Abstract
Deep Earth degassing is a critical forcing factor for atmospheric CO2 variations and palaeoclimate changes in Earth’s history. For the Cenozoic, the key driving mechanism of atmospheric CO2 variations remains controversial. Here we analyse three stages of collision-related magmatism in Tibet, which correspond temporally with the three major stages of atmospheric CO2 variations in the Cenozoic and explore the possibility of a causal link between these phenomena. To this end we present geochemical data for the three stages of magmatic rocks in Tibet, which we use to inform a model calculating the continental collision-induced CO2 emission flux associated with the evolving Neo-Tethyan to continental subduction over the Cenozoic. The correlation between our modelled CO2 emission rates and the global atmospheric CO2 curve is consistent with the hypothesis that the India-Asia collision was the primary driver of changes in atmospheric CO2 over the Cenozoic.
Highlights
Deep Earth degassing is a critical forcing factor for atmospheric CO2 variations and palaeoclimate changes in Earth’s history
Cenozoic magmatic activity can be subdivided into three stages—from early to late—on the basis of compositional differences (Fig. 1) whose origins have been linked to the mantle source regions of the magmas (Fig. 2)
The Stage 2 magmatic rocks (55–25 Ma) are composed of large-scale lava flows and pyroclastic deposits in centralsouthern Tibet (Fig. 1)[14,33]. They have been interpreted to result from upwelling of a mantle transition zone (MTZ)-derived carbonated asthenospheric mantle plume (CMP), induced by the northward subduction of the Indian slab (Fig. 2c, Supplementary Figs. 1–5)
Summary
Deep Earth degassing is a critical forcing factor for atmospheric CO2 variations and palaeoclimate changes in Earth’s history. It is even possible that deep carbon cycle processes associated with the India-Asia collision might have served as critical drivers of both atmospheric CO2 concentration variations and palaeoclimatic changes in the Cenozoic[8,20] Along these lines of logic, recent studies have indicated that the convergence rate between the Indian and Asian continents, together with the magnitude and recycling efficiency of subducted Neo-Tethyan lithosphere, has exerted important controls on the amount of magmatic CO2 emissions and thereby global climate changes in the Cenozoic[19,22]. Despite the fact that the above studies have indicated significant contributions from Tibetan-Himalayan magmatic and metamorphic outgassing to global climate changes, there remains a lack of continuous and quantitative calculations of both magmatic and metamorphic outgassing fluxes from early to late over the whole Cenozoic This has, in turn, precluded a more critical analysis of the tectonic processes involved in the uplift of the Tibetan Plateau as a source or sink of atmospheric CO231,32
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