Many types of dolomites are developed in the Lower Paleozoic in the Jizhong Depression, and hydrothermal dolomites are distributed in many areas. By analyzing the lithology, spatial distribution, and geochemical characteristics of dolomite, the unique characteristics of hydrothermal dolomite are identified. Hydrothermal dolomite has a medium-coarse-sized crystalline structure. The crystalline size is between 0.2~2 mm, mostly subhedral or anhedral. Stylolites and mottled residual structures are visible inside the dolomite.Cathodoluminescence is weak and dark brown. The ordering of dolomites are between 0.73~0.95, averaging 0.75. The molar concentration of CaCO3 is between 49.667%~52.667%, averaging 50.3%. The distribution range of δ13C is -4.669‰ ~0.366‰ (PDB), averaging -1.433‰ (PDB). The distribution range of δ18O is -9.289‰ ~-6.538‰ (PDB), averaging -7.798 ‰ (PDB). The content of MgO and CaO are relatively high, and have a negatively correlation. The Sr contents (ppm) are low. There are two phase gas-liquid fluid inclusions in these dolomites. The homogenization temperature of fluid inclusions ranges between 90 ℃~330 ℃. The dolomites are mainly massive, and are close to the tension faults, the strike slip faults and the Paleogene igneous rocks. These features indicate that the dolomitization occurred in Paleogene. The dolomitization fluid was the tectonic hydrothermal fluid from the early Himalaya movement. The high-quality reservoirs of hydrothermal dolomite are located near the deep basal faults and the Paleogene magmatic rocks.
YAN Wei, JIN Zhenkui, YAO Mengzhu, ZHAO Wenlong. Identification and formation mechanisms of hydrothermal dolomite in the Lower Paleozoic, Jizhong Depression. Petroleum Science Bulletin, 2018, 04: 376-389