Paleozoic Granitoid Magmatism Research Articles

Early Paleozoic Granitoid Magmatism in the East Tannu-Ola Sector of the Tuvinian Magmatic Belt: Geodynamic Setting, Age, and Metallogeny

Abstract —The East Tannu-Ola sector of the Tuvinian magmatic belt is composed of Early Cambrian volcanosedimentary rocks of an island-arc association (Kadvoi, Serlig, and Irbitei Formations), which are intruded by granitoid massifs of different ages (from Cambrian to Devonian) of the Tannu-Ola areal pluton. We analyzed the structural and geologic position, chemical composition, metallogenic signatures, and geochronological (U/Pb) and isotope-geochemical (Sm/Nd and Rb/Sr) characteristics of Early Paleozoic granitoids of the Ungesh pluton (western part of the Tannu-Ola areal pluton). The available and our new data made it possible to establish the specific chemical parameters, age sequence, duration, intensity, and metallogeny of granitoid magmatism in the East Tannu-Ola sector of the Tuvinian magmatic belt. An early Cambrian (534–518 Ma) gabbro–plagiogranite complex similar to the Maina complex in West Sayan has been recognized in the Ungesh pluton. The age and metallogeny of the middle–late Cambrian (508–492 Ma) Tannu-Ola diorite–granodiorite–plagiogranite and Late Ordovician (451–447 Ma) Argolik granite–leucogranite complexes have been refined. Granitoids of the early Cambrian complex formed probably at the initial stage of formation of an island arc, in association with the Kadvoi–Serlig basalt–andesite–rhyolite complex. It is in these granitoids that early low-productivity gold–sulfide–quartz veins and veinlets originated. Granitoids of the Tannu-Ola complex formed at the initial stage of evolution of the accretion–collision system. Magnetite-containing skarns and numerous vein–veinlet zones of late high-productivity gold-sulfide-quartz mineralization evolved in these granitoids. Granitoid massifs of the Argolik complex formed at the final stage of evolution of the accretion–collision system and probably played a crucial role in the regeneration of ore mineralization in some areas.

The Late Silurian Age of the Reference Aralaul Granosyenites–Granite Massif (Northern Kazakhstan)

This work presents the results of U–Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite–granodiorite (Zerenda and Krykkuduk), Early Silurian granite–leucogranite (Borovoe and Karabulak), Late Silurian granosyenites–granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes.

U‐PB LA‐ICP‐MS DATING OF ZIRCONS FROM SUBVOLCANICS OF THE BIMODAL DYKE SERIES OF THE WESTERN TRANSBAIKALIA: TECHNIQUE, AND EVIDENCE OF THE LATE PALEOZOIC EXTENSION OF THE CRUST

Our study investigates a possibility of using isotope ratios of U‐Th‐Pb system in zircon analysis by the LA‐ICP‐MS technique and monitoring of precision, convergence and accuracy. New U‐Pb isotope‐geochronological data has been obtained for the salic and mafic members of the bimodal Late Paleozoic series of subparallel dykes in the central part of the Western Transbaikalia. It is shown that a series of subparallel dykes (290–280 Ma) gives evi‐ dence of extension of the continental crust at the final stage of the Late Paleozoic granitoid magmatism. Similar ages of zircons in the salic and mafic subvolcanic rocks confirm the geological indicators of the coexistence and interactions between the magmas of contrasting compositions.

Late Paleozoic granitoid magmatism of Eastern Kazakhstan and Western Transbaikalia: plume model test

We present results of a comparative study of Late Paleozoic granitoids of Eastern Kazakhstan and Western Transbaikalia composing the large Kalba-Narym and Angara-Vitim batholiths. We have established that despite the different geologic history of these regions, granitoid magmatism there proceeded nearly synchronously at the Carboniferous/Permian boundary (330–280Ma) and was accompanied by mantle magmatism. The regularities of its evolution are considered in terms of the plume model and different stages of interaction of mantle plumes with the lithosphere. The major principles of plume-lithosphere interaction in accretion-collision fold belts have been formulated: (1) Plume-lithosphere interaction results in large-scale melting of sublithospheric mantle, lower lithosphere, and crustal substrates warmed by the preceding orogenic processes; (2) The processes last 30 to 50 Myr and produce large volumes of igneous rocks, mostly granitoids; (3) The sequence of formation of granitoid and basic igneous complexes and the metallogenic specialization can be different and depend on the lithosphere structure and preceding geologic history of the region.

Vendian-Early Paleozoic granitoid magmatism in Eastern Tuva

We summarize results of geological, geochronological, petrogeochemical, and isotope-geochemical (Sr-Nd) studies of Late Vendian-Early Paleozoic granitoid batholiths in Eastern Tuva (Kaa-Khem, East Tannu-Ola, Khamsara, etc.). Analysis of geochronological (U-Pb, Ar-Ar) data has shown that the Late Vendian-Early Paleozoic granitoids in Eastern Tuva formed in several stages in the time interval 562–450 Ma and at different geodynamic stages of the regional evolution: island-arc (562–518 Ma) and accretion-collision (500–450 Ma), with the latter stage characterized by more intense granitoid magmatism. Diorite-tonalite-plagiogranite associations with different petrogeochemical parameters are the most widespread in the region. Petrogeochemical studies of the Late Vendian-Early Paleozoic plagiogranitoid associations have revealed high- and low-alumina varieties reflecting different conditions of formation of parental melts. At the island-arc stage of the regional evolution, only low-alumina plagiogranites of tholeiitic (M-type) and calc-alkalic (I-type) series formed. Their parental melts were generated at 3–8 kbar through the partial melting of N-MORB-type metabasalts in equilibrium with amphibole restite. Isotope-geochemical studies have shown positive £Nd values (6.9-6.3) and low Sr isotope ratios ((87Sr/86Sr)0 = 0.7034-0.7046). The lower (as compared with the depleted mantle) eNd values and specific petrogeochemical composition (negative Nb-Ta and Ti anomalies) of the plagiogranites reflect the subduction nature of metabasic substratum and the subordinate role of ancient crustal material. At the accretion-collision stage of the regional evolution, high- and low-alumina plagiogranitoids of calc-alkalic series (I-type) formed. The high-alumina plagiogranitoids are products of melting of N-MORB-type metabasalts in equilibrium with garnet restite at >15 kbar in the lower part of the collisional structures, and the low-alumina ones formed through the melting of metabasites in equilibrium with amphibole restite at <8 kbar in the upper part of the same structures. The Sr-Nd isotope data for the high- and low-alumina plagiogranitoids generated at the accretion-collision stage show that the rejuvenation of rocks is accompanied by the decrease in eNd (from 6.2 to 3.4) and the increase in their model Nd age !Nd(DM) (from 0.73 87 86 to 0.92 Ga) and ( Sr/ Sr)0 (0.7036-0.7048). This points to the essentially metabasic composition of the parental substratum, as in the case of the island-arc plagiogranitoids, and the progressive supply of ancient crustal material to the magma generation zone.

Geochronology and geochemical constraints on petrogenesis of Early Paleozoic granites from the Laojunshan district in Yunnan Province of South China

The Early Paleozoic Orogen in South China has been a topic of hot debate; in particular with regard to the relative contributions of crustal and mantle sources to the generation of granites. To address this issue, we report geochronological and geochemical data for three related suites of granites (Tuantian, Suite 1, Nanlao, Suite 2, and Laochengpo, Suite 3) from the Laojunshan district in the southeast Yunnan Province, western South China Block (SCB). LA-ICP-MS U-Pb dating of zircons indicates magmatic crystallization ages of ~436Ma, ~430Ma and ~427 Ma for Suites 1, 2, and 3 granites, respectively. The εHf(t) values of magmatic zircons in all three suites are heterogeneous, ranging between +3 and −14. All three suites also contain inherited zircon cores with Proterozoic U-Pb and Hf model ages. Bulk compositions form well-defined mixing arrays, with Suites 1 and 2 being strongly peraluminous (A/CNK >1.1), whereas Suite 3 is weakly peraluminous (A/CNK=1.0–1.1). Suites 1 and 2 have lower TFe2O3, Al2O3, MnO, MgO, CaO, TiO2, Na2O, Mg# and Nb/Ta but higher K2O, Rb/Sr, Rb/Ba and εNd(t) than those of Suite 3. These results suggest that Suite 1 and Suite 2 were formed by partial melting of Proterozoic metasedimentary rocks with little or no input of mantle-derived materials, but Suite 3 was derived from a mixture of a crustal melt with mantle derived mafic magma. The apparent paradox that the mantle-derived component has lower εNd(t) values than the crustal components is consistent with the very low εNd(t) values found in mantle-derived basalts in the SCB. The Wuyi-Yunkai orogenic collapse may have caused lower crustal melting of the Cathaysia Block. The early Paleozoic granitoid magmatism with mafic magma input indicates an extensional environment in the western SCB, in response to post-collisional orogenic collapse. Asthenospheric upwelling and basaltic underplating probably contributed heat and melts triggering felsic magmatism in the western SCB.

Zircon U-Pb geochronology and Hf isotopic composition of granitiods in Russian Altai Mountain, Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) consists of many tectonic terranes with distinct origin and complicated evolutionary history. Understanding of individual block is crucial for the reconstruction of the geodynamic history of the gigantic accetionary collage. This study presents zircon U-Pb ages and Hf isotopes for the granitoid rocks in the Russian Altai mountain range (including Gorny Altai, Altai-Mongolian terrane and CTUS suture zone between them), in order to clarify the timing of granitic magmatism, source nature, continental crustal growth and tectonic evolution. Our dating results suggest that granitic magmatism of the Russian Altai mountain range occurred in three major episodes including 445∼429 Ma, 410∼360 Ma and ∼241 Ma. Zircons from these granitoids yield comparable positive eHf(t) values and Neoproterozoic crustal model ages, which favor the interpretation that the juvenile crustal materials produced in the early stage of the CAOB were probably dominant sources for the Paleozoic magmatism in the region. The inference is also supported by widespread occurrence of short-lived juvenile materials including ophiolites, seamount relics and arc assemblages in the northern CAOB. Consequently, the Paleozoic massive granitic rocks maybe do not represent continental crustal growth at the time when they were emplaced, but rather record reworking of relatively juvenile Proterozoic crustal rocks although mantle-derived mafic magma was possibly involved to serve as heat engine during granitic magma generation. The Early Triassic granitic intrusion may be a product in an intra-plate environment, as the case of same type rocks in the adjacent areas. The positive eHf(t) values (1.81∼7.47) and corresponding Hf model ages (0.80∼1.16 Ga) together with evidence of petrology are consistent with the interpretation that the magma source of the Triassic granitic intrusion was derived from enriched mantle and melted under an usually high temperature condition likely due to basaltic magma that underplated the lower crust. Our data combined with evidence of the regional geology enable us to conclude that the Gorny Altai and Altai-Mongolian terranes possibly have similar tectonic natures, but represent two separate accretionary systems before Devonian collision. The accretion and amalgamation processes resulted in the Paleozoic granitoid magmatism and caused the two terranes to merge as a composite tectonic domain at the Siberian continental margin.

Late Paleozoic granitoids in western Transbaikalia: sequence of formation, sources of magmas, and geodynamics

The evolution of Late Paleozoic granitoid magmatism in Transbaikalia shows a general tendency for an increase in the alkalinity of successively forming intrusive complexes: from high-K calc-alkaline granites of the Barguzin complex (Angara–Vitim batholith) at the early stage through transitional from calc-alkaline to alkaline granites and quartz syenites (Zaza complex) at the intermediate stage to peralkaline granitoids (Early Kunalei complex) at the last stage. This evolution trend is complicated by the synchronous development of granitoid complexes with different sets and geochemical compositions of rocks. The compositional changes were accompanied by the decrease in the scales of granitoid magmatism occurrence with time. Crustal metaterrigenous protoliths, possibly of different compositions and ages, were the source of granitoids of the Angara–Vitim batholith. The isotopic composition of all following granitoid complexes points to their mixed mantle–crustal genesis. The mechanisms of granitoid formation are different. Some granitoids formed through the mixing of mantle and crustal magmas; others resulted from the fractional crystallization of hybrid melts; and the rest originated from the fractional crystallization of mantle products or the melting of metabasic sources with the varying but subordinate contribution of crustal protoliths. Synplutonic basic intrusions, combined dikes, and mafic inclusions, specific for the post-Barguzin granitoids, are direct geologic evidence for the synchronous occurrence of crustal and mantle magmatism. The geodynamic setting of the Late Paleozoic magmatism in the Baikal folded area is still debatable. Three possible models are proposed: (1) mantle plume impact, (2) active continental margin, and (3) postcollisional rifting. The latter model agrees with the absence of mafic rocks from the Angara–Vitim batholith structure and with the post-Barguzin age of peralkaline rocks of the Vitim province.

The first geochronological evidence for late paleozoic granitoid magmatism in the Bureya terrane (East of the Central Asian Fold Belt)

The first geochronological evidence for late paleozoic granitoid magmatism in the Bureya terrane (East of the Central Asian Fold Belt)

Prolonged magmatism, juvenile nature and tectonic evolution of the Chinese Altai, NW China: Evidence from zircon U–Pb and Hf isotopic study of Paleozoic granitoids

Paleozoic granitoid magmatism played an important role in the tectonic evolution of the Chinese Altai, and zircon U–Pb and Hf isotopic compositions have been determined for samples from eleven granitic plutons/batholiths. The Jiadengyu gneissic granitic pluton yielded a zircon U–Pb age of 479 Ma, and thus it does not represent Precambrian basement as suggested previously. Our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30% area of the Chinese Altai during the period from 447 Ma to 368 Ma with a climax at ca. 400 Ma. Ages for zircon overgrowth rims demonstrate additional thermal events at ca. 360 and 280 Ma, respectively. Positive ε Hf( t) values (0 to +9) of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources. Xenocrystic zircon cores are 543–421 Ma old and also give positive ε Hf( t) values (+2.5 to +12), suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly-accreted meterials. The strong magmatism at ca. 400 Ma significantly changed the Hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period. Geophysical, geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca. 400 Ma and the above mentioned change of Hf isotopic composition in the magma source.

Paleozoic granitoid magmatism of the eastern part of the Central Asian Fold Belt and formation of large ore deposits

Evidence on the Paleozoic granitoids of the eastern part of the Central Asian Fold Belt (CAFB) was analyzed. A tectonic chart of orogenic belts was compiled. Sketch maps were constructed for the geodynamic settings of the formation of Paleozoic granitoids and the extensiveness of their occurrence. Two types of deep controlling structures were distinguished: zones of lithospheric faults and plumes, including the newly recognized Jiamusi-Bureya plume. It was sown that the distribution of large and superlarge Paleozoic ore deposits is related to these structures, primarily to plumes. Sites promising for large and superlarge deposits related to the Paleozoic granitoid magmatism were determined in the Russian Far East.