摘要:

AbstractBased on studies of palaeogeography, palaeobiogeography, palaeomagnetism, geochemistry and volcanism, this paper proposes that the Zhen'an ‐Xichuan area was a small Early Palaeozoic block rifted away from South Qinling and suturing onto North Qinling earlier than the other parts of South Qinling. In the Early Palaeozoic Qinling was a small archipelagic ocean basin with 5 rows of islands including the Zhen'an ‐Xichuan block. The drifting of the Yangtze and North China plates and the islands between them in the same direction at different speeds caused their suturing process to be different from the classic plate collision, which is the major feature of the suturing of the multi‐island Tethys ocean basin. This also explains the problem that the Caledonian collision did not result in orogeny in eastern Qi

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001001.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractBased on fission track dating of apatite, and measurement of vitrinite reflectance of rock samples from the Longmenshan (Longmen Mountain)area and the West Sichuan foreland basin and computer modelling it is concluded that (l)the Songpan‐Garzê fold belt has uplifted at least by 3‐4 km with an uplift rate of no less than 0.3‐0.4 mm/a since 10 Ma B.P.; (2) the Longmenshan thrust nappe belt has uplifted at least by 5‐6 km with an uplift rate of more than 0.5‐0.6 mm/a since 10 Ma B.P.; (3) the Longmenshan detachment belt has uplifted by 1‐2 km at a rate of 0.016‐0.032 mm/a since 60 Ma B.P.; (4) the West Sichuan foreland basin has uplifted by 1.7‐3 km at a rate of 0.028‐0.05 mm/a since 60 Ma B.P.; (5) the uplift rate of the area on the west side of the Beichuan‐Yingxiu‐Xiaoguanzi fault for the last 10 Ma is 40 times as much as that on its east side; (6) the uplifting of the the Songpan‐Garzê fold belt and the subsidence of the West Sichuan foreland basin 60 Ma ago exhibit a mirro‐image correlation, i.e. the rapid uplifting of the the Songpan‐Garzê fold belt was corresponding to the rapid subsidence of the basin; the Songpan‐Garzê fold belt has uplifted at a much greater rate than the West Sichuan foeland basin in the last 60 Majand (7) the palaeogeothermal gradient was 25°C/km

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001002.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractChengdeite occurs in chromite orebodies in dimite as well as in placers in their neighbourhood. The mineral occurs as granular aggregates in association with inaglyite and in some cases occurs as graphic intergrowths with native iridium. It is opaque with a metallic lustre, colour steel‐black, streak black,HM= 5.2, VHN50=452 kg/mm2, cleavage not observed, fracture not observed, strongly magnetic. Its reflection colour is bright white with a yellowish tint. It has no internal reflection, bireflectance or pleochrism, and shows isotropism.Thirteen chemical analyses were carried out by means of the electron microprobe. The mean percentages of the data obtained in the 13 analyses are: s 0.001, Fe 7.9, Ni 0.03, Co 0.03, Cu 0.83, As 0.02, Rh 0.19, Pd 0.00, Os 0.06, Ir 88.5, Pt 2.2 and Pb 0.00. The simplified formula is Ir3Fe, which requires Ir 91.17 and Fe 8.83, the total being 100.00 (%).Five strongest lines of X‐ray powder diffraction (hkl, d, I) are: 111, 2.18 (80);200, 1.89 (60); 220, 1.34 (70); 311, 1.142 (100); 222, 1.094 (80).Through indexing of the X‐ray powder diffraction data, the mineral has been determined to be cubic withPm 3m,a=0.3792 (5)nm,V=0.05453nm an

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001003.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractIgneous topazites found recently in South China are closely associated with F‐rich granites in time and space. They have a typical igneous porphyritic texture. The phenocrysts are topaz and quartz, while the groundmass consists mainly of prismatic or acicular topaz microlites and anhedral quartz. Compared with granites, topazites are rich in SiO2(65.06%‐81.12% ) and Al2O3(13.01% ‐18.09%) but poor in MgO and Na2O and strongly péraluminous with A/NKC = 3.204‐37.313. Geochemically, the rocks are evidently depleted in Sr and Ba, but enriched in Sn, W, Nb and F. The concentrations of Sn and partial W in the topazites are 1‐2 orders of magnitude higher than the average of acid rocks. The F‐riched granites related to the topazites in the area usually have much higher ISr(0.7103‐0.7460) and δ18OQ‰ (9.5‐14.24), but lower ǐNd(T) (‐4.8‐ 9.4). It suggests that the topazite is similar to S‐type granites in genesis. Hydroxylated silicate melt inclusions, consisting of several grains of quartz and aqueous fluids, have been found in the quartz phenocrysts. The entrapment temperature of these

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001004.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractA U ‐Pb zircon age of 2774±24 Ma for eclogite from the Bixiling rock body of Anhui Province, central China, indicates that the Dabieshan coesite‐bearing eclogite was probably formed in the Late Archaean. A phengite Ar‐Ar isochron age of 662±13 Ma for the eclogite confines also an upper limit age of its subsequent retrograde metamorphism in the Precambrian. The results of isotopic dating for such type of eclogite coincide with the geological features of its restricted occurrence within the Archaean metamaorphic terrain composed of the Dabie Group. It is believed that the Dabieshan coesite‐bearing eclogite terrain might be a Late Archaean ultra‐high‐pressure metamorphic belt. The Dabie Mountains area was the eastward extension of the southern Qinling structural belt during the Triassic. Both the Dabie Group and the coesite‐bearing eclogite host,ed therein underwent a late‐stage dynamic metamorphic event. The present authors have obtained a muscovite Ar‐Ar isochron age of 192.6± 2.8 Ma from plagioclase gneiss and a hornblende Ar‐Ar plateau age of 230.7±4.6 Ma for the low amphibolite in eclogite respectively, which represent the Indosinian reworking ages of the original metamorphic rocks of the Dabie Group gneiss and c

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001005.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractThe skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and layer‐like bodies in permeable carbonate rocks of the Middle‐Upper Carboniferous Huanglong and Chuanshan Formations which are underlain by impermeable shale or siliceous rocks of the Upper Devonian Wutong Formation. The authors study the dynamics of ore‐forming processes of the ore deposits with the dynamic model of coupled transport and reaction, and the following results are obtained: The salinity gradient and flow rate of the ore‐forming fluids can both promote the mixing and reaction of juvenile water and formation water, and the permeable strata are favourable sites for the intense transport‐reaction of mixing and the formation of deposits. (2) As isothermal transport‐reaction took place along the bedding of strata, the moving transport‐reaction front formed at the contact between the ore‐forming fluids and the rocks advanced slowly along the permeable strata, and then stratiform skarn and ore bodies concordant with the strata were formed. (3) The gradient transport‐reaction taking place across the isotherms in the cross‐bedding direction caused the mineralogical composition to alter gradually from magnesian skarn to

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001006.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractBased on palaeomagnetic studies of the Precambrian gold deposits in the Xiong'ershan area, Henan Province, the authors infer that the ore‐forming processes of the Beiling alteration‐type gold ore deposit and the Dianfang breccia‐type gold ore deposit started in the Proterozoic, and was superimposed by later mineralization, whereas the mineralization age of the Jiguanshan quartz‐vein type gold ore deposit is Yan

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001007.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractThe Xingtai piedmont plain in Hebei Province is a representative area in northern China where endemic fluorosis is serious and shallow high‐F groundwater is distributed. In this paper, the area is selected as a typical study area, and on the basis of large amounts of field work and the experiments, through groundwater geochemical modelling and by applying the theory and method of the coupled model of hydrodynamic transport and chemical reactions in a multicomponent system, the author performed numericalmodelling of the geochemical behaviour of fluoride in a shallow groundwater system, quantitatively studied the hydrodynamic transport and chemical reaction of fluorine migration, transformation and concentration in a water‐heterogeneous unsaturated soil system under the conditions of meteoric water infiltration and quantitatively determined the speciation of fluorine and the saturation state and dissolution/precipitation trend of various solid precipitates in shallow high‐F groundwater, thus deepening the understanding of the geochemical behavious of fluorine in shallow groundwater and revealing the essence of some environmental problems at a higher

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001008.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY

摘要:

AbstractThrough a detailed study of sequence boundaries, it is concluded that sequence stratigraphy is an independent regional and transitional stratigraphic system between local lithostratigraphy and global chronostratigraphy. Therefore, a new tripartite stratigraphic classification scheme has been proposed. By combining organically the concept of sequence boundaries with the GSSP, it is suggested that the GSSP should be chosen in a confórmale portion of a related sequence boundary, and the boundary established in light of this concept is defined as the Best Natural Boundary (BNB). The definition of the BNB points out the working area and stratigraphic level for the GSSP. By referring to a case study of the Permian Guadalupian/Lopingian boundary, the concept of the BNB has been elaborated in detail, and it is proposed that the BNB of the Guadalupian and the Lopingian lies between theMesogondolella grantiZone and theClarkma postbitteriZone, which is also the sequence chronostratigraphic boundary between the Transpecos composite sequence (chronozone)and the UAA ‐ 1 composite sequence (chronozon

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1996.mp9001009.x

出版商:Geological Publishing House    

年代:1996

数据来源: WILEY