US EPA

7481585 

Journal Article 

Paleoproterozoic metamorphic P-T-t path and tectonic significance of the Luoning metamorphic complex at the southern terminal of the Trans-North China Orogen, Henan Province 

Jiang, ZS; Wang, GD; Xiao, LL; Diwu, CR; Lu, JS; Wu, CM 

2011 

27 

12 

3701-3717 

Chinese 

CCC:000299019000016 

The NW-SE-striking Taihua metamorphic complex crop out discretely along the southern margin of the Trans-North China Orogen (TNCO) , among which the Luoning metamorphic terrane is mainly composed of TTG-like gneisses, amphibolitic gneisses and metapelitic gneisses. Garnets in amphibolitic gneisses are commonly embayed and surrounded by amphibole + plagioclase + quartz symplectites. Three generations of mineral assemblages have been recognized in the amphibolites: the prograde assemblage (Ml) is represented by plagioclase + amphibole ± biotite ± epidote + quartz enclosed in garnet porphyroblasts, the peak metamorphic assemblage ( M2) is dominantly composed of garnet porphyroblasts and the matrix minerals plagioclase + amphibole + biotite + quartz, and the retrograde metamorphic assemblage ( M3 ) is represented by the symplectitic intergrowth of amphibole + plagioclase + quartz rimming garnet porphyroblasts. Thermodynamic computation shows that the metamorphic conditions of the plagioclase-amphibole gneisses are 600-680T: at 7. 0 ∼7. 6kbar for the M1 stage, 680-790°C at 9. 5 ∼ 10. 7kbar for the metamorphic peak M2 stage and 580-720°C at 6.5 ∼ 7. 6kbar for the retrograde M3 stage, respectively. Two stages of metamorphic assemblages are preserved in the metapelitic gneisses, the prograde metamorphic assemblages ( M1 ) and the peak metamorphic assemblages ( M 2) . Calculated metamorphic P-T conditions of these two stages are 620 ∼ 710°C at 4. 9 ∼ 5. 6kbar and 710 ∼ 760°C at 7. 3 ∼ 8. 3kbar, respectively. The Taihua metamorphic complex is deciphered to have undergone metamorphism characterized by clockwise P-T paths including the nearly isothermal decompression (ITD) segments, which are inferred to be related to the final amalgamation of North China Craton (NCC) along the TNCO. SIMS and ICP-MS U-Pb dating of metamorphic zircons extracted from amphibolitic gneisses yielded metamorphic ages ranging from 1938Ma to 1967Ma, ca. 100Ma earlier than the ubiquitous ∼ 1850Ma metamorphic event recorded in most of the metamorphic terrains in the TNCO. The amalgamation of NCC along TNCO was a long and somewhat different and complex process. 

Metamorphic geochronology; Metamorphic P-T path; Taihua Complex; Thermobarometer; Trans-North China Orogen; Feldspar; Geochronology; Igneous rocks; Metamorphic rocks; Silicate minerals; Tectonics; Isothermal decompression; Metamorphic conditions; Metamorphic terrains; North China; P-T path; Thermodynamic computations; Garnets; amphibolite; metamorphism; orogeny; P-T conditions; P-T-t path; Proterozoic; tectonic structure; uranium-lead dating; North China Block