Petrogenesis of Adakitic Porphyries in an Extensional Tectonic Setting, Dexing, South China: Implications for the Genesis of Porphyry Copper Mineralization   总被引：71，自引：0，他引：71  

WANG  QIANG; XU  JI-FENG; JIAN  PING; BAO  ZHI-WEI; ZHAO  ZHEN-HUAN; LI  CHAO-FENG; XIONG  XIAO-LIN; MA  JIN-LONG 《Journal of Petrology》2006,47(1):119-144

The Dexing adakitic porphyries (quartz diorite–granodioriteporphyries), associated with giant porphyry Cu deposits, arelocated in the interior of a continent (South China). They exhibitrelatively high MgO, Cr, Ni and Sr contents, high La/Yb andSr/Y ratios, but low Yb and Y contents, similar to adakitesproduced by slab melting associated with subduction. However,they are characterized by bulk Earth-like Nd–Sr isotopecompositions (_Nd(t) = –1·14 to +1·80 and(⁸⁷Sr/⁸⁶Sr)_i = 0·7044 – 0·7047), and highTh (12·6–27·2 ppm) contents and Th/Ce (0·19–0·94)ratios, which are different from those of Cenozoic slab-derivedadakites. Sensitive High-Resolution Ion Microprobe (SHRIMP)geochronology studies of zircons reveal that the Dexing adakiticporphyries have a crystallization age of 171 ± 3 Ma.This age is contemporaneous with Middle Jurassic extension withinthe Shi-Han rift zone, and within-plate magmatism elsewherein South China, indicating that the Dexing adakitic porphyrieswere probably formed in an extensional tectonic regime in theinterior of the continent rather than in an arc setting. Theirhigh Th contents and Th/Ce ratios, and Middle Jurassic age,argue against an origin from a Neoproterozoic (1000 Ma) stalledslab in the mantle. Taking into account available data for theregional metamorphic–magmatic rocks, and the present-daycrustal thickness (31 km) in the area, we suggest that the Dexingadakitic porphyries were most probably generated by partialmelting of delaminated lower crust, which was possibly triggeredby upwelling of the asthenospheric mantle due to the activityof the Shi-Hang rift zone. Moreover, the Dexing adakitic magmasmust have interacted with the surrounding mantle peridotiteduring their ascent, which elevated not only their MgO, Cr andNi contents, but also the oxygen fugacity (fO₂) of the mantle.The high fO₂ could have induced oxidation of metallic sulfidesin the mantle and mobilization of chalcophile elements, whichare required to produce associated Cu mineralization. Therefore,the Cu metallogenesis associated with the Dexing adakitic porphyriesis probably related to partial melting of delaminated lowercrust, similar to the metallogenesis accompanying slab melting. KEY WORDS: adakite; lower crust; delamination; porphyry copper deposit, South China  相似文献   

Geochemical fingerprints and pebbles zircon geochronology: Implications for the provenance and tectonic setting of Lower Cretaceous sediments in the Zhucheng Basin (Jiaodong peninsula,North China)     

JIN-LONG NI  JUN-LAI LIU  XIAO-LING TANG  XIAO-XIAO SHI  HONG ZHANG  SHUAI HAN 《Journal of Earth System Science》2016,125(7):1413-1437

This paper conducts a petrogeochemical analysis of the Lower Cretaceous Laiyang Group’s sandstones, compares the results with the Neoproterozoic and Mesozoic intrusive rocks in the southern Sulu Orogen (also called the Jiaonan Orogen), and performs an LA-ICP-MS zircon geochronology analysis of the granitic gneisses in the conglomerates of the Laiyang Group and the intrusive rocks in the Jiaonan Orogen. The results show that the major element proportions of the Longwangzhuang Formation (LWZ Fm) and Qugezhuang Formation (QGZ Fm) of the Laiyang Group in the Zhucheng Basin are similar. The values of various indices for the LWZ Fm are similar to the average sandstone content of active continental margins, whereas, the values for the QGZ Fm are similar to those of continental island arcs. The comparison shows that the REE characteristics of the LWZ Fm and QGZ Fm of Laiyang Group are similar to those of the Neoproterozoic granitic gneisses in the Jiaonan Orogen but obviously different from those of the Early Cretaceous intrusive rocks. A tectonic setting discrimination diagram reveals that the provenance of the Laiyang Group includes features of active continental margins and continental island arcs. A number of indicators, e.g., the sandstone type, the Chemical Index of Alteration, the Chemical Index of Weathering, the Plagioclase Index of Alteration and the Index of Chemical Constituent Variation, indicated that the sandstones did not undergo intense weathering and were deposited near the source area. The zircon ages of the granitic gneiss material in the conglomerates at the base of the Laiyang Group are 790 ± 8.4 Ma, close to the ages of the Neoproterozoic granitic gneiss in the Jiaonan Orogen (739–819 Ma), and very different from the ages of the Early Cretaceous intrusive rocks. Combining with paleocurrent directions, geochemical character, the Neoproterozoic granitic gneisses in the Jiaonan Orogen may represent the primary provenance of the Laiyang Group in the Zhucheng Basin. During the depositional period of the Laiyang Group, the source rocks did not experience intense weathering, which indicated the Jiaonan Orogen experienced rapid uplift during this time, and coincided with the high exhumed rate of 2.0 km Ma ^?1 from before ca. 128 to 123 Ma in Jiaonan Orogen. The rapid subsidence during the formation of the Laiyang Group in the Zhucheng Basin and the rapid uplift of the Jiaonan Orogen are the result of a single regional extensional event associated with the lithospheric thinning and destruction of North China and peripheral cratons.  相似文献