Dykes composed of basic rocks and granite are formed due to interactions between melts in a wide range of conditions, from contrasting compositions and fluid saturation rates to various tectonic settings and processes at different depths. Textures and petrochemical characteristics of the dykes are thus widely variable. This paper is focused on composite dykes observed in the West Sangilen region in SouthEast Tuva, Russia. The Sangilen wedge is a fragment of the Early Caledonian orogenic structure of the Tuva-Mongolia Massif which evolved in a succession of geodynamic settings, from collision (transpression, 570-480 Ma) to transform faulting (transtension, 480-430 Ma). Intensive tectonic deformation facilitated massive basic-rock and granite magmatism at various layers of the crust and associated heating and metamorphism of the rocks (510-460 Ma). Basic-rock-granite composite dykes were formed in the above-mentioned period in various tectonic settings that controlled conditions of dyke intrusions and their compositions. We distinguish two groups of composite dykes observed on two sites, in the area between the Erzin and Naryn rivers and on the right bank of the Erzin river (Strelka and Erzin Sites, respectively) (Fig. 1). The dykes in both groups originated from one and the same basic-rock melt source. However, mingling of the contrasting melts was carried out by different mechanisms as suggested by the proposed intrusion models. In the area between the Erzin and Naryn rivers (Strelka Site), the host rock of the composite dykes is granite of the Nizhneerzin massif. The mingling dykes are composed of amphibole gabbro and monzogabbro, granosyenite and twofeldspar granite. Contacts between basic and felsic rocks vary from smooth contrasting to complex 'lacerated' flameshaped, and gradual transition zones are present (Fig. 6). The dykes were formed at mesoabyssal or abyssal depths, and the subliquidus heat regime was thus maintained for a long time, and even the smallest portions of the basic-rock melt were consolidated through quite a long period of time. As a consequence, indicators of deformation are lacking in the composite dykes, while transition zones and hybridization are present. On the right bank of the Erzin river (Ersin Site), the dykes cut through migmatite-granite of the Erzin formation in the same-name tectonic zone. Contacts with host rocks are transverse. Melanocratic rocks are represented by smallgrained diorite and quartz diorite, and the felsic composite dykes are composed of medium-and small-grained twofeldspar granite and leukogranite. Transition zones, hornfelsing and contact alterations are absent at contacts of all the types (Fig. 8). The composite dykes of this type intruded and emplaced when the shear zone was subject to extension and fragmentation, which predetermined active intrusion of basic and, possibly, felsic melts through conjugated faults. Crystallization of the melts was rapid, and their potential heat impact on the adjoining rocks was thus excluded, as evidenced by the presence of ...

Based on study of fluid and melt inclusions in minerals from igneous rocks and associated ore-metasomatic objects, we consider the formation conditions of oxidized fluids produced at the final stages of differentiation of alkali-basic, alkaline, lamproitic, and some granitoid melts. These fluids are characterized by wide variations in composition, concentrations, and physicochemical parameters (P, T, Eh, pH, etc.) and are of sulfate-chloride, sulfate-carbonate, sulfate-fluoride, fluoride-sulfate, essentially sulfate, and other types. The specific composition of these magmatogene fluids showing a high extractive power favors the effective removal of ore-forming elements (Fe, Mn, Co, N, Ag, Cu, Pb, Zn, Mo, W, Bi, U, REE, etc.) from melt and their trapping from the host rocks. The set of these elements is determined by P-T-X-parameters, conditions of fluid separation from melts, composition of fluid-generating magmas, and geochemical composition and metal-bearing capacity of rocks through which the fluids migrate. These factors significantly determine the metallogeny of alkaline, alkali-basic, and some granitoid complexes and associated mineralization.

Abstract:In large igneous provinces (LIP) of fold areas, granitoid rocks are dominant, while mantle-derivated rocks play a subordinate role in rock formation. If magma emissions are impulsive, it may take 25-30 million years for a LIP to form and take shape. In this paper, we present the results of 40 Ar/ 39 Ar isotopic studies of Permian-Triassic granitoids in the Altai region, Russia, and clarify the evolution of this region located at the periphery of the Siberian LIP. These granitoids are very diverse and differ not only in their rock set, but also in the composition features. In the study region, the granodiorite-granite and granite-leucogranite association with the characteristics of I-and Stypes as well rare metal ore-bearing leucogranites are observed along with gabbro-and syenite-granite series, including mafic and intermediate rocks with the A2-type geochemical features. The 40 Ar/ 39 Ar data obtained in our study suggest that most of the studied granitoids intruded within a short period of time, 254-247 Ma. This timeline is closely related to the formation of granitoids in the Kuznetsk basin and dolerite dikes in the Terekta complex (251-248 and 255±5 Ma, respectively), as well as intrusions of lamproite and lamprophyre dikes of the Chuya complex (245-242 and 237-235 Ma). Thus, we conclude that the Altai Permian-Triassic granitoids are varied mainly due to the evolution of mafic magmatism.Key words: geochronology; Ar/Ar dating; granitoid magmatism; Altai Аннотация: В складчатых областях крупные изверженные провинции (LIP) характеризуются резким преоб-ладанием гранитоидов при подчиненной роли пород мантийного генезиса. Длительность формирования отдельных LIP может достигать 25-30 млн лет при импульсном характере магматизма. В работе конкретизи-руется схема формирования одного из периферических сегментов Сибирской LIP на основе 40 Ar/ 39 Ar изотоп-ных исследований пермотриасовых гранитоидов Алтая, которые резко различны не только по набору пород, но и по особенностям их состава. Наряду с габбро-и сиенит-гранитными сериями, включающими основные и средние породы с геохимическими характеристиками пород A2-типа, на этом рубеже проявлены гранодио-рит-гранитные и гранит-лейкогранитные ассоциации с характеристиками I-и S-типа, а также рудоносные редкометалльные лейкограниты. Результаты 40 Ar/ 39 Ar датирования свидетельствуют о том, что внедрение большинства изученных интрузий гранитоидов Айского, Теранжикского, Тархатинского, Белокурихинского и Синюшенского массивов, Точильненского и Осокинского штоков-сателлитов произошло в короткий проме-жуток времени -254-247 млн лет. Фиксируется достаточно тесная временная связь формирования гранито-идов с формированием траппов Кузнецкого бассейна и долеритовых даек терехтинского комплекса (251-248 и 255±5 млн лет соответственно), с внедрением даек лампроитов и лампрофиров чуйского комплекса (245-242 и 237-235 млн лет). Таким образом, разнообразие пермотриасовых гранитоидов Алтая определяется, в первую очередь, эволюцией базитового магматизма. GEODYNAMICS & TECTONOPHYSIC...

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