四川雅安地区第四纪以来活动构造及青衣江水系演化
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摘要
青衣江位于青藏高原东缘,在雅安中上游流域成都盆地南部发育有多级河流阶地,沉积有两套较大的砾石层——名山—邛崃砾石层和丹棱—思漾砾石层,河流阶地和砾石层沉积特征不但记录了盆地或阶地的水动力条件和沉积物来源,也记录了区域性的构造活动与气候变化。
通过对河流阶地的调查,得到各级阶地的分布情况、高程数据、以及形成年代,并依此分析了青衣江的下切速率和表面隆升速率。通过对砾石层的调查,了解其分布的范围、分析了砾石的成分、粒度、砾向、形成年代。在此基础上讨论了青衣江的水系演化。主要有以下认识:
1)青衣江阶地特征
除Ⅰ级阶地为堆积阶地外,其余的均为基座阶地。青衣江阶地在不同流域发育级数不一,特征明显的阶地可多达四级,以草坝——万古场阶地最为典型。此外在洪雅南阳平阶地特征也较为明显,阶地级数也有三级。由阶地的年代和高程分析得出在不同时期河流的下切速率和表面隆升速率。
2)砾石层特征
砾石层属于河流成因,二元结构明显。砾石成分主要为石英岩、花岗岩、闪长岩、辉绿岩、砂岩及火山岩等。砾径变化范围较大,1～40cm不等,但在5～25cm之间居多。砾石磨圆较好,分选多数是中一差。风化程度按阶地级数的增加而增加,一般是Ⅰ级阶地无风化,Ⅱ级阶地弱风化,Ⅲ级阶地弱一半风化,Ⅳ级阶地半一强风化。填隙物主要为沙土,强风化的砾石层均粘土化。
3)水系演化历史
我们将青衣江水系演化划分为五个阶段:
1在中更新世早期(Q_2~1)青衣江往北东流,并形成了名、邛砾石层的Ⅳ级阶地。
2从中更新世中期(Q_2~2)到中更新世晚期(Q_2~3),由于熊坡背斜北部隆起,青衣江改道南东流经顺龙、洪雅和中兴附近区域,在中兴以东与古岷江汇合,并形成了两套砾石层的Ⅲ级阶地。
3晚更新世早期(Q_3~1)——中期(Q_3~2)由于构造运动相对减弱,青衣江没有发生明显的改道。Ⅱ级阶地在此期间形成。
4晚更新世中期(Q_3~2)——全新世(Q_4)由于熊坡背斜继续隆起和名、邛台地南端的抬升,青衣江在罗坝以西切断熊坡背斜南端改道南东东,之后相遇丹、思砾石层Ⅱ级阶地,从北端绕道转向南东流,至此两套砾石层的Ⅰ级阶地开始沉积。
5全新世(Q_4)三苏场背斜北端和丹、思盆地的抬升,青衣江在次被阻断,在夹江以西切断三苏场背斜向南改道南东。
The Qingyijiang River is situated in the eastern margin of theQinghai-Tibet, where exists multilevel river terraces in the Yaan area in the south of the Chengdu basin.There are two major gravel beds,which are Mingshan-Qionglai Gravel Bed and Danleng-Simeng Gravel Bed,deposited on the base of these terraces.The river terrace and the gravel beds are not only the record of the hydrodynamic force condition and the origin of deposit,but also marking the local tectonic activity and the climate changes.
After the survey of the river terraces,we get the information of the layout,the height and the age of the terraces.After the survey of gravel beds,we know the area and the age of the two gravel beds,the ingredient,granularity,orientation of the gravels.And according this,we discuss the evolution of the water system of Qingyijiang river.
The results are giving just as following:
1)The river terraces
Except for the terraceⅠ,which is accumulational terrace,all other terraces are bottom terraces.The number of terraces differs from one drainage area to another.An type is the Caoba-Wangu terraces which has 4 terraces,and in Yangping,on the south of Hongya,there are 3 terraces.We have survey the different terraces and got the data of their height and age,based on which we have calculated the incision rate of Qingyijing river and uplift rate of the terraces in different period.
2)The gravel beds
They are fluvial gravel beds,with the charcter of dual structure.The ingredients are quartzite,granite,diorite,dolerite,sandstone and lava.The diamater of the gravels is in the range of 1-40cm,mostly in 5-25cm.The psephicity is good but the sorting coefficient is low.The degree of weathering relates to the number of terraces.Usually, there is no weathering for terracesⅠ,weak weathering for teracesⅡ,weak to semi weathering for terraceⅢand semi to strong weathering for terraceⅣ.The gap filling of the gravels is sand or clunch when the weathering of the gravel bed is strong.
3)The history of the evolution of water system
We partition the history of evolution into 5 phases:
1 In the early mid-Pleistocene Epoch(Q_2~1),the Qingyijiang river flowed from southwest to north east and deposited the terraceⅣof the Mingshan-Qionglai gravel bed.
2 From the mid mid-Pleistocene Epoch(Q_2~2)to the late mid-Pleistocene Epoch (Q_2~3),the Xiongpo anticline uplifted which forced the river changed its way to southeast.After that,the river flow through Shunlong,Hongya and Zhongxing area and joins the Minjiang river.During which,the terraceⅢof the tow gravel beds was deposited.
3 From the early late-Pleistocene Epoch to(Q_3~1)to the mid late-Pleistocene Epoch(Q_3~2),the river had little changes with the weader tectonics movement and deposited the terraceⅡ.
4 From the mid late-Pleistocene Epoch(Q_3~2)to the Holocene Epoch(Q_4),the river had to changed its way to southeast in Yaan area due to the uplift of the Xiongpo anticline and the Mingshan-Qionglai mesa.It cut off the south part of the anticline on the west of Luoba,and met the terraceⅡof Danleng-Simeng gravel bed.It made a detour by the north of the terraceⅡ. Now the terraceⅠstarted to desposited.
5 In the Holocene Epoch(Q_4),Due to the uplift of the Shansuchang anticline and the Danleng-Simeng basin,the Qingyijiang river was interdicted again, which made it to cut off the south part of the anticline and flow to southeast.
通过对河流阶地的调查,得到各级阶地的分布情况、高程数据、以及形成年代,并依此分析了青衣江的下切速率和表面隆升速率。通过对砾石层的调查,了解其分布的范围、分析了砾石的成分、粒度、砾向、形成年代。在此基础上讨论了青衣江的水系演化。主要有以下认识:
1)青衣江阶地特征
除Ⅰ级阶地为堆积阶地外,其余的均为基座阶地。青衣江阶地在不同流域发育级数不一,特征明显的阶地可多达四级,以草坝——万古场阶地最为典型。此外在洪雅南阳平阶地特征也较为明显,阶地级数也有三级。由阶地的年代和高程分析得出在不同时期河流的下切速率和表面隆升速率。
2)砾石层特征
砾石层属于河流成因,二元结构明显。砾石成分主要为石英岩、花岗岩、闪长岩、辉绿岩、砂岩及火山岩等。砾径变化范围较大,1～40cm不等,但在5～25cm之间居多。砾石磨圆较好,分选多数是中一差。风化程度按阶地级数的增加而增加,一般是Ⅰ级阶地无风化,Ⅱ级阶地弱风化,Ⅲ级阶地弱一半风化,Ⅳ级阶地半一强风化。填隙物主要为沙土,强风化的砾石层均粘土化。
3)水系演化历史
我们将青衣江水系演化划分为五个阶段:
1在中更新世早期(Q_2~1)青衣江往北东流,并形成了名、邛砾石层的Ⅳ级阶地。
2从中更新世中期(Q_2~2)到中更新世晚期(Q_2~3),由于熊坡背斜北部隆起,青衣江改道南东流经顺龙、洪雅和中兴附近区域,在中兴以东与古岷江汇合,并形成了两套砾石层的Ⅲ级阶地。
3晚更新世早期(Q_3~1)——中期(Q_3~2)由于构造运动相对减弱,青衣江没有发生明显的改道。Ⅱ级阶地在此期间形成。
4晚更新世中期(Q_3~2)——全新世(Q_4)由于熊坡背斜继续隆起和名、邛台地南端的抬升,青衣江在罗坝以西切断熊坡背斜南端改道南东东,之后相遇丹、思砾石层Ⅱ级阶地,从北端绕道转向南东流,至此两套砾石层的Ⅰ级阶地开始沉积。
5全新世(Q_4)三苏场背斜北端和丹、思盆地的抬升,青衣江在次被阻断,在夹江以西切断三苏场背斜向南改道南东。
The Qingyijiang River is situated in the eastern margin of theQinghai-Tibet, where exists multilevel river terraces in the Yaan area in the south of the Chengdu basin.There are two major gravel beds,which are Mingshan-Qionglai Gravel Bed and Danleng-Simeng Gravel Bed,deposited on the base of these terraces.The river terrace and the gravel beds are not only the record of the hydrodynamic force condition and the origin of deposit,but also marking the local tectonic activity and the climate changes.
After the survey of the river terraces,we get the information of the layout,the height and the age of the terraces.After the survey of gravel beds,we know the area and the age of the two gravel beds,the ingredient,granularity,orientation of the gravels.And according this,we discuss the evolution of the water system of Qingyijiang river.
The results are giving just as following:
1)The river terraces
Except for the terraceⅠ,which is accumulational terrace,all other terraces are bottom terraces.The number of terraces differs from one drainage area to another.An type is the Caoba-Wangu terraces which has 4 terraces,and in Yangping,on the south of Hongya,there are 3 terraces.We have survey the different terraces and got the data of their height and age,based on which we have calculated the incision rate of Qingyijing river and uplift rate of the terraces in different period.
2)The gravel beds
They are fluvial gravel beds,with the charcter of dual structure.The ingredients are quartzite,granite,diorite,dolerite,sandstone and lava.The diamater of the gravels is in the range of 1-40cm,mostly in 5-25cm.The psephicity is good but the sorting coefficient is low.The degree of weathering relates to the number of terraces.Usually, there is no weathering for terracesⅠ,weak weathering for teracesⅡ,weak to semi weathering for terraceⅢand semi to strong weathering for terraceⅣ.The gap filling of the gravels is sand or clunch when the weathering of the gravel bed is strong.
3)The history of the evolution of water system
We partition the history of evolution into 5 phases:
1 In the early mid-Pleistocene Epoch(Q_2~1),the Qingyijiang river flowed from southwest to north east and deposited the terraceⅣof the Mingshan-Qionglai gravel bed.
2 From the mid mid-Pleistocene Epoch(Q_2~2)to the late mid-Pleistocene Epoch (Q_2~3),the Xiongpo anticline uplifted which forced the river changed its way to southeast.After that,the river flow through Shunlong,Hongya and Zhongxing area and joins the Minjiang river.During which,the terraceⅢof the tow gravel beds was deposited.
3 From the early late-Pleistocene Epoch to(Q_3~1)to the mid late-Pleistocene Epoch(Q_3~2),the river had little changes with the weader tectonics movement and deposited the terraceⅡ.
4 From the mid late-Pleistocene Epoch(Q_3~2)to the Holocene Epoch(Q_4),the river had to changed its way to southeast in Yaan area due to the uplift of the Xiongpo anticline and the Mingshan-Qionglai mesa.It cut off the south part of the anticline on the west of Luoba,and met the terraceⅡof Danleng-Simeng gravel bed.It made a detour by the north of the terraceⅡ. Now the terraceⅠstarted to desposited.
5 In the Holocene Epoch(Q_4),Due to the uplift of the Shansuchang anticline and the Danleng-Simeng basin,the Qingyijiang river was interdicted again, which made it to cut off the south part of the anticline and flow to southeast.
引文
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[2]陈竹新,贾东,魏国齐等.川西前陆盆地南段薄皮冲断构造之下隐伏裂谷盆地及其油气地质意义[J].北京:石油与天然气地质.2006,27(4):460-474
[3]戴勇,李正文,张华军等.川西南部地区上三叠统构造及断裂特征[J].成都:天然气工业.2006,26(1):43-45
[4]苟宗海.四川雅安-宝兴地区的侏罗-白垩系[J].北京:中国区域地质.1998,17(2):124-131
[5]苟宗海,赵兵,李勇.四川雅安地区早第三纪地层[J].地层学杂志.1995,19(2):96-103
[6]韩建思,余佳,孟庆伟.西藏阿里地区札达盆地第四纪砾石统计及其意义[J].北京:地质通报.2005,24(7):630-636
[7]何生胤.西宁盆地湟水河流阶地与高原演化特征分析[J].陕西:水利与建筑工程学报.2007,5(3):81-97
[8]何银武.试论成都盆地(平原)的形成[J].北京:中国区域地质,1987,2:169-175
[9]黄圣睦,何天华.从石油人工地震资料分析成都平原地震地质背景的新认识[J].北京:地震地质.2003,25(4):581-594
[10]纪先桃,李廷轩,王昌全.雅安自然景观与地学背景[J].成都:四川农业大学学报.2003,21(1):64-66
[11]李春昱.雅安期与江北期砾石层之生成[J].北京:地质论评.1947,Z1
[12]李吉均,方小敏,潘保田等.新生代晚期青藏高原强烈隆起及其对周边环境的影响[J].北京:第四纪研究.2001,21(5):381-391
[13]李勇,黎兵,Steffen D等.青藏高原东缘晚新生代成都盆地物源分析与水系演化[J].成都:沉积学报.2006,24(3):309-320
[14]李勇,周荣军,Densmore A L等.青藏高原东缘龙门山晚新生代走滑挤压作用的沉积响应[J].成都:沉积学报.2006,24(2):153-164
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