Plume-lithosphere interaction in the generation of the Tarim Large Igneous Province, NW China: geochronological and geochemical constraints

Wei, Xun, Xu, Yi-Gang, Feng, Yue-Xing and Zhao, Jian-Xin (2014) Plume-lithosphere interaction in the generation of the Tarim Large Igneous Province, NW China: geochronological and geochemical constraints. American Journal of Science, 314 1: 314-356. doi:10.2475/01.2014.09


Author Wei, Xun
Xu, Yi-Gang
Feng, Yue-Xing
Zhao, Jian-Xin
Title Plume-lithosphere interaction in the generation of the Tarim Large Igneous Province, NW China: geochronological and geochemical constraints
Journal name American Journal of Science   Check publisher's open access policy
ISSN 0002-9599
Publication date 2014-01-01
Year available 2014
Sub-type Article (original research)
DOI 10.2475/01.2014.09
Open Access Status
Volume 314
Issue 1
Start page 314
End page 356
Total pages 43
Place of publication New Haven, CT, United States
Publisher American Journal of Science
Language eng
Abstract The magmatism in the early Permian Tarim large igneous province (TLIP) in NW China is represented by basaltic lava flows in Keping and ultramafic-mafic-felsic intrusions and mafic dikes in Bachu, northwestern Tarim Craton. This paper reports new Ar-Ar dating results and chemical compositions of Keping basalts and Bachu dikes, with aims of better characterizing the timing of and mantle/crustal contribution to the TLIP. The Keping basalts yield two well-defined Ar-40/(39)A plateau ages of 287.3 +/- 4.0 Ma and 287.9 +/- 4.1 Ma, which, together with age data from the literature, define a magmatic event at similar to 289 Ma. The intrusions and dikes in Bachu are believed to have formed at similar to 279 Ma based on screened literature data. Thus, they together define two magmatic episodes. The Keping basalts, representing the earlier episode, have alkaline affinity (SiO2 = 44.0-47.9 wt.%, Na2O + K2O = 3.7-4.9 wt.%), low MgO (4.3-5.9 wt.%) and high TiO2 (3.8-5.1 wt.%) contents, showing fractionated chondrite-normalized LREE and nearly flat HREE patterns [(La/Yb)(N) = 6.27-7.71; (Dy/Yb)(N) = 1.36-1.48] with noticeable negative Nb and Ta anomalies in the primitive mantle-normalized trace element diagram. They have negative and relatively uniform epsilon(Nd)(t) (-2.3 to -3.8) and low ((206)pb/(204)pb)(i) (17.43-17.57). We argue that these "crustal signatures" cannot be attributed to crustal assimilation because neither ENd(t) nor ((206)pb/Pb-204)1 correlates with SiO2; rather they are more likely derived from a sub-continental lithospheric mantle (SCLM) source metasomatized by subduction-related processes. The Bachu dikes, representing the later episode and confined to the margins of the Tarim Craton, have similar MgO (3.6-5.4 wt.%) and TiO2 (3.1-4.7 wt.%) contents to the Keping basalts, and display more fractionated HREE patterns [(La/Yb)(N) = 10.1-14.0; (Dy/Yb)(N) = 1.79-1.99]. They have variable isotope compositions [epsilon(Nd)(t) = -0.3-4.8, ((206)pb/(204)pb)(i) = 17.50-18.11] and display OIB-like trace element signatures. Correlations between isotopic and trace element ratios indicate that some dikes with low epsilon(Nd)(t) and low initial Pb isotope ratios could have been subjected to crustal assimilation. We propose a model involving plume-lithosphere interaction to account for the two discrete magmatic episodes with distinct mantle sources in the TLIP. The earlier episode was formed in response to the impact of a sub-lithospheric mantle plume at the base of the SCLM. Partial melting of the metasomatized lithospheric mantle was triggered by temperature increase due to conductive heating of the impregnating mantle plume. The later episode was generated by decompression melting of the mantle plume, as a result of deflection of the plume towards the margins of the Tarim Craton with thinner lithosphere.
Formatted abstract
The magmatism in the early Permian Tarim large igneous province (TLIP) inNWChina is represented by basaltic lava flows in Keping and ultramafic-maficfelsic intrusions and mafic dikes in Bachu, northwestern Tarim Craton. This paper reports new Ar-Ar dating results and chemical compositions of Keping basalts and Bachu dikes, with aims of better characterizing the timing of and mantle/crustal contribution to the TLIP. The Keping basalts yield two well-defined 40Ar/39Ar plateau ages of 287.3 ± 4.0 Ma and 287.9 ± 4.1 Ma, which, together with age data from the literature, define a magmatic event at ∼289 Ma. The intrusions and dikes in Bachu are believed to have formed at ∼279 Ma based on screened literature data. Thus, they together define two magmatic episodes. The Keping basalts, representing the earlier episode, have alkaline affinity (SiO2 = 44.0-47.9 wt.%, Na2O + K2O = 3.7-4.9 wt.%), low MgO (4.3-5.9 wt.%) and high TiO2 (3.8-5.1 wt.%) contents, showing fractionated chondrite-normalized LREE and nearly flat HREE patterns [(La/Yb)N = 6.27-7.71; (Dy/Yb)N = 1.36-1.48] with noticeable negative Nb and Ta anomalies in the primitive mantle-normalized trace element diagram. They have negative and relatively uniform εNd(t) (-2.3 to -3.8) and low (206Pb/204Pb)i (17.43-17.57). We argue that these "crustal signatures" cannot be attributed to crustal assimilation because neither εNd(t) nor (206Pb/204Pb)i correlates with SiO2; rather they are more likely derived from a sub-continental lithospheric mantle (SCLM) source metasomatized by subductionrelated processes. The Bachu dikes, representing the later episode and confined to the margins of the Tarim Craton, have similar MgO (3.6-5.4 wt.%) and TiO2 (3.1-4.7 wt.%) contents to the Keping basalts, and display more fractionated REE patterns [(La/ Yb)N = 10.1-14.0; (Dy/Yb)N = 1.79-1.99]. They have variable isotope compositions [εNd(t) = -0.3-4.8, (206Pb/204Pb)i = 17.50-18.11] and display OIB-like trace element signatures. Correlations between isotopic and trace element ratios indicate that some dikes with low εNd(t) and low initial Pb isotope ratios could have been subjected to crustal assimilation. We propose a model involving plume-lithosphere interaction to account for the two discrete magmatic episodes with distinct mantle sources in the TLIP. The earlier episode was formed in response to the impact of a sub-lithospheric mantle plume at the base of the SCLM. Partial melting of the metasomatized lithospheric mantle was triggered by temperature increase due to conductive heating of the impregnating mantle plume. The later episode was generated by decompression melting of the mantle plume, as a result of deflection of the plume towards the margins of the Tarim Craton with thinner lithosphere.
Keyword Geosciences, Multidisciplinary
Geology
GEOSCIENCES, MULTIDISCIPLINARY
Q-Index Code C1
Q-Index Status Confirmed Code
Grant ID 2011CB808906
Y234051001
DP0986542
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
Official 2015 Collection
 
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