查看更多>>摘要：The Mesozoic intermediate-acid intrusive rocks in Tongling area can be divided into two magmatic series, namely the shoshonitic series and the high-potassium (K) calc-alkaline series. The shoshonitic series is characterized by an association of pyroxene monzodiorites+monzodiorites+quartz monzonites, the Rittmann indices of these rocks are greater than 4 (ranging from 4.2 to 5.8), the total of rare earth elements (∑REE) ranges from 210×10-6 to 260×10-6, and has good relationship with gold deposits. The high-potassium calc-alkaline series is by an association of diorite+quartz monzodiorites+granodiorites, the Rittmann indices are less than 4 (1.8-3.2), ∑REE 130×l0-6-180×10-6,and has good relationship with copper deposits. Together with lithoenclave study, it can be concluded that the shoshonitic series magma is derived from the differentiation of the alkaline basic magma in mantle and the high-potassium (K) calc-alkaline series magma is mixture between the differentiated mantle magma and crustal magma.
查看更多>>摘要：Based on clinopyroxene (cpx)-melt equilibrium thermobarometer, this paper deals with the calculation of the elinopyroxene-melt equilibrium temperature and pressure of basalts in Kuandian,Hannuoba and Mingxi areas, eastern China. These basalts all bear mantle xenoliths. The results indicate that the crystallizing temperature and pressure of clinopyroxene phenocrysts in alkaline basalts are commonly higher than those in subalkaline basalts and the crystallizing temperature and pressure of cpx megacrysts are higher than those of phenocrysts, which further confirms that the cpx megaerysts crystallized at higher pressure than cpx porphyritic crystals. The cpx phenocrysts at various pressures indicates that the cpx can crystallize continually along the way the magma moves up.Regression analysis shows, although the basalts bearing mantle xenoliths moved up very rapidly, heat diffusion rather than adiabatic process still occurred. The comparison of temperatures and pressures between the cpx phenocrysts and megacrysts crystallization and xenolith in alkali basalts demonstrates that host magma came deeper than the mantle xenoliths in terms of pressure and the xenoliths are therefore the upper mantle fragments captured by magma along the way up but not the source residues of the host magma as considered previously.
查看更多>>摘要：The convergent boundary between the East Kunlun terrane and the Baryan Hara-Songpan Garze terrane of northern Tibet plateau is a large transpressional zone on the south margin of the East Kunlun Mountains. The deformation structures are different between the eastern segment (A'nyemaqen segment) and western segment (western Datan and eastern Datan segment). The structures of the A'nyemaqen segment are characterized by superimposed thrust slices with southwest orogenic polarity formed during the stage of Indosinian collision-orogeny and brittle sinistrai strikeslip faults formed during Cenozoic. The western Datan and eastern Datan segment consists dominantly of an E-W-trending ductile sinistrai strike slip transpression zone companied by a NW-SE trending fold and fault zone on its both sides, which formed 220 Ma ago. The ductile deformation continued till 220 Ma BP and then the deformation was manifested by the reactivation of the brittle sinistral strike-slip deformation structures. Therefore, the large convergence zone on the south margin of the East Kunlun Mountains is a very special tectonic zone which changed gradually from the "Constrictive compression" in the eastern segment to the "transpression" in the western segment. Its formation was related to northeastward oblique subduction of the Baryan Hara-Songpan Garze terrane beneath the East Kulun terrane since Indosinian.
查看更多>>摘要：The Maowen fault belt is one of important fault belts of the intercontinental orogenic belt of Longmenshan, mainly experienced three stage deformation; they are ductile shearing of thrust napping, brittle thrust napping and sinstral strike-slipping. Although Sc strike of mylonite formed by ductile shearing in early stage was reformed by later two stage brittle deformation, and changed greatly along the strike and inclination, the shear zone, as a whole, strikes NE and inclines NW. The stretching lineation is parallel or nearly parallel to the inclination of the ductile shear zone. According to the development of conjugated joints, the main compressive stress of the two stage brittle deformation is oriented to 306°and 2°, respectively.
查看更多>>摘要：The components of the fluids released from alkali basalts and mantle-derived Iherzolite xenoliths in eastern China have been determined by the vacuum pyrolysis-mass spectrometric (MS) method in the present study. The results show that mantle-derived lherzolites formed in fluids composed mainly of reducing gases such as H2 and CO, and their fluid composition is characterized by a higher H2 content and a lower total content of volatiles. The fluids in alkali basalts are composed mainly of oxidizing gases, such as CO2 an SO2 and characterized by higher contents of SO2 and volatiles,implying that the extraneous oxidized fluids which are composed mainly of SO2 mixed with primary alkali basaltic magmas during their formation and evolution. The fluid compositions of alkali basalts and Iherzolite xenoliths show high nonhomogeneity in the upper mantle source region and difference in alkali basaltic magma evolution in different districts. It can be deduced that the region with higher PH2 could exist in the upper mantle beneath eastern China.
查看更多>>摘要：The Cenozoic volcanic rocks in central Qiangtang are tectonically outcropped in the transitional area where crust of the Qinghai-Tibet Plateau thins northwards and the Passion's ratios of the crust increases abnormally northwards. Of all Cenozoic volcanic rocks of northern Tibet, the volcanic rocks in Qiangtang area is the oldest one with ages from 44.1±1.0 Ma to 32.6±0.8 Ma. Petrological and geochemical studies of the volcanic rocks in central Qiangtang suggest they formed in the extension environment of post collision-orogeny and were the product of mixture of magmas from crust and mantle. The uplift of the northern plateau is closely related to decoupling of mantle lithosphere,crustal extension and thinning as well as volcanism. Therefore, it is inferred that the main uplift of the northern plateau began from about 40 Ma ago.
查看更多>>摘要：In the Sinian-Cambrian strata in the area of Kuruktag, southern Xingjiang, four layers of volcanic rocks occurred in the Early Sinian Beiyixi Formation, Late Sinian Zhamoketi Formation and Shuiquan Formation, and Early Cambrian Xishanbulake Formation, respectively. Volcanics of the Shuiquan Formation and Xishanbulake Formation are of alkali basalt series, those of the Zhamoketi Formation are of alkali basalt series and tholeiite series, and those of the Beiyixi Formation are obviously characterized by bimodal assemblage and mostly belong to alkali volcanics. Multi-element distribution patterns of the rocks show continental tumescence characters of interplate basalt.Fractional crystallization of plagioclase led to negative Eu-anomalies of some volcanics and the cumulation of olivine resulted in high MgO and low SiO2 content of some volcanic rocks. The SiO2 saturability of volcanic rocks of the Xishanbulake Formation and Shuiquan Formation is lower than that of tholeiite of the Zhamoketi Formation. Correspondingly, the abundance of incompatible elements in the first two formations is higher than those in the last formation, and the differences can be attributed to the different degrees of partial melting. The intense fractionation of REE and the obvious depletion of HREE suggest that these volcanic rocks were derived from garnet Iherzolite of the mantle in the continental lithosphere. The Ba/Nb, La/Nb, Ba/La, Ba/Th and Rb/Nb rations demonstrate that these volcanic rocks were exclusively derived from the enriched mantle, mainly the EMI type mantle.
查看更多>>摘要：The Tianshan Mountains is believed to be a typical intercontinental mountain belt, which is formed during the tectonic amalgamation of the Tarim and Tianshan blocks and the Siberian carton in Late Carboniferous-Permian period. A series of basaltic extrusive and intrusive units emplaced primarily into the Late Cretaceous-Paleogene sedimentary rocks in the Tuyon basin and its adjacent area, the South Tianshan Mountains. Geochemical data of the basalts show low Sr and Pb isotopic values and relative high Nd values (87Sr/86Sr = 0.703554 ～ 0.703884; 143Nd/144Nd = 0.512838 ～ 0.512904;206pb/204pb = 18.0063 ～ 18.4720; 207pb/204pb = 15.5060; 208Pb/204P b= 37.8072～37.9290). The data of major elements, trace elements and rare earth elements of the basalts indicate that these basaltic rocks are similar to those beneath the Hawaiian Islands. In the Tuyon basin and its adjacent areas, some Cenozoic alkaline basaltic magmatism may be related to the Cenozoic activity of mantle plume.
NETL
NSTL
万方数据