The latest Cretaceous magmatic activity in the eastern segment of the Lhasa terrane provides important insights for tracking the magma source and geodynamic setting of the eastern Gangdese batholith, eastward of eastern Himalayan Syntaxis. Detailed petrological, geochemical and geochronological studies of the intrusive rocks (monzodiorites and granodiorites) of the eastern Gangdese batholith are presented with monzodiorites and granodiorites giving zircon U–Pb crystallization dates of 70–66 Ma and 71–66 Ma with εHf(t) values of ?4.8 to +6.2 and ?1.9 to +5.3, respectively. These rocks are metaluminous to weakly peraluminous I-type granites showing geochemically arc-related features of enrichment in LREEs and some LILEs, e.g., Rb, Th, and U, and depletion in HREEs and some HFSEs, e.g., Nb, Ta, and Ti. The rocks are interpreted to be derived from partial melting of mantle material and juvenile crust, respectively, which are proposed to be triggered by Neo-Tethyan slab rollback during northward subduction, with both experiencing ancient crustal contamination. The studied intrusive rocks formed in a transitional geodynamic setting caused by Neo-Tethyan oceanic flat subduction to slab rollback beneath the eastern Gangdese belt during the latest Cretaceous. 相似文献
Interaction of magma with wall rock is an important process in igneous petrology, but the mechanisms by which interactions
occur are poorly known. The western outer granodiorite of the Cretaceous Tuolumne Intrusive Suite of Yosemite National Park,
California, intruded a variety of metasedimentary and igneous wall rocks at 93.1 Ma. The May Lake metamorphic screen is a
metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation, disaggregation,
and partial melting. The chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure
of pluton/wall rock interactions. Wall rock xenoliths (mostly pelitic quartzite) are predominantly located in an elongate
horizon surrounded by a hybridized fine-grained granodiorite. Initial Sr and Nd isotopic ratios of the hybridized granodiorite
indicate significant local incorporation of crustal material. Major- and trace-element geochemical data indicate that contamination
of the granodiorite occurred via selective assimilation of both high-K and low-K, high-silica partial melts derived from pelitic
quartzite. Although the hybridized granodiorite shows significant amounts of contamination, adjacent to xenoliths the proportion
of contamination is undetectable more than a meter away. These results indicate that the chemical and isotopic variability
of the Tuolumne Intrusive Suite is not caused by magma contamination via in situ wall rock assimilation. 相似文献