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Porphyry Cu-Mo mineralization and mantle plumes 总被引：1，自引：0，他引：1
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A.P. Berzina V.O. Gimon I.V. Nikolaeva S.V. Palesskii A.V. Travin 《Russian Geology and Geophysics》2009,50(10):827-841
The Erdenetiyn-Ovoo magmatic center (EMC) with a porphyry Cu-Mo deposit includes the following intrusive complexes: Selenga, Shivota, ore-bearing porphyry, and post-ore dike. The EMC formed at 260–200 Ma. The geologic evolution of northern Mongolia in that period was much determined by the effect of a mantle plume, which showed two periods of activity: Late Paleozoic and Early Mesozoic. The long multistage evolution of the EMC was due to its localization on the periphery of the Late Paleozoic and Early Mesozoic areas of the plume’s influence. The Shivota and post-ore basites are considered to be comagmatic to the Late Permian–Early Triassic trachyandesite-basalt and Late Triassic–Early Jurassic trachyandesite series, respectively, which are similar to the products of Late Paleozoic and Early Mesozoic within-plate magmatism in northern Mongolia. The Selenga complex, which formed before the Shivota one, and the porphyry complex, which formed before the post-ore dike one, are differentiated gabbro-granite series. Gabbro-granitoid magmatism was initiated by the melting of rocks of continental lithosphere under the action of a plume. Later on, as the plume ascended to the surface and the lithosphere became thinner, the conditions were created favoring the lithosphere breakthrough and within-plate basaltoid magmatism.In geochemical features (high contents of LILE and LREE, low contents of HFSE and HREE) the studied basites are similar to the products of subduction magmatism. But this contradicts the geologic position of basites formed after the completion of subduction during the transition of the region to the rifting stage and during the rifting. The mantle metasomatized during the preceding subduction is regarded as the main source of basites. The high contents of alkalies and LREE in the volcanics of the post-ore dike complex and the REE patterns similar to the OIB ones evidence the influence of the plume on the magma formation. The high contents of incompatible trace elements and the Nd isotope composition corresponding to the weakly depleted mantle do not exclude a possible plume effect during the formation of the Selenga complex gabbroids. The geochemical features of the Shivota gabbros, comagmatic to volcanics produced during the Late Paleozoic within-plate activity, are partly transformed during the melt evolution in crustal chambers.The REE patterns of the EMC basites evidence that the evolution of ascending magma was accompanied by the fractionation of amphibole. During this process, ore elements were redistributed into mineral and concentrated in amphibole-containing rocks, from which metals were later mobilized by late melts and fluids. The evolution of basaltoid magmatism of the Selenga, Shivota, and porphyry complexes is regarded as a preliminary stage of ore formation, which was considerably responsible for the EMC productivity. 相似文献
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AP® GIS&T Study Group 《The Journal of geography》2018,117(4):165-173
This article presents the findings of a study to determine the degree of consistency in what is taught and learned in high school and college-level introductory courses in geographic information science and technology (GIS&T). A content analysis identified sixteen topics that are generally representative of the knowledge, skills, and abilities developed in introductory undergraduate courses. The findings were used to propose a standard college-level survey course in GIS&T that could inform future efforts to introduce more academically rigorous GIS&T coursework in high schools, such as through the Advanced Placement Program. 相似文献
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The Erdenetuin-Obo porphyry Cu-Mo deposit was formed at the final stage of development of magmatic activity occasionally manifested
in the Late Permian-Early Triassic in the period of at least 40 Ma. Early plutonic (host) and late ore-bearing porphyry intrusive
complexes were formed in that period. The plutonic complex is multiphase, while the porphyry complex is polyrhythmical and
multiphase within rhythms. The obtained data on the U-Pb isotopic composition (SHRIMP II) of zircons from unaltered rocks
of the ore field are discussed: gabbro, diorite, and granodiorite of the plutonic complex and granodiorite-porphyry I and
II of the first and second rhythms of the ore-bearing complex, respectively. Zircons of different age levels and genotypes
were identified in the course of performed investigations. Gabbro are dominated by postmagmatic (superimposed) zircons with
the datings of 239–225 Ma. The age of xenogenic zircon brought out from the basement rocks is estimated at 1146 ± 11 Ma. Zircons
occur as magmatic and postmagmatic (superimposed) minerals dated 252–247, 244–233 Ma in diorite and 244–242, 239–224 Ma in
granodiorite. The ages of postmagmatic zircons from diorite are partially overlapped by datings of magmatic zircons from granodiorite
and granodiorite-porphyry. In the porphyry complex, the datings of magmatic zircons are 240–234 and 222–220 Ma in granodiorite-porphyries
I and II, respectively. There are also inherited zircons with datings coinciding with those of magmatic zircons from precursor
intrusive rocks. Datings of such zircons are 249–241 and 257–231 Ma for granodiorite-porphyries I and II, respectively. As
a whole, zircon datings in all studied igneous rocks forming a virtually uninterrupted range in the period of 257–220 Ma allow
us to suggest the relation of the ore magmatic system to the long-living constantly active deep source occasionally delivering
melt to the upper levels. 相似文献
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A.P. Berzina A.N. Berzina V.O. Gimon R.Sh. Krymskii A.N. Larionov I.V. Nikolaeva P.A. Serov 《Russian Geology and Geophysics》2013,54(6):587-605
Two intrusive complexes are recognized at the Shakhtama deposit: Shakhtama and ore-bearing porphyry. The U–Pb zircon dates (SHRIMP II) are 161.7 ± 1.4 and 161.0 ± 1.7 Ma for the monzonites and granites of the Shakhtama complex and 159.3 ± 0.9 and 155.0 ± 1.7 Ma for the monzonite- and granite-porphyry of the ore-bearing complex. The igneous complexes formed in a complex geodynamic setting in the late Middle Jurassic and early Late Jurassic, respectively. The setting combined the collision of continents during the closure of the Mongol-Okhotsk ocean and the influence of mantle plume on the lithosphere of the Central Asian orogenic belt. The intrusion of the Shakhtama granitoids took place at the end of the collision, and the intrusion of porphyry of the ore-bearing complex, during the change of the geodynamic setting by a postcollisional (rifting) one. The complexes are composed of monzonite–granite series with similar geochemical characteristics of rocks. The performed geological, geochemical, and isotope-geochemical studies suggest that the sources of magmas were juvenile crust and Precambrian metaintrusive bodies. The juvenile mafic crust is considered to be the predominant source of fluid components and metals of the Shakhtama ore-magmatic system. The granitoids of both complexes include calc-alkalic high-K rocks with typical geochemical characteristics and with characteristics of K-adakites. These geochemical features indicate that the parental melts of the former rocks were generated at depths shallower than 55 km, and the melts of the latter, at depths of 55–66 km. K-adakite melts resulted from the melting of crust submerged into the mantle during the lithosphere delamination, which was caused by the crust thickening as a result of the repeated inflow of basic magma into the basement of the crust and tectonic deformations in its upper horizons. The high-Mg monzonitic magma produced under these conditions ascended and was mixed with melts generated in the upper horizons, which accounts for the high Mg contents of the Shakhtama granitoids. The similar compositions and petrogeochemical characteristics of the granitoids of the Shakhtama and porphyry complexes point to the same sources, transport paths, and evolution trend of their parental melts. This indicates that the igneous rocks of both complexes are products of the same long-living magmatic system, which produced Mo mineralization at the final stage. The favorable conditions for the ore production in the magmatic system during the formation of the porphyry complex appeared as early as the preceding stage—during the formation of the Shakhtama complex, which we regard as a preparatory stage in the evolution of the ore-magmatic system. 相似文献
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Several complexes are recognized within the Sora porphyry Cu-Mo deposit: plutonogenic, porphyry (ore-bearing), and dike. They formed since Ordovician till Devonian at the collision, postcollisional, and rift stages of the regional evolution, respectively. Magmatism was manifested at the deposit synchronously with intraplate magmatism, which was widespread within Kuznetsk Alatau and was initiated by the Altai–Sayan mantle plume. In structural position and geochemical characteristics the dike complex is similar to the intraplate complexes in adjacent regions. It formed after the development of the Sora ore-magmatic system including the plutonogenic and porphyry complexes with similar geochemistry and metallogeny. According to the models for the relationship of mantle plumes with ore-magmatic systems, the plutonogenic and porphyry complexes of the Sora deposit developed at the stage of the thermal plume effect on lithosphere, which caused its melting and, as a result, calc-alkalic magmatism. A change of the collision and postcollisional geodynamic regime by the rift one favored the ascent of plume melts, which then participated in the formation of intraplate structures, in particular, the dike complex of the Sora deposit. 相似文献
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