Olivine chemistry of the Quaternary Datong basalts of the Trans-North China Orogen: Insights into mantle source lithology and redox–hydration state

2020 ◽  
pp. SP510-2020-142
Author(s):  
Lubing Hong ◽  
Zhang Yinhui ◽  
Le Zhang ◽  
Yi-Gang Xu ◽  
Zhe Liu ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Partition Coefficients ◽  
North China ◽  
Mantle Wedge ◽  
Content Type ◽  
The Pacific ◽  
Hydration State ◽  
Pacific Slab ◽  
Supplementary Material

AbstractCenozoic intraplate basalts are widespread above the Big Mantle Wedge (BMW) and its front in East Asia. While the mantle source lithology and redox-hydration state have been demonstrated to be crucial in generation of the basalts above the BMW, their nature and role on the basalts above the front of the BMW is poorly constrained. To address this, we report olivine compositions of the Quaternary Datong basalts. The Datong basalts exhibit OIB-like trace-element compositions and depleted Sr-Nd isotopes with slightly enriched signatures (EMI) for tholeiitic basalts. Olivines of the Datong basalts show high Ni and Fe/Mn, and low Ca, Mn, and Mn/Zn values, pointing to a pyroxenite source. Applying V and Ca partition coefficients between olivine and whole-rock, respectively, the Datong basalts lie −0.44 to 0.64 log units above the fayalite-magnetite-quartz buffer for fO2, and contain 2.1-3.4 wt.% H2O but highly variable H2O/Ce values (265-1498). Both fO2 and H2O/Ce in the basalts vary with whole-rock and olivine compositions, indicating the source was the main control, thus, a heterogeneous redox-hydration state in the source: the EMI component being relatively reduced but extremely wet, and recycled oceanic crust being relatively oxidized but dry. The extremely wet EMI component was likely derived from the mantle transition zone. In the light of our findings, we propose a model in which mantle upwelling carried the recycled oceanic crust and EMI component from the MTZ to shallow mantle, due to the Pacific slab stagnating in the MTZ, to form pyroxenite, which subsequently melted to generate the Datong basalts.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5227668

Spatial and temporal influence of Pacific subduction on South China: geochemical migration of Cretaceous mafic–intermediate rocks

2020 ◽  
Vol 177 (5) ◽  
pp. 1013-1024
Author(s):  
Chengshi Gan ◽  
Yuejun Wang ◽  
Tiffany L. Barry ◽  
Yuzhi Zhang ◽  
Xin Qian
Keyword(s):  
South China ◽  
Igneous Rocks ◽  
Geochemical Data ◽  
Content Type ◽  
The Pacific ◽  
Group A ◽  
Temporal Influence ◽  
Pacific Slab ◽  
Supplementary Material ◽  
Group B

The Cretaceous igneous rocks in the South China Block (SCB) were associated with the slab subduction and roll-back of the Pacific Plate. Thus, they provide excellent opportunities to examine the spatial–temporal geochemical migration of magmatism in the retreating subduction margins. The Cretaceous mafic–intermediate igneous rocks from the southeastern SCB were aged between 142 and 71 Ma, and can geochemically be subdivided into three groups: Group A (126–129 Ma and 83–93 Ma), Group B (126–142 Ma and 71–108 Ma) and Group C (116–142 Ma and 70–110 Ma). Group A and B were mainly distributed in the SCB interior and derived from asthenosphere and asthenosphere–lithosphere interaction sources, respectively. Group C occurred to the east of the Ganjiang Fault and originated from slab–lithosphere interaction. From the coastal provinces to the interior, these mafic–intermediate igneous rocks show increasing incompatible element ratios and Nd isotopic compositions, reflective of a westerly decreasing involvement of slab-derived components. They show two similar age-pulses at c. 125 Ma and c. 90 Ma as well as the Cretaceous A-type granites, indicating two episodes of subduction retreat of the Pacific slab during the Cretaceous. This spatial–temporal pattern of the Cretaceous mafic–intermediate igneous rocks suggests that the Cretaceous slab metasomatism of Pacific subduction retreat was limited to the east of the Ganjiang Fault.Supplementary material: Tables of geochemical data and additional figures are available at https://doi.org/10.6084/m9.figshare.c.4938576

Archean, highly unradiogenic lead in shallow cratonic mantle

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 584-588 ◽  
Author(s):  
Jun-Bo Zhang ◽  
Yong-Sheng Liu ◽  
Mihai N. Ducea ◽  
Rong Xu
Keyword(s):  
Pressure Dependence ◽  
Mantle Source ◽  
Negative Pressure ◽  
Upper Mantle ◽  
Partition Coefficients ◽  
North China ◽  
Oceanic Island ◽  
Isotopic Data ◽  
The North ◽  
Cratonic Mantle

Abstract Here, we present coupled geochemical and Sr-Nd-Pb-S isotopic data of Early Cretaceous primitive gabbros from the North China craton. Strikingly, these rocks have highly unradiogenic lead compositions (206Pb/204Pb = 16.58 ± 0.24) and anchor one extreme end member (low 206Pb/204Pb and 143Nd/144Nd) in the global array of oceanic-island volcanics. Our study shows that they originated from an Archean fluid-metasomatized refractory peridotite source, in which highly unradiogenic lead was preferentially released with subducted Archean seawater and sequestered into recrystallized sulfides at shallow mantle depths. Sulfide/silicate partition coefficients for lead show a negative pressure dependence: Lead is more enriched in sulfide with decreasing pressure. Sulfide-bearing and iron-poor harzburgite as well as dunite residues at shallow mantle are expected to develop low U/Pb (and thereby low time-integrated 206Pb/204Pb) relative to a deeper upper-mantle source. Our preferred interpretation is that an Archean, highly unradiogenic lead reservoir may be stored in the spinel-facies refractory cratonic mantle.

scholarly journals Geochemical distinction between altered oceanic basalt- and seafloor sediment-derived fluids in the mantle source of mafic igneous rocks in southwestern Tianshan, western China

2021 ◽  
Author(s):  
Li-Tao Ma ◽  
Li-Qun Dai ◽  
Yong-Fei Zheng ◽  
Zi-Fu Zhao ◽  
Wei Fang ◽  
...  
Keyword(s):  
Trace Elements ◽  
Oceanic Crust ◽  
Mantle Source ◽  
Mantle Wedge ◽  
Igneous Rocks ◽  
Western China ◽  
Arc Magmatism ◽  
Oceanic Basalt ◽  
Southwestern Tianshan ◽  
Seafloor Sediment

Abstract The role of subducting oceanic crust-derived fluids in generating mafic arc magmatism has been widely documented. However, the subducting oceanic crust is generally composed of basaltic igneous crust and seafloor sediment, which may give rise to different compositions of liquid phases causing metasomatism of the mantle wedge. Because of the similarity in enrichment of fluid-mobile incompatible elements in the two sources of subduction zone fluids, it has been a challenge to distinguish between them when studying the products of mafic arc magmatism. This difficulty is overcome by a combined study of whole-rock Li isotopes and zircon O isotopes in addition to whole-rock major-trace elements and Sr-Nd-Hf isotopes in Late Paleozoic mafic igneous rocks from southwestern Tianshan in western China. Zircon U-Pb dating yields consistent ages of 313±3 Ma to 305±1 Ma for magma crystallization. The mafic igneous rocks exhibit arc-like trace element distribution patterns and depleted whole-rock Nd-Hf isotopes but slightly high (87Sr/86Sr)i ratios of 0.7039 to 0.7056. They also show positive zircon εHf(t) values and slightly higher zircon δ18O values of 5.2-7.6‰. There are covariations of whole-rock Sr isotopes with Th/La and Rb/Nb ratios, indicating a contribution from terrigenous sediment-derived fluids to their mantle source in addition to basaltic igneous crust-derived fluids. Based on the slightly higher zircon δ18O values but variably lower whole-rock δ7Li values of -0.8 to 3.5‰ for the target rocks than those of mantle respectively, both altered oceanic basalt- and terrigenous sediment-derived fluids are identified in the mantle source of these mafic igneous rocks. Model calculations for trace elements and Sr-Nd-Li isotopes further confirm that the geochemical compositions of these mafic igneous rocks can be explained by chemical reaction of depleted MORB mantle peridotite with the mixed fluids to generate ultramafic metasomatites at subarc depths. Therefore, chemical metasomatism of the mantle wedge is a key mechanism for the incorporation of crustal components into the source of arc-like mafic igneous rocks above oceanic subduction zones.

Wudalianchi Volcanic Field, NE China: Tectonic Setting, Eruptive History, and Geophysical Insights

2021 ◽  
pp. SP510-2020-67
Author(s):  
Zhengquan Chen ◽  
Yongwei Zhao ◽  
Xiang Bai ◽  
Wei Wei ◽  
Yongshun Liu ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Volcanic Field ◽  
Geophysical Data ◽  
Middle Pleistocene ◽  
Content Type ◽  
The Pacific ◽  
Isotopic Studies ◽  
Supplementary Material ◽  
Seismic Images ◽  
Eruptive Product

AbstractCombined geologic, geochronologic, and geophysical data demonstrate that the evolution of the Wudalianchi Volcanic Field is closely linked to the most recent tectonic movements affecting the Songliao Basin, driven by dynamics associated with the subducting slab of the Pacific Plate. Intense volcanic activity has occurred in the Wudalianchi since the middle Pleistocene, including historical eruptions in 1720, 1721, and 1776. Together with radiometric age data, variations in the geomorphology of the volcanic cones reflect the effects of multiple eruptions at the same locations but during different periods. Geophysical data-including seismic images, tomography, and magneto-telluric profiles-suggest the existence of subsurface low-resistivity bodies beneath some of the volcanoes, posing the potential that these could reactivate and erupt again in the future. To better characterize and elucidate the magmatic and volcanic processes operative in the WDLC over geologic time, it is essential to conduct systematic geochemical and isotopic studies of many more samples of eruptive product, especially those from the older, single volcanoes.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5260046

scholarly journals Petrogenesis of Mediterranean lamproites and associated rocks: the role of overprinted metasomatic events in the postcollisional lithospheric upper mantle

2021 ◽  
pp. SP513-2021-36
Author(s):  
Martina Casalini ◽  
Riccardo Avanzinelli ◽  
Simone Tommasini ◽  
Claudio Natali ◽  
Gianluca Bianchini ◽  
...  
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
Central Italy ◽  
Western Anatolia ◽  
Calc Alkaline ◽  
Content Type ◽  
High K ◽  
Supplementary Material ◽  
The Mediterranean ◽  
Lithospheric Mantle Source

AbstractHigh-MgO lamproite and lamproite-like (i.e., lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine-Himalaya collisional margin, which followed the closure of the Tethys ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g., plugs, dykes, and laccoliths), and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (Northern Italy), through the Late Miocene in Corsica (Southern France) and in Murcia-Almeria (South-Eastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (Central Italy), in the Balkan peninsula (Serbia and Macedonia), and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO, and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent and it is rarely found only in the groudmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatised by at least two different agents: i) a high Th/La and Sm/La (i.e., SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; ii) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterised by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterise areas that were affected by multiple Wilson cycles, as observed in the the Alpine-Himalayan realm.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5414418

scholarly journals Nature of the Cuvier Abyssal Plain crust, offshore NW Australia

2021 ◽  
pp. jgs2020-172
Author(s):  
Matthew T. Reeve ◽  
Craig Magee ◽  
Ian D. Bastow ◽  
Carl McDermott ◽  
Christopher A.-L. Jackson ◽  
...  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Seismic Reflection ◽  
Abyssal Plain ◽  
Magnetic Data ◽  
Borehole Data ◽  
Seismic Reflection Data ◽  
Content Type ◽  
Supplementary Material ◽  
Nw Australia

Magnetic stripes have long been assumed to be indicative of oceanic crust. However, continental crust heavily intruded by magma can also record magnetic stripes. We re-evaluate the nature of the Cuvier Abyssal Plain (CAP), offshore NW Australia, which hosts magnetic stripes and has previously been defined as oceanic crust. We show that chemical data from a basalt within the CAP, previously described as an enriched mid-ocean ridge basalt, could equally be interpreted to contain evidence of contamination by continental material. We also recognize seaward-dipping reflector sequences in seismic reflection data across the CAP. Borehole data from overlying sedimentary rocks suggests that these seaward-dipping reflectors were emplaced in a shallow water (<200 m depth) or subaerial environment. Our results indicate that the CAP may not be unambiguous oceanic crust, but may instead consist of a spectrum of heavily intruded continental crust through to fully oceanic crust. If the CAP represents such a continent–ocean transition zone, then the adjacent unambiguous oceanic crust would be located >500 km further offshore NW Australia than currently thought. This would impact plate tectonic reconstructions, as well as heat flow and basin modelling studies. Our work also supports the growing consensus that magnetic stripes cannot, by themselves, be used to determine crustal affinity.Supplementary material: Enlarged and uninterpreted versions of the magnetic data and seismic reflection lines are available at https://doi.org/10.6084/m9.figshare.c.5332172

Diamondiferous kimberlites from recently explored Upper Muna field (Siberian craton): petrology, mineralogy and geochemistry insights

2021 ◽  
pp. SP513-2021-9
Author(s):  
D. A. Yakovlev ◽  
S. I. Kostrovitsky ◽  
B. R. Fosu ◽  
I. V. Ashchepkov
Keyword(s):  
Mantle Source ◽  
Compositional Data ◽  
Element Distribution ◽  
Trace Element Distribution ◽  
Melt Crystallization ◽  
Content Type ◽  
Group I ◽  
Mineralogical Characteristics ◽  
Supplementary Material ◽  
Ree Patterns

AbstractPetrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe-Mg-rich rocks in the Yakutian kimberlite province (average FeOtotal = 8.4 wt%, MgO = 32.36 wt%, TiO2 = 1.6 wt.%). Striking mineralogical features of Upper Muna kimberlites are: 1) abundance of monticellite and perovskite in the groundmass; 2) rare occurrence of Mg-ilmenite; 3) abundance of phlogopite megacrysts (up to 8 cm across); 4) coexistence of low-Cr (0.1–4wt. % Cr2O3, with 0.8–1.2 wt.% TiO2), and high-Cr (3–8 wt.% Cr2O3, with 0.1-0.6 wt.% TiO2) garnet megacrysts with contrasting REE patterns. The compositional features of groundmass minerals, the relatively low CaO and CO2 contents in kimberlites, and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite-harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide P-T range (40–65 kbar and 900–1350 °C). Mineral geochemistry, trace element distribution and Sr-Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5442956

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