SHRIMP U-Pb zircon dating on Nyainquetanglha granite in central Lhasa block
Abstract The Nyainqentanglha granite, a batholith with an area of 1500 km2 in the central Lhasa block, comprises mainly medium-fine-grained biotite monzonitic granite and medium-coarse-grained biotite monzonitic granite. Their contact relationship suggests that the medium-fine-grained biotite monzonitic granite was crystallized earlier than the medium-coarse-grained monzonitic granite. A SHRIMP U-Pb dating on zircons from representative samples of the batholith shows that the crystallization age of the medium-fine-grained biotite monzonitic granite is 18.3 Ma and that of the medium-coarse-grained monzonitic granite is 11.01 Ma. The emplacement and crystallization of the Nyainqentanglha granite, the youngest granite batholith ever known inside the Lhasa block, have a close relationship with the collisional orogeny, crustal thickening, plateau uplifting,E-W crustal extension and have a dynamic genetic relationship with the crustal partial melting.
SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Comlex in Western Shandong and Its Geological Implications
Abstract The SHRIMP U-Pb zircon dating result of the Tongshi magmatic complex in western Shandong is presented in this paper. The Tongshi magmatic complex comprises fine-grained porphyritic diorite and syenitic porphyry. Eighteen analyses for fine-grained porphyritic diorite gave two concordia ages, in which ten analyses constitute the young age group,giving 206Pb/238U ages ranging from 167.9 Ma to 183 Ma with a weighted mean age of 175.7 ± 3.8 Ma, and the other eight yielded 207Pb/206Pb ages of 2502 Ma to 2554 Ma with a weighted mean 2518 ± 11 Ma. Two analyses for syenitic porphyry gave ages of 2485 Ma and 2512 Ma, respectively. The age of 175.7 ± 3.8 Ma indicates that the crystallization of the Tongshi magmatic complex occurred in the Middle Jurassic, whereas that of 2518 ± 11 Ma is interpreted as the age of inherited magmatic zircons in the Neoarchean Wutai period.
Mesoproterozoic Continental Arc Type Granite in the Central Tianshan Mountains Zircon SHRIMP U-Pb Dating and Geochemical Analyses
Abstract: The Central Tianshan belt in northwestern China is a small Precambrian block located in the southern part of the Central Asia Orogenic Belt (CAOB), which is considered as "the most voluminous block of young continental crust in the world" that comprises numerous small continental blocks separated by Paleozoic magmatic arcs. The Precambrian basement of the central Tianshan Mountains is composed of volcanic rocks and associated volcano-sedimentary rocks that were intruded by granitic plutons. Geochemical analyses demonstrate that the granitic plutons and volcanic rocks were generated in the Andean-type active continental arc environment like today's Chile, and the zircon U-Pb SHRIMP dating indicates that they were developed at about 956 Ma, possibly corresponding to the subduction ofthe inferred Mozambique Ocean under the Baltic-African super-continent.
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