辽北法库构造岩系的锆石SHRIMP年代学研究与华北地台北缘边界

Zircon SHRIMP geochronology of the Faku tectonites in the northern Liaoning Province: Implications for the northern boundary of the North China Craton

由于缺乏可靠的同位素年代学资料,辽北法库地区的变质岩系一直被看作地台基底型建造,近期研究确认它们属于原岩为深成侵入体(五龙山杂岩)和火山-沉积岩系、后经韧性剪切作用而形成的变形变质岩系,它们与遭受同期动力变质作用影响的同构造侵入岩(十间房花岗岩)一道构成了规模巨大的法库构造岩系。精确的SHRIMPU-Pb测年表明,五龙山杂岩侵位于约265±4Ma,十间房花岗岩侵位于约284±3Ma,指示构成法库构造岩系主体单元的深成侵入体并非形成于元古代,而是形成于晚古生代海西期。这些同位素年龄记录一方面暗示法库断凸可能并不存在大规模的前寒武纪变质基底,另一方面为确定华北地台与吉黑造山带(兴蒙造山带东段)在柳河断裂以东的界线提供了重要约束。

For lack of reliable isotopic chronological data, the metamorphic complex in the Faku region of the northern Liaoning province has previously been regarded as the platform basement. Recent studies revealed that these deformed and metamorphosed rocks, with a variety of protoliths of plutonic intrusions and supracrustal volcanic and sedimentary rocks, were genetically related to later ductile shearing events. They, together with the syn-tectonic intrusions (the Shijianfang granites) I constitute a large-scale Faku tectonites. Dating on the volumetrically significant plutonic units using advanced SHRIMP zircon U-Pb technique indicates that the Wulongshan complex and the Shijianfang granites were emplaced at 265 +/- 4 Ma and 284 +/- 3 Ma, respectively. This suggests that these granitic intrusions, the dominant constituents of the Faku tectonites, were emplaced during Late Paleozoic time, not in the Proterozoic as previously thought. These isotopic ages provide important geochronological constraints not only for negating the existence of the large-scale Precambrian metamorphic basement in the Faku Faulted Convex, but also for ascertaining the suturing boundary between the North China Platform and the Xing'an-Mongolian Orogenic Belt to the east of the Liuhe fault.