Late cretaceous intraplate magmatism in Central and South Pamir: Response to edge-driven convection

The Central and South Pamir tectonic blocks contain scarce Late Cretaceous mafic and intermediate-silicic igneous rocks that represent typical intraplate magmatism distant from a continental margin. This paper presents new zircon U - Pb age and Hf - O isotope, and whole -rock geochemical and Sr - Nd isotope data for these rocks in the western part of Central and South Pamir in order to constrain their petrogenesis and geodynamic setting. Zircon U - Pb ages show that the Rushan mafic dikes and Bartang diorites formed concurrently at 67-66 Ma, while the Khorog diorites-granodiorites formed at 77-76 Ma. The Rushan mafic dikes have low SiO 2 (46.6-54.5 wt%) and high MgO (4.3-7.6 wt%) and total alkali (K 2 O + Na 2 O = 5.1-7.6 wt%) contents, and exhibit enrichments in large -ion lithophile elements and depletions in high -field -strength elements. They have depleted Sr-Nd-Hf isotopic compositions ( 87 Sr/ 86 Sr i = 0.7068, e Nd [t] = 2.2-3.5, and zircon e Hf [t] = 5.1-7.7) and mantlelike zircon 8 18 O values (4.6%o-6.0%o). These dikes by through low -degree partial melting of a mixed source consisting of -80% asthenospheric mantle and - 20% metasomatized lithospheric mantle within the stability field of spinel-garnet. The Bartang diorites have a wide range of SiO 2 (58.0-66.3 wt%) and MgO (0.3-3.6 wt%) contents. They also have depleted isotopic compositions ( 87 Sr/ 86 Sr i = 0.7066-0.7072, e Nd [t] = 0.1-1.0, and e Hf [t] = 4.0-6.5) and mantle -like zircon 8 18 O values (4.8%o-5.3%o), similar to those of the Rushan mafic dikes. These diorites formed by fractional crystallization of hornblende, biotite, plagioclase, Fe - Ti oxides, and apatite from mafic magmas represented by the Rushan mafic dikes. The Khorog diorites-granodiorites have intermediate SiO 2 contents (59.9-69.4 wt%), enriched isotopic compositions ( 87 Sr/ 86 Sr i = 0.7050-0.7145, e Nd [t] = -2.7 to -3.5, and e Hf [t] = -0.2 to -4.0), and crust -like zircon 8 18 O values (7.0%o-8.4%o). They formed by partial melting of a mixed source consisting of -60% ancient crustal basement rocks and - 40% juvenile crustal rocks. We propose that edge -driven convection caused by the disparity in lithospheric thickness between the Central and South Pamir tectonic blocks and the Karakum Craton resulted in decompression melting of the mantle and lower crustal sources, and generated the intraplate magmatism.