长石类矿物^(40)Ar-^(39)Ar坪年龄谱图及地质意义研究

^(40)Ar/^(39)Ar PLATEAU AGE SPECTRA OF FELDSPARS AND THEIR GEOLOGICAL IMPLICATIONS

从七个地区,具有不同地质热历史的酸性、碱性花岗岩和火山岩中选出斜长石、条纹长石、云母,角闪石和辉石等共生矿物对,测定14条^(40)Ar-^(39)Ar坪年龄谱。结合矿物学、地质热历史和共生矿物^(40)Ar-^(39)Ar坪年龄谱图分析,讨论了斜长石、条纹长石^(40)Ar-^(39)Ar坪年龄谱图所具的不同地质意义和作为^(40)Ar-^(39)Ar计时方法的适用性范围。

The paragenic minerals plagioclase, perthite, biotite, hornblende and pyroxene in acid-granite, alkali-granite, monzonite and volcanic rocks collected from seven areas different in thermal history have been determined. On the basis of 14 plateau age spectra and isochron ages of paragenic minerals in conjunction with the observed mineral textures, the suitability of plateau age spectra of plagioclase and perthite and their thermo-chronological significance are discuss'ed in this paper.The results indicate that undisturbed feldspar gives satisfactory 40Ar-39Ar plateau ages in consistence with those of paragenic minerals. This means that feldspars from the undisturbed area are suitable for 40Ar-39Ar dating. On the other hand, the age spectra of feldspars as well as of biotite, pyroxene and hornblende affected by tectonic or thermodynamic events appear unsmooth at varying temperatures, thus complicating their interpretation. Feldspars may give an emplacement age of a rock and/or that of the last thermodynamic event depending on the intensity of the event and the retentivity of Ar in the mineral.