The Tibetan Plateau was formed by intense Cenozoic shortening (up to 1100 km) of a composite “proto-Tibet”, itself the product of a long Paleozoic and Mesozoic history of accretion of Gondwana-derived continental fragments and volcanic arcs against the Asian continental margin. The difficult access and the scarcity of outcrops have long limited the possibilities of studying these Mesozoic suture zones in the heart of the Plateau. In this work, we present new U-Pb and 40Ar/39Ar ages from the highly deformed units of the Yushu mélange, along the Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c. 253 Ma) to Middle Jurassic ages (c. 165 Ma) complement the existing dataset and help to refine the chronology of the Paleo-Tethyan oceanic subductions which have structured the northeastern part of the Qiangtang terrane. The Yushu mélange records at least three successive tectono-magmatic events. The opening of a back-arc basin during the northward Paleo-Tethyan subduction along the Longmu Co-Shuanghu Suture during Early to Middle Triassic; then its closure during the southward subduction of the Songpan-Ganze Ocean along the Jinsha Suture in Late Triassic. Finally, a shortening phase related to the continental collision of the Songpan-Ganze and Qiangtang blocks from Late Triassic to Early-Middle Jurassic. No evidence for any high- or mid-temperature Cenozoic reactivation of the Jinsha suture in our study area is recorded.

Pedogenic carbonate is widespread at mid latitudes where combined warm and dry conditions favor soil carbonate growth from spring to fall. The mechanisms and tempo of pedogenic carbonate formation are more ambiguous in the tropics, where longer periods of soil water saturation and higher soil respiration enhance calcite dissolution. This paper provides bulk and clumped isotope values from Quaternary and Miocene pedogenic carbonates in the tropical monsoonal domain of Myanmar where annual rainfall reaches up to 1700 mm. We show that carbonate growth in Myanmar is delayed to the coldest months of the year by sustained rainfall from mid spring to late fall. We propose that high soil moisture year-round in the tropical domain makes carbonate growth more episodic than in temperate ecosystems, and particularly sensitive to the seasonal distribution of rainfall. This sensitivity is also enhanced by high winter temperatures, allowing carbonate growth to occur outside the warmest months of the year. This high sensitivity is expected to be more prominent in the geological record during times with higher temperatures and greater expansion of the tropical realm. The winter bias in TD47 values found in Burmese soils, unique for pedogenic carbonates, constitute a potential signature for past tropical monsoonal (warm summer-wet) climates in paleosols, and are also found in our Miocene samples.