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Wan Y.,Chinese Academy of Geological Sciences | Dong C.,Chinese Academy of Geological Sciences | Wang S.,Shandong Geological Survey Institute | Kroner A.,Chinese Academy of Geological Sciences | And 5 more authors.
Precambrian Research | Year: 2014

Western Shandong Province is a typical area of the North China Craton (NCC) where Neoarchean plutonic and supracrustal rocks are widely distributed. Early studies documented that ~2.7Ga and ~2.5Ga magmato-tectono-thermal events are well developed in the area. Here we report SHRIMP U-Pb ages and Hf-in-zircon isotopic data from ten samples of different magmatic rock types including hornblendite, gneissic tonalite, gneissic trondhjemite and gneissic granite. Magmatic zircon grains have 207Pb/206Pb ages ranging from 2667 to 2598Ma. Some rocks contain ~2.5Ga metamorphic rims and ~2.7Ga zircon cores. The magmatic zircon grains have e{open}Hf(t) values and Hf crustal model ages of -1.1 to +11.3 and 3.02-2.4Ga, respectively. Combined with an earlier study, our main conclusions are that the middle Neoarchean rocks mainly occur together with early Neoarchean rocks in the northeastern portion of the central belt. Juvenile additions to continental crust and crustal recycling played important roles in the middle Neoarchean of western Shandong Province, and the entire Neoarchean tectonic evolution can be divided into middle to early Neoarchean (2.75-2.6Ga) and late Neoarchean (2.6-2.5Ga) events. © 2014 Elsevier B.V. Source

Wan Y.-S.,Chinese Academy of Geological Sciences | Wang S.-J.,Shandong Geological Survey Institute | Ren P.,Chinese Academy of Geological Sciences | Xie H.-Q.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Geoscientica Sinica | Year: 2015

Culaishan is one of the most important areas with well-exposed Neoarchean rocks in western Shandong. In this paper, the authors carried out SHRIMP U-Pb zircon dating on three samples. Tonalitic gneiss has a weighted mean 207Pb/206Pb age of (2711±11) Ma for magmatic zircon with some recrystallization. It is inferred that a metamorphic event occurred at ~2.6 Ga. Zircons from a meta-quartz diorite sample show banded zoning with strong recrystallization, the age of 2.51 Ga is considered to be closer to the metamorphic time, and the intrusive time of the quartz diorite should be between 2.53 Ga and 2.55 Ga. Magmatic zircons from monzogranite show lead loss to different degrees, but the crystallization age might be ~2.5 Ga, as shown by the distribution of age data on concordia. Combined with geochemical study and previous work, the authors determined the Neoarchean geological evolution in the Culaishan area and redefined the boundary between the early Neoarchean (2.60~2.75 Ga) rock belt and the late Neoarchean (2500~2550 Ma) belt of juvenile rocks in the northwestern portion of western Shandong. ©, 2015, Science Press. All right reserved. Source

Xie S.,Chinese Academy of Geological Sciences | Xie H.,Chinese Academy of Geological Sciences | Wang S.,Shandong Geological Survey Institute | Kroner A.,Chinese Academy of Geological Sciences | And 6 more authors.
Precambrian Research | Year: 2014

Eastern Shandong is one of the important early Precambrian areas in the North China Craton, where extensive 2.5, 2.7 and 2.9Ga magmatic activities have been identified, followed by very strong late Neoarchean and Paleoproterozoic tectono-thermal events. We carried out SHRIMP zircon dating, Hf-in-zircon isotope analysis and a whole-rock geochemical study on ca. 2.9Ga Mesoarchean magmatic rocks. These include gneissic diorite, gneissic quartz diorite, gneissic tonalite and gneissic high-Si trondhjemite and were identified in five new areas. All these rocks contain ca. 2.5Ga metamorphic zircons. The dioritic and tonalitic rocks are enriched in large ion lithosphile (LIL) elements (K, Rb, Ba) and depleted in Nb and P with moderate to highly fractionated REE patterns, similar in chemical compositions to Archean TTG rocks worldwide. The high-Si trondhjemites are characterized by very high SiO2 and very low FeOt+MgO. The magmatic zircon grains from all these rocks are similar in their Hf isotopic compositions and have εHf(t) values ranging from +1.3 to +9.9. Combined with previous work, our main conclusions are: (1) eastern Shandong underwent a major magmatic event at ca. 2.9Ga; (2) diorites and tonalites formed by melting of thickened lower crust or the root of an oceanic plateau, whereas the high-Si trondhjemites were derived from melting of intermediate to felsic rocks; (3) the Mesoarchean (ca. 2.9Ga) was a major period of juvenile crustal addition from the depleted mantle, earlier than the major crustal growth period at 2.7-2.8Ga in the North China Craton; (4) the 2.7-2.9Ga rocks underwent strong metamorphism at ca. 2.5Ga, probably as a result of magmatic underplating. © 2014 Elsevier B.V. Source

Liu S.,Chinese Academy of Geological Sciences | Liu S.,National Taiwan University | Jahn B.-M.,National Taiwan University | Wan Y.,Chinese Academy of Geological Sciences | And 6 more authors.
Gondwana Research | Year: 2015

The North China Craton is an ideal place for studying the transition of the Earth's thermal structure and tectonics at the Archean-Proterozoic boundary due to its good preservation of the ~. 2.5. Ga tectono-thermal events. We report the discovery of a high-pressure mafic granulite from the Jiaodong Terrain in the North China Craton. The mafic granulite occurs as garnet-clinopyroxene-orthopyroxene-hornblende gneiss enclaves within a late-Archean trondhjemite-tonalite-granodiorite (TTG) gneiss. Typical high-pressure mineral assemblage of garnet-clinopyroxene-plagioclase-quartz. ±. rutile has been identified. Plagioclase. +. clinopyroxene. ±. orthopyroxene. ±. hornblende symplectite surrounding garnet ("white eye") is also observed. Using the conventional geothermobarometry and the pseudosection modeling, a clockwise metamorphic P-T path with the peak conditions at ~. 17. kbar and ~. 880. °C was determined. Zircon U-Pb analyses (SHRIMP) on the overgrowth rim of zircon grains of two samples from the same outcrop yielded a metamorphic age of 2473. ±. 6. Ma (MSWD. =. 0.8). The analyses on magmatic core gave a probable magmatic age of 2527. ±. 12. Ma (MSWD. =. 1.9). The high-pressure granulite facies metamorphism corresponds to a collisional event between the ~. 2.5. Ga crust and ~. 2.9. Ga crust at the dawn of Paleoproterozoic in the North China Craton. It also represents a new but rare case of a subduction-collision tectonics at the Archean-Proterozoic transition and provides insight into the change of the Earth's thermal structure. © 2014 International Association for Gondwana Research. Source

Wang W.,CAS Institute of Geology and Geophysics | Wang W.,Beijing Center | Zhai M.,CAS Institute of Geology and Geophysics | Wang S.,Shandong Geological Survey Institute | And 6 more authors.
Geological Journal | Year: 2013

The western Shandong Province (WSP) is one of the typical Neoarchaean granite-greenstone belts in the Eastern Block of the North China Craton (NCC) and is an important region to investigate the early Precambrian evolutionary history of the NCC. The Taishan association, consisting of a ~2.7Ga komatiite-tholeiite sequence and a ~2.5Ga felsic volcano-sedimentary sequence, is the major lithological assemblage in the WSP. In the Qixingtai area, the felsic volcano-sedimentary sequence, partly subjected to anatexis, is composed of hornblende gneiss, voluminous fine-grained biotite gneiss and biotite plagioclase gneiss. SHRIMP zircon dating shows that the protolith of the biotite plagioclase gneiss formed after ca. 2.53Ga. The tonalite intrusion into the volcanic protoliths of the fine-grained biotite gneiss and biotite plagioclase gneiss occurred at 2.52Ga. Our age data constrain the time of formation of the felsic volcano-sedimentary sequence in the Taishan area as 2.53-2.52Ga. The majority of zircons from the felsic volcano-sedimentary rocks have intermediate εHf(t) values (-1.2 to +2.1). The whole rock Nd isotopes of the Taishan felsic volcano-sedimentary rocks yield the εNd(t=2522Ma) values of +2.6 to -1.8 and TDM2 ages 3.03-2.68Ga. These values indicate the pre-existing crust was reworked at the end of the Neoarchaean (~2.5Ga). The Taishan felsic volcano-sedimentary rocks are rhyodacite-dacite and andesite in composition. These rocks and the tonalite display similar high SiO2 (65-72wt.%) and low MgO (1-2wt.%) content. In contrast, the minor andesites in the area have lower SiO2 (61-62wt.%) and higher MgO (5.3-6.3wt.%), suggesting more mantle contribution during their petrogenesis. However, the Mg-rich andesites have identical rare earth element and multi-element patterns with the rhyodacite-dacites and distinguish them from the Taishan sanukitoids. We suggest that the 2.53-2.52Ga felsic volcanics of the Taishan association are the products of partial melting of a subducted oceanic crust. The andesites were produced by minor modification of the ascending tonalite-trondhjemite-granodiorite-type magma by the mantle wedge. Our study indicates that (1) the tectonic regime of the WSP greenstone belt was dominated by an arc-subduction system at ~2.52Ga and (2) the 2.53-2.52Ga felsic volcano-sedimentary rocks and intrusive tonalite are the products of crustal reworking. The felsic volcano-sedimentary sequence of the Taishan association and other ~2.5Ga arc-like assemblages in the NCC provide important clues to understand the nature of the tectonothermal events at the end of the Neoarchaean. © 2013 John Wiley and Sons, Ltd. Source

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