extensively quarried for construction and as road metal. Culturally, the sheer cliffs of the Western Ghats provided a setting for ancient cave complexes like the Ajanta Caves and Ellora Caves, which are UNESCO World Heritage Sites. The stepwells of Gujarat, such as the Rani ki vav, were also carved into this rock. The unique hydrology of the basalt layers supports numerous reservoirs and is vital for the water security of cities like Mumbai and Hyderabad. Category:Large igneous provinces Category:Volcanism of India Category:Cretaceous paleogeography Category:Paleogene volcanism