Exhumation P–T path of UHP eclogites in the Hong'an area, western Dabie Mountains, China
Exhumation P–T path of UHP eclogites in the Hong'an area, western Dabie Mountains, China
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DOI：
10.1016/j.lithos.2005.12.002
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发表时间：
2006-06
期刊：
影响因子：
3.5
通讯作者：
Jingbo Liu;K. Ye;M. Sun
中科院分区：
文献类型：
--
作者：
Jingbo Liu;K. Ye;M. Sun
在红安地区超高压榴辉岩中识别出四代矿物组合，记录了四个变质阶段的折返轨迹，即：高压榴辉岩阶段为石榴石+绿辉石+钠长石+多硅白云母+角闪石+绿帘石+石英;绿帘-角闪岩相阶段为角闪石+绿帘石+钠长石-奥长石+钠长石+石英;绿片岩相阶段为阳起石+钠长石和绿帘石+钠长石+钾长石+白云母+珍珠云母+绿帘石+石英。超高压阶段形成的石榴子石被高压阶段的环礁石榴子石过度生长。X射线图像，矿物成分和组成的配置文件表明，超高压石榴石经历了一个变量的Fe-Mg的修改，以响应铁-镁之间的交换石榴石和绿辉石之前的环礁HP石榴石的过度生长。在UHP和HP石榴石之间还观察到体积扩散区。这些矿物组合的P-T条件估计如下：480至560 °C和2.5至2.9 GPa，在超高压阶段的中值为520 °C和2.8 GPa，在高压阶段的中值为575至685 °C和1.6至1.9 GPa，平均结果为634±37 °C和1.8±0.06 GPa，EA阶段为500至640 °C和0.4至1 GPa，GS阶段为160至320 °C和0.2至0.8 GPa。红安超高压榴辉岩从超高压阶段到高压阶段经历了超过100 °C的温度升高，从高压阶段到高压阶段经历了一个近似等温降压的过程，然后从高压阶段到高压阶段经历了一个明显的冷却过程。超高压榴辉岩在折返过程中经历了一系列流体侵入事件，导致不同阶段含水矿物的形成。流体性质由高压阶段的富钾到EA阶段的贫钾再到GS阶段的富钾。
Four generations of mineral assemblages have been identified in ultrahigh-pressure (UHP) eclogites from the Hong'an area, recording four metamorphic stages of the exhumation trajectory, i.e., garnet+omphacite+kyanite+zoisite/epidote+rutile+coesite formed at the UHP stage, garnet+omphacite+paragonite+phengite+amphibole+epidote+quartz at the high-pressure (HP) eclogitic stage, amphibole+epidote+albite–oligoclase+paragonite+quartz at the epidote-amphibolite facies (EA) stage, and actinolite+ albite and pumpellyite+albite+K-feldspar+muscovite+chlorite+margarite+epidote+quartz at the greenschist facies (GS) stage. Garnet formed at the UHP stage was overgrown by atoll garnet at the HP stage. X-ray images, mineral compositions and compositional profiles indicate that the UHP garnet experienced a variable Fe–Mg modification in response to Fe–Mg exchange between garnet and omphacite prior to the overgrowth of atoll HP garnet. A volume diffusion zone was also observed between the UHP and HP garnets. The following P–T conditions were estimated for these mineral assemblages: 480 to 560 °C and 2.5 to 2.9 GPa with median values of 520 °C and 2.8 GPa at UHP stage, 575 to 685 °C and 1.6 to 1.9 GPa with the average results of 634±37 °C and 1.8±0.06 GPa at the HP stage, 500 to 640 °C and 0.4 to 1 GPa at the EA stage, and 160 to 320 °C and 0.2 to 0.8 GPa at the GS stage. The Hong’an UHP eclogites experienced a temperature increase of over 100 °C from the UHP to HP stages and continued to exhume from the HP to EA stages through a process of approximately isothermal depression, which was followed by a significantly cooling from the EA to GS stages. In the process of exhumation, UHP eclogites witnessed a series of events involving fluid influx, resulting in the formation of hydrous minerals at different stages. The nature of fluids changed from K-rich at the HP stage to K-poor at the EA stage and then K-rich again at the GS stage.