POTENTIAL CACHOEIRA DA MULADA GEOSITE: GEOLOGICAL AND CULTURAL HERITAGE IN SERRA GAÚCHA, RS, BRAZIL

The largest volcanic eruptions on Earth

Frontiers in large igneous province research

Secular variability of the thermal regimes of continental flood basalts in large igneous provinces since the Late Paleozoic: Implications for the supercontinent cycle

Flood basalts and metallogeny: The lithospheric mantle connection

Mesozoic and Cenozoic continental flood-basalt provinces, oceanic plateaus, oceanic basin flood basalts, and volcanic passive margins share geologic and geophysical characteristics that indicate an origin distinct from igneous rocks formed at mid-ocean ridges. Such characteristics of mafic large igneous provinces (LIPs) include (1) broad areal extent (>10^5 km^2) of basalts of similar age erupted over ~10^6 yr; (2) lower-crustal bodies characterized by Vp = 7.0–7.6 km·s^–1; (3) some component of intermediate and silicic volcanic rocks; (4) trace element, rare earth element, and isotopic signatures in flood basalts that are distinct from mid-oceanic-ridge basalts (MORBs); (5) thick (10s–100s of meters) individual basalt flows; and (6) long (?750 km) individual basalt flows. In addition, basaltic and gabbroic crustal sections of oceanic LIPs are two to five times thicker than those of “normal” oceanic crust, implying larger magma chambers than at typical mid-ocean ridges and, in the case of some continental flood basalts, resulting in layered intrusive complexes containing chromite. Lastly, some flood-basalt provinces are associated with kimberlites and other ultramafic volcanism. LIPs have formed, on average, every 10 m.y. since 250 Ma. However, despite the lower energy required to obduct relatively high standing oceanic LIPs in contrast to normal oceanic crust, only five obducted oceanic LIPs have been well documented in the Mesozoic and Cenozoic continental and island-arc geologic record. More ophiolite fragments may be obducted sections of volcanic passive margins and oceanic plateaus than we now suppose.

Rifts are segmented linear depressions that are filled with sedimentary and igneous rocks; they form by extension and often evolve into plate boundaries. Flood basalts, a class of large igneous provinces (LIPs), are broad regions of extensive volcanism formed by sublithospheric processes. Typical rifts are not filled with flood basalts, and typical flood basalts are not associated with significant crustal extension and faulting. North America's Midcontinent Rift (MCR) is an unusual combination, because its 3000-km length formed during a continental breakup event 1.1 Ga, but it contains an enormous volume of igneous rocks that are mostly flood basalt. We show that MCR volcanic rocks are significantly thicker than other flood basalts, due to their deposition in a narrow rift rather than across a broad region, giving the MCR a rift's geometry but a LIP's magma volume. Structural modeling of seismic-reflection data shows that LIP volcanics were deposited during two phases—an initial rift phase where flood basalts filled a fault-controlled extending basin and a postrift phase where LIP volcanics and sediments were deposited in a thermally subsiding sag basin without associated faulting. The crust thinned during the initial rifting phase and then rethickened during the postrift phase and later compression, yielding the present thicker crust observed seismologically. The restriction of extension to a single normal fault in each rift segment, steeply inward-dipping rift shoulders with sharp hinges, and persistence of volcanism after rifting ended gave rise to a deep flood basalt–filled rift geometry not observed in other presently active or ancient rifts. The unusual coincidence of a rift and LIP arose when a new rift associated with continental breakup interacted with a mantle plume or overrode anomalously hot or fertile upper mantle.

Flood basalts and large igneous provinces from deep mantle plumes: fact, fiction, and fallacy

We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide‐angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high‐quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high‐velocity structures (Vp ∼ 6.9–7.5 km/sec) are typically found immediately overlying the Moho in layers of order ∼5–15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp ∼ 7.7 km/sec) beneath the enormous Ontong‐Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hot spots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep‐crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ∼6–8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ∼15–18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as “underplating,” are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong‐Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better constraining the overall process of LIP emplacement.

Periodicities in the emplacement of large igneous provinces through the Phanerozoic: Relations to ocean chemistry and marine biodiversity evolution

High-Ti (Ti/Y) flood basalts are widely distributed in the Late Permian Emeishan large igneous province (LIP), SW China, and their spatial distribution and genetic mechanism are important to reveal the role of plume-lithosphere interactions in the LIP origin. Western Guangxi is located on the eastern edge of Emeishan LIP. To explore the genesis of the high-Ti basalt in western Guangxi and any genetic link with the Emeishan LIP, we performed whole-rock geochemical and Sr-Nd isotope and zircon U-Pb-Hf isotope analyses on the Longlin basalts from western Guangxi. The results indicate that the Longlin basalt from Tongdeng area has relatively high SiO2 but low MgO and TFe2O3 contents. The rocks have zircon εHf(t) = −0.42 to 6.41, whole-rock (87Sr/86Sr)i = 0.707167–0.707345, and εNd(t) = −2.5 to −2.14. In contrast, the Longlin basalt from Zhoudong area has relatively low SiO2 but high MgO and TFe2O3 contents. The rocks have whole-rock (87Sr/86Sr)i = 0.706181–0.706191 and εNd(t) = −0.57 to 0.69. Four Longlin basalt samples display LREE enrichments and HREE depletions, and with indistinct δEu and δCe anomalies. LA-ICP-MS zircon U-Pb dating on three Longlin basalt samples (from different localities) yielded consistent weighted average age of 257.9 ± 2.6 Ma (MSWD = 0.55), 259.5 ± 0.75 Ma (MSWD = 3.0), and 256.7 ± 2.0 Ma (MSWD = 0.68), indicating a Late Permian emplacement. Considering the similar age and geochemical features between the Longlin basalt and Emeishan flood basalts, we interpret that the former is spatially, and temporally associated with the Emeishan LIP. Geochemical features show that the high-Ti basalts in western Guangxi resemble Deccan-type continental flood basalts (CFBs), which were derived by decompression melting of the mantle plume. Combined with previous geochemical studies, we suggest that the difference in Ti content and Ti/Y ratio in CFBs are related to the depth and melting degree of mantle source, in which high-Ti features may have been linked to low degree of partial melting in the deep mantle.

‘Large Igneous Provinces (LIPs)’: Definition, recommended terminology, and a hierarchical classification

Formation of continental flood volcanism — The perspective of setting of melting

Reconciling the Conservation of Cultural Heritage with Rural Development

Contemporaneous mass extinctions, continental flood basalts, and ‘impact signals’: are mantle plume-induced lithospheric gas explosions the causal link?

A historical approach to continental flood basalt volcanism: insights into pre-volcanic rifting, sedimentation, and early alkaline magmatism