Abstract:The study of volcanic rocks in orogenic belts aims mainly at retracing the tectono-magmatic evolutionary history of orogenic belts. A general survey of the formation, evolutionary histories of continental orogenic belts both in China and abroad reveals that orogenic belts have often undergone numerous and varied tectono-evolutionary stages, such as palaeocontinental break-up, ocean-land transition, continental matching-collision, intracontinental extension-basin-range coupling, and new tectonic uplift (intracontinental orogeny), which are respectively accompanied by characteristic volcano-magmatisms. We might therefore retrace the tectono-magmatic evolutionary history of orogenic belts in the light of characteristics of volcanic magmatism at different forming and evolutionary stages of orogenic belts and further explore some important scientific problems of global dynamics and comparative planetary dynamics by means of comparison on larger scales. Some important problems on the study of volcanic rocks of orogenic belts, which include volcanic magmatism within the plate, volcanic magmatism at constructive plate margins and volcanic magmatism at destructive plate margins, are discussed and reviewed in this paper.

Abstract:Studies on petrology and major and trace elements of Tianchi Volcano, Wudalianchi Volcano and Tengchong Volcano have been reported in recent years. This paper presents 18 sets of Sr-Nd isotopic data about these three volcanoes, and then discuss the nature of mantle sources and magma evolutions. Magma of Wudalianchi Volcano directly comes from mantle chamber, without any significant fractional crystallization and crustal contamination, and its mantle source is a mixture of EMI and PM. Samples from Tianchi Volcano of various stages show similar features close to PM, which suggests that there probably exist a huge crustal magma chamber beneath Tianchi Volcano, with continual mantle-derived magma replenishment. As to Tengchong Volcano, its high potassic calc-alkali magma source is a mixture of PM and EMII, resulting from crust-mantle interaction within the plate.

Abstract:Emeishan basalts have become a popularly investigated field recently. This paper deals with some problems concerning the study of this topic: temporal_spatial distribution; rock associations; high_Ti and low_Ti basalts; similarity and difference between these basalts and other CFB, and their relation to mantle plume and the genesis of the plume. The new recognition and explanation of these problems are proposed, and the methods for solving them are also suggested. Answering these problems will play an important role not only in the study of the Emeishan basalts and the mantle_plume interaction, but also in the investigation of their relation to mineralization.

Abstract:Late Jurassic trachyandesites from Tiaojishan Formation in Western Hills of Beijing are similar to adakitic rocks in geochemical characteristics. They contain high SiO2(>56%), Al2O3(16.33%~17.9%),Na2O(3.11%~4.8%), Na2O+K2O(6.11%~8.10%), K2O(1.64%~3.59%) and CaO(3.68%~5.82%), low MgO(<3.0%, Mg#≤0.50), high Sr (554×10-6~1 258×10-6), low Yb(<1.70×10-6)and low Y(<21×10-6), and have high Sr/Y, Y/Yb and Na2O/K2O ratios and low Rb/Sr ratios. In addition,they are characterized by strongly fractionated REE and absence of Eu anomaly. It is thought that the trachyan-desites are derived from partial melting of lower-crust calc-alkaline basaltic rock and are related to the underplatingof basic magma. Based on the geochemical features, the depth of magma is less than 50 km.

Abstract:The Proterozoic volcanic rocks in South Qinling are dominated by basic volcanic rocks with SiO245%~57% and acid volcanic rocks with SiO267%~78%. The basic volcanic rocks with spilites and basalts as the major types are close to tholeiite series, whereas the acid rocks with quartz-keratophyre as the major type are close to calc-alkaline series. Both the basic and the acid volcanic rocks are enriched with REE, especially LREE, indicating that they were derived from different sources. Primitive mantle-normalized trace element patterns of the basic volcanic rocks exhibit the continental tholeiitic characteristics with highly-enriched incompatible elements and moderately-depleted Nb and Ti, suggesting that they were formed in the continental rift. According to the Sr-Nd isotopic study, the basic volcanism was closely related to the mantle plume upwelling. All the features demonstrate that the continental rift in South Qinling region was formed in Middle-Late Proterozoic, and the mantle plume activity was the precursor of the break-up of the ancient Qinling Ocean.

Abstract:A set of rich-alkaline and alkaline intrusive complexes occur in Beishan-Alxa region, Northwest China. There exist such types of rocks as syenite, quartz syenite, aegirine-augite syenite, nepheline syenites, monzonite, quartz monzonites, alkaline gabbro, alkaline-feldspar granites and alkaline granite.The distribution, formation time, modes of occurrence, associations and petrochemistry of these complexes are summed up in this paper. Formed in Permian to Triassic, these complexes stretch in east-west direction, they are rich_alkaline to alkaline in petrochemistry, making up a belt of rich-alkaline-alkaline rocks and serving as a part of the gigantic alkaline rock belt along the northern border and the neighboring area of the North China-Tarim platform.

Abstract:Igneous series and distribution of the widespread Yanshanian magmatism, adakite, signification of I- and S-type granite, and the sources, tectonic settings and heat mechanism of granites are discussed in this paper. It is proposed that the tectonomagmatic discrimination diagrams, such as the diagram by Pearce et al . (1984), should be used with caution in distinguishing tectonic settings of granites. The depth of the source is considered to be the most important factor responsible for controlling the nature of granitoid rocks. Acording to the source depth, the authors have classified the granites into three types, viz., mantle-derived, lower-crust-derived, and middle-upper-crust-derived granites. The Yanshanian magmatism in eastern China resulted probably from underplated basaltic magmas generated from upwelling asthenospheric mantle in a continental crust extensional setting, and had nothing to do with the westward subduction of the Paleo-Pacific (or Izanagi) plate. Therefore, the Yanshanian magmatic rocks in eastern China do not belong to the circum-Pacific tectonic-magmatic belt. The reason, time and mechanism of delamination, however, need further detailed studies.

Abstract:Systematic research methods including mineralogy, petrology and geochemistry were used to study the Indosinian alkaline intrusions in Yinshan area. It is concluded that the Indosinian alkaline intrusions in Yinshan area make up two nearly EW_striking rock belts lying in the north and in the south respectively. The southern belt is mainly composed of augite_aegirine syenites, whereas the northern one consists mainly of alkali_syenite. Both belts are enriched in LREE, large-ion lithophile elements and high charge density elements. However, the content of compatible elements such as Cr and Ni are very low. Combined with the isotopic characteristics of Nd, Sr, and Pb, the authors have drawn the conclusion that the Indosinian alkaline intrusions of Yinshan area were generated from the enriched mantal, and during their invasion they were contaminated by crustal materials in different degrees.

Abstract:In view of some disputes that have cropped up in the naming of A-type granite in China, this paper suggests that the term alkaline granitoids should be used to replace the name A_type granite. Alkaline granitoids include alkaline and peralkaline granite, its associated katnosite and quartz syenite, and its associated and compositionally-similar alkali feldspar granite and rich-alkali meta_aluminous granite. These rocks have similar petrochemical compositions, mineral constituents and rock-forming tectonic settings. The term alkaline granitoids is likely to be accepted by Chinese geologists and is especially conducive to the naming of rocks by beginners and geological mapping workers.

Abstract:Petrological and geochemical characteristics, distribution, tectonic settings and forming conditions of adakites are summarized in this paper on the basis of related papers published in the past 20 years. As high_Al (Al2O3>15%) felsic rocks with high Sr content (400×10-6~2 000×10-6) and low Y and Yb content (Y≤18×10-6, Yb≤1.9×10-6), high La/Yb, Sr/Y and low K2O / Na2O (<0.5)ratios,adakites are character- ized by strongly fractionated REE and absence of Eu negative anomaly, resembling Archean high-Al TTG. Cenozoic adakites are exclusively distributed in circum-Pacific regions, while ancient adakites are also found in some orogenic belts. Most adakites were produced by patial melting of young (<25 Ma) and hot subducting oceanic crust, but some might have been produced by melting of underplated basalts, or delamination of lower continental crust. Generally, the melting residues are considered to be eclogites, garnet-bearing amphibolites, or occasionally granulites. Petrological experiments and geological evidence indicate that adakitic rocks could be formed in a relatively wide pressure range (1.0~2.6 GPa).

Abstract:As a global phenomenon, large igneous provinces (LIPs) are continuums of voluminous magnesium_rich and iron_rich effusive rocks, and include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups and ocean basin flood basalts. The representatives of the three major categories are Ontong Java and Kerguelen_Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts. Various LIPs have important temporal, spatial and compositional similarities, characterized exclusively by huge melt volume, high eruption rates and preponderant tholeiite. LIPs represent the largest known volcanic episode on the earth and record the outward significant transfer of material and energy from the Earth's interior. As they cannot be easily explained by plate tectonics, the mantle plume hypothesis is widely applied to interpret the origin of many large igneous provinces. In the thermal plume model, LIPs and many associated hotspot tracks have been ascribed to the melting of a large plume head and a narrow tail respectively. LIPs are crustal manifestations of dynamic processes in the Earth's mantle, and hence LIP parameters may be employed as boundary conditions to invert such processes.

Abstract:Pyroclastic rocks are a kind of transitional and complex rocks between lavas and sedimentary rocks. Petrologists,both at home and abroad have spent a lot of time on the classification of pyroclastic rocks, and suc_cessively put forward the classification of pyroclasts, the petrographic and the petrogenetic classification of pyroclasic rocks. Widely accepted as they are, the classification of pyroclasts and the petrographic classification of pyroclastic rocks stipulated by the IUGS Subcommission on the Systematics of Igneous Rocks fail to consider the classification with Chinese characteristics, which was put forward in 1950s to 1960s and improved in 1980s to 1990s and has since been widely used in China. On the basis of the past schemes, new classifications of pyroclasts and the petrographic as well as the petrogenetic classification of pyroclastic rocks are proposed in this paper. Volcanic sedimentation is a frontier realm between volcanology and sedimentology. The past twenty years have witnessed great development in the study of volcanic sedimentation, both theoretical and methodological. The dynamics, experimentation and simulation of volcanic eruption and sedimentation have become the main trend in the future. Despite of this, the field geology and the character of pyroclastic rocks remain the basis of the petrogenesis of pyroclasic rocks.

Abstract:There are marked differences in petrogeochemistry between granulite xenoliths (Hannuoba) and granulite terranes (Xiwangshan and Manjinggou) in North China craton. The xenoliths are predominantly mafic in composition, whereas the terranes tend to be felsic in composition. Different epochs of rock formation, different depths of origin and different tectonic settings seem to be responsible for their diversities. Hannuoba granulite xenoliths are cumulates of the basaltic melts underplated in the lower crust associated with the extensional tectonics, and the geochemical compositions of the xenoliths are controlled by the proportion of pyroxene to plagioclase. The crustal contamination is not the only reason for Nb, Ta, U and Th depletion of Hannuoba granulite xenoliths. The basaltic melts might have experienced some fractional crystallization of Ti_minerals, which caused the Nb, Ta depletion, whereas metamorphism of granulite facies in the lower crust resulted in the depletion of Th and U in xenoliths. There exists the juxtaposition of different tectonics corresponding to the differences in geochemical composition of granulite terranes, which results from the extrusion uplift.

Abstract:Southwest Fujian is a typical transitional area from Tethyan tectonic regime to Pacific epicontinental tectonic regime. The complex tectonic framework and varied rock-forming and ore_forming environments resulted from multiple-episode tectonic evolutionary processes. The good conditions for hydrothermal activity and deep thermal sources are attributed to multiple-episode and multiple-stage volcanic/intrusive activities for mineralization in the ore-concentrated area. The authors have summed up the time-space evolutionary regularity of mineral deposits in the area, and indicated the relationship between metallogenic series of mineral deposits and tectontc enviroment. The multiple-age, multiple_stratum, multiple_ore element and multiple-genesis mineral deposits result from varied tectonic environments.

Abstract:Historical records of volcanic eruption can be used to determine a most exact time of the eruption, and describe a particular eruption process and its hazard effects. Manchurian data for eruption of Tianchi volcano is the most important database besides Chinese and Korean data of this area. Some of the most interesting myths and legends of volcano and volcanology have been searched out from Manchurian. This paper shows 14 pieces of myths or legends, which are grouped into three types, standing for Tianchi volcanic eruption. It seems clearly that Tianchi volcano erupted lots of times in the last milleniums, some violently, and some gently. There was a strong correlation between the eruption and the lahar or flood around Tianchi volcano. Flood or lahar influenced the ancient people along the Nenjiang riverbanks 460 km away from Tianchi volcano. There are some other historic records for volcanic eruption in China. The determined eruption from Carerdaci volcano in 1951, located in Yutian, Xinjiang, was an event of magma rising and steam blasting.

Abstract:The Late Paleozoic meta_basalts and gabbros exposed in Kuerti area of north Xinjiang are characterized by LREE depletion of different degrees and Nb, Ta negative anomalies, suggesting that they contain both MORB_like and arc-like components. The compositional characters of these meta_basalts and gabbros are much similar to those of the typical back-arc basin basalts (BABB) (e.g., Mariana and Okinawa BABBs). Therefore, they are presently determined to be of Kuerti BAB-ophiolite, most probably representing a crust part of the intraocean back-arc basin produced by subduction of the Paleoasia ocean. Recognition of the Kuerti BAB_ophiolite implies that the north Xinjiang area was an ancient subduction zone in early Late Paleozoic. A Paleoasia Ocean separated Siberian plate from Kazakhstan-Junggar continental plate at that time. The collision between the two continental plates and the subsequent orogeny in this area most likely took place after the disappearance of Paleoasia ocean in Carboniferous-Permian period.

Abstract:The granitoids broadly distributed in eastern Jilin and Heilongjiang have long formation history and complete types. Genetically, the granites are mainly of I-type, with subordinate A-type, minor S-type and rare M-type. The stable isotope compositions of most rock bodies are characterized by low initial Rb-Sr values, normal or lower oxygen isotope values, low204Pb , high206Pb/204 P, 207Pb/204 Pb and 208 Pb/ 204 Pb ratios, and high Nd initial values. These features show that, mixed with much mantle material, the basement rock has low maturity. These characteristics are obviously different from those of the granites in North and South China.

Abstract:There were seven sessions related to igneous petrology in the 31 st International Geological Congress, namely, granitic magmatism and mineralization, granite system and the process of the Proterozoic lithosphere, basalts, genesis and emplacement of alkaline intrusions, carbonatites, kimberlites, lamproites and related rocks, organic acidic and intermediate volcanic rocks, and volcanic processes. Recent progress and the trend of development in igneous petrology have been discussed in this paper based mainly on the 31 st IGC as well as other data. It is concluded that igneous petrology has made great progress in such fields as earth's materials science, lithoprobe, large igneous provinces and mantle superplume, mantle dynamics, physics in magmatic processes, and ultrahigh_pressure experiments.