Oil & Gas Geology ›› 2014, Vol. 35 ›› Issue (1): 33-41.doi: 10.11743/ogg20140105

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Genesis of calcite vein and its implication to petroleum preservation in Jingshan region, Mid-Yangtze

Gao Jian1, He Sheng1, He Zhiliang2, Zhou Yan2, Zhao Mingliang1   

  1. 1. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan, Hubei 430074, China;
    2. Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
  • Received:2013-10-20 Revised:2013-12-30 Online:2014-02-08 Published:2014-03-26

Abstract: Field observation shows that multiple phases of calcite veins occur along fractures in the Ordovician,Permian and Triassic of overthrust belts and fold-thrust belts in Jingshan region,Mid-Yangtze.Using rare earth elements(REE),electron microprobe,oxygen isotope,fluid inclusions and basin modeling,this paper analyzed the genesis of these calcite veins.The REE of calcite veins in the Ordovician and Triassic are characterized by enrichment of LREE,loss of HREE and obvious positive Eu anomaly,indicating that their vein-froming fluids were affected by hydrothermal fluids.Calcite veins in the Permian feature in low REE,only slight enrichment of LREE,flat HREE patterns,and the presence of a moderate negative Ce anomaly,implying that their vein-froming fluids originated from meteoric water infiltration.Analysis of Fe and Mn through electron microprobe indicates that some calcite veins in the Ordovician were derived from the dissolution of surrounding carbonate rocks,the calcite veins in the Permian were derived from leaching and dissolution of carbonates by meteoric water,and those in the Triassic were related to the dissolution of carbonate derived from other horizons.Combined with burial and thermal history modeling of pseudo-wells,analysis of oxygen isotope temperatures and homogenized temperature of fluid inclusions show that the calcite vines filling fractures in these 3 sequences were formed at 150~60 Ma ago at burial depth in the range from 2 000 m to 2 500 m.Based on a comprehensive analysis of geochemical behaviors of the calcite veins,it is believed that hydrothermal fluids,vein-froming fluids and meteoric water infiltration associated with tectonic compression and uplifting during Yanshan Orogeny may have damaged petroleum preservation conditions in Jingshan region to some extent.

Key words: rare earth element, oxygen isotope, calcite vein, petroleum preservation, Middle Yangtze region

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