Study On The Mafic-ultramafic Intrusions And Related Metallogenetic Effects In Tarim Large Igneous Province

The Tarim Large Igneous Province (TLIP) is the second Late Paleozoic LIPs inChina after the recognition of Emeishan Large Igneous Province. This study reportsthe Wajilitag and Puchang complexes and associated magmatic deposits in thenorthwestern Tarim Large Igneous Province. In this contribution, we present mineralchemical and geochronologic data as well as major and trace element and isotopiccompositions for their intrusive rocks, to constraint on its orthomagmaticmetallogenetic effects, which in turn aids in understanding the magmatism,metallogeny and its dynamical process within Tarim Large Igneous Province. Thefollowing achievements and conclusions have been made.1. Here we report for the first time in situ secondary ion mass spectrometric U-Pbage data on perovskite and baddeleyite grainsin a kimberlitic pipe and a kimberliticdyke from the Wajilitag area. Our age data show that the kimberlitic intrusion wasemplaced at ca.300Ma, rather than in the late Permian as previously regarded.Detailed petrographic observations and Nd isotopic data of phlogopite separates,combined with previously reported geochemical data, suggest that the Wajilitagkimberlitic intrusion was most likely derived from a moderately refractory anddepleted subcontinental lithosphere mantle, metasomatised by subduction componentsassociated with an early-middle Paleozoic convergent regime. The kimberlitic magmawas generated by small-degree partial melting of the lithospheric mantle in responseto the impingement of the Tarim mantle plume. The partial melting at relativelyshallow SCLM together with the fractionated nature of the primitive magma suggeststhat the Wajilitag kimberlitic magma is not robust for diamond survival.2. Both secondary ion mass spectroscopy and laser ablation–inductively coupledplasma–mass spectrometry U–Pb dating of zircon grains from the Wajilitag andPuchang complexes yield U–Pb zircon ages of ca.283Ma and ca.275Ma,respectively. Both complexes were most probably derived from a metasomatizedsubcontinental lithospheric mantle, modified by subduction–derived componentsassociated with a middle Paleozoic convergent regime. The Fe–Ti oxide ores could be formed by normal fractional crystallization and crystal accumulation of the Fe–Tioxide crystals from ferrobasaltic parental magmas. The development of massive Fe–Tioxide ores within the Puchang complex could plausibly result from a combination ofthe interaction of the magma with carbonate country rocks and protracted fractionalcrystallization history of a Fe highly enriched melt in an approximately closedmagmatic system by a single injection of basaltic magma.3. The sulfide mineral segregation may have played an important role in PGEdistribution in the Wajilitag and Puchang silicate rocks and ores. Fractionalcrystallization involving abundant magnetite also may have induced sulfide saturationat the later stages of magma evolution. The identification of sulfide mineralsegregation during the late stage of magma evolution in the shallow magma chambersuggests that there is a potential to find economic Cu–Ni sulfide mineralization inthese complexes and other similar types of mafic–ultramafic intrusions in the TLIP.4. The total duration of magmatism in the TLIP appears to long. The mantleplume reached the base of the lithosphere of the Tarim Craton, and triggered meltingof the fusible constituents such as the carbonate and phlogopite veins to produce thekimberlitic rocks at~300Ma. The massive flood basalts and some mafic–ultramaficintrusions were produced by incompatible-enriched lithospheric mantle in response tothe plume-lithosphere interaction during292Ma–275Ma.