Discovery and geological significance of high-pressure mafic granulites in the Pingdu–Anqiu area of the Jiaobei Terrane, the Jiao–Liao–Ji Belt, the North China Craton
Discovery and geological significance of high-pressure mafic granulites in the Pingdu–Anqiu area of the Jiaobei Terrane, the Jiao–Liao–Ji Belt, the North China Craton
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DOI：
10.1016/j.precamres.2017.05.022
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发表时间：
2017-12
影响因子：
3.8
通讯作者：
Pinghua Liu;Fulai Liu;Jia Cai;Fang Wang;Chaohui Liu;Jian-Hui Liu;Hong Yang;Jian-rong Shi;
中科院分区：
文献类型：
--
作者：
Pinghua Liu;Fulai Liu;Jia Cai;Fang Wang;Chaohui Liu;Jian-Hui Liu;Hong Yang;Jian-rong Shi;
High-pressure (HP) mafic granulites in the Pingdu–Anqiu area of the Jiaobei Terrane, in the southwestern segment of the Jiao–Liao–Ji Belt of the North China Craton, occur as irregular lenses or deformed dike swarms within the Paleoproterozoic graphite-bearing paragneisses and marbles. Petrographic examination has revealed three distinct metamorphic mineral assemblages: a peak HP granulite-facies assemblage (M1) that consists of garnet + clinopyroxene + plagioclase + quartz ± amphibole ± Fe–Ti oxides, a post-peak decompression assemblage (M2) that is characterized by symplectites of orthopyroxene + clinopyroxene + plagioclase ± amphibole ± Fe–Ti oxides, and a late cooling assemblage (M3) represented by symplectites of amphibole + plagioclase + Fe–Ti oxides. Pseudosection modeling using THERMOCALC in the NCFMASHTO system and conventional thermobarometers constrained theP–Tconditions of the M1, M2and M3assemblages toP= 1.28–1.44 GPa andT= 757–805 °C,P= 0.50–0.80 GPa andT= 780–840 °C, andP= 0.55–0.73 GPa andT= 665–730 °C, respectively. An integrated study involving laser Raman spectroscopy and scanning electron microscope analysis of mineral inclusions, cathodoluminescence imaging, andin-situU–Pb dating of zircons showed that the protolith ages of the HP mafic granulites are mainly 2200–2000 Ma and that the timing of the peak HP granulite-facies metamorphism ranges from 1950 to 1900 Ma, as recorded by the cores of metamorphic zircons. The medium- to low-pressure amphibolite- to granulite-facies retrogression occurred mainly at 1900–1800 Ma, as recorded by the rims of some zircon grains as well as zircon grains that contain inclusions of clinopyroxene + orthopyroxene + plagioclase + amphibole + sphene. Comprehensive petrographic, mineralogical, and geochronological investigations of the HP mafic granulites defined a clockwiseP–T–tpath involving near-isothermal decompression and near-isobaric cooling, which further suggests that the Jiaobei Terrane had underwent initial crustal thickening during 1950–1900 Ma, followed by relatively rapid exhumation, cooling, and retrogression in the period 1900–1800 Ma. ThisP–T–tpath was probably generated by the Paleoproterozoic collisional orogenesis of the North China Craton.
