柴西南翼山构造上新统狮子沟组混积岩地球化学特征及物源指示意义
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摘要
柴西地区南翼山构造上新统混积岩中含有大量盐类矿物,其物源分析对盐矿物质来源研究有一定的参考价值。本文在野外观察和镜下鉴定的基础上,对南翼山构造上新统狮子沟组混积岩的地球化学特征进行了分析,并结合周缘造山带花岗岩的稀土元素数据,探讨了混积岩中陆源碎屑的物质来源。结果显示:南翼山构造狮子沟组混积岩中碎屑矿物、碳酸盐矿物和黏土矿物呈均匀混合的状态,元素含量与矿物组分密切相关,除Ca、Na、Sr元素外,其余元素含量普遍低于上地壳平均含量,其中CaO和Na_2O受碳酸盐和石盐形成影响,不能用于判别构造背景,而Sc、Th、Zr、Hf等微量元素和稀土元素较完整地保留了源岩的地球化学信息,可用于源区构造背景的判别及物源示踪,同时稀土元素配分模式一致性较好,表明混积岩中陆源碎屑具有相同的物源特征。稀土元素配分模式、La-Th-Sc、Th-Sc-Zr/10、La/Th-Hf图解以及Al_2O_3/TiO_2比值共同指示南翼山混积岩的陆源碎屑组分来源于大陆岛弧背景下的长英质火成岩,通过与周缘造山带花岗岩稀土配分模式对比,推断晚志留世和晚二叠世花岗岩是混积岩中陆源碎屑和盐类矿物的主要源岩,南部的祁漫塔格是主要的物源区,且西部的阿尔金南段也有部分物源贡献。
The Pliocene mixed rocks contain large amounts of salt minerals in the Nanyishan structure of the western Qaidam Basin,and their provenance analyses can be valuable in finding the origin of the salt minerals.Based on field observation and microscopic identification, we analyzed the geochemical characteristics of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure.Combined with rare earth element(REE)characteristics of granites from the surrounding orogenic belts,we discussed the provenance of terrigenous clastics in mixed rocks.The results showed that the detrital,carbonate and clay minerals in mixed rocks were homogeneously mixed,and the elemental contents of the rocks were closely related to the mineral composition.Except for Ca,Na,and Sr,the mixed rocks had generally lower mineral contents than those of the upper continental crust.Considering that CaO and Na_2O are affected by the formation of carbonate and halite,Ca and Na are not suitable for identifying tectonic settings.In contrast,trace elements and REE such as Sc,Th,Co,Zr and Hf,retain mostly the geochemical information of source rocks and therefore can be used to evaluate the tectonic settings of the source area for provenance analysis.The REE patterns showed good consistency,indicating the terrigenous clastics of mixed rocks have the same provenance characteristics.Together with La-Th-Sc,Th-Sc-Zr/10,La/Th-Hf diagrams and Al_2O_3/TiO_2 ratio,our data suggest that the terrigenous clastics components of mixed rocks were derived from the felsic igneous rocks of continental island arc.In comparison with REE patterns in granites from the surrounding orogenic belts,we consider the Late Silurian and Late Permian granites to be the main source rocks for terrigenous clastics and salt minerals in the mixed rock.In addition,we hypothesize that the south part of the study area,Qimantag,is the main source area,and South Altyn Tagh in the west also takes partin the sedimentary source recharge.
The Pliocene mixed rocks contain large amounts of salt minerals in the Nanyishan structure of the western Qaidam Basin,and their provenance analyses can be valuable in finding the origin of the salt minerals.Based on field observation and microscopic identification, we analyzed the geochemical characteristics of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure.Combined with rare earth element(REE)characteristics of granites from the surrounding orogenic belts,we discussed the provenance of terrigenous clastics in mixed rocks.The results showed that the detrital,carbonate and clay minerals in mixed rocks were homogeneously mixed,and the elemental contents of the rocks were closely related to the mineral composition.Except for Ca,Na,and Sr,the mixed rocks had generally lower mineral contents than those of the upper continental crust.Considering that CaO and Na_2O are affected by the formation of carbonate and halite,Ca and Na are not suitable for identifying tectonic settings.In contrast,trace elements and REE such as Sc,Th,Co,Zr and Hf,retain mostly the geochemical information of source rocks and therefore can be used to evaluate the tectonic settings of the source area for provenance analysis.The REE patterns showed good consistency,indicating the terrigenous clastics of mixed rocks have the same provenance characteristics.Together with La-Th-Sc,Th-Sc-Zr/10,La/Th-Hf diagrams and Al_2O_3/TiO_2 ratio,our data suggest that the terrigenous clastics components of mixed rocks were derived from the felsic igneous rocks of continental island arc.In comparison with REE patterns in granites from the surrounding orogenic belts,we consider the Late Silurian and Late Permian granites to be the main source rocks for terrigenous clastics and salt minerals in the mixed rock.In addition,we hypothesize that the south part of the study area,Qimantag,is the main source area,and South Altyn Tagh in the west also takes partin the sedimentary source recharge.
引文
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[4]张雄华.混积岩的分类和成因[J].地质科技情报,2000,19(4):31-34.
[5]杨朝青,沙庆安.云南曲靖中泥盆统曲靖组的沉积环境:一种陆源碎屑与海相碳酸盐的混合沉积[J].沉积学报,1990,8(2):59-66.
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[7]董桂玉,陈洪德,何幼斌,等.陆源碎屑与碳酸盐混合沉积研究中的几点思考[J].地球科学进展,2007,22(9):931-939.
[8]张金亮,司学强.断陷湖盆碳酸盐与陆源碎屑混合沉积:以东营凹陷金家地区古近系沙河街组第四段上亚段为例[J].地质论评,2007,53(4):448-453.
[9]陈世悦,张顺,刘惠民,等.湖相深水细粒物质的混合沉积作用探讨[J].古地理学报,2017,19(2):271-284.
[10]赵会民.辽河西部凹陷雷家地区古近系沙四段混合沉积特征研究[J].沉积学报,2012,30(2):283-290.
[11]徐伟,陈开远,曹正林,等.咸化湖盆混积岩成因机理研究[J].岩石学报,2014,30(6):1804-1816.
[12]MCNEILL D F,CUNNINGHAM K J,GUERTIN L A,et al.Depositional themes of mixed carbonate-siliciclastics in the South Florida Neogene:application to ancient deposits[J].AAPG Memoir,2004,80:23-43.
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[14]张宁生,任晓娟,魏金星,等.柴达木盆地南翼山混积岩储层岩石类型及其与油气分布的关系[J].石油学报,2006,27(1):42-46.
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[16]FENG J L,CAO J,HU K,et al.Dissolution and its impacts on reservoir formation in moderately to deeply buried strata of mixed siliciclastic-carbonate sediments,Northwestern Qaidam Basin,Northwest China[J].Marine and Petroleum Geology,2013,39(1):124-137.
[17]邵磊,刘志伟,朱伟林.陆源碎屑岩地球化学在盆地分析中的应用[J].地学前缘,2000,7(3):297-304.
[18]常华进,储雪蕾,冯连君,等.氧化还原敏感微量元素对古海洋沉积环境的指示意义[J].地质论评,2009,55(1):91-99.
[19]孙林华,桂和荣,陈松,等.皖北新元古代贾园组混积岩物源和构造背景的地球化学示踪[J].地球学报,2010,31(6):833-842.
[20]伏美燕,李娜,黄茜,等.滨岸浅海混合沉积对海平面与气候变化的响应:以塔里木盆地巴麦地区石炭系为例[J].沉积学报,2017,35(6):1110-1120.
[21]郑绵平,张雪飞,侯献华,等.青藏高原晚新生代湖泊地质环境与成盐成藏作用[J].地球学报,2013(2):129-138.
[22]陈宣华,党玉琪,尹安,等.柴达木盆地及其周缘山系盆山耦合与构造演化[M].北京:地质出版社,2010:1-437.
[23]甘贵元,魏成章,常青萍,等.柴达木盆地南翼山湖相碳酸盐岩油气藏特征及形成条件[J].石油实验地质,2002,24(5):413-417.
[24]党玉琪,尹成明,赵东升.柴达木盆地西部地区古近纪与新近纪沉积相[J].古地理学报,2004,6(3):297-306.
[25]付锁堂,张道伟,薛建勤,等.柴达木盆地致密油形成的地质条件及勘探潜力分析[J].沉积学报,2013,31(4):672-682.
[26]于冬冬,张永生,侯献华,等.柴西南翼山构造形成演化及其对油气成藏的控制[J].断块油气田,2017,24(6):740-744.
[27]张涛,宋春晖,王亚东,等.柴达木盆地西部地区晚新生代构造变形及其意义[J].地学前缘,2012,19(5):312-321.
[28]RUDNIK R L,GAO S.Composition of the continental crust[M]∥Treatise on geochemistry.Amsterdam:Elsevier,2003,3:1-64.
[29]TAYLOR S R,MCLENNAN S M.The continental crust:itscomposition and evolution[M].Oxford:Blackwell,1985:57-72.
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