Abstract
The Xingdi No.2 intrusion in the Kuluktag Block of northeastern Tarim Craton, which intrudes into the Palaeoproterozoic basement with an exposed area of ca. 12 km2, is an orthopyroxene-rich mafic-ultramafic intrusion in a continental rift setting. It consists of gabbros, pyroxenites, and peridotites, and exhibits a crystallization sequence of the principal rock-forming minerals from olivine, orthopyroxene, clinopyroxene, to plagioclase. The gabbros show a concordant SHRIMP U-Pb zircon age of 752 ± 5.4 Ma. In addition, the olivine grains have forsterite content values of 78–85 mole% and mostly contain low NiO, MnO, CaO, and Cr2O3. The rocks are relatively enriched in large ion lithophile elements and LREE, and depleted in HSFE, have non-radiogenic Pb, low εNd (t) values (−2.8 to −23), initial 87Sr/86Sr ratios (0.7059–0.7130). It could be concluded that the rocks represent an analogue of siliceous high magnesium basaltic magma originated by the partial melting of a hydrous and enriched subcontinental lithospheric mantle and contaminated by the continental crust.
Highlights
Siliceous high-magnesium basalt (SHMB) is a rare rock type that occurs mostly at the Archean-Proterozoic boundaries
The current identification of SHMB-like magmas in a Neoproterozoic craton suggests that SHMB-like magmas could be generated by AFC and partial melting of hydrated lithospheric mantle in continental rift settings related to the mantle plume activity
It could be inferred that the Xingdi No.2 mafic-ultramafic intrusion in the Kuluktag Block in northeastern Tarim Craton was emplaced at ca. 752 Ma
Summary
Siliceous high-magnesium basalt (SHMB) is a rare rock type that occurs mostly at the Archean-Proterozoic boundaries. It is characterized by high MgO (>8%) and SiO2 (51–55%) along with low TiO2 and HFSE [1,2,3,4,5,6,7,8]. The Xingdi No. and No. intrusions, from the southern margin of the Kuluktag Block in the Tarim Craton contain orthopyroxene and are reminiscent of intrusions derived from Siliceous high-magnesium basalt (SHMB) magmas. Since the Xingdi No. and No. intrusions are mineralized with Ni–Cu sulfide, their origin (possibly linked with SHMB-like magma) is important for the understanding of the petrogenesis of the rocks and the genesis of the associated Ni–Cu sulfide deposits. We study the target rocks by employing the SHRIMP U-Pb dating of their zircon, whole-rock elemental geochemistry, mineral compositions, as well as Sr–Nd–Pb isotope data
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