Two late Carboniferous belts of Nb-enriched mafic magmatism in the Eastern Tianshan: Heterogeneous mantle sources and geodynamic implications

2020 ◽  
Vol 132 (9-10) ◽  
pp. 1863-1880 ◽  
Author(s):  
Yunying Zhang ◽  
Chao Yuan ◽  
Min Sun ◽  
Xiaoping Long ◽  
Zongying Huang ◽  
...  
Keyword(s):  
Mantle Source ◽  
Late Carboniferous ◽  
Eastern Tianshan ◽  
Mafic Magmatism ◽  
Asthenospheric Mantle ◽  
Tectonic Transition ◽  
Tianshan Orogenic Belt ◽  
Heterogeneous Mantle ◽  
Positive Correlations ◽  
Orogenic Belts

Abstract Identification of subduction to post-collisional tectonic transitions is critical to the study of orogenic belts. To characterize such a transition in the Tianshan Orogenic Belt, a systematic study was conducted on the late Carboniferous (305–301 Ma) Hongshankou dolerite and Dikan’er basalt of Eastern Tianshan. The Hongshankou dolerites have relatively high Ti and Nb contents, akin to Nb-enriched arc basalts. Based on the Nb/La ratios, these dolerites can be divided into low-Nb/La (0.35–0.40) and high-Nb/La (0.67–1.4) groups, which were likely derived respectively from slab melt-metasomatized mantle wedge and a mixed mantle source involving depleted super-slab and enriched sub-slab asthenospheric components. Like the low-Nb/La dolerites, the Dikan’er basalts possess low Nb/La (0.42–0.46) ratios, suggesting a mantle source previously modified by slab components. In addition, the Dikan’er basalts have variable Nb contents and can be grouped into normal arc basalts and Nb-rich basalts that can be attributed to a common mantle source with different degrees of mantle melting, as demonstrated by the positive correlations of La/Sm with La and Nb. By integrating available data, two late Carboniferous belts of Nb-enriched mafic magmatism are recognized in the Eastern Tianshan, with one in the Yamansu arc (336–301 Ma) and the other in the Bogda Mountains (305–301 Ma). The former is characterized by low Nb/La (<0.6) ratios, reflecting derivation from mantle metasomatized by slab-derived melt during a subduction process; the latter exhibits an abrupt Nb/La increase from 0.6 to 1.4, indicating significant input of sub-slab asthenospheric mantle that was probably induced by slab break off. Accordingly, we propose that the tectonic transition from subduction to post-collision in the Eastern Tianshan occurred in the latest Carboniferous (305–301 Ma) and was marked by the abrupt input of deep and enriched asthenospheric mantle.

scholarly journals Petrogenesis and Tectonic Significance of the ~276 Ma Baixintan Ni-Cu Ore-Bearing Mafic-Ultramafic Intrusion in the Eastern Tianshan Orogenic Belt, NW China

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 348
Author(s):  
Minxin You ◽  
Wenyuan Li ◽  
Houmin Li ◽  
Zhaowei Zhang ◽  
Xin Li
Keyword(s):  
Orogenic Belt ◽  
Olivine Gabbro ◽  
Early Permian ◽  
Eastern Tianshan ◽  
Nw China ◽  
Tianshan Orogenic Belt ◽  
Tectonic Significance ◽  
Ultramafic Intrusion ◽  
Back Arc ◽  
Duke Island

The Baixintan mafic-ultramafic intrusion in the Dananhu-Tousuquan arc of the Eastern Tianshan orogenic belt is composed of lherzolite, olivine gabbro, and gabbro. Olivine gabbros contain zircon grains with a U-Pb age of 276.8 ± 1.1 Ma, similar to the ages of other Early Permian Ni-Cu ore-bearing intrusions in the region. The alkaline-silica diagrams, AFM diagram, together with the Ni/Cu-Pd/Ir diagram, indicate that the parental magmas for the Baixintan intrusion were likely high-Mg tholeiitic basaltic in composition. The Cu/Pd ratios, the relatively depleted PGEs and the correlations between them demonstrate that the parental magmas had already experienced sulfide segregation. The lower CaO content in pyroxenites compared with the Duke Island Alaskan-type intrusion and the composition of spinels imply that Baixintan is not an Alaskan-type intrusion. By comparing the Baixintan intrusion with other specific mafic-ultramafic intrusions, this paper considers that the mantle source of the Baixintan intrusion is metasomatized by subduction slab-derived fluids’ components, which gives rise to the negative anomalies of Nb, Ti, and Ta elements. Nb/Yb-Th/Yb, Nb/Yb-TiO2/Yb, and ThN-NbN plots show that the Baixintan intrusion was emplaced in a back-arc spreading environment and may be related to a mantle plume.

Temporal variations in the mantle source beneath the Eastern Tianshan nickel belt and implications for Ni–Cu mineralization potential

Lithos ◽  
2018 ◽  
Vol 314-315 ◽  
pp. 597-616 ◽  
Author(s):  
Yun Zhao ◽  
Chunji Xue ◽  
David T.A. Symons ◽  
Xiaobo Zhao ◽  
Guozhen Zhang ◽  
...  
Keyword(s):  
Mantle Source ◽  
Temporal Variations ◽  
Eastern Tianshan ◽  
Mineralization Potential

scholarly journals Mantle Dynamics of the Central Atlantic Magmatic Province (CAMP): Constraints from Platinum Group, Gold and Lithophile Elements in Flood Basalts of Morocco

2019 ◽  
Vol 60 (8) ◽  
pp. 1621-1652 ◽  
Author(s):  
Christian Tegner ◽  
Sandra A T Michelis ◽  
Iain McDonald ◽  
Eric L Brown ◽  
Nasrrddine Youbi ◽  
...  
Keyword(s):  
Mantle Source ◽  
Gold Mineralization ◽  
Potential Temperature ◽  
Primitive Mantle ◽  
Mantle Melting ◽  
Flood Basalts ◽  
Asthenospheric Mantle ◽  
Central Atlantic Magmatic Province ◽  
Platinum Group ◽  
Central Atlantic

Abstract Mantle melting dynamics of the Central Atlantic Magmatic Province (CAMP) is constrained from new platinum group element (PGE), gold (Au), rare earth element (REE), and high field strength element (HFSE) data and geochemical modelling of flood basalts in Morocco. The PGE are enriched similarly to flood basalts of other large igneous provinces. The magmas did not experience sulphide saturation during fractionation and were therefore fertile. The CAMP is thus prospective for PGE and gold mineralization. The Pt/Pd ratio of the Moroccan lavas indicates that they originated by partial melting of the asthenospheric mantle, not the subcontinental lithospheric mantle. Mantle melting modelling of PGE, REE and HFSE suggests the following: (1) the mantle source for all the lavas was dominated by primitive mantle and invariably included a small proportion of recycled continental crust (<8%); (2) the mantle potential temperature was moderately elevated (c. 1430°C) relative to ambient mantle; (3) intra-lava unit compositional variations are probably a combined result of variable amounts of crust in the mantle source (heterogeneous source) and fractional crystallization; (4) mantle melting initially took place at depths between c. 110 and c. 55 km and became shallower with time (c. 110 to c. 32 km depth); (5) the melting region appears to have changed from triangular to columnar with time. These results are best explained by melting of asthenospheric mantle that was mixed with continental sediments during the assembly of Pangaea, then heated and further mixed by convection while insulated under the Pangaea supercontinent, and subsequently melted in multiple continental rift systems associated with the breakup of Pangaea. Most probably the CAMP volcanism was triggered by the arrival of a mantle plume, although plume material apparently was not contributing directly (chemically) to the magmas in Morocco, nor to many other areas of CAMP.

Genesis of Recent Mafic Magmatism in the Taupo Volcanic Zone, New Zealand: Insights into the Birth and Death of Very Large Volume Rhyolitic Systems?

2020 ◽  
Vol 61 (2) ◽  
Author(s):  
Georg F Zellmer ◽  
Jun-Ichi Kimura ◽  
Claudine H Stirling ◽  
Gert Lube ◽  
Phil A Shane ◽  
...  
Keyword(s):  
New Zealand ◽  
Trace Element ◽  
Large Volume ◽  
Mantle Source ◽  
Source Parameters ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
Mafic Magmatism ◽  
Mafic Magmas ◽  
Rhyolitic Volcanism

Abstract Mafic magmatism of the rifting Taupo Volcanic Zone (TVZ) of the North Island, New Zealand, is volumetrically minor, but is thought to tap the material that provides the heat source for voluminous rhyolite production through partial melting of the crust, which ultimately results in very large volume explosive eruptions. We have studied the major and trace element chemistry of 14 mafic samples from across the entire TVZ, and the U isotopic composition of whole-rocks, groundmasses and separates of mafic mineral phases from a selection of nine samples (with the remaining five too sparsely phyric for mineral separation). Some minerals yield significant 234U enrichments despite groundmass and whole-rock close to 238U–234U secular equilibrium, pointing to uptake of variably hydrothermally altered antecrystic minerals prior to the eruption of originally sparsely phyric to aphyric mafic magmas. However, incompatible trace element patterns indicate that there are three chemically distinct groups of samples, and that samples may be used to derive primary melt compositions. We employ the latest version of the Arc Basalt Simulator (ABS5) to forward model these compositions, deriving mantle source parameters including mantle fertility, slab liquid flux, mantle volatile content, degree of melting, and P–T conditions of melt segregation. We show that mafic rocks erupted in areas of old, now inactive calderas constitute low-degree, deep melts, whereas those in areas of active caldera-volcanism are high-degree partial melts segregated from a less depleted source at an intermediate depth. Finally, high-Mg basaltic andesites erupted in the SW and NE of the TVZ point to a fertile, shallow mantle source. Our data are consistent with a petrogenetic model in which mantle melting is dominated by decompression, rather than fluid fluxing, and progresses from shallow to deeper levels with time. Melt volumes initially increase to a tipping point, at which large-scale crustal melting and caldera volcanism become prominent, and then decrease owing to progressive depletion of the mantle wedge by melting, resulting in the dearth of heat provided and eventual cessation of very large volume rhyolitic volcanism. ABS5 modelling therefore supports the notion of a direct link between the chemistry of recently erupted mafic magmas and the long-term activity and evolution of rhyolitic volcanism in the TVZ.

Pre-Variscan metagabbro from NW Sardinia, Italy: evidence of an enriched asthenospheric mantle source for continental alkali basalts

2003 ◽  
Vol 38 (2) ◽  
pp. 145-159 ◽  
Author(s):  
Marcello Franceschelli ◽  
Gabriele Cruciani ◽  
Mariano Puxeddu ◽  
Daniela Utzeri
Keyword(s):  
Mantle Source ◽  
Alkali Basalts ◽  
Asthenospheric Mantle
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