摘要
对采自河北省迁西县太平寨ＨＢＴ１麻粒岩中的辉石、角门石、斜长石进行了４０Ａｒ－３９Ａｒ年龄测定，并对上述三种矿物做了４０Ｋ－４０Ａｒ同位素封闭温度计算，进而根据封闭温度与年龄的关系，研究了该区麻粒岩体的冷却抬升历史。分别得到辉石坪年龄为２．１６Ｇａ，封闭温度为６２０℃；角闪石坪年龄为１．９７Ｇａ，封闭温度为５１７℃；斜长石坪年龄为１．６６Ｇａ，封闭温度为２６５℃。从２．５Ｇａ（麻粒岩相变质年龄）到２．１６Ｇａ，岩体抬升速率为１４．１ｍ／Ｍａ，冷却速率为０．３９℃／Ｍａ；从２．１６Ｇａ到１．９７Ｇａ岩体抬升速率为１８．５ｍ／Ｍａ，冷却速率为０．５５℃／Ｍａ，从１．９７Ｇａ至１．６６Ｇａ岩体抬升速率为２９．１ｍ／Ｍａ，冷却速率为０．８１℃／Ｍａ。Ａｒ－Ａｒ法给出的这些同位素证据，反映了冀东太古代麻粒岩体变质作用晚期多阶段冷却抬升的漫长历史。
The 4oAr-39Ar dating technique is used to examine cooling and uplift histories of the granulites in Taipingzhai area by applying the theories for blocking temperature and cooling age.Some useful 40Ar-39 Ar isotope ages of Taipingzhai granulite are given and their geological implications are discussed in this paper.HBT1-1 pyroxene, HBT1-2 hornblend and HBT1-3 plagioclase were separated from the granulites are about 2.5Ga which is believed to be the granulites factes metamorphic age. These samples were irradiated in Beijing 492 reactor using a next-to-core H4 facility which has a fast neutron flux of about 6. 6×10￣12n/cm2. sec, and the duration is 59. 2 hrs. Inter-laboratory standards 77-600 hornblende and ZBH-25 biotite were measured in the modified RGA-10 mass spectrometer, operated in static mode. The following factors and constants were used asflux monitors. Their Ar-Ar ages are 414±3. 1 Ma and 132. 7±0. 1 Ma, respectively. The ratios of argon isotopes were used: (36Ar/37Ar)ca = 2. 64×10-4, (37Ar/38Ar)ca= 3. 81±10-5, (39Ar/37Ar)ca= 6. 87×10-4, (38Ar/39Ar)K=0.01, (40Ar/39Ar)K = 7.15×10-3, (38Ar/36Ar)a= 0. 1869, (40Ar/36Ar)a= 294. 1, λ= 5. 543×10-10/year, t1/2= 35. 1 days (37Ar). The 4oAr-39Ar step heating experiment was performed on the pyroxene,hornblende and plagioclase. And the closure temperatures and ages of the plutons reflect the late stage of the granulite factes metamorphic process. The cooling and uplife rates of the granulite plutons are 0. 39℃ /Ma and 14. 1m/Ma from 2. 5 Ga to 2. 16 Ga, 0. 55 ℃ /Ma and 18. 5m/Ma from 2. 16 Ga to 19. 7 Ga and 0. 81℃ /Ma and 29. 1m/Ma from 1. 97 Ga to 1. 66 Ga, respectively. Obviously, the cooling and uplifting of granulite plutons were of slowly at different rates since 2. 5 Ga.
出处
《岩石学报》
CSCD
北大核心
1996年第3期390-400,共11页
Acta Petrologica Sinica
基金
国家自然科学基金
关键词
麻粒岩
辉石
角闪石
斜长石
年龄
氩同位素40
ranulites
￣40Ar-￣39Ar age
Cloure temperature
Uplift rate
Cooling rate
Eastern Hebe Province
