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Compositional changes of successively emplaced magmatites can be used to infer changes in their petrogenetic evolution and geodynamic setting. The central-northern Lhasa terrane hosts extensive Late Cretaceous magmatism, however, the mechanism that triggered the magmatism and its relationship to the directly preceding Late Cretaceous tectonic transition in the central Tibetan Plateau is still unresolved. Therefore, we conducted a detailed petrological, geochronological, geochemical, and isotopic study on recently identified Late Cretaceous doleritic and granodioritic rocks in the Xiongmei area, northern Lhasa subterrane. The potassic (K2O/Na2O ratios >1) dolerites (ca. 80 Ma) display a post-collisional basaltic shoshonitic signature with uniform moderately enriched whole-rock Sr–Nd and zircon–Hf isotopic compositions ((87Sr/86Sr)t = 0.7070 to 0.7095, whole-rock εNd(t) = – 2.4 to – 1.3, and zircon εHf(t) = – 5.9 to +1.9), suggesting that they evolved from a similar parental magma and were likely derived by partial melting of an enriched lithospheric mantle metasomatized by hydrous fluids. The granodiorites are geochemically divided into medium-K and high-K calc-alkaline rocks. The medium-K samples (ca. 80 Ma) are generally characterized by low K2O/Na2O ratios 2O/Na2O ratios >1. The medium-K samples have positive zircon εHf(t) values from +4.8 to +6.5 and uniform whole-rock ɛNd(t) values from – 2.4 to – 1.3, which significantly differ from those of the high-K samples that have negative to positive zircon εHf(t) values from – 1.9 to +2.8 and negative whole-rock ɛNd(t) values from – 8.4 to – 5.1. The medium-K samples are characterized by high Sr contents and Sr/Y ratios, coupled with low Y and HREE contents, similar to adakitic compositions, and were interpreted to have been derived from deep partial melting of the foundering juvenile garnet-bearing mafic lower crust at relatively low temperatures. Compared to the medium-K samples, the high-K samples have lower Sr/Y and (La/Yb)N ratios, coupled with flat HREE patterns and distinct negative Eu, Sr and Ti anomalies and are most likely derived from shallower partial melting of the K-rich juvenile lower crust at relatively high temperatures. Considering the occurrence of variable magmatism in the central-northern Lhasa subterrane during the Late Cretaceous, the change in magma composition and lower crustal melting conditions (cold-deep vs. hot-shallow) suggest that the lithospheric mantle keel was partially detached by small-scale mantle convection in response to the low-angle Neo-Tethys-associated subduction between 85 and 70 Ma.

The Qulong and Xiongcun porphyry deposits in the Gangdese Copper (Molybdenum) Metallogenic Belt (GCMB) are both giant porphyry deposits. They were located in the eastern and the central GCMB (about 400 km apart), and were generated in the Miocene and the Jurassic, respectively. In order to reveal why the two asynchronous deposits could occur in the same metallogenic belt, the in-situ zircon U-Pb, zircon and apatite fission track (ZFT and AFT), and apatite (U-Th)/He (AHe) dating were conducted. Their associated exhumation amounts and histories were compared, and finally the prospecting significance was evaluated. AHe ages of the Qulong deposit indicate it underwent an amount of at least 1.3–2.8 km exhumation since 13.8–13.1 Ma. However, AFT data and modeling results reveal that the Xiongcun deposit experienced two stages of rapid cooling at 20–13 Ma and 13–8 Ma, respectively. The temperature decreases from 160 °C to 40 °C after ∼20 Ma and the corresponding exhumation amount is about 4–6 km. Integrated the regional thermochronological data, exhumation amounts of 4–6 km and

Field measurements of the thermal infrared (TIR) reflectance from drill hole samples proved to be an effective method to map variations in garnet species associated with hydrothermal alteration zonation of the Jiama porphyry-skarn Cu deposit 1# skarn orebody, Tibetan Plateau, China. The TIR mineral spectral information was combined with electron probe micro-analysis (EPMA) measurements to provide geological insights on effectively determining (a) garnet end components and providing a format for further research on the type and genesis of the deposit, (b) the significance of the characteristic spectrum of garnet to the variation of mineralization environment, (c) the relationship between the characteristic spectrum of garnet and Fe/Al content, (d) the garnet characteristic spectrum to the economic mineralization. The results suggest that garnet characteristics of the thermal infrared spectrum can be used as an indicator for skarn deposit prospecting.

The quartz porphyries at Yaguila, Tibet, host important polymetallic ore deposits, but their age, source and evolution have received insufficient attention. In this study, LA-ICP-MS U–Pb zircon ages revealed that these quartz porphyries were formed in two stages, i.e. pre-collisional Early Cretaceous period (ca. 128 Ma) and late subduction to initial collision Palaeogene period (ca. 65 Ma). Geochemical evidence including whole-rock major element, trace element and rare earth element, zircon Hf isotopes together with sulphide Pb isotopes suggests the Early Cretaceous quartz porphyries could have formed by means of partial melting of crustal materials from Lhasa Terrane basement in a thickened crustal tectonic setting, whereas the Palaeogene quartz porphyries by enhanced input of mantle components probably were associated with slab rollback and breakoff at that time. Granitoid magmas produced in this way ascended to upper crustal level and interacted with marbles and breccias to form Pb–Zn–Ag ore bodies and Mo ore bodies, respectively. Age and geochemical constraints on the Early Cretaceous and Palaeogene polymetallic ore bodies not only have favoured a skarn and hydrothermal vein origin over a submarine exhalative sedimentary origin but also have consummated ore deposits metallogenic series and built up a reconnaissance model along the Lhasa Terrane. Copyright © 2015 John Wiley & Sons, Ltd.