共查询到20条相似文献，搜索用时 484 毫秒
1.
Andrew R. Farrant Peter M. Hopson Mark A. Woods Kathryn A. Booth David J. Evans 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(3):533-536
The Chalk Group of the Central Downs of the Isle of Wight forms a relay ramp between two major inverted extensional faults. Mortimore (2011) presented a structural model of this key area based on a geological map constructed from detailed logging of a limited set of exposed sections. The area has been recently mapped at 1:10,000 scale by the British Geological Survey. Our interpretation of the geological structure differs significantly from that proposed by Mortimore, and suggests that Chalk has relatively uniform dips that progressively steepen towards the hanging wall of the E-W oriented basement faults. However, a suite of mapped extensional faults indicates an element of differential movement or transpression along the main basement structures. 相似文献
2.
3.
4.
《Journal of African Earth Sciences》2000,30(3):717-726
The outer sector of the Neoproterozoic Katangan Orogen of Central Africa is characterised by nappes thrust northwards, toward the foreland region, the major part of which occurs in the Democratic Republic of Congo (DRC). The rocks called R.A.T. (‘Roches Argilo-Talqueuses’) are terrigenous clastics traditionally considered as the oldest stratigraphical interval of these allochthonous units. They are correlated with the terrigenous clastic sediments at the base of the autochthonous Katangan succession in Zambia to the south, which were deposited at the opening stage of the Katangan Rift Basin. The lower interval of the R.A.T. represents red beds, whereas the upper one was deposited in anoxic conditions. Therefore, they are called red and grey R.A.T., respectively. This paper presents stratigraphic, structural and geochemical arguments against the traditional stratigraphical view and demonstrates that the R.A.T. rocks are younger than previously considered. They are interpreted here as synorogenic sediments of the Katangan foreland basin.Olistostromes with R.A.T. olistoliths, which occur either interbedded within ‘normal’ R.A.T. sediments or overlie angular unconformities, testify to pronounced tectonic movements and palæotopography of the basin in which the R.A.T. sediments were deposited. The provenance of other olistoliths implies that, contrary to the previous views, the R.A.T. olistostromes are younger than the overlying rock complexes and the contact between the two is tectonic. Clastic dykes of the incompetent R.A.T. lithologies injected into the overlying competent units suggest that the former were partly unconsolidated sediments over-ridden by the Katangan nappes. Plots of the geochemical compositions point to two distinct tectonosedimentary cycles and two types of sources, each related to a different stage of orogen evolution. The terrigenous materials of the Katangan autochthonous strata (Roan and Kundelungu Groups) and correlative allochthonous units are derived from basement granitic and metamorphic rocks eroded during the opening of the Katagan rift basin. By contrast, the R.A.T. rocks are related to the closure of the basin. Their provenance is from the orogenic source-the Katangan nappes advancing towards the foreland region in the north.The autochthonous Roan Group rocks in Zambia and their allochthonous correlatives in DRC contain one of the richest Cu-Co deposits known. In accord with the previous correlation, the CuCo mineralisation in the grey R.A.T. rocks was considered of the same age as the Zambian deposits. However, the results presented in this paper imply that the grey R.A.T. deposits represent a second generation of mineralisation in the Katangan belt, younger than the Roan Group orebodies. The R.A.T. Cu-Co mineralisation is related to the anoxic stage of the foreland basin, and the advancing nappes containing Roan-correlative orebodies acted as the sources of the metals. In conclusion, points pertaining to the revision of stratigraphical classification of the Katangan Supergroup are proposed. 相似文献
5.
6.
7.
I. A. Tararin Z. G. Badredinov S. I. Dril’ V. M. Chubarov N. S. Gerasimov G. P. Sandimirova N. N. Il’ina 《Petrology》2014,22(6):588-616
The problem of the geochemical classification of granitoid magmatism in the zone of interaction of oceanic and continental plates is considered in this paper by the example of Mesozoic granitoids of the Krutogorova and Kol’ intrusive complexes of the Sredinny Range, Kamchatka. Based on new geological, petrological, and geochemical data (including the Sr, Nd, and Pb isotope systematics of rocks), it was shown that the protoliths of the granitoids were volcanic-terrigenous sequences accumulated within a Cretaceous marginal basin in the eastern Asian continent. The granitoids crystallized at ～80 Ma (SHRIMP U-Pb age) under the conditions of the andalusite-sillimanite depth facies corresponding to a pressure of approximately 2 kbar and induced contact metamorphism in the host sequences, which are made up of sediments with sheetlike bodies of mafic and ultramafic volcanics (Kikhchik Group and its metamorphic analogues of the Kolpakova, Kamchatka, and Malki groups). The lower age boundary of sedimentation of the host sequences and the time of basic volcanism coincide with the beginning of the formation of the Okhotsk-Chukotka volcanic belt. Such a correlation is not accidental and reflects a genetic connection between the processes of magmatic activation in the continental-margin sedimentary basin and the formation of the continental margin volcanic belt in eastern Asia. The development of basic volcanism in the sedimentary basin accompanied by the ascent of deep fluids resulted in the entrainment of crustal materials into magmatic processes and the formation of crustal magma chambers, the activity of which was manifested by the eruption of intermediate and silicic lavas and emplacement of shallow granitoid intrusions of considerable areal extent. These intrusions induced contact metamorphism in the enclosing volcanosedimentary complexes. The subsequent Eocene (60-50 Ma) collision processes related to the obduction of the oceanic segment of the crust of the transitional zone onto the Asian continental margin resulted in the tectonic piling of the rocks of Central Kamchatka and strong crustal thickening, which was favorable for its metamorphic alteration reaching the kyanite-sillimanite depth level of the amphibolite facies under the influence of a thermal front and deep fluids affecting lower crustal zones. The Eocene regional metamorphism caused not only metamorphic transformations, migmatization, and granitization in the sequences of the Sredinny Range, which underwent only contact hornfels formation during the first stage, but also metamorphism, migmatization, and extensive foliation in the igneous rocks of the Kol’ and Krutogorova complexes, which were transformed into gneissic metagranites. 相似文献
8.
9.
This reply tackles the three main points of discussion of the comment, carefully distinguishing those constructive contributions from the potentially confusing ones. (1) We accept that we should have utilised previously published datings of the middle terrace, even if we consider them to be less reliable than the used ones, so broadening the slip-rate range from 0.23–0.33 mm/y to 0.16–0.33 mm/y. Nevertheless, their revision of the post-middle terrace slip rate charges us two contradictory imputations: that we underestimate the throw in a 25% (36 m vs. 47 m) and that this results in ‘anomalously high slip rates’. We analyse the adduced error, and we confirm our initial estimate based on our more reliable stratigraphic marker, so rejecting both criticisms. (2) About the paleoseismological interpretation at Los Baños trench, we appreciate the hint about displacement partitioning on the master fault and in our hypothetical blind normal fault during the last three events; however, such partitioning was already considered in our retrodeformation analysis. We believe that there is enough evidence for the two events questioned by the commenters, as well as for the interpretation of the colluvial wedge that evidences one of them. (3) With respect to the fault affecting the youngest terrace: (a) both traces exposed on orthogonal road-cut slopes belong to the same normal fault, and we prove it by means of basic structural constructions, and (b) it does not exhibit any feature suggesting a non-tectonic origin, as the commenters state. 相似文献
10.
Colin J. N. Wilson Terry M. Seward Aidan S. R. Allan Bruce L. A. Charlier Léa Bello 《Contributions to Mineralogy and Petrology》2012,164(2):359-368
Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO2 activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO2 activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO2 activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved. 相似文献
11.
12.
13.
14.
T. N. Palechek A. V. Moiseev I. V. Gul’pa 《Stratigraphy and Geological Correlation》2016,24(4):381-406
New data on the structure, age, and composition of the tectonostratigraphic complexes of the western part of the Koryak Highland are presented. The conclusions on the sedimentation conditions are drawn and primary relations are interpreted for most complexes. New Kimmeridgian–Tithonian and Berriasian assemblages of radiolarians are established. Campanian radiolarians are found for the first time in the region. 相似文献
15.
16.
《地质学报》1932,11(2):101-105
In opening the meeting, the chairman made the following address: "It is my agreable duty to announce and make the award of the Grabau Medal to two members of our Society, Drs. J. S. Lee and Davidson Black. "The Grabau Medal was founded in 1925 by Mr. C. Y. Wang. the then President of the Geological Society. It was so named in honor of Dr. Grabau 相似文献
17.
Fe–Ti oxides (magnetite, Ti-magnetite, ilmenite, and associated high-Al spinel) in the ferrogabbroids of the Middle Paleoproterozoic Elet’ozero syenite–gabbro intrusion are intercumulus minerals usually surrounded by coronitic rims of two types. The first type usually represents multilayer amphibole–biotite ± olivine coronas along contacts of Fe–Ti oxides with cumulus moderate-Ca plagioclase and more rarely, clinopyroxene. Two-layer rim is developed in contact with high-Ca plagioclase; the inner rim consists of pargasite and spinel, while the outer rim is made up of sadanagaite and spinel. The second type is represented by two-stage coronitic textures developed along boundaries of olivine and Fe–Ti oxide clusters with plagioclase. Initially, the olivine was surrounded by orthopyroxene rim, while Fe–Ti oxides were rimmed by pargasite with thin ingrowths of high-Al spinel (hercynite). At the next stage, the entire cluster was fringed by a common symplectite reaction rim, the composition of which also depended on the composition of plagioclase matrix: the spinel–sadanagaite rim was formed in contact with high-Ca plagioclase, while pargasite–muscovite–scapolite rim was formed in contact with moderate-Ca plagioclase. The formation of the outer rims occurred after hydration of the inner parts of coronas around olivine and oxides within the clusters. It is suggested that the Fe–Ti oxides and surrounding coronitic rims were microsystems formed by crystallization of drops of residual hydrous Fe-rich liquid. 相似文献
18.
A thermodynamic model of the behavior of heavy metals in bottom sediments during their eutrophication is developed. The results
show that liberation of heavy metals from the reduced ferrous sorbent is accompanied by sorption on clay and organic sorbents.
The process is complicated by competitive correlations between heavy metals and calcium ions, while the formation of carbonate
cement in the sediments yields additional sorption. As a result, the predicted concentrations of the majority of microelements,
namely heavy metals, in the interstitial water of the reduced bottom sediments do not exceed the maximum permissible concentration
(MPC). 相似文献
19.