Oceanic Large Igneous Provinces Research Articles

Geochemistry of Cretaceous volcaniclastic sediments in the Nauru and East Mariana basins provides insights into the mantle sources of giant oceanic plateaus

Abstract Cretaceous volcaniclastic sediments sampled at the Nauru and East Mariana basins were chemically and isotopically analysed in order to learn more about the formation and mantle source of the Ontong Java Plateau, an oceanic large igneous province. Despite their variably altered state, the volcanogenic sedimentary components still contain petrogenetic tracers (e.g. high field strength elements, and Nd- and Pb-isotopes) that can be used to constrain the composition of their respective mantle sources. The Nauru volcaniclastics have incompatible trace-element and Nd- and Pb-isotope compositions typical of the Kwaimbaita-type tholeiitic lavas of the Ontong Java Plateau. Combined with the results of recent investigations, the presence of Kwaimbaita-type volcaniclastics in the Nauru Basin reinforces the proposal that the Kwaimbaita-type lavas comprise the bulk of the giant plateau. On the other hand, the East Mariana volcaniclastics have high incompatible trace-element concentrations and Nd- and Pb-isotope ratios typical of alkalic ocean island basalts. Their source is either the Limalok Guyot in the Ratak seamount chain of the Marshall-Gilbert Islands or the ancestral Manihiki-Hikurangi Plateau. Other geological data argue for the Manihiki-Hikurangi Plateau as the source. This implies that the mid-Cretaceous Pacific upper mantle was dominated by the sources of lavas that formed giant oceanic plateaus.

Numerical modelling of a mantle plume: the plume head–lithosphere interaction in the formation of an oceanic large igneous province

The thermomechanical processes associated with formation of large igneous provinces (LIPs) remain poorly understood owing to fundamental difficulties in simulating plume–lithosphere interactions in current numerical models. These models, which aim to simulate the rise of mantle plume and the spread of plume head material, imply a mechanically over-simplified lithosphere and, commonly, a flat lithosphere (zero vertical displacement) as the upper boundary condition. We propose a new numerical model, derived from lithospheric-scale models. It has a high numerical resolution in the lithospheric domain and explicitly accounts for: (1) free upper surface boundary condition, (2) elastic–plastic–ductile lithospheric rheology, including surface faulting, and (3) vertical strength variations in the lithosphere. We study the final stages of plume ascent and we focus on surface and lithospheric evolution and intra-plate strain localisations. The experiments predict that the first surface elevation occurs in less than 0.2 Ma after plume initiation at 400 km depth. Variation of rheological parameters results in different surface elevations (500–2500 m), ascent (2–10 m/yr) and base plate strain rates (10 −12–10 −15 s −1). Fast (0.2–0.3 m/yr) plume head flattening starts at the moment when the plume head reaches the base of the lithosphere. It leads to large-scale extension and deep normal faulting at the centre of the plateau, and to strong thermomechanical erosion at its base. The erosion is maximal not under the plume centre (as was predicted before), but in two large bordering zones. Our study locally is the igneous province of the Caribbean plate where the pre-existing (Farallon) lithosphere has been affected by the Galapagos hotspot activity that generated thermal perturbations and crustal thickening with two main episodes of volcanism and underplating.

Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial

Large igneous provinces (LIPs) are constructed when Two objectives of ODP Leg 183 were to sample the copious amounts of mantle-derived magma enter the submarine LIP in as many locations as possible to: (1) Earth’s crust in localized regions. Although the Kerguelen determine the temporal variation in magma production; Plateau and Broken Ridge are now submarine, they (2) constrain the origin and evolution of the volcanic formed as a contiguous, largely subaerial LIP during rocks forming the LIP. Studies of igneous basement Cretaceous time in the eastern Indian Ocean. Subrecovered during Leg 183 complement continuing studies sequently, they were separated by sea-floor spreading of the Cenozoic subaerial lavas that form the Kerguelen beginning in Middle Eocene time along the Southeast Archipelago. This volume includes a collection of papers Indian Ridge (SEIR; Fig. 1). The Kerguelen Archipelago that address these objectives by using data for lavas is a Cenozoic feature constructed on the Northern Kerforming the Kerguelen Plateau, Broken Ridge and Kerguelen Plateau (NKP; Fig. 1). Together with the guelen Archipelago. >82–38 Ma hotspot track formed by the Ninetyeast High-quality radiometric age determinations are critRidge, the Kerguelen Plateau, Broken Ridge and Kerical for understanding rates of LIP formation, their causguelen Archipelago represent >119 Myr of volcanism ative dynamic mantle processes, and their temporal that has been attributed to the Kerguelen mantle plume. relationships to potentially related environmental Although the igneous basement of the Kerguelen Plateau changes. Duncan employs the Ar/Ar technique to had been sampled at Sites 738, 747, 749 and 750 (Fig. determine ages at all of the ODP Leg 183 igneous 1) by Ocean Drilling Program (ODP) Legs 119 and 120, basement drill sites (Fig. 1). In general, ages young Leg 183 was the first leg dedicated to understanding the northwards on the Kerguelen Plateau, from >119 Ma origin and evolution of an oceanic LIP. Five sites (1136, at Site 1136 in the south to >34 Ma at Site 1140 in the 1137, 1138, 1139, 1140) penetrated igneous basement north. Emplacement of the conjugate Central Kerguelen of the Kerguelen Plateau, and at two sites (1141, 1142) Plateau (CKP) and Broken Ridge falls within an >5 Myr the first basement samples were obtained from Broken Ridge (Fig. 1). window from >100 to >95 Ma. An unanticipated result

Maximum size and distribution in time and space of mantle plumes: evidence from large igneous provinces

Our recently published database of 304 possible large igneous provinces (LIPs) extending back to 3.8 Ga is used to explore the maximum size and distribution in time and space of large mantle plume heads. Maximum plume head size has been estimated using various techniques for two of the largest continental LIPs, the 1.27 Ga Mackenzie, and 0.20 Ga CAMP events, as well as two of the largest oceanic LIPs, Ontong Java and Manihiki. Each is consistent with an underlying flattened plume head radius of about 1000 km, a value considered normal for a plume rising from the deep mantle, and suggesting that even plumes associated with major mantle upwellings are normal size. The LIP record is semi-continuous back to at least 3.0 Ga, and there is no obvious periodicity, indicating that plume activity is probably not cyclic. Apparent increases in plume activity between 0.15 Ga and present, and perhaps, between 2.8 and 2.7 Ga, can be explained by increased preservation of oceanic LIPs. Clusters of plumes in time and space are common in the LIP record. At 6 times since 1.3 Ga, multiple LIPs whose ages span 10 Myr or less are linked to more than one plume centre. At an additional 37 times since 3.0 Ga, LIPs are found on more than one continental block and may represent multiple plumes. However, better-constrained continental reconstructions are required in order to determine which of these are due to a single plume and which require more than one plume. Some synchronous plume centers are clustered regionally suggesting a common mantle perturbation at depth while others are widely separated and, if genetically linked, would imply a global core–mantle event. In addition, some regional clusters of LIPs show a range in age greater than 10 Myr. However, in most such cases it is unknown whether these represent linked events or whether they are random associations in a dense age spectrum of LIPs.

Prolonged Magmatic and Tectonic Development of the Caribbean Igneous Province Revealed by a Diving Submersible Survey

Using the diving submersible survey NAUTICA we investigated the central part of the Caribbean large igneous province (CLIP) to observe and sample internal portions of this proposed oceanic plateau. Most of the samples are gabbroic and doleritic rocks; basalts are scarce. Radiometric dating by 40Ar/39Ar incremental heating experiments indicate that the intrusive rocks are Campanian in age (81–75 Ma). In some places these intrusive rocks underlie older Santonian (85–83 Ma) extrusive basaltic rocks, suggesting that the Campanian rocks represent a sill injection and an underplating episode. Results of the diving program supplemented by information from ODP and DSDP drilling sites document a 20 m.y. period (94–75 Ma) of igneous activity in the submerged portion of the Caribbean large igneous province (CLIP). In the northern part of the Beata Ridge late Campanian and/or post Campanian uplift is documented by prominent Maastrichtian (71–65 Ma) erosion and the establishment of a Paleocene-middle Eocene (65–49 Ma) carbonate platform. During and after the uplift an extensional period is indicated by seismic images and the subsidence (3 km depth) of the carbonate platform. Paleocene ages (55–56 Ma) determined on some volcanic samples are attributed to localised decompression mantle melting that accompanied the extension. We document a prolonged period of magmatic and tectonic events that do not fit with the current models of short-lived plateau formation during mantle plume initiation but shares many similarities with the constructional histories of other oceanic large igneous provinces.

Geophysical response of flood basalts from analysis of wire line logs: Ocean Drilling Program Site 642, Vøring volcanic margin

Analysis of wire line logs at Ocean Drilling Program Site 642, the deepest scientific hole yet drilled in an offshore large igneous province (LIP), reveals the main features of the extrusive complex constructed during formation of a volcanic margin. A characteristic cyclic log response images tholeiitic lavas and thin tuffs corresponding to the seaward dipping reflectors in the seismic record. Flows are 0.6–18.5 m thick, while most sediments are <l m thick. Porosity dependent sonic, density, neutron porosity and resistivity logs respond to gently decreasing porosity in upper 5–7 m of the flow and rapid porosity increase near the flow base. Velocity and density top and bottom gradients are largely independent of flow thickness, with velocity gradients of 400 to 600 s−1 and −1000 to −2000 s−1, respectively. A positive correlation between flow thickness and mean velocity simply reflects increased proportion of massive basalt in thicker flows. There is also an overall increase in mean fine‐grained basalt velocity with depth with a gradient of 0.8±0.3 s−1. Flow velocity‐density relations show a downward velocity strengthening related to a decrease in high aspect ratio voids. High velocities near the flow base correlate with high, >2000 Ω‐m, focused resistivity kicks. The large flow‐scale variations in physical properties show that representative core measurements must be densely sampled. Both on flow and sequence scales Site 642 log responses appears typical for the North Atlantic Volcanic Province and other LIPs but differs from logs in deep ocean crustal holes. Principal differences in log responses reflect mode of crustal emplacement and alteration. Hence Site 642 forms a reference hole for extrusive constructions on oceanic LIPs.