Mantle Plume-related Magmatism Research Articles

Discovery of mafic dikes in northeastern Tibet plateau belonging to the Emeishan large igneous province: Implications for paleocontinental reconstruction and mineral exploration

Due to the lack of paleomagnetic data and paleoclimatic records, the paleocontinental belonging of the Yidun terrane in northeastern Tibet plateau is debated. In this paper, we use the distribution of the Emeishan large igneous province (ELIP) to put the issue to rest. The ELIP is the product of mantle plume activity, which took place at 260 ± 3 Ma in the western margin of the Yangtze craton. The Yangtze craton is the northern part of the South China paleocontinental block. Our new discovery of four mafic dikes in the Yidun terrane with ages and chemistry like the ELIP strongly supports a new interpretation that this terrane was an integral part of the Yangtze craton during the ELIP magmatic event. Baddeleyites from these mafic dikes yield the U–Pb ages of 257.1 ± 4.8, 259.8 ± 8.5, 260.2 ± 4.5 and 261.5 ± 6.8 Ma for each of these dikes, which are similar to the zircon U-Pb ages of the mafic–ultramafic intrusions of the ELIP within the Yangtze craton. The Yidun mafic dikes and some high-Ti basalts of the ELIP within the Yangtze craton have similar Sr-Nd isotope compositions and mantle-normalized incompatible trace element distribution patterns, indicating similar mantle source compositions. Mixing calculation using Sr-Nd isotope compositions shows that the parental magmas for the Yidun mafic dikes experienced only 2–3 % crustal contamination. Partial melting modelling shows that the primary magmas for the Yidun mafic dikes were produced by 5–6 % mantle partial melting at the depths > 85 km below surface, consistent with mantle plume-related magmatism in a continental setting. The Yidun terrane is a new exploration frontier for magmatic Fe-Ti-V oxide deposits that are present elsewhere in the ELIP.

A combination of plume and subduction tectonics contributing to breakup of northern Rodinia: Constraints from the Neoproterozoic magmatism in the Dunhuang-Alxa Block, northwest China

Neoproterozoic igneous rocks are widely distributed in the Dunhuang-Alxa Block, northwest China, and record geodynamic processes caused by the assembly and break-up of Rodinia. In this study, we present new petrological, geochemical, and zircon U-Pb-Hf isotope data for the Langshan gabbros in the northeastern Alxa Block. Langshan gabbros (827−819 Ma) have depleted whole-rock Nd (+3.2 to +4.9) and zircon Hf (+4 to +21) isotopic compositions and weak enrichments in large-ion lithophile elements. These rocks were probably derived by partial melting of a depleted mantle wedge metasomatized by fluids released from a subducted slab in a back-arc basin environment. Geochemical and zircon Hf isotope data for early Neoproterozoic igneous rocks are consistent with the presence of a long-lived (ca. 930−810 Ma) retreating subduction zone along the northern margin of the Dunhuang-Alxa Block, indicating it was located at the northern margin of Rodinia. Some mantle plume-related magmatism, including A1-type silicic volcanic rocks in the Langshan Group and Jinchuan ultramafic-mafic intrusions, occurred in the interior of the Dunhuang-Alxa Block, which was similar to early Neoproterozoic plume-related magmatism (ca. 850−820 Ma) in the interior of northern Rodinia. The temporal link between subduction and extension suggests that this retreating subduction zone along the northern margin of Rodinia, in combination with a mantle plume beneath its interior, resulted in lithospheric extension and break-up of Rodinia during ca. 850−810 Ma.

Neoproterozoic protracted arc basaltic magmatism in the southern margin of the Yangtze Block, south China: New constraints from mafic-ultramafic intrusive rocks

Mantle plume activity and subduction are two popular geodynamic models that have been used to explain the widespread Neoproterozoic basaltic magmatism in the Jiangnan Orogenic Belt along the southern margin of the Yangtze Block, South China. We have evaluated the competing hypotheses using new geochronological, petrological and geochemical data of two mafic–ultramafic intrusions in the Yuanbaoshan (YBS) area of this orogenic belt, namely the YBS south and west intrusions. Zircons from the YBS south intrusion yielded a U-Pb age of 835 ± 3 Ma. This new age and the previously reported age for another mafic–ultramafic intrusion situated < 10 km to the northwest (the YBS west intrusion) reveal a protracted (12–20 Myr) episode of mafic magmatism in a very small area. Such temporal-spatial relationship is more consistent with the style of subduction-related magmatism than that of mantle plume-related magmatism. The YBS south and west intrusions are characterized by arc-like geochemical features such as light REE enrichments and pronounced negative Nb-Ta anomalies in whole rocks. Olivine Mn/Fe and Ca contents, clinopyroxene AlZ/TiO2 and Cr-spinel TiO2/Al2O3 of these intrusions are similar to those of some undisputed subduction-related mafic–ultramafic intrusions elsewhere in the world. Zircons from the YBS south intrusion have mantle-likeHf-O isotope compositions, with εHf(t)varying from + 3.3 to + 8.7 and δ18Oof5.32 ± 0.29‰. The whole rock samples yielded εNd(t) from + 5.2 to + 8.8 and (87Sr/86Sr)i from 0.7034 to 0.7051 for the YBS south intrusion, and εNd(t) from + 1.7 to + 5.2 and (87Sr/86Sr)i from 0.7036 to 0.7051 for the YBS west intrusion. The Sr-Nd isotope compositions of these intrusions are similar to those of global Cenozoic arc basalts, but are also consistent with mantle plume-derived magma with < 5% of crustal contamination. However, the lack of correlation between Th/Nb and εNd(t) or (87Sr/86Sr)i for the intrusive rocks is inconsistent with the contamination model. The results from this study support for a popular view that northward oceanic subduction beneath the southern margin of the Yangtze Block took place in the Neoproterozoic.

Mantle source of the 2.44–2.50-Ga mantle plume-related magmatism in the Fennoscandian Shield: evidence from Os, Nd, and Sr isotope compositions of the Monchepluton and Kemi intrusions

Aims. To identify the range of emotional labour employed by healthcare professionals in a healthcare setting and implications of this for staff and organisations. Background. In a healthcare setting, emotional labour is the act or skill involved in the caring role, in recognizing the emotions of others and in managing our own. Design. A thematic synthesis of qualitative studies which included emotion work theory in their design, employed qualitative methods and were situated in a healthcare setting. The reporting of the review was informed by the ENTREQ framework. Data sources. 6 databases were searched between 1979–2014. Review methods. Studies were included if they were qualitative, employed emotion work theory and were written in English. Papers were appraised and themes identified. Thirteen papers were included. Results. The reviewed studies identified four key themes: (1) The professionalization of emotion and gendered aspects of emotional labour; (2) Intrapersonal aspects of emotional labour – how healthcare workers manage their own emotions in the workplace; (3) Collegial and organisational sources of emotional labour; (4) Support and training needs of professionals Conclusion. This review identified gendered, personal, organisational, collegial and socio-cultural sources of and barriers to emotional labour in healthcare settings. The review highlights the importance of ensuring emotional labour is recognized and valued, ensuring support and supervision is in place to enable staff to cope with the varied emotional demands of their work.

The basaltic volcanism of the Dumisseau Formation in the Sierra de Bahoruco, SW Dominican Republic: A record of the mantle plume-related magmatism of the Caribbean Large Igneous Province

The basaltic volcanism of the Dumisseau Fm in the Sierra de Bahoruco, SW Dominican Republic, offers the opportunity to study, on land, the volcanism of the Caribbean Large Igneous Province (CLIP). It consists of an at least 1.5km-thick sequence of submarine basaltic flows and pyroclastic deposits, intruded by doleritic dykes and sills. Three geochemical groups have been identified: low-Ti tholeiites (group I); high-Ti transitional basalts (group II); and high-Ti and LREE-enriched alkaline basalts (group III). These geochemical signatures indicate a plume source for all groups of basalts, which are compositionally similar to the volcanic rocks that make up various CLIP fragments in the northern region of the Caribbean Plate. Trace element modelling indicates that group I magmas are products of 8–20% melting of spinel lherzolite, group II magmas result 4–10% melting of a mixture of spinel and garnet lherzolite, and group III basalts are derived by low degrees (0.05–4%) of melting of garnet lherzolite. Dynamic melting models suggest that basalts represent aggregate melts produced by progressive decompression melting in a mantle plume. There is no compositional evidence for the involvement of a Caribbean supra-subduction zone mantle or crust in the generation of the basalts. Two 40Ar/39Ar whole-rock ages reflect the crystallisation of group II magmas at least in the late Campanian (~74Ma) and the lower Eocene (~53Ma). All data suggest that the Dumisseau Fm is an emerged fragment of the CLIP, which continues southward through the Beata Ridge

Alkaline basalts in the Karamay ophiolitic mélange, NW China: A geological, geochemical and geochronological study and implications for geodynamic setting

Alkaline basalts are common constituents in many ophiolite belts and accretionary complexes. Here we report geological, geochronological, geochemical, and whole-rock Sr–Nd isotopic data for alkaline basalts from the Karamay ophiolitic mélange of West Junggar, southern Central Asian Orogenic Belt (CAOB). In the ophiolitic mélange, imbricate thrusts, duplexes, “web” structures, pinch-and-swell structures, tilted structures in pillow metabasalts, and shear band cleavages are widely developed. U–Pb analyses of zircon grains from a representative basalt by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded crystallization age of ca. 395±3Ma, suggesting formation during the Middle Devonian. Geochemically, all the samples bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with high concentrations of Na2O+K2O (4.22–7.28wt.%) and TiO2 (1.72–2.89wt.%), LILE and LREE enrichment and HREE depletion ((La/Yb)N=8.4–15.6), with very strong or no Eu anomalies (Eu/Eu*=0.6–1.1), and no obvious Nb, Ta or Ti negative anomalies. The rocks display consistent Sr–Nd isotopic compositions (initial 87Sr/86Sr ratios=0.70326–0.70453, εNd(t)=+3.1–+7.6). The results suggest that all the alkaline basalts were derived from a mantle plume-related source in an intra-oceanic setting with ca. 1–3% degree partial melting of garnet lherzolite. These observations, in combination with previous work, indicate that the alkaline basalts from Karamay ophiolitic mélange can be correlated to a Middle Devonian mantle plume-related magmatism within Paleo-Asian Ocean. We further suggest that the plume-related activity in the CAOB was generally continuous during the development of the Paleo-Asian Ocean.

Panxi region (South-West China): Tectonics, magmatism and metallogenesis. A review

Abstract The Panxi region of SW China makes up most of the western margin of the Yangtze craton. Its structural pattern, defined by NS-trending deep faults, is superimposed on a zone of late Proterozoic crustal extension. The Panxi region seems to have evolved as a continental rift in the Permian, and was subsequently subjected to compression, caused mainly by the Himalayan collision. This induced the uplift of its axial and western parts, generating a horst-type structure within the former rift graben. At ca. 260 Ma, mantle plume-related magmatism in the Panxi region generated the Emeishan flood basalts together with ultramafic and silicic volcanic rocks and with numerous intrusive bodies (peridotites, pyroxenites, layered gabbros, syenites, granites). A geochemical distinction between high-Ti and low-Ti Emeishan basalts can be made, but just with the significance of compositional end-members since the published data define a continuous variation of the entire compositional range. Similar compositional variation occurs in the ultramafic lavas (picrites and komatiites) intercalated in the sequence of the Emeishan basalts, which are considered to be the products of undifferentiated primary magmas. Based on the geochemical data, the primary magmas could have been generated from distinct source materials (mantle plume, asthenosphere, lithospheric mantle), from compositionally heterogeneous mantle plume source or from a common source but with various degrees of mantle melting and crustal contamination. Considering the picritic composition of the primary magmas, a deep-seated differentiation of large volume of magma is needed to produce the extrusion of the relatively evolved Emeishan basalts. World class Fe–Ti–V oxide ore deposits are associated with the layered gabbros, while the ultramafic intrusions can host small Ni–Cu and PGE sulfide deposits. The intrusions containing Fe–Ti–V oxide deposits show remarkably continuous layering and probably derived from mafic magmas differentiated in relatively large chambers. The ultramafic intrusions hosting Ni–Cu(–PGE) sulfide ores most likely formed from sulfide saturated magma moving through conduits.

Geochronology and geochemistry of basaltic rocks from the Sartuohai ophiolitic mélange, NW China: Implications for a Devonian mantle plume within the Junggar Ocean

The West Junggar domain in NW China is a distinct tectonic unit of the Central Asian Orogenic Belt (CAOB). It is composed of Paleozoic ophiolitic mélanges, arcs and accretionary complexes. The Sartuohai ophiolitic mélange in the eastern West Junggar forms the northeastern part of the Darbut ophiolitic mélange, which contains serpentinized harzburgite, pyroxenite, dunite, cumulate, pillow lava, abyssal radiolarian chert and podiform chromite, overlain by the Early Carboniferous volcano-sedimentary rocks. In this paper we report new geochronological and geochemical data from basaltic and gabbroic blocks embedded within the Sartuohai ophiolitic mélange, to assess the possible presence of a Devonian mantle plume in the West Junggar, and evaluate the petrogenesis and implications for understanding of the Paleozoic continental accretion of CAOB. Zircon U–Pb analyses from the alkali basalt and gabbro by laser ablation inductively coupled plasma mass spectrometry yielded weighted mean ages of 375±2Ma and 368±11Ma. Geochemically, the Sartuohai ophiolitic mélange includes at least two distinct magmatic units: (1) a Late Devonian fragmented ophiolite, which were produced by ca. 2–10% spinel lherzolite partial melting in arc-related setting, and (2) contemporary alkali lavas, which were derived from 5% to 10% garnet+minor spinel lherzolite partial melting in an oceanic plateau or a seamount. Based on detailed zircon U–Pb dating and geochemical data for basalts and gabbros from the Sartuohai ophiolitic mélange, in combination with previous work, indicate a complex evolution by subduction–accretion processes from the Devonian to the Carboniferous. Furthermore, the alkali basalts from the Sartuohai ophiolitic mélange might be correlated to a Devonian mantle plume-related magmatism within the Junggar Ocean. If the plume model as proposed here is correct, it would suggest that mantle plume activity significantly contributed to the crustal growth in the CAOB.

A Neoproterozoic seamount in the Paleoasian Ocean: Evidence from zircon U–Pb geochronology and geochemistry of the Mayile ophiolitic mélange in West Junggar, NW China

The Mayile ophiolitic mélange (MOM) is located in the southwestern part of the West Junggar (NW China) and forms part of the Southern Altaids. The MOM comprises ultramafic rocks, gabbro, pillow and massive lavas, abyssal radiolarian cherts and volcaniclastic rocks. Zircons with magmatic crystallization features including oscillatory zoning and high Th/U values from the isotropic gabbro within the MOM yield LA-ICP-MS U–Pb age of 572±9Ma (MSWD=1.0) marking the timing of crystallization of these rocks as late Neoproterozoic. Geochemically, the basalts of the corresponding gabbros from MOM display OIB-type alkali basalt and E-MORB-type tholeiitic basalt features. Both of these groups are characterized by LILE and LREE enrichment and HREE depletion, very weak or no Eu anomalies (Eu/Eu*=0.9–1), and no obvious Nb, Ta and Ti negative anomalies, suggesting a typical OIB affinity. We propose that these volcanic rocks were derived from a mantle plume-related magmatism associated with the evolution of the Paleoasian Oceanic system, with the mantle source containing 2%–5% garnet, ∼2% spinel and ∼2% amphibole. The basalts show within-plate affinity marked geochemical similarities with those from Hawaii and Xigaze seamount, suggestive of their intra-oceanic setting. Subduction of the oceanic lithosphere commenced during late Cambrian to early Ordovician, with the eventual accretion of the seamounts in the fore-arc together with oceanic fragments forming the Mayile ophiolitic mélange.

Petrogenesis and tectonic implications of paleoproterozoic mafic rocks in the Black Hills, South Dakota

Four suites of mafic to intermediate intrusions and flows that occur in the Precambrian core of the Black Hills were analyzed for major and trace elements to establish tectonic settings of magmatism during the late Archean and early Proterozoic history of the region. Most of the mafic rocks were later metamorphosed to amphibolites during the Black Hills orogeny, the collision of the Wyoming and Superior cratons which began at ∼1760 Ma. Compositions of the mafic suites define at least two distinct tectonic settings of magmatism between 2480 and 1880 Ma. The 2.48 Ga Blue Draw intrusion, located on the eastern edge of the Precambrian core, is differentiated with compositions ranging from gabbro to granodiorite. It is a calcalkaline intrusion with relatively high SiO 2 from 51.8 to 60.5 wt.% and K 2O mostly >1 wt.%. REE patterns are slightly concave upward and show LREE enrichment. The intrusion is also enriched in Ba, Rb, Th, and Zr. These and other geochemical discriminants are typical of modern calcalkaline basalts. The intrusion's calcalkaline character is similar to the neighboring, slightly older 2.56 Ga Little Elk granite-gneiss. These two intrusions support the presence of late Archean/early Proterozoic arc magmatism on the eastern margin of the Wyoming craton. The three other mafic suites comprising metamorphosed flows and sills occur within a sequence of deep marine sediments, including black shales, limestones, iron formations, and cherts. U–Pb zircon ages suggest their emplacement between 2.01 and 1.88 Ga. Mafic rocks in the eastern half of the Precambrian core in the Mt. Rushmore and Pactola Dam quadrangles and near Bear Mountain on the western margin of the Precambrian core have slightly depleted to enriched tholeiitic compositions with SiO 2 ∼50 wt.% and K 2O generally <0.5 wt.%. They have flat to slightly light-enriched REE patterns. The chemical characteristics of these two suites point to E-MORB-type magmatism that characterizes present-day, mantle plume-related magmatism at oceanic spreading centers. A mantle plume source is especially evident in the composition of mafic rocks in the Rochford district in the north-central part of the Precambrian core. These mafic rocks have LREE-enriched patterns. They have the highest TiO 2 concentrations, typically >2.5 wt.%, and the lowest SiO 2 concentrations, typically <50 wt.%. They also have the highest Nb/Yb and Ta/Yb ratios and are relatively depleted in Y. With the Bear Mountain and Rushmore–Pactola suites, the Rochford suite provides evidence for rifting of the crust over a mantle plume that has produced a submarine spreading center. This plume-related magmatism in the Black Hills was apparently coeval with 2.01 Ga basic magmatism in southeastern Wyoming and together these locations may indicate an extended presence of a mantle plume under the eastern Wyoming craton. The plume may have led to the break-up of the previously proposed paleocontinent Kenorland.

Geochemistry of mafic rocks of the Karakaya complex, Turkey: evidence for plume-involvement in the Palaeotethyan extensional regime during the Middle and Late Triassic

The Karakaya Complex within the Early Mesozoic Cimmerian Orogeny in northern Turkey represents the remnants of the Palaeotethys. It includes slivers and/or mega-blocks of slightly metamorphic basic volcanic rocks associated with fossiliferous sediments as well as hypabyssal and intrusive rocks with basaltic-andesitic to ultramafic compositions. They display two distinct compositional groups; namely alkaline and variably tholeiitic. The alkaline basalt samples are more akin to oceanic-island basalts (OIB) with relatively enriched trace element characteristics together with strong partitioning in HREE ([La/Yb]N = 5.8–16.2), suggesting that garnet is present as a residual phase in the source of those basalts. The variably tholeiitic samples apart from diabases display E-MORB characteristics; being relatively depleted compared to the alkaline counterparts and less fractionated REE patterns ([La/Yb]N = 2.1–3.6). The diabases, on the other hand, are distinctively different with a significant negative Nb anomaly (Zr/Nb = 28.9–43.4) and flat REE patterns ([La/Yb]N = 0.8–1.4), suggesting their generation above a supra-subduction zone, probably a back-arc basin. These results may suggest that a mantle plume-related magmatism associated with extensional oceanic system should have been installed within Palaeotethys during Middle-Late Triassic time, which was then incorporated into subduction–accretion prism forming the final picture, that is, “the Karakaya Complex”.

The Os and Nd isotopic systematics of c. 2.44 Ga Akanvaara and Koitelainen mafic layered intrusions in northern Finland

We have determined Os and Nd isotopic compositions of various rock types in and adjacent to the c. 2.44 Ga Akanvaara and Koitelainen layered intrusions which are part of the extensive Paleoproterozoic, ultramafic to felsic, mantle plume-related magmatism in the Fennoscandian Shield. The initial ε Nd in the layered sequences of both intrusions fall within a limited range around -2.0, being compatible with results from other coeval layered intrusion in the shield. The initial Os isotopic ratios in chromitites are near-chondritic: the total range of γ Os( T) is from −1 to +6 with the highest values reported for low-Os chromites. No systematic differences are found in the osmium isotopic compositions of the chromites between the intrusions or relative to the stratigraphic position of the sample. The studied intrusions share similar isotopic and geochemical features with rocks from younger flood basalt provinces, and also the same problem of the origin of the lithospheric source component, viz. crustal assimilation versus melt generation within lithospheric mantle. The observed Nd–Os isotopic systematics of the intrusions require that the magmas had negative ε Nd values already before emplacement and can best be accounted for by 15–25% deep-crustal contamination of a komatiitic melt initially having a near-chondritic Os isotopic composition, coupled with additional minor in situ assimilation of country rock material. This hypothesis is supported by the existence of coeval, crustally contaminated komatiitic volcanism on the Fennoscandian Shield.