Mixing of asthenospheric and lithospheric mantle-derived basalt magmas as shown by along-arc variation in Sr and Nd isotopic compositions of Early Miocene basalts from back-arc margin of the NE Japan arc

Lithos ◽  
2007 ◽  
Vol 96 (3-4) ◽  
pp. 453-474 ◽  
Author(s):  
Makoto Sato ◽  
Kenji Shuto ◽  
Masahiko Yagi
Keyword(s):  
Lithospheric Mantle ◽  
Early Miocene ◽  
Isotopic Compositions ◽  
Back Arc ◽  
Ne Japan

Sr and Nd isotopic compositions of the magma source beneath north Hokkaido, Japan: comparison with the back-arc side in the NE Japan arc

2004 ◽  
Vol 134 (1-2) ◽  
pp. 57-75 ◽  
Author(s):  
Kenji Shuto ◽  
Yuka Hirahara ◽  
Hiroyuki Ishimoto ◽  
Atsushi Aoki ◽  
Akira Jinbo ◽  
...  
Keyword(s):  
Magma Source ◽  
Isotopic Compositions ◽  
Back Arc ◽  
Ne Japan

scholarly journals Geochemical Variation of Miocene Basalts within Shikoku Basin: Magma Source Compositions and Geodynamic Implications

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Shuang-Shuang Chen ◽  
Tong Hou ◽  
Jia-Qi Liu ◽  
Zhao-Chong Zhang
Keyword(s):  
Japan Sea ◽  
Isotopic Signature ◽  
Magma Source ◽  
Isotopic Compositions ◽  
Enriched Mantle ◽  
Shikoku Basin ◽  
Depleted Mantle ◽  
Parece Vela Basin ◽  
Back Arc ◽  
Ocean Ridge

Shikoku Basin is unique as being located within a trench-ridge-trench triple junction. Here, we report mineral compositions, major, trace-element, and Sr-Nd-Pb isotopic compositions of bulk-rocks from Sites C0012 (>18.9 Ma) and 1173 (13–15 Ma) of the Shikoku Basin. Samples from Sites C0012 and 1173 are tholeiitic in composition and display relative depletion in light rare earth elements (REEs) and enrichment in heavy REEs, generally similar to normal mid-ocean ridge basalts (N-MORB). Specifically, Site C0012 samples display more pronounced positive anomalies in Rb, Ba, K, Pb and Sr, and negative anomalies in Th, U, Nb, and Ta, as well as negative Nb relative to La and Th. Site 1173 basalts have relatively uniform Sr-Nd-Pb isotopic compositions, close to the end member of depleted mantle, while Site C0012 samples show slightly enriched Sr-Nd-Pb isotopic signature, indicating a possible involvement of enriched mantle 1 (EM1) and EM2 sources, which could be attributed to the metasomatism of the fluids released from the dehydrated subduction slab, but with the little involvement of subducted slab-derived sedimentary component. Additionally, the Shikoku Basin record the formation of the back-arc basin was a mantle conversion process from an island arc to a typical MORB. The formation of the Shikoku Basin is different from that of the adjacent Japan Sea and Parece Vela Basin, mainly in terms of the metasomatized subduction-related components, the nature of mantle source, and partial melting processes.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

scholarly journals Igneous Rock Associations 26. Lamproites, Exotic Potassic Alkaline Rocks: A Review of their Nomenclature, Characterization and Origins

2020 ◽  
Vol 47 (3) ◽  
pp. 119-142
Author(s):  
Roger H. Mitchell
Keyword(s):  
Partial Melting ◽  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Alkaline Rock ◽  
Mantle Metasomatism ◽  
Geochemical Evolution ◽  
Alkaline Rocks ◽  
Isotopic Compositions ◽  
Economic Significance ◽  
Rock Types

Lamproite is a rare ultrapotassic alkaline rock of petrological importance as it is considered to be derived from metasomatized lithospheric mantle, and of economic significance, being the host of major diamond deposits. A review of the nomenclature of lamproite results in the recommendation that members of the lamproite petrological clan be named using mineralogical-genetic classifications to distinguish them from other genetically unrelated potassic alkaline rocks, kimberlite, and diverse lamprophyres. The names “Group 2 kimberlite” and “orangeite” must be abandoned as these rock types are varieties of bona fide lamproite restricted to the Kaapvaal Craton. Lamproites exhibit extreme diversity in their mineralogy which ranges from olivine phlogopite lamproite, through phlogopite leucite lamproite and potassic titanian richterite-diopside lamproite, to leucite sanidine lamproite. Diamondiferous olivine lamproites are hybrid rocks extensively contaminated by mantle-derived xenocrystic olivine. Currently, lamproites are divided into cratonic (e.g. Leucite Hills, USA; Baifen, China) and orogenic (Mediterranean) varieties (e.g. Murcia-Almeria, Spain; Afyon, Turkey; Xungba, Tibet). Each cratonic and orogenic lamproite province differs significantly in tectonic setting and Sr–Nd–Pb–Hf isotopic compositions. Isotopic compositions indicate derivation from enriched mantle sources, having long-term low Sm/Nd and high Rb/Sr ratios, relative to bulk earth and depleted asthenospheric mantle. All lamproites are considered, on the basis of their geochemistry, to be derived from ancient mineralogically complex K–Ti–Ba–REE-rich veins, or metasomes, in the lithospheric mantle with, or without, subsequent contributions from recent asthenospheric or subducted components at the time of genesis. Lamproite primary magmas are considered to be relatively silica-rich (~50–60 wt.% SiO2), MgO-poor (3–12 wt.%), and ultrapotassic (~8–12 wt.% K2O) as exemplified by hyalo-phlogopite lamproites from the Leucite Hills (Wyoming) or Smoky Butte (Montana). Brief descriptions are given of the most important phreatomagmatic diamondiferous lamproite vents. The tectonic processes which lead to partial melting of metasomes, and/or initiation of magmatism, are described for examples of cratonic and orogenic lamproites. As each lamproite province differs with respect to its mineralogy, geochemical evolution, and tectonic setting there is no simple or common petrogenetic model for their genesis. Each province must be considered as the unique expression of the times and vagaries of ancient mantle metasomatism, coupled with diverse and complex partial melting processes, together with mixing of younger asthenospheric and lithospheric material, and, in the case of many orogenic lamproites, with Paleogene to Recent subducted material.

Late Eocene post-collisional magmatic rocks from the southern Qiangtang terrane record the melting of pre-collisional enriched lithospheric mantle

2021 ◽  
Author(s):  
Yue Qi ◽  
Qiang Wang ◽  
Gang-jian Wei ◽  
Xiu-Zheng Zhang ◽  
Wei Dan ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Trace Element ◽  
Partial Melting ◽  
Early Cretaceous ◽  
Lithospheric Mantle ◽  
Late Eocene ◽  
The Tibetan Plateau ◽  
Mafic Rocks ◽  
Isotopic Compositions ◽  
Qiangtang Terrane

Diverse rock types and contrasting geochemical compositions of post-collisional mafic rocks across the Tibetan Plateau indicate that the underlying enriched lithospheric mantle is heterogeneous; however, how these enriched mantle sources were formed is still debated. The accreted terranes within the Tibetan Plateau experienced multiple stages of evolution. To track the geochemical characteristics of their associated lithospheric mantle through time, we can use mantle-derived magmas to constrain the mechanism of mantle enrichment. We report zircon U-Pb ages, major and trace element contents, and Sr-Nd isotopic compositions for Early Cretaceous and late Eocene mafic rocks in the southern Qiangtang terrane. The Early Cretaceous Baishagang basalts (107.3 Ma) are characterized by low K2O/Na2O (<1.0) ratios, arc-like trace element patterns, and uniform Sr-Nd isotopic compositions [(87Sr/86Sr)i = 0.7067−0.7073, εNd(t) = −0.4 to −0.2]. We suggest that the Baishagang basalts were derived from partial melting of enriched lithospheric mantle that was metasomatized by subducted Bangong−Nujiang oceanic material. We establish the geochemistry of the pre-collisional enriched lithospheric mantle under the southern Qiangtang terrane by combining our data with those from other Early Cretaceous mafic rocks in the region. The late Eocene (ca. 35 Ma) post-collisional rocks in the southern Qiangtang terrane have low K2O/Na2O (<1.0) ratios, and their major element, trace element, and Sr-Nd isotopic compositions [(87Sr/86Sr)i = 0.7042−0.7072, εNd(t) = −4.5 to +1.5] are similar to those of the Early Cretaceous mafic rocks. Based on the distribution, melting depths, and whole-rock geochemical compositions of the Early Cretaceous and late Eocene mafic rocks, we argue that the primitive late Eocene post-collisional rocks were derived from pre-collisional enriched lithospheric mantle, and the evolved samples were produced by assimilation and fractional crystallization of primary basaltic magma. Asthenosphere upwelling in response to the removal of lithospheric mantle induced the partial melting of enriched lithospheric mantle at ca. 35 Ma.

Isotopic analyses of clinopyroxene in mantle xenoliths demonstrate the effects of kimberlite melt metasomatism upon the lithospheric mantle

2020 ◽  
Author(s):  
Angus Fitzpayne ◽  
Andrea Giuliani ◽  
Janet Hergt ◽  
Jon Woodhead ◽  
Roland Maas
Keyword(s):  
Trace Element ◽  
Lithospheric Mantle ◽  
Mantle Metasomatism ◽  
Mantle Xenoliths ◽  
Isotopic Compositions ◽  
Isotopic Analyses ◽  
Cretaceous Magmatism

<p>As clinopyroxene is the main host of most lithophile elements in the lithospheric mantle, the trace element and radiogenic isotope systematics of this mineral have frequently been used to characterise mantle metasomatic processes. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100–200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40–75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., <sup>87</sup>Sr/<sup>86</sup>Sr<sub>i</sub> = 0.70369–0.70383; εNd<sub>i</sub> = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples indicate equilibration depths of 135–155 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites, which derive from shallower depths (<130 km), and have higher Sr (~350–1000 ppm) and LREE contents, corresponding to higher La/Zr of >~0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g., εNd<sub>i</sub> = -12.7 to -4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable <sup>87</sup>Sr/<sup>86</sup>Sr<sub>i</sub> values (0.70526–0.71177), which might be explained by the interaction between peridotite and melts from different enriched sources with the lithospheric mantle. In contrast, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that an early, pervasive, alkaline metasomatic event caused MARID and lherzolite genesis in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.</p>

Sign in / Sign up

Export Citation Format

Share Document