Late Cenozoic Intraplate Volcanism Research Articles

Subduction‐Induced Asthenospheric Flow Around the Songliao Basin in NE China Revealed by Shear Wave Splitting Measurements of Dense Seismic Arrays

AbstractThe traditional mantle plume model fails to explain late Cenozoic intraplate volcanism in Northeast China (NEC). We constrained the pattern of upper mantle deformation to study the origin of intraplate volcanism by quantifying the shear wave splitting parameters captured by three NW‐SE linear seismic arrays in NEC. The dense station spacing (10 km) allowed us to image the small‐scale variations in anisotropic structures in unprecedented detail. The WNW‐ESE oriented subduction‐parallel anisotropy is likely induced by the asthenospheric return flow in the big mantle wedge convection associated with Pacific subduction. Therein the most notable feature is a toroidal pattern of anisotropy beneath the Songliao Basin, which is distinguished by a larger splitting time (approximately 1.0 s) relative to weak anisotropy in the center. The toroidal anisotropy pattern coincides with a high‐velocity anomaly extending from uppermost mantle down to ∼300 km depth, presumably indicating early stage foundering lithosphere. The asthenospheric return flow then moved around the foundering lithosphere and induced the corresponding toroidal anisotropy. The decompression partial melting of upwelling asthenospheric materials erupted along weak zones generating late Cenozoic intraplate basalts on both flanks of the Songliao Basin. The high‐density seismic array reveals that the Pacific subduction and early stage lithospheric foundering processes controlled the genesis of late Cenozoic volcanism in NEC.

Electrical resistivity structure across the Late Cenozoic Abaga-Dalinor volcanic field, eastern China, from 3-D magnetotelluric imaging and its tectonic implications

The Abaga-Dalinor volcanic field (ADVF) in Inner Mongolia, China, located to the west of the North-South Gravity Lineament (NSGL), is the largest and less known area of Late Cenozoic intraplate volcanism in Northeast China. Knowledge of the subsurface structure beneath the ADVF will improve our understanding of its evolution process and formation mechanisms. New broadband magnetotelluric (MT) data were collected along a profile of about 300 km that crosses the major basaltic areas exposed at the surface in the ADVF and a series of east-north-east (ENE) trending faults. The electrical resistivity structure of the crust and uppermost mantle across the ADVF was generated by 3-D inversion of full impedance tensor and tipper data. This model reveals a thick high-resistivity layer (>1000 Ωm) in the upper crust that may represent the Precambrian basement and Late Paleozoic-Mesozoic granitic plutons. In contrast, high conductivity anomalies dominate the middle-lower crust. The northward-dipping high-conductivity feature at depths of 20–40 km below sea level under the Chagan Obo fault is suggested to be the involvement of the Early Paleozoic subducted oceanic crust. A remarkably high-conductivity zone (1–20 Ωm) exists in the middle-lower crust beneath the Abaga and Dalinor volcanic areas. It is explained to be a saline fluid zone of ∼0.45%–0.48% that exsolved from the partial melts as magma ascent rapidly. The impermeable upper crust traps these fluids in the middle-lower crust. A moderately high-conductivity anomaly in the uppermost mantle below near the Solonker Suture Zone (SSZ) is attributed to a minimum partial melt of ∼3–4% associated with the localized asthenospheric upwelling, which feeds the Abaga and Dalinor volcanos as a common magma source. Integrating our resistivity model with previous geophysical and geochemical studies, we suggest that intraplate volcanism in the ADVF is mainly controlled by the pre-existing tectonic weak zones. The lithosphere within the SSZ is susceptible to thermal perturbation from the upwelling mantle, providing the preconditions for melt generation. A set of ENE trending faults and an inferred NW-SE trending fault jointly dominated the vertical transport of magma and lateral extension along the faults, which may have influenced the spatial distribution of basalts and volcanic cones at the surface in the ADVF. In addition, we tend to suggest that Late Cenozoic intraplate volcanism in the ADVF could be the result of decompressing melting within the localized small-scale asthenospheric upwelling induced by the edge-driven convection near the NSGL, which is indirectly related to the westward subduction and retreat of the (Paleo-)Pacific plate during the Late Mesozoic to Cenozoic.

Ambient noise Rayleigh wave tomography across the Madagascar island

SUMMARYThe unusual complex lithospheric structure of Madagascar is a product of a number of important geological events, including: the Pan-African Orogeny, episodes of Late Cenozoic intraplate volcanism and several phases of deformation and metamorphism. Despite this rich history, its detailed crustal structure remains largely underexplored. Here, we take advantage of the recently obtained data set of the RHUM-RUM (Réunion Hotspot and Upper Mantle–Réunions Unterer Mantel) seismological experiment, in addition to previously available data sets to generate the first Rayleigh wave group velocity maps across the entire island at periods between 5 and 30 s using the ambient noise tomography technique. Prior to preliminary data preparation, data from Ocean Bottom Seismometers are cleaned of compliance and tilt noise. Cross-correlating noise records yielded over 1900 Rayleigh wave cross-correlation functions from which group velocities were measured to perform surface wave tomography. Dispersion curves extracted from group velocity tomographic maps are inverted to compute a 3-D shear velocity model of the region. Our velocity maps have shown relative improvement in imaging the three sedimentary basins in the western third of the island compared to those of previous studies. The Morondava basin southwest of the island is the broadest and contains the thickest sedimentary rocks while the Antsirinana basin at the northern tip is narrowest and thinnest. The lithosphere beneath the island is characterized by a heterogeneous crust which appears thickest at the centre but thins away towards the margins. A combined effect of uneven erosion of the crust and rifting accommodates our observations along the east coast. Average 1-D shear velocity models in six different tectonic units, support the causes of low velocity zones observed in the west coast of the island and reveal an intermediate-to-felsic Precambrian upper and middle crust consistent with findings of previous seismic studies. Our findings, especially at short periods provide new constraints on shallow crustal structure of the main island region.

Late Cenozoic intra-plate basalts of the Greater Khingan Range in NE China and Khangai Province in Central Mongolia

This paper presents new major and trace element data, Sr-Nd-Pb isotopic ratios and K-Ar ages from volcanic rocks of the Greater Khingan Range of NE China (Nuomin–Keluo and Arxan–Chaihe volcanic fields) and the Khangai volcanic province of Central Mongolia. These data are discussed in correlation with available in literature geological, geochronological, geochemical, isotopic, petrologic and geophysical data from intra-plate volcanic fields of Central and East Asia. All volcanic rocks possess geochemical affinities to intra-plate oceanic and continental basalts. The Nuomin-Keluo samples (2.75 and 0.41 Ma) show enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE; La/YbN = 43.6–91.5), as well as depletion in heavy REE (HREE), and Nb peaks relative to La and Th (Nb/Lapm = 0.61–1.24; Nb/Thpm = 0.96–1.70) in the multi-element spectra. The Arxan-Chaihe basalts (0.91 and 0.53–0.27 Ma) have lower K, less fractionated REE (La/YbN = 15.7–28.1), but higher Nb peaks (Nb/Lapm = 1.56–1.74; Nb/Thpm = 1.27–1.79), as well as higher epsilon Nd and 206Pb/204Pb, but lower Sr isotopic ratios. The Khangai volcanic province consists of central and peripheral areas, which are dominated by low–alkali and high–alkali varieties, respectively. The central Khangai have lower LREEs and LILEs, and lower Gd/YbN ratios compared to the peripheral Khangai. In the 143Nd/144Nd vs. 87Sr/86Sr diagram, the Nuomin-Keluo and Khangai samples plot close to EM1, whereas the Arxan-Chaihe samples possess less enriched compositions. In Pb isotope diagrams, the Nuomin-Keluo and peripheral Khangai samples plot between DM and EM1, whereas the Arxan-Chaihe and central Khangai samples plot near PREMA. Geochemistry-based melting modeling indicates that all the volcanic rocks were derived from garnet-bearing, probably enriched, mantle sources melted at variable degrees Based on the whole set of new and previous data we suggest that the Great Khingan and Khangai volcanic rocks were probably produced by hydrous mantle plumes generated in the MTZ and ascending from the subducted Pacific slab stored therein. In general, the late Cenozoic intra-plate volcanism in Central and East Asia can be triggered by the material, which has accumulated beneath the Asian continent and metasomatized the mantle underneath since the amalgamation of Laurasia and formation of the Central Asian Orogenic Belt at ca. 300–250 Ma.

Western US volcanism due to intruding oceanic mantle driven by ancient Farallon slabs

The origin of late Cenozoic intraplate volcanism over the western United States is debated. One important reason is the lack of a clear understanding of the mantle dynamics during this volcanic history. Here we reconstruct the mantle thermal states beneath North America since 20 million years ago using a hybrid inverse geodynamic model with data assimilation. The model simultaneously satisfies the past subduction kinematics, present mantle tomographic image and the volcanic history. We find that volcanism in both the Yellowstone volcanic province and the Basin and Range province corresponds to a similar eastward-intruding mantle derived from beneath the Pacific Ocean and driven mostly by the sinking Farallon slab below the central-eastern United States. The hot mantle that forms the Columbia River flood basalt and subsequent Yellowstone–Newberry hotspot tracks first enters the western United States through tears within the Juan de Fuca slab. Subsequent coexistence of the westward asthenospheric flow above the retreating Juan de Fuca slab and eastward-propagating mantle beyond the back-arc region reproduces the bifurcating hotspot chains. A similar but weaker heat source intrudes below the Basin and Range around the southern edge of the slab, and can explain the diffuse basaltic volcanism in this region. According to our models, the putative Yellowstone plume contributes little to the formation of the Yellowstone volcanic province. Volcanism in the western US may result from warm oceanic mantle beneath the Pacific Ocean being drawn eastwards by mantle flow induced by the sinking of Farallon slabs, according to numerical model simulations.

Late Cenozoic intraplate volcanism in Changbai volcanic field, on the border of China and North Korea: insights into deep subduction of the Pacific slab and intraplate volcanism

Late Cenozoic intraplate volcanism in the Changbai volcanic field straddles the border between China and North Korea, forming basic (alkali basalts and tholeiites) and intermediate–acidic (trachytes and peralkaline rhyolites) volcanic rocks with ages ranging from 19.9 Ma to the present. Major and trace elements and Sr–Nd–Pb isotopic compositions indicate that the basic magmas were formed by partial melting of the depleted mid-ocean ridge basalt-source mantle and contaminated by aqueous fluids with EM1-like isotopic signatures from the lower continental crust, whereas the intermediate–acidic magmas resulted from assimilation–fractional crystallization processes on the basic magmas. On the basis of petrological and geochemical studies, we propose that a magma underplating model could be used to explain the genesis of the Late Cenozoic intraplate volcanism. In this model, the mantle-derived basaltic magma was underplated at the base of the continental crust and contaminated by EM1-like aqueous fluids liberated from the lower crustal granulites. Geodynamic processes responsible for the magma underplating and subsequent eruption might be lithospheric extension and small-scale thermal upwelling, induced by episodic changes in convergence rates between the Eurasian and Pacific plates, indicating a genetic link between the intraplate volcanism and deep subduction of the Pacific slab.

Isotope geochemistry of Jeongok basalts, northernmost South Korea: Implications for the enriched mantle end-member component

South Korea separates two mantle source domains for Late Cenozoic intraplate volcanism in East Asia: depleted mid-ocean-ridge basalt (MORB) mantle-enriched mantle type 1 (DMM-EM1) in the north and DMM-EM2 in the south. We determined geochemical compositions, including Sr, Nd, Pb, and Hf isotopes for the Jeongok trachybasalts (∼0.51 to 0.15Ma K–Ar ages) from northernmost South Korea, to better constrain the origin and distribution of the enriched mantle components. The Jeongok basalts exhibit light rare earth element (LREE)-enriched patterns ([La/Yb]N=9.2–11.6). The (La/Yb)N ratios are lower than that of typical oceanic island basalt (OIB). On a primitive mantle-normalized incompatible element plot, the Jeongok samples show OIB-like enrichment in highly incompatible elements. However, they are depleted in moderately incompatible elements (e.g., La, Nd, Zr, Hf, etc.) compared with the OIB and exhibit positive anomalies in K and Pb. These anomalies are also prime characteristics of the Wudalianchi basalts, extreme EM1 end-member volcanics in northeast China. We have compared the geochemistry of the Jeongok basalts with those of available Late Cenozoic intraplate volcanic rocks from East Asia (from north to south, Wudalianchi, Mt. Baekdu and Baengnyeong for DMM-EM1, and Jeju for DMM-EM2). The mantle source for the Jeongok volcanics contains an EM1 component. The contribution of the EM1 component to East Asian volcanism increases toward the north, from Baengnyeong through Jeongok to Mt. Baekdu and finally to Wudalianchi. Modeling of trace element data suggests that the Jeongok basalts may have been generated by mixing of a Wudalianchi-like melt (EM1 end-member) and a melt that originated from a depleted mantle source, with some addition of the lithospheric mantle beneath the Jeongok area. In Nd–Hf isotope space, the most enriched EM1-component-bearing Jeongok sample shows elevation of 176Hf/177Hf at a given 143Nd/144Nd compared with OIB. Recycled pelagic sediments may explain the EM1-end-member component of northeastern Asian volcanism, possibly from the mantle transition zone.

The geochronology and origin of mantle sources for late cenozoic intraplate volcanism in the frontal part of the Arabian plate in the Karacadağ neovolcanic area of Turkey. Part 2. The results of geochemical and isotope (Sr-Nd-Pb) studies

A geochemical and isotope-geochemical (Sr-Nd-Pb) study has been carried out for the Karacadag neovolcanic area, which is situated within the frontal part of the Arabian plate. The obtained data and the results of petrological modeling show that the petrogenesis of parental magmas in the Karacadag neovolcanic area involved two compositionally different mantle sources; one consisted of garnet-bearing peridotites of the asthenosphere mantle and the other was spinel-bearing peridotites of the enriched subcontinental lithosphere mantle. During early stages in the evolution of the magmatic system, deep-seated asthenospheric magmas were ascending to the surface while intensively interacting with the melts that had been generated at upper mantle depths. The interaction gradually diminished, so that the later effusive rocks mostly have compositions that are similar to those of the primitive asthenospheric magmas. It is shown that a significant (up to 17–18 wt % of the mantle melt) assimilation of crustal material could take place only during the initial phases of the magmatism. Periodic replenishment of the magma chambers by primitive magmas, which resulted in an observable high degree of homogeneity in the composition of young effusive rocks, was also of importance in the petrogenesis of lavas during the evolution of volcanic activity.

The geochronology and origin of mantle sources for late cenozoic intraplate volcanism in the frontal part of the Arabian plate in the Karacadağ neovolcanic area of Turkey. Part 1. The results of isotope-geochronological studies

This paper considers results from isotope-geochronological (K-Ar) studies of the products of Neogene-Quaternary volcanism in the Karacadag area, which is situated within the northern frontal part of the Arabian plate. It was found that magmatic activity has been evolving at this location for at least the last 11–10 Myr and was distinctly discrete in character. Three stages of volcanism have been identified: (I) Early or Miocene, ∼11–6.7 Ma; (II) Middle or Pliocene-Early Quaternary, 4–1 Ma; and (III) Late or Late Quaternary, 0.4–0.1 Ma. The most recent manifestations of magmatic activity in the region date back to about 100000 years ago.

우리나라 상부암석권 맨틀: 페리도타이트 포획암으로부터의 고찰

우리나라 백령도, 제주도, 보은, 아산, 평택, 간성일대에는 맨틀 페리도타이트들이 알칼리 현무암류에 포획되어 온 형태로 분포하고 있다. K-Ar 전암연대측정 자료에 의하면 이들 화산암류는 약 0.1-18.9Ma에 분출하였다. 페리도타이트의 광물조합은 감람석-사방휘석-단사휘석-첨정석이며, 함수광물이나 석류석이 보고된 바는 없다. 암석의 종류는 레어조라이트에서 하즈버가이트에 걸쳐있다. 감람석은 <TEX>$Fo_{88.4-92.0}$</TEX>이고, 단사휘석은 투휘석, 사방휘석은 엔스터타이트가 풍부하며, 첨정석은 Cr이 풍부하다(Cr# = 7.8-53.6). 주성분 원소함량에 의하면 이들 페리도타이트는 부화된 중앙해령현무암 근원 맨틀로부터 대략 26%까지의 부분용융을 겪은 후에 남은 잔류물로 추정된다. 그러나 맨틀에서의 이차적인 변성교대작용의 흔적이 미량원소의 함량에 기록되어 있는 경우도 있다. 양휘석 지온계에 의하면 우리나라 페리도타이트 포획암의 평형온도는 대략 <TEX>$850-1050^{\circ}C$</TEX> 범위이다. Sr-Nd 동위원소비는 결핍된 중앙해령현무암의 근원맨틀 성분(DMM)에서부터 지구전암(BSE) 성분 값까지 넓은 범위에 걸쳐있어, 오랜 시간의 성장과 진화의 역사를 대변하고 있다. Sr-Nd-Pb 동위원소비에 의하면 우리나라 암석권 맨틀은 대개 맨틀 단성분 중 DMM과 EM2의 혼합으로 설명되며, 상부 대륙지각과 연계될 수 있는 남북 내지는 동서방향으로의 지역성을 기록하고 있지는 않다. 이는 동아시아의 신생대후기 판내부기원 현무암류들이 기록하고 있는 남북간의 이분성과는 매우 대조적인 것으로, 동아시아 연약권 맨틀의 지역성을 시사하고 있다. Os 모델연대에 기초하면 우리나라 암석권 맨틀이 연약권으로부터 분리된 시기는 약 1.8-1.9 Ga로 추정된다. Peridotite xenoliths hosted by alkali basalts from South Korea occur in Baengnyeong Island, Jeju Island, Boeun, Asan, Pyeongtaek and Ganseong areas. K-Ar whole-rock ages of the basaltic rocks range from 0.1 to 18.9 Ma. The peridotites are dominantly lherzolites and magnesian harzburgites, and the constituent minerals are Fo-rich olivine (<TEX>$Fo_{88.4-92.0}$</TEX>), En-rich orthopyroxene, Di-rich clinopyroxene, and Cr-rich spinel (Cr# = 7.8-53.6). Hydrous minerals, such as pargasite and phlogopite, or garnet have not been reported yet. The Korean peridotites are residues after variable degree of partial melting (up to 26%) and melt extraction from fertile MORB mantle. However, some samples (usually refractory harzburgites) exhibit metasomatic enrichment of the highly incompatible elements, such as LREE. Equilibration temperatures estimated using two-pyroxene geothermometry range from ca. 850 to <TEX>$1050^{\circ}C$</TEX>. Sr and Nd isotopic compositions in clinopyroxene separates from the Korean peridotites show trends between depleted MORB-like mantle (DMM) and bulk silicate earth (BSE), which can be explained by secondary metasomatic overprinting of a precursor time-integrated depleted mantle. The Korean peridotite clinopyroxenes define mixing trends between DMM and EM2 end members on Sr-Pb and Nd-Pb isotopic correlation diagrams, without any corresponding changes in the basement. This is contrary to what we observe in late Cenozoic intraplate volcanism in East Asia which shows two distinct mantle sources such as a DMM-EM1 array for NE China including Baengnyeong Island and a DMM-EM2 array for Southeast Asia including Jeju Island. This observation suggests the existence of large-scale two distinct mantle domains in the shallow asthenosphere beneath East Asia. The Re-Os model ages on Korean peridotites indicate that they have been isolated from convecting mantle between ca. 1.8 and 1.9 Ga.

Sr, Nd, Pb and Hf isotopic compositions of late Cenozoic alkali basalts in South Korea: Evidence for mixing between the two dominant asthenospheric mantle domains beneath East Asia

We have determined the Sr, Nd, Pb and Hf isotopic compositions of 13 samples from six late Cenozoic centers of basaltic volcanism in South Korea, including Baengnyeong Island, Jogokni, Ganseong, Jeju Island, Ulleung Island and Dok Island, in order to understand the nature of the mantle source and melt-generating processes. The basalts have OIB-like trace element abundance patterns, and also contain mantle-derived xenoliths of primarily spinel peridotite. Combining our new isotopic data with previously published data from areas with late Cenozoic basalts throughout East Asia shows that the mantle source has a DMM–EM1 array for northeast China and a DMM–EM2 array for Southeast Asia. The Korean Peninsula basalts we have studied are geographically located between these two broad domains, and interestingly, define an array between DMM and an intermediate end member between EM1 and EM2 on various isotopic correlation diagrams. Variations along the array on isotopic correlation diagrams are systematic regionally, with EM2 signatures predominant on Jeju Island and EM1 becoming increasingly more important toward Ulleung and Dok Islands, the Ganseong area, and Baengnyeong Island. This is without any corresponding changes in the basement and the lithospheric mantle beneath the region. These observations suggest that the Korean Peninsula late Cenozoic basalts we have studied and other East Asia late Cenozoic intraplate volcanism are sourced in the asthenospheric mantle. This mantle is characterized by two distinct, large-scale domains — one a mixture of DMM and EM1 components, and the other a mixture of DMM and EM2. Previous studies on East Asian Cenozoic volcanic rocks have advocated origins by either plume activity or decompressional melting of the mantle lithosphere in a rift environment. On the basis of our new trace element and isotopic compositions, which have OIB-like characteristics, we rule out an origin in the mantle lithosphere. Furthermore, because of the absence of typical hotspot tracks with clear age progressions, and so far, lack of unequivocal tomographic images delineating distinct, deep-seated thermal anomalies that could be interpreted as plumes, we suggest that the late Cenozoic alkalic magmatism in East Asia originated in the shallow asthenosphere, largely in response to dramatic changes in stress regimes. The interplay between the India–Eurasia collision and subduction of the Pacific Plate beneath the eastern margin of Eurasia resulted in a late Cenozoic tensile setting in East Asia capable of inducing melting in the asthenosphere by decompression. This is contrary to previous studies which advocated a plume or a mantle lithospheric origin for the East Asia late Cenozoic alkalic volcanism.