西藏蓬湖西镁质榴辉岩中的出溶物及其地质意义*

南京大学学报(自然科学版) ›› 2013, Vol. 49 ›› Issue (3): 356–393.

西藏蓬湖西镁质榴辉岩中的出溶物及其地质意义*

夏斌^1.2，刘维亮^1.2**，周国庆³，韦振权^2.4，王冉^2.5，李建峰²，钟云¹，胡西冲¹

出版日期:2015-11-06 发布日期:2015-11-06
作者简介: (1.中山大学海洋学院，广州，510275;2.中国科学院广州地球化学研究所，广州，510640;
3.南京大学地球科学系，南京，210093;4.广州海洋地质调查局，广州，510075;5.长安大学，西安,710031)
基金资助:
国家"973”计划(2012CB214705)，中国地质调查局“青藏高原重大关键地质问题研究”计划项日(1212011120987,1212011121259,1212011221105)

Exsolutions in a magnesian eclogite and the geologic significance
from western Peng Lake，Tibet

Xiu Bin^1’2,Liu Wei一Lung ^1’2 ,Zhou Guo一Qing³,Wei Zhen一Quan^2,⁴,Wang Ran^2.5Li Jian Feng ²，Zhong Yun¹，Hu Xi-Chong¹

Online:2015-11-06 Published:2015-11-06
About author: (1 .School of Marine Scicnces,Sun Yat-Scn Univcrsity,Guangzhou，510275,China;2. Guangzhou institute of
Geochemistry,Chinese Academy of Scicnces,Guangzhou，510640,China;3. Department of Earth Sciences,
Nanjing University,Nanjing,210093,China;4. Guangzhou Marine Geological Survcy,Guangzhou，510075,China;
5. Chang’an Univcrsity,Xi’an,710031 ,China)

摘要/Abstract

摘要： 西藏蓬湖西发现了有别于一般榴辉岩和石榴石辉石岩的超高压镁质榴辉岩，具有平衡变晶结
构，广泛发育复杂多期的出溶结构.根据矿物出溶关系可分出三个世代的单斜辉石(Cpx)和三个世代的
石榴石(Grt)和对应地三个单斜辉石(Cpx)一石榴石(Grt)对，此外还有出溶的斜方辉石、铝铬铁矿和钠长
石.对具代表性的单斜辉石一石榴石和单斜辉石一斜方辉石矿物对，得到三个阶段温度压力:阶段III一1的
平衡条件为4GPa和1113?C一1129 ?C;阶段III- 2的平衡条件为3GPa和863?C一1033?C;阶段III一3
平衡条件为2 GPa和502?C -667?C.蓬湖西镁质榴辉岩P-T路径经历了三个阶段:阶段I，蓬湖西榴
辉岩形成，压力范围可能为0. 5 -1. 5GPa;阶段II，特提斯洋关闭，洋壳向深部俯冲，致使镁质榴辉岩从
尖晶石二辉橄榄岩稳定域穿过石榴石二辉橄榄岩稳定域并最终到达1400?C和5GPa的柯石英稳定域，
形成了在超高压条件下结构均一的、稳定的“单斜辉石+石榴石+斜方辉石”固溶体;阶段III，洋壳折返
过程中温度和压力降低使得原来稳定的“单斜辉石+石榴石+斜方辉石”固溶体发生出溶作用，形成多
期次、多种类型的出溶物.阶段III再分为三个次阶段，其温压变化范围大，为2 - 4 GPa, 502?C
1129?C.镁质榴辉岩中矿物出溶肯定与压力一温度降低有关.

Abstract: Ultrahigh-pressure magnesiann eclogite was found in western Peng Lake，Tibet. Different from common
eclogite and garnet pyroxenite, it contames equilibrium crystalloblastic texture and complex multi-phase exsolution
texture. According to the exsolution relationship,three generations of clinopyroxenes(Cpx)and garnets(Grt) can be
identified:1.The bigger clinopyroxene and garnet are under equilibrium with a granular equilibrium crystalloblastic
texture,and form a Cpxl一Grtl pair. 2. The host crystal forms second generation rodlike Cpx2一Grt2 pair within the
exsolution crystal of Cpxl and Urtl respectively. 3. In host crystal Cpxl，the two Magnesian eclogue parallel exsolu-
tion Grt3s hold several Cpx3s parallclly,and they form Grt3-Cpx3 pair.There arc also orthopyroxene,alumochromitc
and albite exsolutions. We work out the equilibrium condition, by choosing"clinopyroxene-garnet"and"clinopyroxene-
orthopyroxene"pair and get the temperature and pressure of the 3 stages III Stagem一1，the equilibrium condition of
Cpxl一Grtl is 4 GPa and 1113?C一1129?C ;Stage III一2，the equilibrium condition of Cpx2一Grt2 is 3 GPa and 863
0c一1033?C ;Stage III一3，the equilibrium condition of Cpx3一Grt3 is 2 GPa and 502?C一667?C.The P一T path of
magnesiann eclogue of Western Peng Lake underwent three 3 stages. Stage I:the eclogue is formed in a 0. 5一1.5
GPa pressure range. Stage II:when Tethys ocean closed，the oceanic crust were subducted into the depth,sequcntialy
the magnesiann eclogue go from spl--lherzolite stable field across Grt lherzolite stable field into Cocsite stable field of
1400?C and 5 GPa,and forming homogeneous and a stable"clinopyroxene+garnet+orthopyroxene"solid solution
under ultrahigh pressure. Stage III;The decline of temperature and pressure with exhumation of the subducted ocean-
is crust makes the original stable" clinopyroxenc+garnet+orthopyroxene" solid solution to exsolve and to form
polyphasic and polytypic cxsolutions.This stage can be divided into 3 secondary stages in which the range of the tem-
perature and pressure is wider(2一4GPa,502?C一1129?C).It is certain that the mineral exsolution of magnesiann
eclogue do have relation with the pressurrtemperature decline.

夏斌^1.2，刘维亮^1.2**，周国庆³，韦振权^2.4，王冉^2.5，李建峰²，钟云¹，胡西冲¹. 西藏蓬湖西镁质榴辉岩中的出溶物及其地质意义*[J]. 南京大学学报(自然科学版), 2013, 49(3): 356–393.

Xiu Bin^1’2,Liu Wei一Lung ^1’2 ,Zhou Guo一Qing³,Wei Zhen一Quan^2,⁴,Wang Ran^2.5Li Jian Feng ²，Zhong Yun¹，Hu Xi-Chong¹. Exsolutions in a magnesian eclogite and the geologic significance
from western Peng Lake，Tibet
[J]. Journal of Nanjing University(Natural Sciences), 2013, 49(3): 356–393.

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