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 (M1) 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 600~680℃ at 7.0~7.6kbar for the M1 stage, 680~790℃ at 9.5~10.7kbar for the metamorphic peak M2 stage and 580~720℃ 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 (M2). Calculated metamorphic P-T conditions of these two stages are 620~710℃ at 4.9~5.6kbar and 710~760℃ 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.
The Chagangnuoer and Zhibo iron deposits occurring in eastern segment of western Tianshan,were hosted primarily by the Late Carboniferous volcanic rocks,which mainly contain basalt,basaltic andesite,trachyte and andesitic tuff.The tectonic setting and age of the volcanic rocks are key elements in the reconstruction of ore genesis.In this paper,representative samples of volcanic rocks from the Chagangnuoer and Zhibo iron deposits were analyzed for major,trace elements and zircon U-Pb dating to validate their tectonic setting and formation ages.Geochemical data indicate that most of the volcanic rocks range in composition from calc-alkaline,high-K calc-alkaline to shoshonitic,with light rare earth element(LREE)and large ion lithophile element(LILE;e.g.,Rb,Th,K)enrichment and almost flat heavy rare earth element(HREE)patterns as well as strongly negative Nb,Ta and Ti anomalies,similar to features of arc volcanic rocks.In the plots of tectonic discrimination,the basaltic volcanic rocks are mainly projected in arc setting regions.LA-ICP-MS U-Pb dating of magmatic zircons from the rhyolite and dacite yield weighted average 206Pb/238U ages of 301.8±0.9Ma and 300.3±1.1Ma,respectively.In addition,weighted average 206Pb/238U ages from 303.8Ma to 305Ma were obtained for two diorites.The similar geochemical characteristics and formation ages of volcanic rocks and diorites indicated that they were sourced from the same parent magma and may formed in the same tectonic setting.Combined with the regional geological data,we therefore suggest that the high-K calc-alkaline to shoshonitic volcanic rocks were probably the products of continental island-arc magmatism during the late stage of subduction.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
