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甘肃天水东岔镇一带出露的宽坪岩群位于北祁连—北秦岭—华北板块交界地带,呈残留体状分布于花岗岩之中,主体为一套低角闪岩相变质的片麻岩、片岩夹斜长角闪岩。利用西北大学大陆动力学重点实验室LA-ICP-MS(激光剥蚀等离子体质谱)方法,对其中的斜长角闪岩进行单颗粒锆石微区U-Pb同位素测定,获得1753±14Ma的上交点年龄,为古元古代晚期;并反映出415±2Ma～383±2Ma的变质年龄信息。结合前人研究成果,认为区域上宽坪岩群主体形成年龄为中元古代,而研究区的宽坪岩群形成于古元古代,受到加里东晚期和华力西早期构造—热事件的改造。推测研究区的宽坪岩群可能属于华北古老基底南缘的组成部分。
The Kuanping group, appearing in the vicinity of Dongcha, Tianshui, Gansu Province, is located in the junction zone of the North Qilian-North Qinling-North China Plate and remains in the shape of granite. The main body is a set of low-amphibolite- Rock, schist Claye amphibolite. Using the method of LA-ICP-MS (Laser Ablation Plasma Mass Spectrometry), Key Laboratory of Continental Dynamics, Northwest University, single-grain zircon U-Pb isotope measurements were carried out on the amphibolite to obtain an upper 1753 ± 14Ma The age of intersection was the late Paleoproterozoic, and the metamorphic age of 415 ± 2Ma ~ 383 ± 2Ma was also reported. Combined with the previous research results, it is considered that the main age of the Kantingping Group in the area is Mesoproterozoic, while the Kuanping group in the study area was formed in the Paleoproterozoic and was rebuilt by the tectono-thermal events in the late Caledonian and Early Variscan . It is speculated that the Kuanping group in the study area may belong to the southern margin of North China.