Microfabric Characteristics of Ultrahigh Pressure Jadeite-Quartzite and Its Rheology Significances in Shuanghe, Dabie Mountains
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摘要: 硬玉石英岩是大别—苏鲁超高压(UHP) 变质带内重要超高压岩石类型之一, 其变形机制和动力学背景参数(应变、应力、应变速率) 对于全面了解超高压造山带的形成和演化有非常重要的意义.对大别山双河地区超高压硬玉石英岩3个样品中的主要组成矿物硬玉和石英进行显微组构和透射电镜(TEM) 的初步研究.晶格优选方位(LPO) 测量成果表明: 硬玉组构类型与绿辉石相近, 为L, LS型; 石英组构类型主要为单斜对称.TEM研究表明硬玉滑移系以(100) [001]、(110)[001]及(110)1/2[110]为主.石英中位错发育, 滑移系以(0001)[1120]底面滑移为主, 代表硬玉石英岩折返过程中经历的区域性剪切作用Abstract: Jadeite-quartzite of Dabie Mountains is one of the important rock types occurring in ultrahigh-pressure (UHP) metamorphic belts. It is significant to study the jadeite-quartzite's deformation mechanisms and geodynamical parameters (such as stress, strain, strain rate) for the knowledge on the formation and evolution of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belts. Three representative samples of the Shuanghe jadeite-quartzite from Dabie UHP belt were undertook by the microfabric and TEM for lattice preferred orientation (LPO). The results show that the LPOs of jadeite are similar to those of omphacite. Their LPOs are L- and LS-type. However, the LPOs of quartze are monoclinic symmetry type. The slip systems of jadeite are mainly (100), (110) and (110) 1/2. Abundant dislocations develop in quartz, which is of dominant slip system of (0001) -derived from basal glide. The slip system represented regional shearing durin g the exhumation of the UHP belt.
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图 1 安徽省潜山县双河地区1∶10 000地质图
1.第四纪; 2.二长花岗片麻岩; 3.碱性花岗片麻岩; 4.黑云斜长片麻岩; 5.二云母片麻岩; 6.榴辉岩; 7.角闪岩; 8.硬玉石英岩; 9.大理岩; 10.宽剪切带; 11.断层; 12.地质边界; 13.推测地质边界; 14.河流; 15.采样点; 16.坝; 17.水库
Fig. 1. Geological map of Shuanghe region, Qianshan, Anhui Province (scale: 1∶10 000)
图 2 硬玉石英岩及硬玉中的显微构造
a, b.ZH92B、X92, 硬玉中的柯石英包体; c.X4, 拉长的硬玉和石榴石, XZ面; d, e.X4, 硬玉颗粒内的2组裂隙及其中发育的反应边结构, XZ面; f.X4, 穿过不同拉长硬玉颗粒的后期穿透性裂隙, XZ面; g.ZH92B, XZ面; h.WL49B, XZ面, 拉长及成层分布的硬玉和石榴石. a, d, g为单偏光模式, b, c, e, f, h为正交偏光, b为正交锥光模式; Jd.硬玉; Grt.石榴石; Cs.柯石英; Qtz.石英; Sym.后成合晶, Ru.金红石; Zr.锆石
Fig. 2. Optical micrographs of the studied jadeite-quartzite and microstructures of jadeite
图 3 硬玉晶格优选方位(LPOs)
双河地区硬玉石英岩中硬玉的晶格优选方位, 等面积下半球投影.等密级为1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%.S.页理面; L.线理
Fig. 3. LPOs of jadeite in pole figures
图 4 绿辉石晶格优选方位(LPOs) [据金淑燕和焦述强(1998)修改]
a.大别双河地区绿辉石晶格优选方位(DS-23号样) (下半球投影, 108颗粒, 等密级1%, 3%, 5%, 7%); b.法国西部绿辉石晶格优选方位(C22号样) (下半球投影, 150颗粒, 等密级1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%)
Fig. 4. LPOs of omphacite in pole figures (modified from Jin and Jiao (1998))
图 5 双河硬玉石英岩中的石英C轴组构
双河地区硬玉石英岩中石英C轴组构, 等面积下半球投影.等密级分别为2%, 4%, 6%, 16%;1%, 4%, 7%, 16%;1%, 5%, 9%, 29%.S.页理面; L.线理.测量石英颗粒数分别为165, 152, 156
Fig. 5. C-axis fabrics of quartz in Shuanghe jadeite quartzites
图 6 透射电镜衍衬法测定硬玉位错滑移系(样品号: WL49B)
a.g002双束条件下的明场像, 5条位错线可见; b.硬玉位错的透射电镜明场像
Fig. 6. Determination of split systems of jadeite with TEM diffraction contrast method (specimen No.WL49B)
图 7 硬玉石英岩中石英的透射电镜照片
a.样品ZH92B中石英的透射电镜明场像; b.样品WL49B中石英的TEM明场像
Fig. 7. TEM photos of quartz in jadeite-quartzite
表 1 双河硬玉石英岩中石榴石、硬玉电子探针数据及峰期变质p-T条件估算值
Table 1. Composition of garnets and jadeites in Shuanghe jadeite quartzite and p-T estimates for peak metamorphism
wB/% 
表 2 样品WL49B中所测得的硬玉的滑移系
Table 2. Slip system characteristics observed in jadeite of sample WL49B by TEM
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