SHRIMP U-Pb Geochronology And Hf Isotope Study Of The Detrital Zircons In The Mesozoic And Cenozoic Sedimentary Rocks From The Central-northern Lanping Basin, Yunnan Province

Lanping basin, located at Sanjiang Tethyan orogenic belt in western Yunnan, lies between the Lancangjiang fault and Jinshajiang fault, extends from Yangtze block in the east, to Yunnan-Tibet block in the west, and connects Simao basin in the south and Changdu basin in the north. The basin is filled with Mesozoic and Cenozoic sediments, and contains huge amount of metal resources. Previous researches were mainly concentrated on the genesis model of the deposits, and the source of ore-forming elements, however, there is short of studies on detrital zircons used to constrain the source of sedimentary for Lanping basin. Therefore, petrological geochemistry, SHRIMP U-Pb age and Hf isotope of detrital zircons were studied on Mesozoic and Cenozoic clastic sedimentary rocks (include east side--Early Cretaceous Jingxing formation located in Jinzhu and Baiyangping district, intermediata--Middle Jurassic Huakaizuo formation-Early Cretaceous Jingxing formation-Paleocene Yunlong formation situated in Jinding district; west-side Middle Jurassic Huakaizuo formation located in Jin Man and Liancheng district), which located in Lanping basin.The clastic sedimentary rocks basically belong to quartz sandstone. The REE patterns of rocks mainly show the right inclined feature with LREE-enriched relatively to HREE, negative Eu anomaly. All these characteristics are consistent with upper-crust REE pattern, which suggests source of sandstone comes from upper crust.SHRIMP U-Pb dating and LA-ICP-MS Hf isotope on detrital zircons from research area were detected, and the results show:1.In spite of different areas and strata, the detrital zircons all contain the age of 2529 Ma,1852 Ma, 749-1059 Ma, specifically some show Middle-Early Archean age of 2977 Ma,3270 Ma. Zircons with age of 2529 Ma show the value of ??Hf(t) ranging from -4 to+8, and TDMC from 2550 to 3450 Ma. Zircons of 1853 Ma display the value of ?Hf(t) from -9 to+5 and TDMC from 2300 to 3100 Ma. Zircons of 749-1059 Ma exhibit the ?Hf(t) between -30 and+13 and TDMC from 900?3500 Ma.2. Detrital zircons from the basins all display similar peak value of 441 Ma age. Most of detrital zircons show the value of ?Hf(t) between -20 and+ 16 and its TDMC from 400 Ma to 2500 Ma.3. Detrital zircons from Lanping basin sedimentary rocks usually reveal the peak of 247-265 Ma (late Permian-early Triassic). Besides, late Triassic detrital zircons with peak of 222-236 Ma are generally displayed in middle and west of basin included Jin Man, Liancheng and Jinding districts. Whilst, detrital zircons of late Cretaceous Jingxing formation located in Jinzhu and Baiyangping areas from the east basin lack the zircon of 200-230 Ma. The Main values of ?Hf(t) from zircons (200-300 Ma) is-13?+13, and TDMC is 500?2000 Ma.4. Detrital zircons from late Cretaceous, Paleocene samples show a few Jurassic and late Cretaceous zircon. Zircons of Late Cretaceous Jingxing formation from Jinding area show visible 159 Ma peak. Most of zircons(104-200 Ma) with value of ?Hf(t) ranging from -12 to+6, and TDMC from 900 to 1950 Ma.On the basis of the study on detrital zircons from Lanping basin, the following results are obtained:1. The Yunlong formation and Jingxing formation from Jinding ore district contain this kind of zircons which are younger than Triassic. This result supports that the sandstone containing minerals belongs to late Cretaceous formation. It is the youngest age of the Jinding ore district. The result is of great significance in metallogenic research and mineral exploration.2. Detrital zircons from east basin show 200-230 Ma peak, whilst the zircon from west basin lack the zircon of 200-230 Ma. The source of Lanping basin may be affected by the topographic feature, the source of east and west basin comes from different area.3. Peaks of detrital zircons of Mesozoic and Cenozoic sedimentary rocks from basin Mainly concentrate in Paleozoic and Mesozoic, and most of zircon is oscillatory zoing. and show the peak of Precambrian, which shows source of basin Marily comes from beside magmatite, and Precambrian source also contribute.4. All detrital zircons from different strata display the Precambrian zircon. The characteristics of relative probability is the same with that of the Yangtze block, indicating the affinity of the sediments to the block.5. It is the first time that Paleo-mesoarchean detrital zircons (2977 Ma and 3270 Ma) were found in the Lanping basin which include Middle Cretaceous Huakaizuo formation situated in intermediate Jinman district and Middle Cretaceous Huakaizuo formation located in Jin Man and Liancheng district. The Hf isotope of Mesoarchean detrital zircons indicates their derivation from the depleted mantle. This zircon may come from the Yangtze block.6. The Hf isotope characteristics of detrital zircons suggest that the source displays crust-mantle interactions occurred in 2523 Ma,1800 Ma,749-1059 Ma,444 Ma,247-265 Ma,222-236 Ma, respectively, which indicates multi-period crust growth and crust recycling.