Stability of ilmenite and titanomagnetite in the presence of carbon dioxide — A thermodynamic evaluation     

Houng-Yi Yang 《Contributions to Mineralogy and Petrology》1987,95(2):202-206

The stability of ilmenite and titanomagnetite in the presence of CO₂ gas was evaluated thermodynamically. Ilmenite with a composition Ilm₉₀Hm₁₀ breaks down to the assemblage siderite-hematite-anatase below 270° C at 1,000 bars and below 300° C at 2,000 bars. Titanomagnetite with a composition Usp₅₀Mt₅₀ breaks down to the same assemblage below 345° C at 1,000 bars and below 385° C at 2,000 bars. During the low-grade metamorphism of basaltic rocks, a CO₂ partial pressure of only a few hundreds bars is sufficient to alter ilmenite and titanomagnetite to the assemblage siderite-hematite-anatase.  相似文献   

Continuity of the North Qilian and North Qinling orogenic belts, Central Orogenic System of China: Evidence from newly discovered Paleozoic adakitic rocks   总被引：7，自引：0，他引：7  

Chien-Yuan Tseng  Huai-Jen Yang  Houng-Yi Yang  Dunyi Liu  Cailai Wu  Chiu-Kuang Cheng  Cheng-Hong Chen  Choon-Muar Ker 《Gondwana Research》2009,16(2):285

Adakitic intrusive rocks of  430–450 Ma were discovered in the North Qilian orogenic belt, the western section of the Central Orogenic System (COS) in China. These adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal Ce/Pb, Nb/U, Ti/Eu, and Nd/Sm ratios and radiogenically enriched (⁸⁷Sr/⁸⁶Sr)_i of 0.7053–0.7066 and ε_Nd(t) of − 0.9 to − 1.7. While they are all characterized by low Yb (< 1.1 ppm) and Y (< 11.5 ppm) abundances with high Sr/Y (> 65) and (La/Yb)_N (> 13.7) ratios, these adakitic rocks are classified into the low-MgO–Ni–Cr and high-MgO–Ni–Cr groups. The low-MgO samples were derived from partial melting of thickened lower crust, whereas the high-MgO samples were melts from delaminated lower crust, which subsequently interacted with mantle peridotite upon ascent. Adakitic rocks from the adjacent North Qinling orogenic belt also originated from thickened lower crust at  430 Ma. In addition, the North Qilian and North Qinling orogenic belts both consist of lithological assemblages varying from subduction-accretionary complexes at south to central arc assemblages, which include adakitic rocks, then to backarc phases at north. Such a sequence reflects northward subduction of the Qilian and Qinling oceans. In these two orogenic belts, the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern Qilian and western Qinling, forming a > 1000 km Early Paleozoic orogenic belt. In such a tectonic configuration, the Qilian and Qinling oceans that subducted from south possibly represent parts of the large “Proto-Tethyan Ocean”. This inference is supported by the coexistence of Early Paleozoic coral and trilobite specimens from Asia, America and Australia in the North Qilian orogenic belt. Post-400 Ma volcanic rocks occur in the North Qinling orogenic belt but are absent in the North Qilian orogenic belt, indicating that these two orogenic belts underwent distinct evolution history after the closure of the Proto-Tethyan Ocean ( 420 Ma).  相似文献   

Petrology of an Arc-Oceanic Crust Contact Zone in the Laohushan Back-arc Basin, the Eastern Section of the North Qilian Mountains, NW China     

YANG Houng-Yi  WU Yenming  Department of Earth Sciences  Cheng Kung University  Tainan  Chinaand WU Cailai Institute of Geology  Chinese Academy of Sciences  Beijing  China 《《地质学报》英文版》2002,76(1):1-14

A contact zone sandwiched between an arc and an oceanic crust was discovered in the Laohushan area in the present study. It consists of a series of north-dipping imbricated thrust sheets and is exposed on the surface as a narrow arcuate belt, which extends for about 30 km in an E-W direction and measures about 1-3 km wide. Lithologically, it can be divided into four subzones. Subzone 1 consists of meta-andesite and metasandstone; subzone 2, psammitic schists; subzone 3, psammitic and pelitic schists, quartz diorite and hornfelses; and subzone 4, metagabbro, epidote amphibolite and pelitic schists. The metamorphism has the following grading sequence: low greenschist facies in subzone 1 → high greenschist facies in subzone 2 →low amphibolite facies in subzone 3→ epidote amphibolite facies in subzone 4. Petrographic and geochemical evidence shows that rocks in subzones 1, 2 and 3 are arc rocks, whereas those of subzone 4 are oceanic crustal rocks. The metamorphic mineral assemblages and especially miner  相似文献   

Occurrence of Alaskan-type mafic-ultramafic intrusions in the North Qilian Mountains, northwest China: Evidence of Cambrian arc magmatism on the Qilian Block   总被引：2，自引：0，他引：2  

Chien-Yuan  Tseng  Guo-Chao  Zuo  Huai-Jen  Yang  Houng-Yi  Yang  Kuo-An  Tung  Dun-Yi  Liu  Han-Quan  Wu 《Island Arc》2009,18(3):526-549

Field relationships, mineralogy and petrology, whole‐rock chemistry, and age of the Zhamashi mafic–ultramafic intrusion in the North Qilian Mountains, northwest China, have been studied in the present work. The Zhamashi intrusive body consists of ultramafic, gabbroic, and dioritic rocks in a crudely concentrically zoned structure. The ultramafic rocks are layered cumulates with rock types varying continuously from dunite through wehrlite and olivine clinopyroxenite to clinopyroxenite. The gabbroic and dioritic rocks are also layered or massive cumulates with rock types varying continuously from noritic gabbro through hornblende gabbro to diorite. The ultramafic and adjoining gabbroic rocks are discontinuous in lithology and discordant in structure across the interface. The interface is steep, sharp, and fractured. Contact metamorphic zones are well developed between the Zhamashi intrusive body and the country rock. The concentrically zoned structure of the intrusive body and the intrusion into the continental crust are the two main pieces of evidence for considering that the Zhamashi intrusion is Alaskan‐type. The mineral chemistry of the chromian spinels (Cr‐spinels) and clinopyroxenes, and the variation trend of the whole‐rock compositional plot in the (Na₂O + K₂O)–FeO–MgO (AFM) diagram are also supportive of this consideration. The age of the Zhamashi intrusive body, determined with sensitive high mass‐resolution ion microprobe on the zircon grains, is 513.0 ± 4.5 Ma. Parental magma of the Zhamashi intrusion is compositionally close to the primitive magma produced by partial melting of the mantle peridotite. It was differentiated by fractional crystallization at low total pressure and under H₂O‐rich conditions in an arc environment to form all the major rock types. The concentrically zoned structure of the Zhamashi intrusive body was constructed in two stages: formation of a stratiform‐type layered sequence, followed by diapiric re‐emplacement. The occurrence of the Alaskan‐type intrusion suggests an active continental margin and Cambrian arc magmatism for the northern margin of the Qilian Block.  相似文献