Publication Date:
2009-09-08
Description:
High-grade pelitic metasedimentary rocks (khondalites) are widely distributed in the northwestern part of the North China Craton and were named the Khondalite Belt'. Prior to the application of zircon geochronology, a stratigraphic division of the supracrustal rocks into several groups was established using interpretative field geology. We report here SHRIMP U-Pb zircon ages and Hf-isotope data on metamorphosed sedimentary and magmatic rocks at Daqingshan, a typical area of the Khondalite Belt. The main conclusions are as follows: (1) The early Precambrian supracrustal rocks belong to three sequences: a 2.56-2.51 Ga supracrustal unit (the previous Sanggan group'), a 2.51-2.45 Ga supracrustal unit (a portion of the previous upper Wulashan group') and a 2.0-1.95 Ga supracrustal unit (including the previous lower Wulashan group', a portion of original upper Wulashan group' and the original Meidaizhao group') the units thus do not represent a true stratigraphy; (2) Strong tectono-thermal events occurred during the late Neoarchaean to late Palaeoproterozoic, with four episodes recognized: 2.6-2.5, 2.45-2.37, 2.3-2.0 and 1.95-1.85 Ga, with the latest event being consistent with the assembly of the Palaeoproterozoic supercontinent Columbia; (3) During the late Neoarchaean to late Palaeoproterozoic (2.55-2.5, 2.37 and 2.06 Ga) juvenile, mantle-derived material was added to the crust.
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