Heavy mineral characteristics and its implication for provenance of the Triassic, NW Junggar
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    Abstract:

    Objectives:Heavy mineral is the extremely sensitive indicator of provenance. In NW Junggar, the provenance and the heavy minerals of the Triassic are studied. In order to identify the characteristics of heavy minerals and provenance position, this research applied several statistic methods to study 20 samples of sandstones and glutenite in northwestern margin of Junggar Basin. It is alsosignificant to the further illustration of the source- to- sink background. Methods: This research chose 5 profiles of well- developed outcrops to investigate, and collected glutenite and sandstone samples back. Several methods such as single mineral analysis, heavy mineral combinations, mineral percentage distributions, main factor analysis and correlation analysis are applied to research the types and characteristics of heavy minerals of Triassic. Then the source rocks and provenance are concluded. Results: According to the analysis of heavy mineral characteristics and parameters, 18 heavy minerals are identified in the Middle to Upper Triassic samples in the NW Junggar, with most of the grains being angular to subangular and subangular to subround; the contents of zircon, tourmaline and iron ore was found to be commonly high. Among these minerals, there are two zircon types: a yellowish- pink type and a rose- colored type. Brown tourmaline is contained in samples, and a certain content of hornblende, mica debris, apatite, monazite and a few metamorphic minerals and alteration mineral clastics are also included, with the grains exhibiting partial limonitization. 4 heavy mineral combinations are classified in the NW Junggar: zircon—tourmaline—monazite—apatite—anatase, rutile—ilmenite—leucoxene—apatite—galenite, hematite—limonite—pyrite and magnetite—epidote—hornblende. The first two combinations are mainly composed of stable minerals, while the unstable mineral content of the latter two are relatively higher. According to the separation, grinding and heavy mineral stableness of the grains, it is concluded that most are probably from the near- provenance, although the sediments compose the near and distal deposits. There is large amount of columnar zircon, worm- shaped tourmaline of an automorphic to hemiautomorphic form exhibiting characteristics of magmatic origin. Due to the content of rutile, monazite, apatite, pyroxene, hornblende and abundant iron, especially magnetite and ilmenite, it is predicted that intermediate—acid magmatite is included in the source rocks. Subrounded to rounded sedimentary zircon and tourmaline indicate that sedimentary rocks are also included. Some symbol minerals of metamorphic rocks, such as garnet, allanite, epidote, and so on also suggest that a few metamorphic rocks are included. Conclusions: The provenance of the study area is the Qier—Halaalat Mountain area located northwest—north of the study area, belonging to the Front Zaire Mountain. The source rocks are composed of intermediate—acid magmatite, sedimentary rocks and metamorphic rocks from the Tailegula Formation, and are mainly intermediate—acid magmatite. The intermediate—acid magmatite probably consists of tuff, andesite, andesitic porphyrite and granite and granodiorite intrusive bodies. Siltstones and fine- grain sandstones are the main sedimentary source rocks. The metamorphic content may be caused by partial chloritization and epidotization from the regional dynamic metamorphism.

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HE Miao, JIANG Yong, ZHANG Heng, LI Zechao, LI Junjie.2019. Heavy mineral characteristics and its implication for provenance of the Triassic, NW Junggar[J]. Geological Review,65(2):464-476.

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History
  • Received:March 21,2018
  • Revised:January 31,2019
  • Adopted:
  • Online: March 15,2019
  • Published: