摘要
太行山南段赞皇变质杂岩中黑云母给出了1827～1793Ma的^(40)Ar/^(39)Ar坪年龄,代表了变质基底在经历高温热扰动后冷却到300℃时的热事件年龄。结合华北克拉通变质岩的其他年代学资料,认为1800Ma士华北克拉通内经历了一次广泛而强烈的构造热伸展事件,致使克拉通基底岩石快速抬升到中上地壳,其冷却速率>6℃/Ma,隆升速率>200m/Ma。赞皇变质杂岩内苍岩寺、岗西-榆底-黑水河东和坡底-郝庄韧性剪切带内糜棱岩中黑云母分别给出了1689Ma、1633Ma和1645Ma的^(40)Ar/^(39)Ar坪年龄,代表了剪切带变形的主变形时代,这一年龄也为约束长城系的底界年龄提供了新的信息。结合已有的热年代学资料,推断华北克拉通内部赞皇变质地区中元古代的冷却速率约0.4℃/Ma,隆升速率为15m/Ma。由此也表明,自中元古代以来华北克拉通内部未受到后期构造热事件的强烈扰动,赞皇变质杂岩并非中生代变质核杂岩,而是早元古代变质穹隆。
Biotites separated from two Zanhuang metamorphic rocks in south Taihang mountains respectively yield well-defined 40Ar/39Ar plateau ages of 1792. 61±2. 26 Ma and 1826. 83±0. 76 Ma for about 70% released 39 Ar. These ages are interpreted to date the tectonothermal event of postmetamorphic cooling through appropriate argon closure temperatures (ca. 300℃. A significant tectonothermal extension event was overprinted at ca. 1800 Ma in North China Craton, resulting in the rapid uplifting of the metamorphic basement to middle-upper crust level with a cooling rate of >6℃/Ma, corresponding to a uplifting rate >200m/Ma. Three biotites separated from mylonites respectively from the Canyansi-Yingfangtai, Podi-Guandu and Yudi- Gangxi-Heishuihe NNE-trending ductile shear zones, give the 40 Ar/39 Ar plateau ages of 1688. 9±2. 4 Ma, 1632. 7±2. 0 Ma and 1645. 0?. 0 Ma for over 75% released 39 Ar. These ages are interpreted to date the cooling through 40 Ar/39 Ar closure temperatures following synkinematic growth of biotite as a consequence of mylonitic overprinting. These ages are also close to the lower-limited age of Changcheng Group. Assuming that the geothermal gradient is 30'C/Ma, a slow average cooling rate of ca. 0. 4℃/Ma and the corresponding uplifting rate of ca. 15m/Ma can be calculated since Mesoproterozoic era. Our observations appear to suggest that the Zanhuang metamorphic complex has not been overprinted by younger thermal event over than 300℃ since ca. 1800 Ma. It is also unlikely for the shear zones to reactivate after ca. 1633 Ma. This means that the Zanhuang metamorphic complex might be a Paleoproterozoic metamorphic dome rather than a Mesozoic metamorphic core-complex, i. e. , the total uplifting magnitude is no more than 10km since Mesozoic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2003年第1期131-140,共10页
Acta Petrologica Sinica
基金
国家自然科学基金(编号:49973021)
中国科学院知识创新工程项目(KZCX2-102
KZCX1-107)
