ArticlePDF Available

Where was South China located in the reconstruction of Rodinia?

Authors:
3"卷 第"
"112J地学前缘!中国地质大学"北京#北京大学$
$%&()*+,-*,.&/-+,&0!
7(+-%[-+_,&0+
;/:Z,/0*+,-*,0
"
C,+
B
+-
=
#
<,b+-
=[-+_,&0+
;
$
g/6K3"H/K"
F
9
&K"112
北京西山官地杂岩的形成时代及构造意义
颜丹平
3
!
"
!
!周美夫
!
!
!宋鸿林
"
!
!刘敦一
J
!
!王彦斌
J
!
!汪昌亮
"
!
!董铁柱
"
3U 中国科学院 广州地球化学研究所与南海海洋研究所边缘海地质重点实验室"广东 广州 231IJ1
"U 中国地质大学 地球科学与资源学院"3111#!
!U 香港大学 地球科学系"国 香港
JU 中国地质科学院 地质研究所"3111!L
^FH ‘%-W
9
+-
=
3
"
"
"
VQE[ G,+W:?
!
"
)EHZ Q/-
=
W6+-
"
"
O][ ‘?-W
;
+
J
"YFHZ ^%-W5+-
J
"
YFHZ7(%-
=
W6+%-
=
"
"
EHZ 4+,Wc(?
"
3U
F#G*/#&*/
)
*
2,#/
5
-+#0%.#9.*0*
5)
"
9#+
5
H8*;+1&-&&.*
29.*"8.3-1&/
)C %*&8$8-+#
%.#;+1&-&&.*
2I".#+*0*
5)
"
$8-+.1.6"#(.3
)*
2%"-.+".1
"
9#+
5
H8*
231IJ1
"
$8-+#
"7
%"8**0*
2E#/&8%"-.+".1#+( ,-+./#0=.1*/".1
"
$8-+#J+->./1-&
)*
29.*1"-.+".1
"
?.-
K
-+
5
3111#!
"
$8-+#
!7
D.
B
#/&3.+&*
2E#/&8%"-.+".1
"
:8.J+->./1-&
)*
2L*+
5M*+
5
"
L*+
5M*+
5%6=
"
$8-+#
J7
;+1&-&&.*
29.*0*
5)
"
$8-+.1.6"#(.3
)*
29.*0*
5
-"#0%"-.+".1
"
?.-
K
-+
5
3111!L
"
$8-+#
/01 23,4
5
6,
7
"
89:; <)64*=
"
>:1? 9@,
7
4A6,
"
)B3A#07
)@-C+@,@A@
7
6-3A-@,.B+36,BB@BC)?=3,D6-@E
5
A)F
"G).B)+, 96AA.@*
H)6
I
6,
7
"
3,D6B.6E
5
A6-3B6@,.*@+BC)B)-B@,6-)J@A=B6@,#
!"#$%&()*)+#,*$()#-
"
KK&
"
%
!
$%
!!4!!L
收稿日期!
"11J 3" 1I
#修回日期!
"11J 3" "I
基金项目!国家自然科学基金资助项目!
J13L"1L1
"
J1JL"31I
"
J1JL"31I
$#中国科学院广州地球化学研究所与南海海洋研究所边缘海地
质重点实验室开放基金资助项目#PZ7
!
4/G.V
$
作者简介!颜丹平!
3MIJ
&!$""博士" "构造地质学专业"主要从事构造地球化学和盆地构造分析的教学和研究工作$W8%+6
%
;
%-@
9
/
*?
=
5K,@?K*-
0M.B+3-B
%
4(,Z?%-@+*/8
9
6,f/?*&/
9
0/-5/(’(,-/&(%-@0/?(0+@,0/:(,.%-
=
0(%-9
6?/-
"
%-@*/-0+00
/:/&(/
=
-,+00%-@%8
9
(+5/6+,K4(,&,(%_,5,,-@+::,&,-+-,&
9
&,%+/-0:/&(,/&+
=
+-/:(,Z?%-@+7/8
9
6,f
/>+-
=
/(,6%*b/:%
=
,*/-0&%+-0K4(,*/-&/_,&0
;%60/&,0?6,@+-@+::,&,-+-,&
9
&,%+/-0:/&(,,*/-+*
:&%8,>/&b%-@,_/6?+/-/:(,Y,0,&-Q+660/:C,+
B
+-
=
K4(+00?@
;
0(/>0(%(,c+&*/-
=
&%+-0/:Z?%-@+/&W
(/
=
-,+00(%_,+
=
-,/?0*/&,0%-@9
&/5%56
;8,%8/&
9
(+*&+80K)QP]G<]]&,0?60
;
+,6@%-?
99
,&+-,&*,
9
%
=
,
/:!
"2"3 h "1
$
G%!
MID */-:+@,-*,
"
G)Y‘+03KJ
$
K4(+0?
99
,&+-,&*,
9
%
=
,+0*/-0+@,&,@%0(,5,0,0+W
8%,/:(,*&
;
0%66+c%+/-%
=
,
"
>(+*(&,
9
&,0,-0%-+-&?0+/-’(%/**?&&,@+-(,O%, F&*(,%-K4(,&,:/&,
"
(,Z?%-@+*/8
9
6,f+0+-,&
9
&,,@%0%9
%&/:(,F&*(%,%-5%0,8,-KF5%0,8,-@,%*(8,-:%?60,
9
%&%,0
(,F&*(,%-Z?%-@+7/8
9
6,f:&/8+0/_,&6
;
+-
=0&%% !
G,0/
9
&/,&/c/+*\+f+%-0
;
0,8’/(,O/>,&<%6,/c/+*
0&%%
$
K4(,.%-
=
0(%-9
6?/-+-&?@,@’(,@,%*(8,-:%?6’5?’@+@-/’%::,*(,V+&*/- [W<5%
=
,/:(,
Z?%-@+7/8
9
6,fK4(+0,_+@,-*,0?
99
/&0(,*/-*6?0+/-(%(,Z?%-@+7/8
9
6,f+0%G,%8/&
9
(+*7/&,7/8W
9
6,f:/&8,@5,:/&,(,.%-
=
0(%-+-&?0+/-K
N)
OP@+D.
%
Z?%-@+7/8
9
6,f
#
)QP]G<]]c+&*/-[W<5%
=
,
#
O%,F&*(,%-
#
.%-
=
0(%-G,%8/&
9
(+*7/&,7/8
9
6,f
!!出露于北京西山房山岩体南北两侧的官地杂岩!主要由正片麻岩"斜长角闪岩组成!局部具混合岩化
#对官地杂岩的形成时代及出露原因一直存在很大的争议#一种观点认为官地杂岩形成时代为太古宙!
出露于中生代早期的区域伸展体制下!另一种观点则认为官地杂岩是中新元古界或古生界泥质变质岩!
山岩体侵位过程中发生接触变质作用的产物#研究表明!官地杂岩是一套正片麻岩!其中的锆石核部为岩浆
成因!而外部普遍发育较窄的浅色边#
)QP]G<]]锆石铀铅年龄测定获得锆石的一致曲线与不一致曲线上
万方数据
颜丹平!周美夫!宋鸿林!"
地学前缘
$%&()*+,-*,.&/-+,&0
"112
3"
"
!!!!!
!!
交点年龄值为!
"2"3 h "1
"G%
#代表了新太古代的岩浆结晶年龄#从而证明官地杂岩原岩形成于新太古代$
构造分析表明#官地杂岩与上覆中元古代蓟县系至早古生代地层间为剥离断层接触关#并为房山岩体侵位
和改造#证明是一个形成于房山岩体侵位前的变质核杂岩构造$但房山岩体的侵位并未对锆石的岩浆年龄和
变质年龄产生明显影响$
关键词!官地杂岩%
)QP]G<]]锆石%
[W<5年龄%新太古代%房山变质核杂岩
中图分类号!
<2##U!
!文献标识码!
F!文章编号!
3112 "!"3
!
"112
"
1" 1!!" 1I
1
!
官地杂岩呈带状出露于北京西山房山岩体南北
两侧!最早由北京地质学院西山队命名0#3
$%
于没有确切的地质年代学约束!长期以来!对官地杂
岩的成因争议很大!进而引起对区域构造关系解释
和认识的严重分歧%
历史上对于官地杂岩的时代和成因主要有两种
观点%一种观点认为!官地杂岩是寒武纪地层强烈变
质的产物&
3
!或为新元古代青白口系下马岭组的千枚
岩在房山岩体侵入作用过程中!发生混合岩化后的产
&
"
!
!
!而且区内出的地序与山地本可
以对比%另一种观点则认为!官地杂岩的形成时代为
新太古代!岩石学和岩石化学特征与北京北部燕
构造带内出露的山神庙群相似%新一轮的3X2万区
域地质调查结果1也支持此种认识!并认为官地杂岩
与上覆从中新元古代至古生代不同地层间为剥离
层接触关系!一个印支期区域伸展作用下形成的
质核杂岩构造!因此与区域比较!在地层层序上有大
规模的构造缺失%核杂过了期多
的叠加和改造!中最显著的是印支晚期至燕山早期
的近南北向挤压作用&
J
和燕山期房山岩体的侵入作
!使区内构造变形复杂化&
2
!
M
%
解决上述认识分歧的关键在于确定官地杂岩的
形成时代%笔者应用)QP]G<]]方法!对官地杂岩
中锆石进行测定!得了[W<5年龄!其结果
证明!官地杂岩形成于新太古代!从而可以澄清有关
对官地杂岩成因的认!为周口店及燕山板内造山
带区域构造格架与演化认识提供佐证%
3
!地质背景
北京西山位于燕山板内造山带西南%区内主体
构造格架呈东西向和北北东向!地层出露完整!
太古宇(中新元古界(古生界和中新生界%
官地杂岩出露于房山深成侵入体南北两侧!
露总面积约1U!Lb8
"#3
$%主要岩性为黑云母角
闪斜长片麻岩(斜长角闪岩(黑云母角闪石变粒岩
!局部具混合岩化特征!内部层序不清%官地杂岩
岩石化学成分较为复杂!据区域地质调查结果2!
长角闪岩及片麻岩等球粒陨石标准化稀土元素配分
模式具有明显的$?正异常!均具有正片麻岩特点!
原岩以火成岩为主%
官地杂岩与房山侵入体间呈明显的侵入接触关
!在侵入岩体南北边缘部分!有大量的片麻岩等捕
虏体)沿杂岩的片麻理或构造软弱部位!发育大量的
花岗闪长岩脉!岩脉成分与岩体一致%
官地杂岩与上覆不同地层间表现为剥离断层接
触关系%由于剥离断层的作用!造成杂岩与上覆层
间地层不程度!从而与杂岩直
接接触的地层!可以是中新元古界到下古生界的不
同地层#3
$% !这个剥离断层也是区域伸展
构造和房山变质核杂岩的重要组成部分%剥离断层
及其他变质核杂岩构造均被卷入到近东西向的印支
晚期挤压构造变形!如东西向的褶皱和由南向北的
冲推#3
$%地质关系表明!
岩的形成时代可能为印支期%
房山复式岩体侵入于房山变质核杂岩之中!
改造和叠加在前期构造之上%这一侵入作用还改造
了西部北岭复式向斜!使其形成围绕岩体西北部分
的弧%角闪石和黑云母NWF&J1
F&W
!M
F&
年代学测定结果表明!房山岩体的主体侵位时代为
3J2
!
3"# G%
2!&
!
!
31
!是燕山构造事件的产物%
在北侧官地杂岩出露区!南北走向的南大寨
冲推覆构造由南东东向北西西将长城系逆冲至太
宇及古生界之上!这一逆冲构造切过了北岭向斜的北
0
1
2
北京地质学院西山队K
周口店幅区域地质调查报告#
3X2 $
K
3MI!K
北京地质矿产局和中国地质大学#武汉$
U中华人民共和国区域地
质及矿产地质调查报告周口店幅#
3X2$
K3M##K
郭沪祺K
北京房山岩体北侧*片麻岩+的岩石学特征及其成因K
国地质科学硕士研究生毕业论文U3M#3U
万方数据
!!J
!! !!
颜丹平!周美夫!宋鸿林!"
地学前缘
$%&()*+,-*,.&/-+,&0
"112
3"
"
3
!周口店地区地质图
#$
#
%修改&
.+
=
K3 !Z,/6/
=
+*%68%
9
/:(,V(/?b/?@+%-%&,%>+(%&,
9
&,0,-%+_,
6
S
6
i
=
,/6/
=
+*%60,*+/-
$
#
%
下图为
6
S
6
i
剖面!剖面位置标在地质图中
东端!并将长城系逆冲于上古生界地层之上#3
&
!!在图3域的!新生代近南北向向东倾的 高角度正断层切割了上述构造!并构成了华北#
&平原和北京西山的分界
万方数据
颜丹平!周美夫!宋鸿林!"
地学前缘
$%&()*+,-*,.&/-+,&0
"112
3"
"
!!!!2
!!
"
!样品及分析测试
.
=
W!采自
母片麻岩#经薄片鉴定和分析!属正片麻岩#
I1!用常规电磁选和磁选获得纯度大于M1D
的锆石!再在双目镜下进行挑纯#最终得到的锆石
外表浑圆!! 311!
"11
3
8!长宽比约为!X3
#阴极发光显微照片显示!
"
!.ZW!锆石阴极发光照片
.+
=
K"
!7%(/@/6?8+-,0*,-*,9
(//0/:c+&*/-0:&/8
0%8
9
6,.ZW!/:(,Z?%-@+*/8
9
6,f
!
0(/>+-
=
(%c+&*/-=
&%+-0(%_,
+
=
-,/?0*/&,0>+(’+-&+80
"
0,,.+
=
K!
#
颗粒核部具有岩浆成因环带!而边部颜色较浅
石内部较暗!大多具有清晰的环带结构!具有岩浆成
因特征$边缘部分较!颜色均一且呈浅色!可能表
明受到了构造
W
热事件的干扰%"
&#
将锆石与标准锆石4$G 粘贴在环氧树脂表面
%标准锆石[W<5年龄为J3L G%
&!抛光后将待测锆
石进行透射光反射光和阴极发光扫描电镜显微照
#[W<5素分析在地质
实验中心的)QP]G<W]]离子探针上用标准测定程
序条件进行(
33
)
#数据处理程序参见O?@>+
=
(
3"
)
!
析结果列于表3
#
!
!分析结果及区域构造意义
3"颗锆石进行了3J 个点的 [W<5同位素测
%3
&#
3J 个分析点中!三个测试点
N
%
"1I
<5
&"
!
!.ZW!)QP]G<]]锆石 [W<5年龄测定结果
.+
=
K!
!)QP]G<]][W<5c+&*/-@%+-
=
&,0?60:/&0%8
9
6,
.ZW!:&/8’(,/&(/
=
-,+00/:Z?%-@+*/8
9
6,f
其中一致曲线与不一致曲线上的交点年龄为%
"2"3 h "1
&G%
!
而下交点年龄为%
I#3 h 3J1
&G%
N
%
"!#[&值明显偏小%
.Z!W2
.Z!WI .Z!W3!
&!
与后期<5 的丢失有关#如不将这三个点计算在
!33 个点的
N
%
"1I
<5
&"
N
%
"!#[&!
N
%
"1L
<5
&"
N
%
"!2[&
N
%
"1L<5
&"
N
%
"1I<5
&值较为一致![W
<5<5W<5年龄在误差范围内一致性较好!并基本
沿不一致曲线呈线性分布%!
&# 33
得的不一致曲线与一致曲线的上交点年龄为
%
"2"3 h "1
&
G%
%
3
:
!
G)Y‘T3KI
!可信度IMD&!
下交点年龄则为%
I#3h 3J1
&
G%
#其中上交点年龄
值大于冀东地区双山子群的"J21 G%角闪石 [W<5
(
3!
!
3J
)
!应代表新太古代岩浆岩的结晶年龄%
!
&!表明官地杂岩的成岩年龄为新太古代$而下交点
年龄由于误差太大!其意义不能确定#
在房山岩体两侧!与官地杂岩直接接触的地层!
可以是从中元古代蓟县系雾迷山组至寒武奥陶系!
其间缺失了整个长城!中新元古界至古生界则不
同程度地减薄或缺失#在接触界线上野外可普遍观
万方数据
!!I
!! !!
颜丹平!周美夫!宋鸿林!"
地学前缘
$%&()*+,-*,.&/-+,&0
"112
3"
"
%
!Q?4!>9(R<S ;4SM分析结果
4%56,3
!)QP]G< [W<5c+&*/-@%%:/&(,0%8
9
6,.ZW!/:Z?%-@+*/8
9
6,f
分析号 在锆石中
的位置
!
#
"1I
<5
*$
"
D
普通 <5校正后的比值
N
#
"1I
<5
$
"
N
#
"!#[$"
D
N
#
"1L
<5
$
"
N
#
"!2[$"
D
N
#
"1L
<5
$
"
N
#
"1I
<5
$误差"
D
.Z!W3 7/&, 1K13 1KJ"LJ "K3 MKI! "K" 1K3I!JI 1KJ1
.Z!W" P+8 1KML 1KJL3 !K" 33K3" 2K3 1K3L3! JK1
.Z!W! 7/&, 1K1" 1KJ#3 "K" 33K1I "K" 1K3IIML 1K2!
.Z!WJ 7/&, 1K3! 1KJL" "K" 31KII "KJ 1K3I!M 1KM2
.Z!W2 7/&, 1K"M 1K!I22 "K" #K!2 "KJ 1K3I2# 1K#2
.Z!WI 7/&, 1K2# 1K"M2" "KM IKLL JK" 1K3II! !K1
.Z!WL 7/&, 1K13 1K!MM" "K3 #KMI "K" 1K3I"#1 1K!#
.Z!W# 7/&, 1K31 1KJ"L! "K" MKL1 "K! 1K3IJI 1KIM
.Z!WM 7/&, 1K1! 1KJ"22 "K! MK2! "K! 1K3I"!L 1KJ"
.Z!W31 7/&, 1K3J 1KJ"!M "K3 MK23 "K" 1K3I"I# 1KJ2
.Z!W33 7/&, 1K"2 1KJLL !K" 31K2I !KL 1K3I1L 3K#
.Z!W3" 7/&, 1KI" 1KJ#" "KL 31KLL !K! 1K3I"1 3KM
.Z!W3! P+8 1K2L 1KJ1M "KL #K!M !KI 1K3J#M "KJ
.Z!W3J P+8 1K1J 1K"#L2 "KL 2KI# !K1 1K3J!J 3K!
分析号 在锆石中
的位置
!
#
[$
"#
3
=
K
=
S3$
!
#
4(
$
"#
3
=
K
=
S3$
N
#
"!"
4(
$
"
N
#
"!#[$
"1I
<5
"
"!#[
年龄"
G%
"1L
<5
"
"1I
<5
年龄"
G%
.Z!W3 7/&, "I# 3!2 1K2" ""MJhJ3 "JM3K#hIKL
.Z!W" P+8 # J 1K2! "J##hII "2L1hII
.Z!W! 7/&, 33# #" 1KL3 "2!1hJ2 "2"LK2hMK1
.Z!WJ 7/&, 312 I" 1KI3 "JM3hJ2 "JMIh3I
.Z!W2 7/&, M! J! 1KJL "11#h!# "232h3J
.Z!WI 7/&, 32 I 1KJ" 3IILhJ! "2"3h21
.Z!WL 7/&, !2L 33J 1K!! "3I2h!M "J#2K1hIK!
.Z!W# 7/&, 33# I1 1K2! ""MJhJ" "21!h3"
.Z!WM 7/&, !I3 "II 1KLI ""#2hJ! "J#1K2hLK1
.Z!W31 7/&, "1L M" 1KJI ""L#hJ3 "J#!KLhLKI
.Z!W33 7/&, 3I 3I 3K1# "23!hIL "JI!h !1
.Z!W3" 7/&, 32 3I 3K1I "2!Ih2I "JLLh!"
.Z!W3! P+8 3I "1 3K"L ""1Mh23 "!!!hJ3
.Z!W3J P+8 2M" L# 1K3J 3I"Mh!M ""IMh"!
!
#
"1I
<5
*$为普通"1I
<5 占总"1I
<5 的质量分数%误差为3
:
!标准误差是1KJ#D%普通 <5用测量的"1J
<5 %
<5 校正时假定"1I
<5
"
"!#[W
"1L
<5
"
"!2[年龄和"1I
<5
"
"!#[W
"1#
<5
"
"!"
4(年龄具一致性&
察到糜棱岩变余糜棱岩和各种韧性变形标志及断
泥和微构(
2
)#3
$!由此可以断定在
两者之间发育了一个具有区域构造意义的脆 韧性
剥离断层!正是由于这个断层的作用!造成了大规模
地层减薄和缺失&因此!官地杂岩基底剥离断层及
其上覆构造体共同构成了房山变质核杂岩构造(
2
)
&
显然!房山岩体是侵入于变质核杂岩构造之中!
并对其进行了叠加和改造#3及剖面$&由于并未
片麻
!可以认为!房山侵入体对官地杂岩改造所引起的
强烈热接触变质作用!特别是达到混合岩化的变质
作用仅限于较小区域!较大范围内主要还是表现为
中低级变质作用的叠加&这与区域内进行的古地热
异常分布研究的结果是相吻合的(
M
)
&
J
!
#
3
$官地杂岩原岩形成的锆石[W<5 地质年代
#
"2"3 h"1
$
G%
!应属新太古代&从岩石组合及
岩石地球化学特征上可以与北京以北山神庙群等新
太古代变质岩系对比&
#
"
$官地杂岩与上覆地层间以剥离断层接触!
与上覆中新元古界和古生界及其间发育的剥离断层
系一起!构成一个典型的印支期变质核杂岩构造&
傅昭仁教授!万天丰教授和李建威教授对项目研究和文
章初稿提出了建设性意"香港大学王焰!夏小平协助进行
了测试!数据整理和计算"稿
建设性意见"在此一并致以谢意#
万方数据
颜丹平!周美夫!宋鸿林!"
地学前缘
$%&()*+,-*,.&/-+,&0
"112
3"
"
!!!!L
!!
()*)+),-).
!
#
3$
!QE 40/6+-KF-?-?0?%6
9
/&
9
(
;
&++*,f?&,/:(,.%-
=
0(%-
=
&%-/@+/&+, #
\
$
K
?00.&-+*
29.*0*
5
-"#0%*"-.&
)*
2$8-+#
!
3M!L
!
3I
%
J3LWJ"1K
#
"$
!Z[E Q?
d
+K<,&/6/
=
+*%6*(%&%*,&+0+*0%-@/&+
=
+-/:
=
-,+00+*
&/*b0%6/-
=-/&(,&-:6%-b /:.%-
=
0(%-+-&?0+/-
!C,+
B
+-
=
#
\
$
K
?00.&-+*
2
&8.;+1&-&&.*
29.*0*
5)
!
$8-+.1.6"#(.3
)
*
29.*0*
5
-"#0%"-.+".1
!
3M#2
!
3!
%
312W3!1 &
+-7(+-,0,
K
#
!$
!O][ Z?/(?+
!Y[\+%0(%-KG,%8/&
9
(+*c/-,0/:(,.%-
=
0W
(%-%&,%+-(,Y,0,&-Q+660/:C,+
B
+-
=#
\
$
K
?00.&-+*
2
&8.
$8-+.1.6"#(.3
)
*
29.*0*
5
-"#0%"-.+".1
!
3M#L
!
3I
%
33!W3!I
&
+-7(+-,0,
K
#
J$
!)EHZ Q/-
=
6+-
!
Z$ G,-
=
*(?-K4(,]-@/0+-+%-8/_,8,-+-
(, Y,0,&- Q+660 /: C,+
B
+-
=@+0*?00,@+- (,6+
=
(’/:’(,
0&?*?&%6*(%&%*,&+0+*0#
\
$
K
9.*0*
5
-"#0=.>-.!
!
3M#J
!
!1
%
LLW#1 &
+-7(+-,0,
K
#
2$
!)QFH Y,-6%-
=
!
)EHZ Q/-
=
6+-
!
.[ V(%/&,-
!
,%6K
4/-+<
"-
B
#01
!
,.&8*(1#+( 4/#"&-".1*
2%&/"&/#06+#0
)
1-1
#
G$
K
Y?(%-
%
7(+-%[-+_,&0+
;/:Z,/0*+,-*,0<&,00
!
3MM3
%
3W3I1
&
+-7(+-,0,
K
#
I$
!YFHZ7 ^KE-’(,*(6/&+/+@5,6+-(, Y,0,&- Q+660/:
<,b+-
=#
\
$
K
?00.&-+*
29.*0*
5
-"#0%*"-.&
)*
2$8-+#
!
3M23
!
!3
&
3WJ
%
"!K
#
L$
!VQ$HZ\+%-@/-
=
K4(,=
,/6/
=
+*%60&?*?&,/:V(/?b/?@+%-W
4?/6+
!
C,+
B
+-
=#
\
$
K
9.*0*
5
-"#0M+*!0.(
5
.
!
3M2L
!
2
%
32 &
+-
7(+-,0,
K
#
#$
!)EHZ Q/-
=
6+-K 7(%&%*,&+0+*0 /: .%-
=
0(%- 8,%8/&
9
(+*
*/&,*/8
9
6,f
!
C,+
B
+-
=%-@%@+0*?00+/-%5/?+0/&+
=
+- #
\
$
K
9.*1"-.+".
!
3MMI
!
31 &
"
%
3JLW32# &
+-7(+-,0,
K
#
M$
!)EHZ Q/-
=
6+-
!
VQ[ H+-
=
K$%&6
;G,0/c/+*@,:/&8%+/-:%*+,0%-@
9
%6,/
=
,/(,&8%6%-/8%6
;
+-0/?(,&-9
%&/:(, Y,0,&- Q+660/:
C,+
B
+-
=#
\
$
K
9.*1"-.+".
!
3MM#
!
3"
%
!1"W!31 &
+-7(+-,0,
K
#
31
$
!Fg])Z F!
VQ$HZ^‘
!
YFHZ 7
!
,%6KG,0/c/+*,*/-+*
,_/6?+/-/:(,^%-0(%-:/6@%-@’(&?0’5,6
!
>+(,8
9
(%0+0/-
Q,5,+%-@O+%/-+-
=9
&/_+-*,0
!
-/&(,&- 7(+-% #
\
$
K
9.*0*
5
-"#0
%*"-.&
)
*
263./-"#,.3*-/
!
"113
!
3MJ
%
3L3W3M"K
#
33
$
!7EG<)4EH])
!Y]OO]FG)7 GK[W<5=
,/*(&/-/6/
=;/:
c+&*/-0:&/8O?-%&C&,**+%L!"3L?0+-
=
%0,-0++_,(+
=
(8%00W
&,0/6?+/-+/- 8+*&/
9
&/5, #
\
$
K
A*/+#0*
29.*
B
8
)
1-"#0=.<
1.#/"8
!
3M#J
!
#M
%
2"2W2!JK
#
3"
$
!O[‘Y]Z N PK
%
O
-(
371"
!
-+#J1./
%
1,#+#0
#
G$
KC,&b,W
6,
;
%C,&b,6,
;Z,/*(&/-/6/
=
+*%6 7,-,&
!)
9
,*+%6 <?56K"
!
"113
%
3W3MK
#
3!
$
!7Q$H ^?
d
+K
:8.9.+./#0-&
)=.
5
-*+#0 9.*0*
5) *
2$8-+#
#
G$
KC,+
B
+-
=
%
Z,/6/
=
+*%6<?56+0(+-
=Q/?0,
!
3MMJ
%
3W23L
&
+-
7(+-,0,
K
#
3J
$
!VQFHZ a+?0(,-
=
K
9.*0*
5)#+( ,.&#00*
5
.+
)*
2&8.E#/0
)
4/."#3G/-"#+-+$8-+#
%
4/*
K
."&
M3
;+&./+#&-*+#09.*0*
5
-"#0
$*00#G*/#&-*+4/*
5
/#33.N#&-*+#0P*/@-+
59/*
B*
2$8-<
+#
#
G$
K7(%-
=
*(?-
%
\+6+- <,/
9
6, <&,00
!
3M#J
%
3W2!I &
+-
7(+-,0,
K
参考文献!
#
"$
!郭沪祺K北京房山岩体北侧(片麻岩)的岩石学特征及其成因
#
\
$
K中国地质科学院地质研究所所刊!
3M#2
!
3!
%
312W3!1K
#
!$
!刘国惠!伍家善K京房山地区的变质带#
\
$
K中国地质科学
院院报!
3M#L
!
3I
%
33!W3!IK
#
J$
!宋鸿林!葛梦春K构造特征论北京西山的印支运动#
\
$
K
质论评!
3M#J
!
!1
%
LLW#1K
#
2$
!单文琅!宋鸿林!傅照仁!K构造变形分析的理论*方法与实
#
G$
K武汉%中国地质大学出版社!
3MM3
%
3W3I1K
#
L$
!郑剑东K京周口店 坨里一带的地质构造#
\
$
K地质知识!
3M2L
!
2
%
32K
#
#$
!宋鸿林K北京房山变质核杂岩的基本特征及其成因探讨#
\
$
K
现代地质!
3MMI
!
31
&
"
%
3JLW32#K
#
M$
!宋鸿林!朱宁K北京西山南部中生代早期的构造变形相和古
地热异常#
\
$
K现代地质!
3MM#
!
3"
%
!1"W!31K
#
3!
$
!程裕祺K中国区质概#
G$
K北京%地质出版社!
3MMJ
%
3W23LK
#
3J
$
!张秋生K中国早前寒武纪地质及成矿作用%国际地质合作计
划第M3项目中国工作组#
G$
K长春%吉林人民出版社!
3M#J
%
3W2!IK
万方数据
... The LSTC has experienced a rich and protracted tectonic history and many aspects of the history continue to be debated. Multiple tectonic episodes have been identified, including: the formation of metamorphic basement, the assembly of supercontinent Rodinia, the breakup of Rodinia and the formation of the Sinian-Paleozoic passive continental margin, the Late Paleozoic continental rift and mantle plume, the Mesozoic Paleotethys orogenic cycle and the Cenozoic formation of the Tibetan Plateau during collision between the Indian and Eurasian continents, (e.g., SBGMR, 1991;Zhou et al., 2002;Yan et al., 2011;Li et al., 2016;Zheng et al., 2016). The superposition of younger deformation on older events (tectonic inheritance) has hindered interpretations of the older history. ...
... (2) Metamorphic basement: Are Archean rocks present within the LSTC? Metamorphic rocks of low metamorphic grade crop out along the margins of the South China Block, including the LSTC, have been determined to be of igneous origin with volcanic features and dated at 830-725 Ma (Li et al., 1995;Zhou et al., 2002;Zhao et al., 2011a,b). However, the tectonic significance of these rocks has long been debated. ...
... Both mafic intrusions were dated at 812 ± 3 and 806 ± 4 Ma, respectively, by (Zhao and Zhou, 2007a, 2007b, 2008. D: A proposed Neoproterozoic tectonic reconstruction of the Yangtze block by Zhou et al. (2002a); E: a possible reconstruction of the Yangtze block/South China block in the Rodinia supercontinent (Yan et al., 2002). ...
Article
The Longmenshan Tectonic Complex (LSTC), along the eastern margin of the Tibetan Plateau, the site of devastating earthquakes such as the magnitude 8.0 (Wenchuan) earthquake on 12 May 2008, preserves an exceptionally complete history of the tectonic evolution of the Yangtze block and its relations to adjacent tectonic units. Due to sequential tectonic superposition and tectonic reactivation, the tectonic nature of the LSTC, and in particularly the older history, has been profoundly debated and many different tectonic models have been proposed. Herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex, highlighting problems left to be solved by future work, including: (1) The nature and constraints for at least 6 regional tectonic events, i.e., building of the metamorphic basement (Art), the Columbia/Nuna supercontinent (Pt1t), the Rodinia supercontinent (Pt3t), the Paleozoic passive continental margin (Pzt), the Paleotethys orogeny (Mzt) and the Neotethys orogeny (Kzt); (2) Metamorphic basement exposures and their tectonic implications, including rock types and geochronological constraints for the Archean, Paleoproterozoic and Neoproterozoic basements; (3) Nature of the present LSTC and its affinity with adjacent tectonic units; (4) Consideration of the NE-striking Longmenshan thrust belt and arcuate-shape Yanyuan-Muli thrust belt as parts of a single tectonic feature; (5) Mountain-basin coupled systems recording past tectonic eposides. We draw the following conclusions and tectonic models based on published research combined with our own recent studies: (1) The well preserved Archean Yudongzi gneiss group in the LSTC has a genetic affinity with the Kongling group, and thus belongs to the Yangtze block; (2) The Paleoproterozoic Hejiayan group, juxtaposed adjacent to the Archean Yudongzi group, may represent a 2000–1800 Ma orogenic belt, which corresponds to the supercontinent Nuna/Columbia amalgamation event; (3) A Neoproterozoic trench-arc-basin system, which is reconstructed based on identification of a Neoproterozoic ophiolite complex, arc-type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the Yangtze block and the LSTC, may represent the record of eastward subduction of the Neoproterozoic Mozambique oceanic lithosphere beneath the Yangtze block during the assembly of the Rodinia supercontinent; (4) A complete bidirectional Wilson cycle was reconstructed by the formation of the late Permian to the middle-late Triassic back-arc Ganze-Litang rift and ocean following the early Paleozoic Mianlue continental rift and ocean, and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision. This relatively uncommon bidirectional Wilson cycle might be attributed to the formation of the three-armed rift system in the eastern Paleotethys associated with the late Permian Eemeishan Large Igneous Province in the LSTC; (5) A three-stage tectonic sequence of, in-sequence imbricate thrust in the LSTC during India-Eurasian collisional orogeny at 55–15 Ma, extrusion from 15 to 5 Ma and the plateau uplift since ∼5 Ma resulting from lower crustal channel flow, is proposed for the formation of the present LSTC.
... Wang et al. 2017;Zhao et al. 2017). This correlation also suggests that the Yangtze Block was probably adjacent to NE India and both continents were located on the periphery of the Rodinia supercontinent (Yan et al. 2002. Ge et al. (2016) reported that the upper amphibolite-granulite facies metamorphism (660-700°C, 11-12 kbar) at c. 830-800 Ma in the Tarim Block followed a counter-clockwise P-T-t path, which also supports the model of peripheral subduction (Fig. 13). ...
Article
The evolutionary history of the NW Yangtze Block is important to interpret its location and relationship with the Rodinia supercontinent. Although Neoproterozoic arc-related tectono-thermal event is recognized in the Micangshan area, NW Yangtze Block, its timing and pressure-temperature (P-T) conditions are poorly constrained so far. This study focuses on the garnet-biotite gneiss that represents the main lithology of the Huodiya Group in the NW margin of the Yangtze Block to address this issue. This gneiss is predominantly composed of garnet, biotite, feldspar and quartz. The peak mineral assemblage consists of garnet + biotite + quartz + plagioclase + K-feldspar in the matrix. The retrograde stage is characterized by embayed rim of garnet and its associated biotite in the matrix. P-T conditions in the peak and retrograde stages are constrained to 7-8kbar/c.710oC and 5-6kbar/650-675oC, respectively, and suggested that 4-5vol.% melt was produced during an upper amphibolite-granulite facies metamorphic event. The first report of monazite U-Pb dating in the Huodiya Group, Micangshan area yielded a weighted mean 206Pb/238U age of 802 ± 5Ma. Studied samples contained detrital, igneous zircons with 206Pb/238U dates>800Ma, whereas metamorphic zircons yielded weighted mean 206Pb/238U age of 797 ± 9Ma. We propose that the Yangtze Block was probably located on the periphery of the Rodinia with consideration of compressional tectonic environment and previous studies.
... MIS has been identified as a key segment in the reconstruction of the Rodinia supercontinent, as it forms part of a pulse of activity linking Madagascar, the Seychelles, NW India and South China. Their spatial position has been envisaged either at supercontinent peripheral or as a separate tectonic micro-plate off the supercontinent (Ashwal et al., 2002;Cawood et al., 2013Cawood et al., , 2017Merdith et al., 2017;T.H. Torsvik et al., 2001;Wang and Zhou, 2012;Yan et al., 2002;Zheng, 2004;Zhou et al., 2006). Moreover, petrogenetic models for MIS are varied and at times, contradictory (rift-related, A-type, plume-related, subduction-related and even associated with mantle delamination) and continue to be debated (Ashwal et al., 2013). ...
Article
The Neoproterozoic Malani Igneous Suite (MIS) is described as the largest felsic igneous province in India. The linearly distributed Sindreth and Punagarh basins located along eastern margin of this province represent the only site of bimodal volcanism and associated clastic sediments within the MIS. The in-situ zircon U-Pb dating by LA-ICPMS reveals that the Sindreth rhyolites were erupted at 769–762 Ma. Basaltic rocks from both the basins show distinct geochemical signatures that suggest an E-MORB source for Punagarh basalts (low Ti/V ratios of 40.9–28.2) and an OIB source (high Ti/V ratios of 285–47.6) for Sindreth basalts. In the absence of any evidence of notable crustal contamination, these features indicate heterogeneous mantle sources for them. The low (La/Yb)CN (9.34–2.10) and Sm/Yb (2.88–1.08) ratios of Punagarh basalts suggest a spinel facies, relatively shallow level mantle source as compared to a deeper source for Sindreth basalts, as suggested by high (La/Yb)CN (7.24–5.24) and Sm/Yb (2.79–2.13) ratios. Decompression melting of an upwelling sub-slab asthenosphere through slab window seems to be the most plausible mechanism to explain the geochemical characteristics. Besides, the associated felsic volcanics show A2-type granite signatures, such as high Y/Nb (5.97–1.55) and Yb/Ta (9.36–2.57) ratios, consistent with magma derived from continental crust that has been through a cycle of continent-continent collision or an island-arc setting. A localized extension within an overall convergent scenario is interpreted for Sindreth and Punagarh volcanics. This general convergent setting is consistent with the previously proposed Andean-type continental margin for NW Indian block, the Seychelles and Madagascar, all of which lay either at the periphery of Rodinia supercontinent or slightly off the Supercontinent.
Article
Full-text available
The Yunkai Magmatic Arc (YKMA) is located southwest of the South China Block. It has experienced the amalgamation, splitting, and intracontinental orogeny caused by multistage tectonic thermal events. It is also a concentrated area of strong earthquakes in South China. On 12 October 2019, the Beiliu M5.2 earthquake occurred in the hinterland of the YKMA. To reveal the deep electrical structure of the YKMA and the seismogenic environment of the Beiliu earthquake, 101 high-quality data from the magnetotelluric (MT) survey points were acquired. The deep electrical structure images were obtained by three-dimensional electromagnetic inversion imaging. The results indicated that the deep part of the hinterland of the YKMA is characterized by a mushroom-shaped electrical structure composed of ultra-high resistance (R1, with a resistivity value exceeding 10,000 Ωm) and sub-high resistance (R2, with a resistivity value of about 1,000–10,000 Ωm) bodies. The epicenter of the Beiliu M5.2 earthquake was located in R1, close to the contact region between R1 and R2. There are broad low resistivity zones on the southeast and northwest sides of the YKMA. The low resistivity zones is considered to be correspond to the deep extension of the Wuchuan-Sihui and Hepu-Beiliu brittle-ductile shear zones, respectively. The brittle-ductile shearing of the boundary zones and the oblique upwelling of deep mantle-derived magma from the Leiqiong region are the main reasons for the activation of faults and the activity of moderate and strong earthquakes in the YKMA. In this geodynamic environment, local stress and strain accumulation easily occur in the brittle high resistivity body (R1). When the strain energy accumulation exceeded the threshold value that the rock could withstand, new fracture dislocations occurred in the weak region where R1 and R2 contact, which finally resulted in the 2019 Beiliu M5.2 earthquake.
Article
The Longsheng mafic-ultramafic suite consists of more than 100 mafic and ultramafic intrusions and are extensively distributed within the Neoproterozoic Danzhou Group along the Jiangnan Orogenic Belt in northern Guangxi, China. The suite has been a hotly debated subject in the context of emplacement age, source of magmas, and tectonic setting for several decades. In this article, we present newly obtained LA-ICP-MS zircon U-Pb age data, whole-rock major and trace elemental data, and Sr-Nd and zircon Lu-Hf isotopic data. These data support a middle Neoproterozoic intrusive emplacement mechanism as a result of asthenospheric underplating and subsequent lithospheric thinning, extension, and rifting. This integrated process might well correspond to the early stage of the Rodinia breakup. For example, five mafic-ultramafic rock samples yielded an emplacement age of 774 ± 2 Ma. The samples contain a large number of inherited zircon xenocrysts dated at 821 ± 3 Ma, 1.4–2.1 Ga, and 2.3–2.8 Ga, indicative of crustal contamination. The mafic-ultramafic rocks are characterized by calc-alkaline to shoshonitic associations; their Zr/Nb, Th/Yb, La/Nb, Ba/La ratios, trace, and REE patterns show an OIB affinity. Their initial 87Sr/86Sr values range from 0.697721 to 0.708579 with an average of 0.702352. They have relatively low initial 143Nd/144Nd values of 0.511530–0.511859 with an average of 0.511661. Sixteen magmatic zircon grains from diabase samples show 176Hf/177Hf values of 0.281326–0.282638, εHf(t) values of − 34.48–11.89, and TDM2 of 925–3819 Ma. Their Nb/U and Th/Ta ratios support crustal contamination as well. It is concluded that the Longsheng mafic-ultramafic suite was originated from partial melting of the enriched upper mantle (EM-I type) due to asthenospheric underplating and lithospheric extension during the incipient Rodinia breakup, and that the magmas were contaminated with crustal material during ascent.
Article
Studies on the metamorphic and related magmatic rocks within the Jiangnan Orogen are important to understand the formation and evolution of the Neoproterozoic Jiangnan Orogen because they can provide evidence for revealing the tectonic evolution of the South China Block. However, the stratigraphic correlation and framework of the low‐grade metamorphosed basement have often been misused in previous studies. The present study presents first‐hand information on the composition and deformation of the basement in the East Jiangnan Orogen. The sedimentary rocks in the north of the East Jiangnan Orogen are composed of the ordered Shangxi Group and the overlying Likou Group with a clear regional unconformity between them. The Likou Group includes Zhentou Formation (Fm) and Dengjia Fm, and the former Puling Fm is the basalt interlayer within the Dengjia Fm. The Xucun granodiorite pluton of ∼830 Ma intrudes the Shangxi Group, thereby resulting in a 100 m‐wide hornfels zone within the wall rocks and indicating that the formation of the Shangxi Group occurred earlier than that of the Xucun pluton. By contrast, the Xikou Group in southern metamorphic rocks and the overlying Jingtan Fm are flaky, disordered, and strongly deformed. The Jingtan Fm is roughly equivalent to the Heshangzhen Group and includes Zhoujiacun conglomerates in the lower part and rhyolite in the upper part with a basalt interlayer. Therefore, we present different Neoproterozoic stratigraphic sequences and magmatic rocks in the east of Jiangnan Orogen from many previous studies. The present study emphasizes that the explanation of analytical results, particularly geochronology, should be consistent with field facts.
Article
Full-text available
Meso-Neoproterozoic magmatic rocks widely occur in three Chinese blocks of China (North China, South China and Tarim blocks). Based on a large number of geochronologic data, the Meso-Neoproterozoic magmatic events in the North China Block can be divided into seven stages (1.78Ga, 1.70Ga, 1.63Ga, 1. 32Ga, 1.23Ga, 0. 93Ga and 0. 83Ga), in which 1.78Ga and 1. 32Ga magmas have a large influence range and form the large igneous provinces, respectively. The Meso-Neoproterozoic magmatic rocks in the North China Block formed in the intracontinental extensional environment indcating that North China Block was not involved in the assembly process of the Rodinia supercontinent. The Meso-Neoproterozoic magmatic events in the South China Block can be divided into eight stages (1. 78Ga, 1. 72Ga, 1. 67Ga, 1. 5Ga, 1. 42Ga, 1. OGa, 0. 84Ga and 0. 77Ga), the four stages of magmatic events from 1.78 Ga to 1. 5 Ga were formed in extensional environment. The sporadic 1.4 Ga magmatic rocks likely formed in an assembly setting in local área. The magmatic stages around 1. OGa performed differently in different parts of the South China Block, indicating the different blocks have been aggregated together. Magmatic events from 0. 95Ga to 0. 82Ga, mainly distributed in the Jiangnan Orogen and the northern margin of the Yangtze massif, led to the coherent Yangtze massif (or Yangtze Block) and Cathaysia massif (or Cathaysia Block) into the South China Block. Subsequently, magmatic events from 0. 78Ga to 0. 72Ga were almost ali over the South China Block, reflecting the extensional process after the formation of the entire continental block. The Meso-Neoproterozoic magmatic events in the Tarim block can be subdivided into eight stages (1.78Ga, 1. 5Ga, 1.43Ga, 1. IGa, 0. 92Ga, 0. 83Ga, 0. 74Ga and 0. 65Ga). The magmatic events of 1. 78Ga and 1. 5Ga are only locally distributed, and they formed in the extensional setting. 1.4 Ga magmatic events performed differently in the northern and southwestern margins of the Tarim Block. Calc-alkaline magmatic rocks in the northern margin emplaced in the continental are setting, while A2 type granites in the southwestern margin were formed in the tensional setting. During the period of 0. 96 ~ 0. 88Ga, the granites in the southeastern and northern margins of Tarim Block are dominated by I-type and S-type and formed in the active continental margin, while in the southwestern margin of Tarim Block, bimodal volcanic rocks in the Sailajiazitage Group formed in the intra-continental rift environment. During 0.88 ~ 0. 82Ga, magmatic sequences, related to subduetion and aceretion, were formed in Kuruktagh área on the northern margin, while bimodal volcanic rocks related to extensional tectonic setting were formed on the southeastern margin. The difference of magmatic rock assemblages in different locations and stages of the Tarim Block denotes that the Tarim Block originally is not originally a unified block, but likey assembled by different massifs in different periods. The differential evolutions of the Meso-Neoproterozoic magmatic rocks reveal their independem processes in the North China, South China and Tarim blocks in this period.
Article
Leaching, transportation, and enrichment of uranium in orogenic belts are closely associated with tectonic transition and progressive deformation of brittle-ductile shear zones. As such, detailed structrural analysis on shear zones of regional and district scales are of critical importance in better understanding uranium ore genesis. The giant low-temperature uranium metallogenic belt in South China is distributed along and around the Jiangnan Orogenic Belt. Most uranium deposits within that belt have formed in the Late Paleozoic and Cenozoic, both being controlled by the brittle-ductile shear zones. Previous studies have focused on characteristics of mineralization of individual uranium deposits, the relationship between uranium mineralization and regional tectonic transition remain poorly understood.This has led to ambiguous interpretation of the ore genesis. In this paper, we present geological and structural data of two representative uranium deposits (No.376 and 374 deposits) within the Motianling dome in the southwesternmost Jiangnan orogenic belt, aiming to provide a genetic linkage betweent the regional tectonics and uranium mineralization. We suggest the Motianling dome experienced at least five strucrural stages, including Neoproterozoic (~ 820Ma) (D1) with ~EW-trending folding and syn-tectonic magmatic intrusion, Calidonian top-to-NW thrusting (453 ~ 426 Ma) (D2), post-Calidonian NE-trending normal ductile shearing (426 ~295 Ma) (D3), Late Yanshanian-Himalayan brittle-ductile extension (87 ~ 47 Ma) (D4) and tectonic uplift and erosion since Himalayan (47 Ma to present) (D5), of which the D3 and D4 are the pivotal period of the uranium metallogenesis combined with microstructure and electronic probe microanalysis. Based on geological and structural analysis, relationship between progressive deformation of the brittle-ductile shear zones cutting through the Sanfang granite and formation of the Sanqiliu, Sanqisi uranium deposits is established. The results suggest that the ductile to brittle transformation of the Motianling dome had fundamental control on the release, migration and enrichment of uranium along the brittle-ductile shear zone. A new tectonic model with two types of uranium deposits in the Motianling dome highlighting the control of progressive brittle-ductile deformationon uranium mineralizatrion is proposed. This model has implications for the exploration of uranium deposits in the South China.
Article
Full-text available
The Indosinian orogeny plays an important role in the tectonic evolution of the South China block (SCB). As the biggest basin associated with the Indosinian orogeny on the southern margin of the SCB, the Nanpanjiang basin draws great attention in the geological community. Although many advances have been achieved, the time of the tectonic regime transition from extension to compression of the Nanpanjiang basin remains in dispute. In the central Nanpanjiang basin, the Paleozoic and Triassic strata are well outcropped around the Xilin faulted block, which provides an ideal studying object on revealing the basin evolution. In order to reveal the tectonic evolution of the Nanpanjiang basin, we have conducted a detailed sedimentary faces analysis, paleo-current measurement and frame-work clast statistics in the south flank of the Xilin faulted block. Our detailed field investigations show that the Lower Triassic on the south flank of the Xilin faulted block is composed of three subsequences which outcrop one by one in a southward younger order: (1) Tidal flat and lagoon deposits consist of mudstone, marlstone and calcarenite with tuff layers; (2) Mass-transport deposits (MTD) alternated with turbidite fan deposits include conglomerate, pebbly sandstone, fine sandstone and siltstone; and (3) Turbidite fans deposits include medium-coarse sandstone, siltstone and mudstone. The Middle Triassic consists of a sequence of coarse sandstone, fine sandstone, siltstone and mudstone which is interpreted to be a turbidite deposition. The facies' evolution indicates a deepening sediment environment during the Early to Middle Triassic. The paleocurrent and detrital composition analysis indicate that the detritus of the Lower Triassic in the Xilin area were mainly sourced from the Xilin fault block, while the Middle Triassic deposits in the basin were from composed provenances including the Jiangnan orogenic belt, the Kangdian massif, the Yunkai massif, the Emeishan basalt and the faulted blocks. The sediment facies ' and provenance evolutions varying with time documented a sedimentary environmental evolution of the Nanpanjiang basin from the isolated carbonate platform to the half-deep sea turbidite basin. The Early Triassic MTD is the direct sedimentary records of the basin opening. The geological facts acquired in this study suggest that the Nanpanjiang basin was controlled by a regional extension regime in the Early Triassic, and the isolated carbonate platform with the Paleozoic strata is faulted blocks formed during the basin opening. In accord with this study, the mafic dikes (ca. 258 ∼248Ma) inside the basin intruding into underlying strata of the Lower Triassic and tuff interlayers (ca. 249. 4 ± 1. 2Ma) in the Lower Triassic in the Xilin area also suggest an extension regime coeval with the basin opening during the Late Permian and the Early Triassic. The Middle Triassic turbidite fans are dominant deposits in the Nanpanjiang basin, which indicates the basin extension continued to the Middle Triassic. The opening of the Nanpanjiang basin is highly coincident with the closure of a branch of the Paleotethys Ocean in temporal and spatial, indicating that the basin was the part of subduction system of the Paleoethys oceanic lithosphere during the Late Permian to Middle Triassic. The absence of the Upper Triassic in the Napanjiang basin and adjacent areas indicates that the basin extension or subduction of the Paleotethys oceanic lithosphere terminated after the Middle Triassic.
Article
Full-text available
Well W117 in the Sichuan Basin reveals a suite of ~814 Ma quartz monzonites, unconformably overlain by Sinian clastic and carbonate sediments. The quartz monzonites contain no muscovite and amphibole, and are characterized by high SiO2 (72.26–77.93%), total alkali, and TFe2O3/MgO content, and low P2O5 and CaO abundance, with variable A/CNK ratio (0.93–1.19), classified as metaluminous to weakly aluminous highly fractionated I-type granites. They are preserved in the Neoproterozoic rift and exhibit restricted negative εNd(t) values (−7.0 to −5.2) and variable zircon εHf(t) values (−13.9 to 2.3), suggesting their generation via melting of both ancient and juvenile crustal materials in an extensional setting. Their parent magmas were formed in a low-temperature condition (831–650 °C) and finally emplaced at ca. 9–10 km below the surface, indicating that the intrusion underwent exhumation before the deposition of Sinian sag basin. Such geological processes, together with evidence for Neoproterozoic structures in the surrounding area, support that the Upper Yangtze craton experienced two main phases of rifting from 830–635 Ma. The Well W117 granites and its overlying sediments record a geodynamic evolution from orogenic collapse to continental rifting, and to thermal subsidence, probably related to the Rodinia supercontinent breakup.
ResearchGate has not been able to resolve any references for this publication.