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Quaternary Volcanic Activity And Magma Evolution In North Hainan Island

Posted on:2004-06-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q SunFull Text:PDF
GTID:1100360122998104Subject:Structural geology
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Volcanic activity is one of the most splendid geological phenomenon on the earth. Studying on volcano, especially on active volcano that has potential danger of eruption, not only has great geological significance, but also has great importance to resource protection and persistent development of society. Based on the field work of Cenozoic volcano in North Hainan Island, this paper uses some new theories and methods, such as tectonics, petrology, chronology, volcanology, geochemistry and geodynamics, to solve several doubtful problems, including the structural background of volcanic rock formation, division of eruption periods, character of magma source and dynamic mechanism of phreatomagmatic eruption. Up to now, we have made some new progresses.North Hainan Island refers generally to the land area to the north of the EW-trending Wangwu-Wenjiao fault, belonging to tectonically part of Leiqiong depression. High frequency Cenozoic volcanic activity is vivid feature in this region. In this area four groups of active faults can be identified, they are nearly EW-trending, NE-trending, NEE-trending and NW-trending faults. EW- trending faults play an important role in the crustal movement. Furthermore, the EW-trending Wangwu-Wenjiao Fault controled Cenozoic deposition and volcanic activity of North Hainan Island. Since Quaternary, the activity of NW-trending faults has enhanced. They dominated Quaternary volcanic activity in Shishan-Yongxing area. In this area, the arrangement of Holocene volcanic cones is obviously NW-trending. Development and evolvement of regional tectonic stress field controlled the direction and character of faults. Since Mesozoic, North Hainan Island has long been controlled by SN-directing tectonic stress field. In this period, EW-structure was characterized by compressional feature, resulting in the NE-directing and NW- directiin structures. During the period of Cenozoic, the character of nearly EW-directing faults were transformed from compressional to tensional due to the expansion of Nanhai basin. This variation has resulted in EW-directing compressional stress, which strengthened the compressional feature of NW- directing structures. These structures become the main channels of Cenozoic volcanic eruption.The eruption of Cenozoic volcanoes in North Hainan Island is characterized by multiple activities and periods. Different eruptive period has different tectonic background, eruptive intensity, distribution of lava flow and character of magma. According to several principles, such as stratigraphic relationship, chronology, weathering degree of volcanic rock, landform and lithology, the Cenozoic volcanic rock in this region can be divided into several groups. From old to young, they are Liushagang period and Weizhou period (Eogene), Xiayang period, Jiaowei period, Penglai period and Jinniuling period (Neogene),Duowenling period, Dongying period, Daotang period and Leihuling period (Quaternary). Field observation reveals that most Holocene volcanic cones are located on the margin of Pleistocene maars. For example, some volcanic cones are distributed around the margin of Ruhuangling maar, and Haochangling volcanic cone is located on the margin of earlier maar. According to different lithology and eruptive sequence, four volcanic systems can be recognized in the Holocene volcanic region, they are Meishe-Changdao-Chuncang-Guoqun, Haochang-Ruqun, Leihuling and Ma' anling volcanic system. Meishe-Changdao-Chuncang-Guoqun volcanic system is located in the southeast of Ma' anling, being an arcuate volcanic system. The K-Ar age of Meisheling, Chuncangling and Changdaoling are dated to be 0. 94Ma, 0.21Ma and 0. 06Ma respectively. It is undoubtful that this volcanic system belongs to Pleistocene according to its K-Ar age, and belongs to alkaline olivine basalt according to its lithology. It is different from olivine tholeiite of Ma' anling volcanic system. The rest volcanic systems were formed in Holocene. The ages of sandstone xenolith from the Leihuling basalt have been dated by TL method to be...
Keywords/Search Tags:North Hainan Island, Quaternary volcano, chronology, Geochemistry, Phreatomagmatic eruption, magma evolution
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