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Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rocks types have contrasting temporal-spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K 2 O/Na 2 O tend to display lower Y and higher SiO 2 , suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, unradiogenic 143 Nd/ 144 Nd and the dramatic decrease of zircon ε Hf (t) values since ~35 Ma shown by postcollisional adakites should be interpreted as reflecting the crust input from Indian continental crust. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that special caution is needed if we attempt to probe into the nature of mantle lithosphere using isotopic tracers from the Tibetan ultrapotassic rocks.

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The genetic mechanisms of the secondary pore development zones in the lower part of the fourth member of the Shahejie Formation (Es 4 x ) were studied based on core observations, petrographic analysis, fluid inclusion analysis, and petrophysical measurements along with knowledge of the tectonic evolution history, organic matter thermal evolution, and hydrocarbon accumulation history. Two secondary pore development zones exist in Es 4 x , the depths of which range from 4200 to 4500 m and from 4700 to 4900 m, respectively. The reservoirs in these zones mainly consist of conglomerate in the middle fan braided channels of nearshore subaqueous fans, and the secondary pores in these reservoirs primarily originated from the dissolution of feldspars and carbonate cements. The reservoirs experienced ''alkaline-acidic-alkaline-acidic-weak acidic'', ''normal pressure-overpressure-normal pressure'', and ''formation temperature increasing-decreasing-increasing'' diagenetic environments. The diagenetic evolution sequences were ''compaction/gypsum cementation/halite cementation/pyrite cementation/siderite cementation-feldspar dissolution/quartz overgrowth-carbonate cementation/ quartz dissolution/feldspar overgrowth-carbonate dissolution/feldspar dissolution/quartz overgrowth-pyrite cementation and asphalt filling''. Many secondary pores (fewer than the number of primary pores) were formed by feldspar dissolution during early acidic geochemical systems with organic acid when the burial depth of the reservoirs was relatively shallow. Subsequently, the pore spaces were slightly changed because of protection from early hydrocarbon charging and fluid overpressure during deep burial. Finally, the present secondary pore development zones were formed when many primary pores were filled by asphalt and pyrite from oil cracking in deeply buried paleoreservoirs.

There are wide spread Cenozoic volcanic rocks in Tengchong (CVRT), Yunnan province, SW China. These rocks comprise three rock types: basalt, andesite (dominant type) and dacite. Most samples are sub‐alkaline, and among the sub‐alkaline rocks, most are high‐K calc‐alkaline. These rocks have a SiO2 range of 49.1 wt.% to 66.9 wt.%. TiO2 contents are not high and have a variation of 0.7 wt.%–1.6 wt.%. Trace element concentrations and element ratios (such as Nb/U, Ce/Pb, Nb/La, etc.) of these rocks have a large variation. 87Sr/86Sr values fall in the range of 0.7057–0.7093 and 143Nd/144Nd values change from 0.5120 to 0.5125. 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios are in the range of 17.936–19.039, 15.614–15.810, and 38.894–39.735, respectively. These geochemical characteristics of CVRT make them resemble island‐arc volcanic rocks. We suggest that the magmas were generated in the lithospheric mantle that had already been metasomatized by previous subduction processes. By the study of the uplift history of the Tibetan Plateau, we found that the beginning of the geotectonic processes to the eruption of CVRT was coeval with one uplift event. Therefore, we propose that the uplift of the Tibetan Plateau caused collapse of the collisional orogeny in Tengchong, which further triggered the generation and eruption of the CVRT magmas.

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