福建晋江地区混合花岗岩及浅粒岩的^(40)Ar/^(39)Ar同位素年龄测定

^(40)Ar/^(39)Ar ISOTOPIC DATING OF MIGMATIC GRANITE AND GRANULITITE FROM THE JINGJIANG AREA, FUJIAN

中生代以来,闽粤沿海变质带经历了十分复杂的构造岩浆演化过程。强烈的区域变质作用及大规模韧性剪切作用成为这一地区最引人注目的地质事件。通过对该变质带代表性岩石进行系统^(40)Ar/^(39)Ar阶段升温测定,结果表明晋江地区混合岩和浅粒岩形成于距今99—98Ma以前,后期的北西向韧性剪切则是发生在75Ma以前。

The Fujian-Guangdong coastal metamorphic belt may be devidcd into three zones: the migmatite zone in the southeast, the grauulitite zone in the middle, and the metavolcanic rocks zone in the northeast.Biotite of sample JJ-27 was sampled from the migmatio granite of the migmatite zone, while muscovite of sample JJ-10 from the leucogranulitite of the granulitite zone.The authors measured the samples with the ^(40)Ar/^(39)Ar incremental heating technique on the mass spectrometer MM-1200, and obtained a plateau age of 99. 57±0.48Ma, and an isochron age of 99.07±1.49Ma for biotite of sample JJ-27 and a plateau age of 97.85±0.01Ma and an isochron age of 97.28±0.87Ma for muscovite of sample JJ-10.The results indicate that migmatite and leucogranulitite in the Jingjiang area should be formed 99-98Ma ago, representing the main thermal and metamorphic events in the area, and the. later NW ductile shearing took place about 75Ma ago.