Plume Generation Zones Research Articles

An Absolute Paleogeographic Positioning of the Early Permian Tarim Large Igneous Province

AbstractThis paper presents a quantitative characterization of the early Permian latitude and longitude of the Tarim block and its relationship to the supercontinent Pangea using a combination of newly acquired paleomagnetic data and inferences drawn from the plume generation zone reconstruction method. Early Permian magmatic rocks from Tarim have previously been interpreted as constituents of a large igneous province (LIP) and were therefore possibly derived from a mantle plume originating at the core‐mantle boundary. Here, we present the results of a paleomagnetic investigation of early Permian rocks (~288 Ma) in the Keping area of northwestern Tarim. A stable high‐temperature component (HTC) was isolated from 413 samples from 51 sites. The directions of this HTC pass the fold test and are of exclusively reversed polarity, which is consistent with their acquisition during the late Carboniferous to mid‐Permian Kiaman Reverse Polarity Superchron, suggesting that the HTC is likely primary. From these results, we compute a new early Permian pole for Tarim: 50.1°N, 170.5°E, A95 = 3.6°. Taking the estimated eruption center of the Tarim LIP (41°N, 80°E) as a reference point, this pole restores the LIP to a paleolatitude of ~30° at 288 Ma. Given this paleolatitude estimate, we attempt to fit the LIP to the edge of one of the large low shear velocity provinces in the lowermost mantle. It is not feasible to reconstruct the Tarim LIP directly above the margins of either the African or Pacific large low shear velocity provinces, but its reconstructed position could potentially be associated with the “Perm” anomaly.

Comment on Beronaguirre, Puelles, Ábalos, Gil Ibarguchi, García de Madinabeitia: short-duration regional metamorphic event recorded in a Variscan subduction channel (Malpica–Tui eclogites, NW Iberia). International Journal of Earth Sciences (2019) 108:2037–2046

Beranoaguirre et al. (Int J Earth Sci 108:2037–2046, 2019) have added a valuable piece of information to the Carboniferous tectono-thermal record of Europe by documenting a short-term pulse of heating in high-pressure metamorphic rocks of the NW-Iberian allochthons (c. 350 Ma, Malpica–Tui unit). They correctly state that the short duration of the thermal event is untypical of orogenic subduction/collision processes, but still envisage short-time heating within the subduction channel. The present comment is intended to point out that short-term thermal events of similar age are widespread in Europe and are part of a polyphase metamorphic history controlled by episodic heating from the mantle, probably over the plume-generation zone TUZO.

The Caribbean and Farallon Plates Connected: Constraints From Stratigraphy and Paleomagnetism of the Nicoya Peninsula, Costa Rica

AbstractPlate kinematic reconstructions play an essential role in our understanding of global geodynamics, but become increasingly difficult to constrain back in geological time due to the subduction of oceanic lithosphere. Here, we attempt to kinematically reconstruct the Cretaceous and older plate tectonic history of the Caribbean Plate within the Mesozoic Panthalassa (paleo‐Pacific) Ocean. To this end, we present new paleomagnetic data from Jurassic and Cretaceous oceanic sedimentary and volcanic Large Igneous Province‐related rocks of the Nicoya Peninsula and Murciélago Islands of northwestern Costa Rica. We use these data, in combination with constraints from marine magnetic anomalies to infer the age of the lithospheric basement, seismic tomography to locate deep‐mantle plume generation zones, and general kinematic feasibility, to test different reconstruction scenarios connecting the Caribbean Plate to the Farallon Plate as restored from Pacific spreading records. Our resulting reconstruction implies that the western Caribbean subduction zone initiated around 100 Ma, in an intraoceanic setting, breaking up oceanic lithosphere of at least 70 Myr old.

A Mantle Plume Origin for the Scandinavian Dyke Complex: A “Piercing Point” for 615 Ma Plate Reconstruction of Baltica?

AbstractThe origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than ca. 320 million years (pre‐Pangea) are contentious research problems. Here we study the petrology of a 615–590 Ma dolerite dyke complex that intruded rift basins of the magma‐rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Caledonian Wilson Cycle. The >1,000‐km‐long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75–250 °C above ambient mantle. Although the trace element modelling solutions are nonunique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present‐day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear‐wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi‐stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.

Earth history: A journey in time and space from base to top

The invention of a robust and accurate sea-going chronometer transformed navigation in the mid-eighteenth century. The calibration of longitude against the prime meridian at Greenwich, in combination with latitude derived from the positions of celestial bodies gave mariners for the first time confidence that they could calculate their position on the Earth's surface. Until recently, Earth scientists have been in a comparable position of having no way of calculating the longitudes of continents before the Cretaceous. Here I discuss Phanerozoic polar wander and paleogeographies and describe ways of quantitatively establishing ancient longitudes which also establish how the Earth's interior can be linked to its surface in geological time. The first method makes use of the fact that longitudinal uncertainty of continents that were assembled in Pangea can, for subsequent times, be eliminated, if longitude motion is known for only one of these continents. The best assumption is zero-longitude motion for Africa and with this assumption we can show that large igneous provinces (LIPs) and kimberlites almost exclusively erupted above the margins of TUZO and JASON in the lower mantle. This remarkable observation, also considering the effect of true polar wander, has led to a second method the plume generation zone reconstruction method unlocking a way forward in modelling absolute plate motions before Pangea and exploring links between plate tectonics, intra-plate volcanism and Deep Earth dynamics. Conceptually, that link can be viewed as a simple mass-balance: subducted lithosphere slabs restore mass to the mantle and trigger the return flow toward the surface including mantle plumes rising from the margins of TUZO and JASON. The surface manifestations of plumes are hotspot lavas, kimberlites and LIPs.

The integration of palaeomagnetism, the geological record and mantle tomography in the location of ancient continents

AbstractConstructing palaeogeographical maps is best achieved through the integration of data from hotspotting (since the Cretaceous), palaeomagnetism (including ocean-floor magnetic anomalies since the Jurassic), and the analysis of fossils and identification of their faunal and floral provinces; as well as a host of other geological information, not least the characters of the rocks themselves. Recently developed techniques now also allow us to determine more objectively the palaeolongitude of continents from the time of Pangaea onwards, which palaeomagnetism alone does not reveal. This together with new methods to estimate true polar wander have led to hybrid mantle plate motion frames that demonstrate that TUZO and JASON, two antipodal thermochemical piles in the deep mantle, have been stable for at least 300 Ma, and where deep plumes sourcing large igneous provinces and kimberlites are mostly derived from their margins. This remarkable observation has led to the plume generation zone reconstruction method which exploits the fundamental link between surface and deep mantle processes to allow determination of palaeolongitudes, unlocking a way forward in modelling absolute plate motions prior to the assembly of Pangaea. The plume generation zone method is a novel way to derive ‘absolute’ plate motions in a mantle reference frame before Pangaea, but the technique assumes that the margins of TUZO and JASON did not move much and that Earth was a degree-2 planet, as today.

The nature of the Palaeozoic oceanic basin at the southwestern margin of Gondwana and implications for the origin of the Chilenia terrane (Pichilemu region, central Chile)

The Coastal Accretionary Complex of central Chile constitutes the product of early Carboniferous to Late Triassic subduction at the rear of Chilenia, a continental terrane likely derived from Laurentia and accreted to southwestern margin of Gondwana during the Mid to Late Devonian. The complex contains basaltic metavolcanic sequences of the subducted oceanic lithosphere accreted to the active margin. In this paper, we address the tectonic setting of these rocks by means of a geochemical study in the coastal area of Pichilemu region, central Chile. The accreted fragments of oceanic crust occupy different structural levels, exhibit variable metamorphic grade, and have geochemical fingerprints that reveal a compositional heterogeneity of the subducted oceanic crust. The amphibolites have N to E-MORB compositions. Greenschist units include N-MORB and E-MORB transitional to OIB, and blueschists and greenschists interleaved within a single metavolcanosedimentary sequence have OIB signatures. Neodymium isotopic systematics indicate depleted and enriched mantle sources, whereas strontium isotopic systematics indicate seawater/rock interaction. The variety of rocks suggests formation in an oceanic setting characterized by shallow and deep mantle sources, such as plume-influenced ridge. Based on the geological, petrological, geochemical, and isotopic characteristics, we propose that the metavolcanic protoliths of the Pichilemu region formed relatively close to the western margin of the Chilenia terrane during the initial stage (late Cambrian–Early Devonian) of seafloor development and drifting of this continental block. Geochemical similarities with oceanic units accreted to the active margin south of the Pichilemu region indicate a regional pattern of the oceanic crust subducted under the Palaeozoic Chilean margin between, at least, 34°S and 39°S latitude, strongly supporting the activity of a mantle plume. This, in turn, can be correlated with the location of the Pacific plume generation zone in early Palaeozoic era, corroborating a Laurentian origin for the Chilenia terrane.

Thermochemical piles in the lowermost mantle and their evolution

Two Large Low Shear-wave Velocity Provinces (LLSVPs) lie beneath Southern Africa and Southern Pacific Ocean. These LLSVPs may be thermochemical in origin. Studying the dynamic evolution of these thermochemical piles will help us understand the earth’s present structure and history. We investigate the entrainment and evolution of an initially isolated high viscosity thermochemical pile in detail. The entrainment rate of the dense pile increases with time until it being totally entrained. The pile’s survival time does not monotonically varies with its viscosity. The chemical pile obstructs the horizontal flow along CMB and turns it into upwelling flow. This may help explain the observation of plume generation zones. The morphology and location of the dense pile oscillate with time. A high viscosity pile can keep its location and morphology roughly unchanged for hundreds of millions years if the convective structure in the surrounding mantle keeps steady.

Plate Tectonics, the Wilson Cycle, and Mantle Plumes: Geodynamics from the Top

By 1968, J. Tuzo Wilson had identified three basic elements of geodynamics: plate tectonics, mantle plumes of deep origin, and the Wilson Cycle of ocean opening and closing, which provides evidence of plate tectonic behavior in times before quantifiable plate rotations. My pre-1968 experience disposed me to try to play a part in testing these ideas. Most recently, with colleagues, I have been able to show that deep-seated plumes of the past ∼5.5 × 108 years have risen only from narrow plume generation zones (PGZs) at the core-mantle boundary (CMB) mostly on the edges of two Large Low Shear wave Velocity Provinces (LLSVPs) that have been stable, antipodal, and equatorial in their present positions for hundreds of millions of years and perhaps much longer. A need now is to develop an understanding of Earth that embodies plate tectonics, deeply subducted slabs, and stable LLSVPs with plumes that rise from PGZs on the CMB.

Palaeoposition of the Seychelles microcontinent in relation to the Deccan Traps and the Plume Generation Zone in Late Cretaceous-Early Palaeogene time

Abstract The Early Palaeogene magmatic rocks of North and Silhouette Islands in the Seychelles contain clues to the Cenozoic geodynamic puzzle of the Indian Ocean, but have so far lacked precise geochronological data and palaeomagnetic constraints. New 40 Ar/ 39 Ar and U–Pb dates demonstrate that these rocks were emplaced during magnetochron C28n; however, 40 Ar/ 39 Ar and palaeomagnetic data from Silhouette indicate that this complex experienced a protracted period of cooling. The Seychelles palaeomagnetic pole (57.55°S and 114.22°E; A9512.3°, N =14) corresponds to poles of similar ages from the Deccan Traps after being corrected for a clockwise rotation of 29.4°±12.9°. This implies that Seychelles acted as an independent microplate between the Indian and African plates during and possibly after C27r time, confirming recent results based on kinematic studies. Our reconstruction confirms that the eruption of the Deccan Traps, which affected both India and the Seychelles and triggered continental break-up, can be linked to the present active Reunion hotspot, which is being sourced as a deep plume from the Plume Generation Zone. Supplementary material: Experimental data are available at http://www.geolsoc.org.uk/SUP18482 .

The North Atlantic Igneous Province reconstructed and its relation to the Plume Generation Zone: the Antrim Lava Group revisited

SUMMARY Large igneous provinces (LIPs) have recently been suggested to originate at the edges of low-velocity zones on the core mantle boundary (Plume Generation Zones). If true, LIPs can potentially be used to constrain paleolongitude in plate tectonic reconstructions. To validate the hypothesis, it is essential to study LIPs of which the paleolongitude can be constrained by other methods, such as hotspot reference frames. An ideal candidate to this end is the early Cenozoic North Atlantic Igneous Province (NAIP). Despite being the largest volcanic unit of the British Tertiary Igneous Province (BTIP, part of the NAIP), the age and paleoposition of the Antrim Lava Group (ALG) in Northern Ireland, which is key to the NAIP as a whole, was hitherto poorly constrained. In this paper, we therefore present an integrated high-resolution paleomagnetic and geochronological study. The ALG is divided into three formations: the Lower Basalt Formation (LBF), Interbasaltic Formation (IBF) and the Upper Basalt Formation (UBF). The IBF is mostly lateritic and encloses the Tardree rhyolite. We offer new age constraints from all three formations using the 40 Ar/ 39 Ar method and propose that 62.6 ± 0.3, 61.3 ± 0.3 and 59.6 ± 0.3 Ma (1σ , internal uncertainties) are sound estimates of the age of emplacement of the LBF, Tardree rhyolite (IBF) and UBF, respectively. This constrains the nominal duration of emplacement of the ALG to 3 ± 0.6 Ma (1σ ). This reevaluation of the magnetic signature in the ALG revealed reverse polarity remanence in all three formations and an overall paleomagnetic north pole at latitude 78.9 ◦ N, longitude 167 ◦ E( A95= 6.3; age ∼61 Ma) in the European reference system. This appears consistent with paleomagnetic poles from the rest of the NAIP; both in Europe and Greenland, as well as predictions from modern apparent polar wander paths. The new radiometric ages span magnetochron C26r, C27n and C27r. The normal polarity chron C27n most probably occurred during the IBF hiatus, explaining why no normal polarity remanence was detected in the paleomagnetic investigation. Emplacement of the LBF falls in magnetochron C27r, making this one of the oldest lava sequence in the NAIP; older than the C27n lava pile in Western Greenland. The 60 Ma position of the NAIP in a paleomagnetic reference frame, puts it close to the northern edge of the African large low shear wave velocity anomaly at the core–mantle boundary and therefore in the line with the Plume Generation Zone hypothesis. However, the back-projected Icelandic hotspot, normally considered to have formed the NAIP, is located ∼1500 km north of the latitude at which the NAIP erupted. The northward motion of the north Atlantic lithosphere since the late Cretaceous challenging the existing correlation of the NAIP to the Icelandic hotspot, normally used to explain the observed pre- and syn-breakup North Atlantic magmatism (63–55 Ma), and either an additional plume located further south in the North Atlantic may be invoked to create the NAIP, or the Icelandic hotspot must have

Plume Generation Zones at the margins of Large Low Shear Velocity Provinces on the core–mantle boundary

Large Igneous Province (LIP) eruption sites of the past 300 My lie vertically above 1% slow shear wave velocity ( V s) contours bounding the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) at the core–mantle boundary (CMB), or in the cases of the Siberian and Columbia River LIPs, bounding one or other of two smaller, Low Shear Velocity Provinces (LSVPs). Steep gradients in V s at the CMB coincide with those 1% slow contours. The sites of 24 active hotspot volcanoes project down to the same narrowly defined borders of the LLSVPs at the CMB. Plumes that have generated LIPs and major hotspot volcanoes have risen only from the immediate neighbourhoods of the 1% slow V s contours at the CMB which thus define Plume Generation Zones (PGZs). PGZs projected vertically upward approximately match the + 10 m elevation contour of the geoid showing that the LLSVPs are a dominant control on the positively elevated geoid. Minima in the frequency distribution of shear wave velocities in the lowermost mantle near V s = − 1% indicate that regions with more negative velocities, forming ∼ 2% of total mantle mass, are likely to be of material compositionally different from the rest of the mantle. Because all LIP eruption sites with ages younger than 300 Ma lie above the borders of LLSVPs or LSVPs at the CMB, PGZ footprints are inferred to have remained in the same places for the past 300 My. Because no plumes have risen from the interior of the LLSVPs and because no lithospheric slabs have penetrated those bodies the volumes of the LLSVPs are inferred to have also remained unchanged for the past 300 My. Because the LLSVPs are the dominant control on the positively elevated areas of the geoid those too must have remained as they now are since 300 Ma. The LLSVPs are not rising buoyant objects but stable features of the deep mantle. LIPs have been erupted throughout the past 2.5 Gy indicating that PGZs comparable to those of the past 0.3 Gy and LLSVPs (of which PGZs mark the margins at the CMB) have also existed for at least that long. LLSVPs could thus form the isolated reservoir invoked by some to explain the distinctive isotopic compositions of terrestrial rocks. PGZs lie at places where the boundaries of: (i) The outer core, (ii) one of the LLSVPs or LSVPs, and (iii) the seismically faster part of the deep mantle meet. Horizontal temperature gradients across the steeply inclined margins to the LLSVPs, the interiors of which are hotter than the surrounding mantle, at the CMB are key controls for the generation of plumes. Near the CMB the association of the high temperature of the outer core with an inclined thermal boundary layer at the margins of LLSVPs facilitates the generation of mantle plumes in the PGZs.