Early Mesozoic Granitoids Research Articles

Geodynamic Settings of Late Paleozoic–Early Mesozoic Granitoid Magmatism at the Arctic Continental Margins: Insights from New Geochronological and Geochemical Data from the Taimyr Peninsula

Despite significant progress in Arctic geological studies, a number of principal questions concerning the Paleozoic collisional events remain unanswered. Therefore, the Taimyr Peninsula, representing the only outcropped high Arctic region where magmatic complexes, formed by Hercynian collision between the Siberian Craton and the Kara Block, are well exposed, is crucially important. In this paper we report new geochemical and geochronological data for intrusions in the poorly studied northeastern part of the Taimyr Peninsula. The obtained results in combination with published data show that supra-subduction magmatism at the southern active margin of the Kara Block continued from ca. 345 to 285 Ma (Early Carboniferous to Early Permian), and was followed by a post-collisional magmatic pulse that affected the whole Taimyr across terrane boundaries at ca. 280 Ma in the Early Permian. After cessation of the post-collisional magmatism at ca. 265 Ma, the Taimyr experienced extension, and voluminous magmatic series associated with a Siberian mantle plume were formed between 251 and 228 Ma during the Triassic. The studied post-collisional and plume-related intrusions of the Northeastern Taimyr are generally classified as evolved high-K I-type granites with adakitic affinity. The latter is a regional feature because the majority of the analyzed plume-related granitoids are geochemically similar to high potassium continental adakites. It is suggested that the adakitic geochemical characteristics of the plume-related granitoids resulted from melting of hydrated mafic lower crustal protoliths and were controlled by the source lithology. Comparison of the new results with data available for adjacent areas allows for correlation of terranes on a regional scale and sheds light on the evolution of the Arctic continental margins in general. In the Early–Middle Paleozoic, the Kara Block was part of a continental terrane that formed at the northern edge of Baltica as a result of Neoproterozoic Timanian orogeny. In the Early Carboniferous, the southern margin of Kara turned into an active margin, while its inferred continuation in the eastern Uralian margin of Baltica remained a passive margin until the Early Permian. This discrepancy can be explained by dextral displacement of Kara relative to Baltica that took place in the Early Carboniferous and was later accommodated by the formation of the Taimyr collisional belt in the course of the Early Permian collision between Kara and Siberia. After collision, the Taimyr was incorporated into the northern Eurasian margin as an uplifted block that experienced surface erosion and supplied clastic material in surrounding basins.

Regional variation of biotite composition of granitoid and its significance to deep crust component and mineralization: A case study on biotite from Early Mesozoic granitoid in the Qinling orogen

Regional variation of biotite composition of granitoid and its significance to deep crust component and mineralization: A case study on biotite from Early Mesozoic granitoid in the Qinling orogen

Petrogenesis of the Triassic Dongjiangkou pluton in the South Qinling orogenic belt, Central China: Insufficient magma mixing of mafic and felsic magmas

Magma mixing or mingling between mafic and felsic magmas is a common phenomenon in granitoid magmatism, and chemical and mechanical interactions between the magmas are frequently observed in granitic rocks. The Dongjiangkou pluton is an example of magma mixing among the numerous early Mesozoic granitoid plutons that are exposed in eastern South Qinling. This pluton is predominantly composed of granodiorite and contains abundant mafic/intermediate microgranular enclaves (MMEs) and is sporadically intruded by mafic dykes. Both the granodiorite and MMEs were crystallized at 224–214 Ma and have inherited zircons of similar age ranges. The granodioritic rocks had metaluminous to weak peraluminous features and adakitic signatures and belong to the high-K calc-alkaline series, whereas the MMEs and dioritic dykes had low SiO2 contents and metaluminous features and belong to the high-K calc-alkaline to shoshonite series. All of the rocks had high Mg# values and similar geochemical characteristics regarding trace elements and Sr isotopes, but they had diverse whole-rock Nd-Pb and zircon Hf isotopic compositions. The Dongjiangkou granodiorite was produced by partial melting of old basement rocks and Paleozoic juvenile crust beneath South Qinling triggered by asthenospheric upwelling. Magma(s) of the Dongjiangkou MMEs may have been derived from deep mantle and injected into and mixed with the magma(s) of the granodiorite, but chemical and isotopic homogenization was not achieved during the magma mixing process. Clastic rocks may have played a major role in the formation of crust-derived magma(s), causing strong Nd-Hf isotopic decoupling of several granitoid plutons in South Qinling.

Late Paleozoic and early Mesozoic granitoids in the northwestern Bureya Massif, Central Asian Orogenic Belt: Timing and tectonic significance

ABSTRACT The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic–early Mesozoic granitoids that are ideal for investigating the tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic–early Mesozoic tectonism in the eastern CAOB. The zircon U–Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219–212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing’an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

Petrogenesis and tectonic implications of the early Mesozoic granitoids in the northern Alxa region, Central Asian Orogenic Belt

AbstractThe northern Alxa region is located in the central segment of the southern Central Asian Orogenic Belt. Many controversies and deficiencies still exist regarding the magma source characteristics, petrogenesis and tectonic regimes during the late Palaeozoic – early Mesozoic period within this region. This study presents whole-rock compositions and zircon U–Pb and Lu–Hf isotopic data for three early Mesozoic I- and A-type granitic plutons occurring in the northern Alxa region. The Haerchaoenji and Chahanhada I-type granitoids yielded zircon 206Pb–238U ages of 245 ± 5 Ma and 245 ± 2 Ma, respectively. The variable positive zircon ϵHf(t) values between +1.8 and +11.8, with young TDM ages of 425–837 Ma, indicate that these I-type granitoids were mainly derived from juvenile crustal materials. The Wulantaolegai pluton has a zircon 206Pb–238U age of 237 ± 2 Ma and is classified as having high-K calc-alkaline A-type affinity. Furthermore, the positive zircon ϵHf(t) values of the Wulantaolegai granite range from +3.3 to +8.7 with young TDM ages of 545–778 Ma, suggesting the involvement of a juvenile crustal source as well. Furthermore, the major-element compositions of the Chahanhada and Wulantaolegai granites suggest the input of metasedimentary components. Geochemically, the Haerchaoenji and Chahanhada I-type granitoids show an arc affinity, while the Wulantaolegai granite exhibits a post-collisional affinity. However, with regional data, we suggest that the Haerchaoenji and Chahanhada I-type granitoids were also emplaced in a post-collisional setting, and the arc affinity was probably inherited from recycled subduction-related materials. These lines of evidence obtained in this study enable us to argue that the Palaeo-Asian Ocean in the central segment of the Central Asian Orogenic Belt closed before Middle Triassic time.

Late Paleozoic–Early Mesozoic granitic rocks in Eastern Peninsular Malaysia: New insights for the subduction and evolution of the Paleo-Tethys

• The granitoids in East Malaya were emplaced at 289–244 Ma. • The granitoids were formed in response to the Paleotethyan subduction . • The slab roll-back of the Eastern Paleotethyan initially occur at ∼ 270 Ma. • Subduction-related granitoids in East Malaya can extend to SW China and W Borneo. Well-preserved Late Paleozoic–Early Mesozoic igneous rocks in Peninsular Malaysia are important for investigating the Paleotethyan tectonic evolution. This study presents new zircon U-Pb dating, whole-rock geochemical, and Sr-Nd-Pb-Hf isotopic data for granitoids identified from the East Malaya. By utilizing all available data, the Permian–Middle Triassic granitoids in Eastern Peninsular Malaysia can be divided into three groups. Group A (289–270 Ma) I-type granites have higher ε Nd (t) values of − 6.6 to − 2.6 and zircon ε Hf (t) values of − 7.1 to + 4.9 than Group B S-type granites (285–272 Ma) with ε Nd (t) = − 10.1 and zircon ε Hf (t) = − 23.1 to + 1.5. Group C (254–244 Ma) with A-type characteristics, has ε Nd (t) and zircon ε Hf (t) values ranging from − 7.3 to − 3.8 and − 8.9 to + 2.2, respectively. The Pb isotopic values for three groups are similar with ( 206 Pb/ 204 Pb) i = 18.71–19.43, ( 207 Pb/ 204 Pb) i = 15.66–15.71 and ( 208 Pb/ 204 Pb) i = 38.27–39.43. Group A was derived from metaigneous rocks with a juvenile mafic component, while Group B was from metasedimentary rocks. Group C had a mixed source of “ancient” meta-mafic rocks with a juvenile mafic component. This study proposes that the Late Paleozoic–Early Mesozoic granitoids were formed in response to the subduction of the Paleotethyan Ocean, and that a tectonic transition from subduction to slab roll-back might occur at ∼ 270 Ma. Subduction-related granitoids in East Malaya can northernly extend to the Tachileik Batholith in eastern Myanmar and Jinghong in SW China, and southernly link with W Borneo.

Early Mesozoic granitoids in southern Vietnam and Cambodia: A continuation of the Eastern Province granitoid belt of Thailand

This study examines three granitoid plutons, intruded during the latest Triassic - earliest Jurassic, that are exposed in south-western Vietnam and south-eastern Cambodia. On geochemical and petrological grounds the two plutons in Vietnam (Hon Da Bac and Hon Khoai island) are composed of slightly peraluminous I-type granitoids, with a high-K calc-alkaline affinity. The Cambodian pluton (Tamao) consists of peraluminous S-type granitoids, with high-K calc-alkaline and ferroan affinity. Based on zircon U-Pb geochronology the Hon Da Bac granitoids were intruded between 200.7 ± 2.7 and 196.2 ± 3.0 Ma, those from Hon Khoai between 199.6 ± 2.7 and 197.6 ± 2.7 Ma and the Tamao granitoids at 187.8 ± 3.2 Ma. These ages are consistent with intrusion during and soon after the Indosinian II Event of the Indosinian Orogeny, which was driven by docking of the Sibumasu and Indochina Blocks. Although these granitoids have some geochemical signatures similar to those of arc-related magmas, we conclude that they are more likely derived from syn to post-collisional magmatism. In terms of timing of their emplacement and geochemistry, all three plutons can be convincingly correlated with the Late Triassic-Early Jurassic Eastern Province granitoids in the Loei Fold Belt, which stretches along the western margin of the Indochina Block, extending through eastern Thailand and southern Cambodia. By this correlation we show that in fact, the Eastern Province granitoid belt extends further southeast than previously thought, occurring in south-eastern Cambodia and south-western Vietnam.

Timing and Nd-Hf isotopic mapping of early Mesozoic granitoids in the Qinling Orogen, central China: Implication for architecture, nature and processes of the orogen

The Qinling orogen, one of the most important orogens in Asia, belongs to the northeastern part of the Tethyan orogen. The architecture and processes of the Qinling orogen remain controversial. In this study, we present 15 new zircon U–Pb ages, 20 whole-rock geochemical and 46 Sm-Nd isotopic analyses, and 30 zircon Lu–Hf isotopic data for early Mesozoic granitoids in this orogen, combining with data from literature, to delineate the crustal architecture and processes of the orogen. A total of 181 zircon U–Pb ages show three phase (252–230, 230–198, and 190–185 Ma) of granitoids. The first-phase granitoids occur mainly in the westernmost segment of the orogen and formed in a subduction setting during the closure of the Mianlue Ocean (a northern branch of the Paleo-Tethyan Ocean). The second- and third-phase granitoids, distributed in the middle to eastern parts of the Qinling orogen, were generated in late syn-collisional and post-collisional tectonic settings, respectively. Whole-rock Nd and zircon Hf isotopic mapping of these granitoids yield six and seven isotopic provinces, respectively. These provinces display that the southern margin of the North China Block and the northern margin of the South China Block are dominated by ancient deep crust, that is, early Paleoproterozoic (2.3–1.8 Ga) and late Paleoproterozoic (∼1.7 Ga) components, respectively. By way of camparison, the North Qinling contains younger Mesoproterozoic [eNd(t) = −10.7 to −0.2; TDM = 1.4–1.0 Ga] basement, evidencing that it is an independent terrane different from the North China Block. The isotopic mapping also reveals a deep-seated NNE–SSW-trending zoned architecture that is approximately perpendicular to the WNW–ENE-trending of the orogen. This provides new evidence for the “Spaghetti Junction model” for the Qinling orogen. The old Nd (2.2–1.0 Ga, mostly 2.0–1.2 Ga) and Hf (2.3–0.8 Ga, mostly 2.0–1.2 Ga) model ages indicate that the continental growth in this orogen occurred mainly during the Paleoproterozoic and Mesoproterozoic, with only minor amounts of juvenile [eNd(t) = ∼0, TDM = ∼0.1 Ga] continental growth along the Shangdan and Mianlue sutures. These characteristics suggest that the Qinling orogen is dominantly formed by the collision of ancient continental blocks, distinct from some typical accretionary orogens, such as the Central Asian Orogenic Belt with voluminous juvenile crust.

Mechanisms of generation and exudation of Tibetan medicine Shilajit (Zhaxun)

BackgroundShilajit is a commonly used Tibetan medicine, and its water extract is mainly used for various heat-related syndrome, especially that of stomach, liver and kidney. Shilajit is found to exudate from rocks of cliff at an altitude of 2000–4000 m as a water-soluble mixture of black paste and animal feces of Trodocterus spp. or Ochotona spp. Because it is difficult to reach the exudation points so as to explain the its formation process, the source of Shilajit still remains unclear and controversial, which severely impedes its safety and efficacy in clinical application.MethodsIn this work, a series of investigations as rock flakes identification, porosity determination, rock mineral analysis, scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS) have been carried out to clarify the source of Shilajit, including the storage condition and exudation process of its organic matter, and to investigate the geological structure of the exudation points as well as physical and chemical characteristics of the mother rocks.ResultsThe Shilajit exudation points were mainly distributed on the steep cliffs, where there were cavities and sections that could not be eroded by rainwater. The fundamental structure of the exudation points was determined by the rock’s bedding planes, joints, fracture surfaces and faults, and developed into micro-topography later. The exudation points were distributed in the Triassic strata and scattered in the Early Mesozoic granitoids. The lithologic features were mainly slate, carbonaceous slate and sandy slate etc. The background rocks were characterized by intergranular pores, dissolved pore, joint and fracture development. Organic matter was widely distributed in these pores and fissures, which had condition for storage and exudation of organic matter.ConclusionsShilajit mainly distributed on sunny steep slopes and cliffs with a slope of 60° or above at altitude of 2000–4000 m. The lithology character of the Shilajit exudation area were mainly various metamorphic rocks of sedimentary rocks that were rich in organic carbon. The organic matter in Shilajit was found to flow out naturally from rocks along pore, structural plane and even accumulate on the surface of rock as a result of storage environment change caused by rock tectonic action.

Constraints on the tectonic evolution of the southern central Asian orogenic belt from early Permian–middle Triassic granitoids from the central Dunhuang orogenic belt, NW China

The Dunhuang orogenic belt (DOB), located in the southern Central Asian Orogenic Belt (CAOB), exposes Precambrian and Paleozoic intrusive-metamorphic rocks. To better understand its evolution, we carried out detailed petrological and geochronological investigations on the major lithologies of the central DOB. The central DOB can be divided into two terranes, the north and the south, with contrasting geological history. The north is characterized by Precambrian crystalline rocks (ca. 3.1–1.6 Ga) overprinted by Devonian tectono-thermal events. The Precambrian rocks show evidence for major juvenile crust growth with additions of older crustal materials at 2.7–2.5 Ga, a major crustal reworking event at 2.0–1.9 Ga, and juvenile additions with minor crustal reworking at 1.8–1.7 Ga. In contrast, the south is characterized by early Devonian (ca. 406 Ma) TTG-gneiss and amphibolite gneiss, and some Late Paleozoic–early Mesozoic granitoid rocks (ca. 284–238 Ma). The Late Paleozoic–early Mesozoic granitoid rocks from the south were emplaced in two phases: early Permian (ca. 284–275 Ma) and late Permian–middle Triassic (ca. 255–238 Ma). They belong to the high-K calc-alkaline I-type series which were generated from mixing juvenile materials with Mesoproterozoic continental crust. The early Permian and the late Permian–middle Triassic granitoid rocks are considered as arc/subduction-related and post-collisional rocks, respectively. These suggest that the final assembly of the DOB with the Beishan or final assembly within the DOB happened in the middle Permian (ca. 275–255 Ma). The DOB formed by accretion/collision of multiple terranes/microcontinents, similar to other areas in the CAOB.

Early Mesozoic magmatism and tectonic evolution of east-central Tibet

The Early Mesozoic granitoids in the east-central Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study, three stages of Early Mesozoic granitic magmatism were indicated by LA-ICP-MS zircon U–Pb dating on 14 samples. The Early Triassic (248–243 Ma) and the Late Triassic (213–208 Ma) were distributed in the North Qiangtang terrane, and the Early Jurassic (ca. 187 Ma) occurred in the Tongka and Jiayuqiao blocks. The Late Triassic and Early Jurassic granitoids show similar negative zircon eHf(t) values (− 5.5 to − 16.6) with TDM2 model ages of 1.60–2.28 Ga, suggesting a Paleoproterozoic crustal source, whereas the Early Triassic granitoids have zircon eHf(t) values from − 3.4 to + 5.3 with TDM2 model ages of 0.94–1.50 Ga, indicating a Mesoproterozoic crustal source. Based on the whole-rock geochemical data, we suggest that the Early Triassic rocks from the North Qiangtang terrane include I- and S-type granites and the Late Triassic rocks are S-type granites, which were related to the northward subduction of the Longmu Tso–Shuanghu–Dingqing Paleo-Tethys Ocean and subsequent collision between the North Qiangtang terrane and Tongka block, respectively. The Early Jurassic granitoids from the Tongka and Jiayuqiao blocks also included both I- and S-type granites and were probably generated in an arc-related setting during the northward subduction of the Bangong–Nujiang Tethys Ocean. Therefore, we suggest a collision–accretion model that attributes the Early Mesozoic tectonic-magmatic event to the sequential multistage subduction and collision in the east of central Tibet.

Granitoid Petrogenesis and Tectonic Implications of the Late Triassic Baoji Pluton, North Qinling Orogen, China: Zircon U-Pb Ages and Geochemical and Sr-Nd-Pb-Hf Isotopic Compositions

AbstractThe Qinling orogenic belt in central China resulted from the final collision of the North China and South China blocks in the Triassic. Early Mesozoic granitoids are widespread in the Qinli...

A review of the Early Mesozoic granitoids in the Qinling Orogen: Implication for gold metallogeny

The Qinling Orogen is located between the North China and South China blocks, and considered to form by the multiple accretionary processes, being also characterized by development of voluminous magmatic intrusions as well as abundant mineral resources. Here we compile the geological, geochemical and geochronological data of the Early Mesozoic granitoids from the Qingling Orogen and attempt to constrain the Early Mesozoic tectonic evolution and mechanism of gold mineralization in this region. The Early Mesozoic granitoids are most widespread in the Qinling Orogen, especially in western part, and can be classified into S‐, I‐, I‐A‐types, with the I‐type constituting the major variety. The isotopic ages of the three types granitoids are 200–222 Ma, 185–248 Ma, 210–227 Ma, respectively, indicating overlapping ages with a wide span of I‐type granitoids. The S‐, I‐, I‐A‐type granitoids show obvious zonation characteristics, that is the S‐type granitoids only occurred in southern South Qinling Belt, the I‐type granitoids are most widespread in the western Qinling Orogen, and the I‐A‐type granitoids are mainly exposed in the North Qinling Belt. The S‐type granitoids crystallized at relatively low temperature (800–850 °C) and deep‐crustal level (ca. 8 kb) and derived mainly from partial melting of a clay‐poor psammitic source. The I‐type granitoids formed at high temperature (>925 °C) and pressures above the garnet‐in phase boundary (>1.2 GPa) and derived from greywackes and partially igneous source. Moreover, the I‐A‐type granitoids probably derived from distinct sources with sufficient interaction, or common origin but underwent different degrees of crustal contamination, and generated at high temperatures (ca. 950 °C) and low pressures (1.0–0.2 GPa) conditions. These features indicate the Qinling Orogen experienced subduction, syn‐collisional, and post‐collisional during the Early Mesozoic, and also suggest the S‐, I‐, I‐A‐types granitoids underwent an episodic growth documenting the tectonic regime switchover at this stage. The gold deposits in the western Qinling Orogen can be classified as orogenic, Carlin‐type, and Carlin‐like gold deposits with the formation age of Late Triassic. The orogenic and Carlin‐type gold deposits have no genetic relation to granitic magmatism, but the Carlin‐like gold deposits is related to the synchronous magmatism. Combined with regional geology and metallogenic systems, we suggest that the multi‐stage Qinling Orogenesis resulted in the formation of the Early Mesozoic S‐, I‐, I‐A‐type granitoids and different types of gold deposits with some characteristic differences.

Phanerozoic granitoids in the central and eastern parts of Central Asia and their tectonic significance

The widespread occurrence of voluminous granitoids is a typical characteristic of the Central Asian Orogenic Belt (CAOB) in the central and eastern parts of Central Asia. The granitoids occupy a total area more than 8 million km2, with three major area peaks at Cambro-Ordovician, Carboniferous-Permian, and Jurassic. Six zircon age peaks at ca. 500, 430–370, 330–300, 290–260, 210–170 and 145–110Ma.The early Paleozoic granitoids (540–440Ma, with age peak at ca. 500Ma) mainly occur in the northwestern CAOB, and are of calc-alkaline I-type. They probably formed in a subduction setting (500–480Ma) within the Paleo-Asian Ocean (PAO) and subsequent microcontinental-collision (ca. 460Ma). The middle Paleozoic granitoids (430–370Ma) predominately occur in the NW and southern CAOB, and are characterized by a high-K calc-alkaline affinity, suggesting an accretionary and/or a collisional setting. The late Paleozoic (350–260Ma) granitoids are widespread in the CAOB and formed in variable tectonic settings within an intra-continental regime or active continental margins in the PAO and in the evolving Mongol-Okhotsk Ocean (MOO). Carboniferous granitoids (350–300Ma) in the northern and northwestern CAOB exhibit A-type, alkaline features and formed in a post-accretionary settings, whereas granitoids in the southern CAOB show I-type, calc-alkaline features and were generated in an arc setting. Permian granitoids (290–270Ma) are predominantly of I-A, A-type with alkaline signatures, associated with coeval mafic magmatism and suggesting a post-collisional or intraplate setting, contemporaneous with a Large Igneous Province (LIP) in the Tarim Craton. Some 270–250Ma calc-alkaline granitoids also occur in the southernmost CAOB. Combined with 250–245Ma high Sr/Y granitoids, these rocks reflect final closure of the PAO during 270–250Ma.Early Mesozoic (mainly Triassic) granitoids occur mainly in the eastern CAOB or eastern Central Asia. The early-phase granitoids (250–230Ma) are of I- and S-types, whereas the mid- and late-phase granitoids (ca. 230–190Ma) are of A-type and transitional I-A type or highly fractionated I-type. All these granitoids occur in variable settings (intraplate, post-orogenic, and continental arc) related to three tectonics regimes, namely the Paleo-Asian Ocean (PAO), the Mongol-Okhotsk Ocean (MOO), and the Paleo-Pacific Ocean (PPO). Late Mesozoic granitoids mainly occur in eastern Central Asia and were emplaced during 6 major magmatic events at 190–180, 180–165, 165–145, 145–135, 135–100 and 100–60Ma. The 190–165Ma granitoids are of I-type, calc-alkaline/high-K calc-alkaline, and evolved along active margins related to the Mongol-Okhotsk and Paleo-Pacific ocean domains. The 145–120Ma granitoids are highly fractionated I-, transitional I-A or, A-types, with high-K calc-alkaline/shoshonitic signatures. The magmatic evolution from the Late Jurassic to Early Cretaceous coincided with a tectonic transition from contractional, thickened crust to extensional thinning. The 120–65Ma granitoid magmatism displays a southeastward younging trend, suggesting a roll-back of the Paleo-Pacific oceanic plate.The granitoids in the CAOB of eastern Central Asia show variable whole-rock Nd and Hf-in-zircon isotopic compositions, and most have juvenile signatures. In some regions (e.g., Altai-Junggar and Great Xing’an), the volume of juvenile and slightly juvenile crust (<1.0Ga) is much higher than that of other orogens (such as the Qinling in Central China. The proportion of juvenile vs. old crust may be a marker to identify a typical accretionary orogen from a collisional orogen.

Jurassic cooling ages in Paleozoic to early Mesozoic granitoids of northeastern Patagonia: 40Ar/39Ar, 40K–40Ar mica and U–Pb zircon evidence

U–Pb SHRIMP zircon crystallization ages and Ar–Ar and K–Ar mica cooling ages for basement rocks of the Yaminue and Nahuel Niyeu areas in northeastern Patagonia are presented. Granitoids that cover the time span from Ordovician to Early Triassic constitute the main outcrops of the western sector of the Yaminue block. The southern Yaminue Metaigneous Complex comprises highly deformed Ordovician and Permian granitoids crosscut by undeformed leucogranite dikes (U–Pb SHRIMP zircon age of 254 ± 2 Ma). Mica separates from highly deformed granitoids from the southern sector yielded an Ar–Ar muscovite age of 182 ± 3 Ma and a K–Ar biotite age of 186 ± 2 Ma. Moderately to highly deformed Permian to Early Triassic granitoids made up the northern Yaminue Complex. The Late Permian to Early Triassic (U–Pb SHRIMP zircon age of 252 ± 6 Ma) Cabeza de Vaca Granite of the Yaminue block yielded Jurassic mica K–Ar cooling ages (198 ± 2, 191 ± 1, and 190 ± 2 Ma). At the boundary between the Yaminue and Nahuel Niyeu blocks, K–Ar muscovite ages of 188 ± 3 and 193 ± 5 Ma were calculated for the Flores Granite, whereas the Early Permian Navarrete granodiorite, located in the Nahuel Niyeu block, yielded a K–Ar biotite age of 274 ± 4 Ma. The Jurassic thermal history is not regionally uniform. In the supracrustal exposures of the Nahuel Niyeu block, the Early Permian granitoids of its western sector as well as other Permian plutons and Ordovician leucogranites located further east show no evidence of cooling age reset since mica ages suggest cooling in the wake of crystallization of these intrusive rocks. In contrast, deeper crustal levels are inferred for Permian–Early Triassic granitoids in the Yaminue block since cooling ages for these rocks are of Jurassic age (198–182 Ma). Jurassic resetting is contemporaneous with the massive Lower Jurassic Flores Granite, and the Marifil and Chon Aike volcanic provinces. This intraplate deformational pulse that affected northeastern Patagonia during the Early Jurassic (Sinemurian–Pliensbachian) was responsible for the partial (re)exhumation of the mid-crustal Paleozoic basement along reactivated discrete NE–SW to ENE–WSW lineaments and the resetting of isotopic systems. These new thermochronological data indicate that Early Permian magmatic rocks of the Nahuel Niyeu block were below 300 °C for ca. 20 Ma prior to the onset of the main magmatic episode of the Late Permian to Triassic igneous and metaigneous rocks of the Yaminue block.

Mesozoic gold mineralization in Hainan Province of South China: Genetic types, geological characteristics and geodynamic settings

Numerous gold deposits and occurrences in Hainan Province of South China, predominantly of Mesozoic age account for more than 143t of proven gold reserves. The Au mineralization occurs either along a group of NE-, NNW- and WNW-trending shear zones or within NW- to NNW-trending intraformational detachment faults which are closely related to folding, shearing and transpressional to transtensional deformation. Combined with the Mesozoic tectonics and associated magmatism, the ore geology, fluid inclusion geochemistry, C-H-O-S-(Pb) isotopes and geochronology consistently indicate that there are at least two gold deposit-types in Hainan Island, i.e., orogenic-type and intrusion-related.The predominant orogenic gold mineralization, which produces more than 95% of gold metal reserves in Hainan Island, formed in the Early Mesozoic (ca. 228–224Ma). This ore deposit-type, represented by the Baolun, Gezhen, and Wangxia deposits, is generally hosted by metamorphosed volcaniclastic sedimentary rocks of the Paleo- to Mesoproterozoic, the Silurian and the Permian ages, and is closely associated with brittle-ductile shearing. These deposits, with native gold as main gold occurrence and low sulfide abundance (<5% by volume), are derived from the CO2-rich (mainly 4.8–16.8mol%), near neutral (pH=∼7), low-salinity (generally 3–10.5wt.% NaCleq.), and intermediate-temperature ore fluids. In combination with the paleomagnetism, sedimentation, and petrographical and geochemical features of the Late Paleozoic to Early Mesozoic granitoids, the orogenic gold mineralization is considered to be formed in a post-collisional tectonic setting, in response to the Indosinian orogeny in South China triggered by the closure of the Paleotethys Ocean. Abundant Bi-As-Te-Mo-S phases, which grew synchronously with the gold minerals, suggest a possible involvement of magmatic fluids, especially for the large-scale, high-grade Baolun deposit.The Fuwen Au-dominated Au-Ag deposit, which is hosted by Lower Cretaceous continental clastic rocks, was interpreted as an intrusion-related deposit and most likely formed in the Late Cretaceous. This deposit is endowed with high gold grade (average 28–95g/t Au), extremely high sulfide abundance (>50% by volume), Au-Ag-Cu-Pb-Zn metal association, and small amounts of alteration minerals (pyrite, quartz, sericite, chlorite and calcite). The rare isotopic data of O-H-S-Pb, and the ore occurrences mainly in the intraformational detachment fault zones and subordinately within the Late Cretaceous adakite-like granitoids (zircon U-Pb age of ca. 100Ma), suggest that the Fuwen deposit had an intimate genetic link to the arc-related extension-type magmatism, due to asthenospheric upwelling triggered by the slab roll-back of the subducted Paleo-Pacific plate beneath the South China Block.

Early Mesozoic granitoid and rhyolite magmatism of the Bureya Terrane of the Central Asian Orogenic Belt: Age and geodynamic setting

Early Mesozoic granitoids and volcanic rocks are widespread throughout the structures of all of the continental massifs in the eastern part of the Central Asian Orogenic Belt, although its tectonic setting is not yet clear. Generally, they are associated with subduction and plume processes or rifting. Such uncertainty is mostly explained by the unequal investigation of Early Mesozoic magmatism. This paper presents the results of geochemical, Sm-Nd isotope, and U–Pb geochronologic (ID-TIMS) studies of “key-type” Early Mesozoic magmatic rock complexes of the Bureya Terrane. This is one of the largest continental massifs in the eastern Central Asian Orogenic Belt and knowledge of its geological structure is of fundamental importance in understanding the history of its formation. It has been established that the leucogranites of the Altakhtinsky Complex and the trachyrhyolites of the Talovsky Complex are practically coeval (~209–208Ma). The subalkaline leucogranites of the Kharinsky Complex have a slightly younger age of ~199Ma. These data correspond to the general stage of Early Mesozoic magmatic and metamorphic events (236–180Ma) in most continental massifs in the eastern Central Asian Orogenic Belt. We believe that large-scale Early Mesozoic events were related to the amalgamation of the continental massifs of the eastern Central Asian Orogenic Belt into a single continental structure (the Amur superterrane or microcontinent Amuria) and collision with the North Asian Craton. It should be noted that the collision processes were followed by crustal thickening, thus creating the conditions for metamorphism and formation of magmatic rock complexes of various geochemical types.

Granitoid magmatism in the Qinling orogen, central China and its bearing on orogenic evolution

The Qinling orogen is a typical composite orogen for understanding multi-stages of magmatism and orogenic processes. Many studies have been carried out on the magmatic rocks in the Qinling orogen but their petrogenesis is still controversial. This paper presents a review of all granitoid rocks based on previous and new studies of geochronology and geochemistry. Four distinct periods of granitoid magmatism, Neoproterozoic (979–711 Ma), Paleozoic (507–400 Ma), Early Mesozoic (250–185 Ma) and Late Mesozoic (160–100 Ma), have been recognized from the Qinling orogen according to zircon U-Pb ages, intrusion associations and deformation, as well as regional geology. The Neoproterozoic granitic rocks consist of three stages at 979–911, 894–815 and 759–711 Ma, respectively, corresponding to strongly deformed S-type, weakly deformed I-type and A-type granitoids. They can be interpreted as magmatic occurrences in syn-collisional, post-collisional and extensional settings, respectively, in response to old continental terranes of the Neoproterozoic tectonomagmatic events in the old continents of China, such as South China and Tarim cratons. Although this continental terrane would be involved in the Phanerozoic Qinling orogeny, the Neoproterozoic magmatic rocks are not the products of the Qinling orogenic processes. The Paleozoic magmatic rocks can be classified into three stages at 507–470, 460–422 and 415–400 Ma, respectively. The first-stage magmatism is temporally associated with ultra-high pressure metamorphism in the North Qinling terrane. These magmatic rocks are interpreted as magmatic occurrences in subductional, syn-collisional and post-collisional settings, respectively. The Early Mesozoic magmatic rocks occur in two stages at 252–185 and 225–200 Ma, respectively. The first-stage granitoids are mainly represented by I-type quartz diorites and granodiorites, and the second stage by granodiorites and monzogranites with the I-to A-type characteristics and some with rapakivi textures. Their emplacement ages and geochemical parameters such as A/CNK, K2O/Na2O ratios and eNd(t) values do not show any polarity change in perpendicular to subduction/collision zone. Therefore, all these Early Mesozoic granitoids are unlikely the product of continental subduction as some researchers suggested. Instead, they are plausibly related to the subduction of the Mianlue Ocean and the subsequent collision between the South China Craton and the South Qinling terrane. The Late Mesozoic granitoids were emplaced mainly at two stages of 160–130 and 120–100 Ma, and characterized by the evolution from I- to I-A- and A-type granitoids. These characteristics are consistent with the granitoid magmatic evolution from contractional to extensional settings during the Jurassic/Cretaceous in eastern China. Accordingly, the Late Mesozoic granitoid rocks in the Qinling orogen probably have a similar petrogenetic mechanism to those of the huge magmatic belt along the western Pacific margin, i.e., intra-continent magmatism related to a far-field effect of the subduction of Paleo-Pacific plate.

Origins of Early Mesozoic granitoids and their enclaves from West Kunlun, NW China: implications for evolving magmatism related to closure of the Paleo-Tethys ocean

Early Mesozoic granitoids and microgranular enclaves (MEs) are widespread in the West Kunkun, northwestern Tibetan plateau, and record the tectonic evolution of Eurasia–Tethys in this area. This study reports geochemistry, zircon U–Pb and Hf isotopic data for a suite of granitoids and their MEs from the Middle Triassic Bulunkou pluton (BP) and the Late Triassic Akazishan pluton (AP) from the West Kunlun. LA-ICP-MS U–Pb zircon dating of a sample from the BP host monzogranite and an enclave, as well as a AP monzogranite, yielded ages of 236 ± 2, 230 ± 7 and 208 ± 1 Ma, respectively. The BP monzogranite and its enclaves from the northwestern part of the West Kunlun are mainly weakly peraluminous granites characterised by relatively high Rb, Th, Rb/Sr (2.64–9.03) and HREE contents, and low Mg#, Sr/Y and negative Eu anomalies. Zircons from the BP monzogranite have eHf(t) values from −5.7 to −1.6. Zircons from enclaves of the BP show more variable eHf(t) values from −4.1 to 3.8. We consider that the BP granites are likely to have been formed by partial melting of metasedimentary rocks at shallow crustal depth, and their enclaves, composed of quartz + biotite + plagioclase + garnet + K-feldspar, are relics from the melting of a source at middle crustal depths. The AP host and its enclaves from the southeastern part of the West Kunlun have low Rb, Rb/Sr (0.15–1.90) and weakly negative Eu anomalies but high HREE contents indicating limited fractionation of plagioclase without residual garnet in their source. The inferred protolith is an intermediate igneous rock in the middle or lower crust. MEs hosted in the AP have high Mg# (39.7–45.0) and Nb and weakly negative Eu anomalies, as well as high Sr, P and Ti, corresponding to a medium-K basaltic rock, which may have originated from mixing of partial melting of metasomatised mantle wedge that has been modified by upwelling asthenospheric mantle and crustal melting in the deep source. Post-collisional southeasternward younging of Mesozoic granitoids in the West Kunlun records a transition from shallow level, mid-crustal melting to deeper level, lower-crustal melting. The post-collisional granitoids show significant mantle input increasing from northwest to southeast, which was closely associated with mafic magma-driven partial melting of mantle and crustal sources as a consequence of slab break-off. Syn- to post-collisional Early Mesozoic granites emplaced along the Mazar–Kangxiwar suture zone suggest that these tectonomagmatic processes followed the closure of the Paleo-Tethys ocean during the Tarim and Karakorum–Qiangtang continental collision.

Petrogenesis of the Triassic Bayan-Ulan alkaline granitic pluton in the North Gobi rift of central Mongolia: Implications for the evolution of Early Mesozoic granitoid magmatism in the Central Asian Orogenic Belt

The 221Ma Bayan-Ulan (BU) granitic pluton occurs in the North Gobi rift of central Mongolia which was superimposed on the Paleozoic Central Asian Orogenic Belt (CAOB), an area characterized by voluminous juvenile crust. This large (>1000km2) pluton is part of an Early Mesozoic granitoid province in the central part of the CAOB. It consists mainly of alkali feldspar granites containing mesoperthite with interstitial quartz, minor Ca–Na and Na amphiboles and rare Fe-rich biotite. Graphic texture is common. The BU granites are fractionated, leucocratic, alkaline, A-type rocks that are enriched in incompatible elements, particularly Rb and Th and depleted in Ba, Sr, Eu and Ti. Most have ɛNd(T) values of +1.4 to +1.7 and TDM model ages ∼800 and 1200Ma, and lie within the range of other A-type granites of the CAOB granitoid province. The granites are interpreted to have formed by the partial melting of underplated, Neoproterozoic, mildly-alkaline basalts in the lower crust, followed by fractional crystallization dominated by feldspars. The formation of the BU pluton and the coeval Khentei batholith, the largest Late Triassic intrusion in north-central Mongolia, appears to be related either to a plume or to the closure of the Mongol–Okhotsk ocean. North Gobi rift magmatism extends across the Mongol–Okhotsk suture, so a plume-related origin is more consistent with available data. This plume, which would provide the heat source for magmatism in this area, explains the eastward movement of large scale magmatism over time, from the Tarim traps (300–275Ma), through Khangai (270–240Ma), to Khentei (230–195Ma) in central Mongolia.