| The most important tectonothermal event in the NCC took place at ca. 1800 Ma. The event was traditionally interpreted as the "Luliang Movement", marking the finial cratonization of the NCC. Recently, however, two distinct tectonic models have been postulated to account for the event of the NCC. One suggested that the ca. 1800 Ma metamorphism and subsequent extension-uplift-magmatism were caused by a mantle plume related to break-up of a global pre-Rodinia supercontinent. Alternatively, the continental collision models postulated that the NCC consists of two Archean blocks (the Eastern and the Western), separated by ca. 1800 Ma Proterozoic erogenic belt. The 1870-1800 Ma metamorphism marked a continental collision event, whereas the following extension-uplift-magmatism (1800-1750Ma) were related to the post-collision and intracontinent rifting, representing a change of tectonic regime in the NCC. In order to achieve a better understanding of the ca.1800 Ma tectonothermal event of the NCC, it is very important for characterizing that magmatism related to the event is associated with either mantle plume or subduction/collision. The occurrence of the dyke swarm predominately distributed in Central Zone of the NCC, which is the important geological signature of the ca. 1800.Ma event. These mafic dykes may provide some important insights about the mantle processes at ca. 1800-1700 Ma and their geodynamic implications. Unfortunately, more attention has been paid to palaeomagnetic, petrologic, lithochemical and K-Ar geochronological studies of these mafic dykes. However, the nature of the mantle source of the NCC at ca.1800 Ma remains poorly understood due to the poorly precise geochronology and systematical geochemistry of these mafic dykes.We have conducted a set of 40Ar-39Ar geochronological, geochemical and Sr-Nd isotopic data on the unmetamorphosed mafic dykes in southern Taihang Mountains that are the cells of the Peterozoic dyke swarm of the Central Zone of the NCC in order to better understand the tectonic nature of the ca. 1800 Ma event and characterize the nature of the mantle source of paleoproterozoic mafic dyke swarm. The major conclusions are as follow:(1) The high-Fe tholeiites are firstly recognized in the southern Taihang Mountains(FeOt=l 3.0-16.1 %).(2) The mafic rocks from Zanhuang domain in southern Taihang Mountains can be divided into two groups: normal series and high-Fe series, they show different geochemicial characteristics. Comparing the high-Fe series, the normal series characterized by lower FeOt, TiO2, higher SiO2, AbOs and Mg# values. The normal series posses a (La/Yb)cn range of 4.27 to 7.22, a Nb/La range of 0.22 to 0.35. (Gd/Yb)cn=l.58-2.13, and depleted Nb, Ta, Th, U. The four samples of the high-Fe series(99JX-69, 99JX-70, 99JX-73, 99JX-76) posses a (La/Yb)cn range of 3.03 to 3.96, a Nb/La ranges of 0.29 to 0.31, (Gd/Yb)cn=1.25-1.37. similar to the normal series, which characterized by depleted Nb, Ta, Th, U, and have negative Zr, Hf, Sr anomalies too. However, other high-Fe samples show the flat primitive mantle normalized diagrams, possesing a Nb/La ranges of 0.54 to 0.90, a (La/Yb)cn range of 1.83 to 4.28, (Gd/Yb)cn=0.92-1.59.(3) The initial 87Sr/86Sr(t) ratio of the "normal tholeiites" in Zanhuang is in range from 0.704062 to 0.70574 and e Nd(t) =-2.75 ~ -5.52. the initial 87Sr/86Sr(t) ratio of "high-iron tholeiites" ranges from 0.704618 to 0.705988 and E Nd(t) =+0.28 ~ -2.62. Two groups of rocks show enriched Sr-Nd isotopes.(4) Three samples from Zanhuang domain devoid of deformation and metamorphism yielded well-defined 40Ar/39Ar plateau ages of 1765.28 1.12 Ma, 1774.65 0.66 Ma and 1780.71 0.48 Ma respectively. Which suggests that these mafic dykes have similar age of 1780-1765 Ma.(5) The geochemical and isotopic characteristics of mafic dykes from Zanhuang domain indicate that the "normal tholeiites" originated from the enriched lithospheric mantle modified by subduction-related fluid-fluid metasomation. However, the "high-Fe tholei...
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