A THERMAL PULSE INDUCED BY PERMIAN MANTLE PLUME IN TARIM BASIN, SOUTHWEST CHINA, IMPLICATION FROM CLUMPED ISOTOPE THERMOMETRY, SOLID-STATE BOND REORDERING AND IN-SITU CALCITE U-PB DATING

The deep to ultra-deep (6000-8000m) Ordovician carbonate intervals of Tarim basin are hot spots for hydrocarbon exploration. However, high burial temperature (>140℃) and a lack of material for traditional thermal proxies significantly hindered the thermal history understanding. Clumped isotopes thermometry in combination with solid-state reordering models provides a new methodology for thermal history reconstruction of Paleozoic carbonate successions. Different calcite fabrics (micrites, cements and veins) of carbonate rocks from six wells were measured for Δ₄₇ and the maximum estimates of peak burial temperature ranges were modeled. Meanwhile, in-situ U-Pb dating of calcite was applied to these fabrics to give starting anchors for thermal history modeling. The Δ₄₇ apparent temperatures span a wide range from 72.14℃ to 95.84℃ in the North and from 150.13℃ to 179.78℃ in the South. Most samples have experienced solid-state reordering under elevated temperature without full equilibration at peak burial temperatures and could thus be used for thermal history reconstruction. The upper limits of the reconstructed peak burial temperatures reveal a thermal pulse residing in the range of 160℃ to 190℃ during Late Permian, with slight differences varying between different areas, while the lower limits are considered to be the present-day burial temperatures. The calculated maximum geothermal gradients at the time of peak burial temperature have a range of 26.75℃/km to 69.29℃/km and exhibit southward decreasing trend. The Late-Permian regional erosion event and heating of Permian mantle plume were considered two possible causes for the thermal pulse. Assuming the Late-Permian regional erosion event as the only cause, the geothermally simulated eroded thickness would greatly exceeds previous estimates. Otherwise, the spatial patterns of peak burial temperature and geothermal gradients closely correspond to the distribution of Permian Large Igneous Province and proposed models for giant mantle plume in Tarim basin. The reconstructed thermal history will contribute significantly to the understanding of source-rock generating history, hydrocarbon accumulation history and fluid flow history in tectonically-complex basins.