Mineralization Epochs of Granitic Rare-Metal Pegmatite Deposits in the Songpan – Ganz ê Orogenic Belt and Their Implications for Orogeny

Granitic pegmatite deposits, which are usually products of orogenic processes during plate convergence, can be used to demonstrate regional tectonic evolution processes. In the eastern Tibetan Plateau in China, the Jiajika, Dahongliutan, Xuebaoding, Zhawulong, and Ke’eryin rare metal pegmatite deposits are located in the southern, western, northern, midwestern, and central areas of the Songpan–Ganzê orogenic belt, respectively. In this study, we dated two muscovite Ar–Ar ages of 189.4 ± 1.1 Ma and 187.0 ± 1.1 Ma from spodumene pegmatites of the Dahongliutan deposit. We also dated one zircon U-Pb age of 211.6 ± 5.2 Ma from muscovite granite, two muscovite Ar–Ar ages of 179.6 ± 1.0 Ma and 174.3 ± 0.9 Ma, and one columbite–tantalite U-Pb age of 204.5 ± 1.8 Ma from spodumene pegmatites of the Zhawulong deposit. In addition, we dated one muscovite Ar–Ar age of 159.0 ± 1.4 Ma from spodumene pegmatite of the Ke’eryin deposit. Combining these ages and previous studies in chronology, we concluded that the granitic magma in the Jiajika, Xuebaoding, Dahongliutan, Zhawulong, and Ke’eryin deposits intruded into Triassic metaturbidites at approximately 223, 221, 220–217, 212, and 207–205 Ma, respectively, and that the crystallization of the corresponding pegmatite ceased at approximately 199–196, 195–190, 189–187, 180–174, and 159 Ma, respectively. In this study, we demonstrated that the peak in magmatic activity and the final crystallization age of the pegmatite lagged behind one another from the outer areas of the orogeny belt to the inner areas. The pegmatite–parented granitic magmas were sourced from Triassic metaturbidites that were melted by shear heating along the large-scale decollement resulting from Indosinian collisions along the North China block, Qiangtang–Changdu block, and Yangtze block. As a result, the above temporal and spatial regularities indicated that the tectonic–thermal stress resulting from the collisions of three blocks was transferred from the outer areas of the orogenic belt to the inner areas. A large amount of heat and a slow cooling rate at the convergent center of thermal stress in two directions will lead to crystallization and differentiation of magma in the Songpan–Ganzê orogenic belt, forming additional rare metal deposits.


Introduction
Li-Cs-Ta (LCT) [1] pegmatites are sources of strategic metals [2].They are usually orogenic products of magmatic activity [1,3] occurring in the plate convergence process [4,5].As a result, the evolution of global pegmatites, from their inception and peak to their decline and eventual extinction, is associated with changes in the tectonics of the lithosphere [6].In addition, the main peaks in the LCT pegmatite age distribution are generally consistent with the epochs of supercontinent assembly [4].For example, the occurrence peaks of LCT-type pegmatite from 2368 Ma, 1800 Ma, 962 Ma, 529-485 Ma, and 371-274 Ma coincide with the assemblies of Sclavia and Superia, Nuna, Rodinia, Gondwana, and Pangea, respectively [4].Therefore, pegmatites and pegmatite-type rare metal deposits are used to trace tectonic history, particularly continental orogenic processes.
For example, through regional pegmatite, Pedrosa et al. [7] studied the opening of the South Atlantic, and Galetskiy [8] and Mints [9] discussed the tectonic evolution of the Eastern Baltic and Ukrainian shields, respectively.Mohammedyasin et al. [10] claimed that the rare metal mineralization of the Kenticha deposit in southern Ethiopia marked the end of the East African Orogeny, and Makrygina et al. [11] concluded that the Ol'khon rare metal pegmatoid granites marked the beginning of the Hercynian within-plate stage in the eastern Baikal area of Russia.
The Songpan-Ganzê orogenic belt, located in the eastern Tibetan Plateau, is one of the most important granitic pegmatite mineralization belts in China [12].It has a complex tectonic history as a result of the interactions between three major continental blocks (North China, Yangtze, and Qiangtang-Changdu) during the closure of the Paleo-Tethys in the Late Triassic [13,14].In this tectonic setting, widespread granitic pegmatite-type rare metal deposits were formed [15].Although a number of studies regarding the ages of regional pegmatite and related granitic intrusions have been published to date [16][17][18][19], there has not been a systemic summary of the regional diagenesis and mineralization process.By supplementing several essential dating results, in this paper we systematically summarize the spatiotemporal distribution of rare metal pegmatite deposits in the Songpan-Ganzê orogenic belt.In addition, we estimate the cooling rate and time of different pegmatite ore fields according to the closure temperatures of different isotope dating systems.Based on the results, we investigate the implications of these pegmatite-type deposits for orogeny in the Songpan-Ganzê orogenic belt.

Regional Geological Features
The Songpan-Ganzê orogenic belt is in contact with the Yangtze, North China, and Qiangtang-Changdu blocks along the Longmenshan thrust-nappe belt [20], Miaulue-A'nyemaqen suture [21], and Jinsha suture, respectively (Figure 1).In the Songpan-Ganzê orogenic belt, Sinian strata are distributed along the eastern edge of the belt.Triassic flysch sediments, composed primarily of sandstone and slate, are distributed in the main section of the belt with a thickness of more than 10,000 m [22].The flysch sediments have undergone metamorphism to different degrees, resulting in serial medium-pressure metamorphic domed bodies, including the Yajiang, Ke'eryin, Zhawulong, and Zhibosong domes.Usually, pegmatite dikes and their parental granites intrude into the core of these metamorphic domes; however, Indosinian tectonic movement shortened the crust as a result of the collision of the Yangtze, Qiangtang-Changdu, and North China blocks [15].

Jiajika Li-Be-Ta-Nb Deposit
The Jiajika pegmatite deposit, located in the southern Songpan-Ganzê orogenic belt (location A; Figure 1), is hosted in the Yajiang metamorphic dome.In the Jiajika pegmatite field, pegmatite dikes surround the granite body both horizontally and vertically (Figure 2).The wall rocks of the two-mica granite and pegmatites are composed of mudstone and sandstone from the Late Triassic period.The main tectonic features controlling ore distribution are joints and fissures that formed before or during pegmatite emplacement.The rocks that contain the Jiajika granite underwent multistage metamorphism during magmatism, leading to the development of five distinct metamorphic zones that surround the granite; from the inner zones to the outer zones, these are the diopside, staurolite, andalusite-staurolite, andalusite, and biotite zones.The total area of the metamorphic zones is approximately 500 km 2 [27].
In the Jiajika deposit, a total of 498 pegmatite dikes with a length × width of more than 20 m 2 are distributed in an area of approximately 80 km 2 .On the basis of mineral paragenetic associations, each pegmatite dike can be divided into three to five mineral zones.On the basis of the main mineral zones, the pegmatite dikes can be classified into five types: microcline pegmatite (I), microcline-albite pegmatite (II), albite pegmatite (III), spodumene pegmatite (IV), and lepidolite (muscovite) pegmatite (V; Figure 2).Farther away from the type-V pegmatite zone, many quartz veins are present.The major minerals in the pegmatite dikes are microcline, albite, quartz, and muscovite.These coexist with rare metal-element-bearing minerals, such as spodumene, titanium samarskite, beryl, thorite, cyrtolite, cymatolite, and sicklerite, as well as volatile-bearing minerals, such as tourmaline and fluorite [27].In the metamorphic domes of the Songpan-Ganzê orogenic belt, granitic pegmatite deposits occur around granitic intrusions and contain abundant rare metal resources (Figure 1), including lithium.The Jiajiaka, Dahongliutan, and Ke'eryin rare metal deposits are also super-large lithium deposits, containing Li 2 O reserves of more than 2,000,000, 3,000,0000, and 2,000,000 tons, respectively [12,[23][24][25][26].The Xuebaoding deposit is famous worldwide for its infrequent platy beryl crystals and integral scheelite crystals [27], and the Zhawulong deposits may potentially be super-large rare metal deposits [28].In addition, these granitic pegmatite deposits contain high-grade rare metal elements of more than 1.2 wt.% Li 2 O at shallow burial depth.

Jiajika Li-Be-Ta-Nb Deposit
The Jiajika pegmatite deposit, located in the southern Songpan-Ganzê orogenic belt (location A; Figure 1), is hosted in the Yajiang metamorphic dome.In the Jiajika pegmatite field, pegmatite dikes surround the granite body both horizontally and vertically (Figure 2).The wall rocks of the two-mica granite and pegmatites are composed of mudstone and sandstone from the Late Triassic period.The main tectonic features controlling ore distribution are joints and fissures that formed before or during pegmatite emplacement.The rocks that contain the Jiajika granite underwent multistage metamorphism during magmatism, leading to the development of five distinct metamorphic zones that surround the granite; from the inner zones to the outer zones, these are the diopside, staurolite, andalusite-staurolite, andalusite, and biotite zones.The total area of the metamorphic zones is approximately 500 km 2 [27].

Dahongliutan Li-Be-Nb-Ta Deposit
The Dahongliutan pegmatite deposit is located in the western area of the Songpan-Ganzê orogenic belt (location B; Figure 1).In the Dahongliutan ore field, more than 110 pegmatite dikes occur in an outcrop area of approximately 31.5 km 2 surrounding the Yanshanian two-mica granite (Figure 3).Irregular schlieren pegmatite dikes occur within the granite.In addition, in the middle Proterozoic biotite schist and sillimanite-andalusite-biotite-quartz schist, muscovite-microcline, muscovite-microcline-albite, and spodumene pegmatite dikes occur proximally to distally from the granite in that order.The spodumene pegmatite dikes, including dikes No. 90, 91, 93, 102, and 104, are composed primarily of an albite-spodumene zone and quartz-spodumene zone with several In the Jiajika deposit, a total of 498 pegmatite dikes with a length × width of more than 20 m 2 are distributed in an area of approximately 80 km 2 .On the basis of mineral paragenetic associations, each pegmatite dike can be divided into three to five mineral zones.On the basis of the main mineral zones, the pegmatite dikes can be classified into five types: microcline pegmatite (I), microcline-albite pegmatite (II), albite pegmatite (III), spodumene pegmatite (IV), and lepidolite (muscovite) pegmatite (V; Figure 2).Farther away from the type-V pegmatite zone, many quartz veins are present.The major minerals in the pegmatite dikes are microcline, albite, quartz, and muscovite.These coexist with rare Minerals 2019, 9, 280 5 of 25 metal-element-bearing minerals, such as spodumene, titanium samarskite, beryl, thorite, cyrtolite, cymatolite, and sicklerite, as well as volatile-bearing minerals, such as tourmaline and fluorite [27].

Dahongliutan Li-Be-Nb-Ta Deposit
The Dahongliutan pegmatite deposit is located in the western area of the Songpan-Ganzê orogenic belt (location B; Figure 1).In the Dahongliutan ore field, more than 110 pegmatite dikes occur in an outcrop area of approximately 31.5 km 2 surrounding the Yanshanian two-mica granite (Figure 3).Irregular schlieren pegmatite dikes occur within the granite.In addition, in the middle Proterozoic biotite schist and sillimanite-andalusite-biotite-quartz schist, muscovite-microcline, muscovite-microcline-albite, and spodumene pegmatite dikes occur proximally to distally from the granite in that order.The spodumene pegmatite dikes, including dikes No. 90, 91, 93, 102, and 104, are composed primarily of an albite-spodumene zone and quartz-spodumene zone with several albite-lepidolite aggregations.The lithium oxide (Li 2 O) reserves of five spodumene pegmatite dikes are greater than 50,000 t and have a Li 2 O content of 1.24-1.62%[23].albite-lepidolite aggregations.The lithium oxide (Li2O) reserves of five spodumene pegmatite dikes are greater than 50,000 t and have a Li2O content of 1.24-1.62%[23].The legend for the diagram in the upper right-hand corner is provided in Figure 1.

Xuebaoding W-Sn-Be Deposit
The Xuebaoding granitic pegmatite deposit, located in the northern area of the Songpan-Ganzê orogenic belt (location C; Figure 1), is hosted in the Zhibosong metamorphic dome.In the ore field, the Pankou and Pukou muscovite plagiogranites intruded into the Middle Triassic strata composed of sericite-quartz phyllite, under the control of the dome core (Figure 4).The Pukou and Pankou granitic intrusions contain cassiterite, scheelite, chalcopyrite, galena, sphalerite, molybdenite, and pyrite with clear zonal structures of marginal, transitional, and core zones.Fissures in the Triassic wall rock provided pathways and precipitation sites for pegmatite-forming fluid exsolved from granitic magma.Most mineralized pegmatite dikes occur, as a group, between the Pankou and Pukou

Xuebaoding W-Sn-Be Deposit
The Xuebaoding granitic pegmatite deposit, located in the northern area of the Songpan-Ganzê orogenic belt (location C; Figure 1), is hosted in the Zhibosong metamorphic dome.In the ore field, the Pankou and Pukou muscovite plagiogranites intruded into the Middle Triassic strata composed of sericite-quartz phyllite, under the control of the dome core (Figure 4).The Pukou and Pankou granitic intrusions contain cassiterite, scheelite, chalcopyrite, galena, sphalerite, molybdenite, and pyrite with clear zonal structures of marginal, transitional, and core zones.Fissures in the Triassic wall rock provided pathways and precipitation sites for pegmatite-forming fluid exsolved from granitic magma.Most mineralized pegmatite dikes occur, as a group, between the Pankou and Pukou granite (Figure 4).The main metal minerals in pegmatite dikes are scheelite, cassiterite with other metallic sulfides, quartz, muscovite, fluorite, feldspar, and beryl.Scheelites, which are normally present in the outer sections of pegmatite dikes, are often white or pale yellow cubic-bipyramidal crystals, some of which weigh up to 1 kg.Beryl crystals are short hexagonal prisms, white or light green in color, and can weigh up to 1 kg [29].The Yanggonghai intrusion is also located in the northern area of the Songpan-Ganzê orogenic belt.It is located approximately 100 km west of the Xuebaoding deposit, with outcrop areas of 980 km 2 (Figure 1) [27].The granite intruded into the Late Triassic sandstone.In addition, many mineralization-barren granitic pegmatite dikes are present within the granitic intrusions and their wall rocks.This granite-pegmatite system is similar to the Xuebaoding deposit, although it has The Yanggonghai intrusion is also located in the northern area of the Songpan-Ganzê orogenic belt.It is located approximately 100 km west of the Xuebaoding deposit, with outcrop areas of 980 km 2 (Figure 1) [27].The granite intruded into the Late Triassic sandstone.In addition, many mineralization-barren granitic pegmatite dikes are present within the granitic intrusions and their wall rocks.This granite-pegmatite system is similar to the Xuebaoding deposit, although it has undergone strong erosion [27].

Zhawulong Li-Be-Ta-Nb Deposit
The Zhawulong pegmatite deposit is located in the midwestern areas of the Songpan-Ganzê orogenic belt (location D; Figure 1).The Quaternary coverage of the ore field is greater than 50%, and the outcropped strata are Triassic mudstone and sandstone.The Zhawulong muscovite granite, which is the metallogenic parent rock of the rare metal deposit, intruded into Triassic mudstone and sandstone (Figure 1) along the Zhawulong anticline, occurring as an irregular fusiform intrusion with an outcrop area of 58 km 2 .The residual roof of wall rock still remains at the top of the granitic intrusion, indicating a low degree of regional denudation.
In the ore field, 111 pegmatites are mainly distributed around the contact zone of the Zhawulong granitic intrusion and the Triassic sediments; 36% of them show mineralization of rare metals (Figure 5).More than 20 pegmatites demonstrate significant mineralization with Li 2 O content ranging from 1.2% to 1.5%.Among them, pegmatite No. 14 has the largest Li mineralization scale, with a surface outcropping extension of approximately 2000 m and a thickness of approximately 5 m.The entire vein is mineralized with an average Li 2 O grade of 1.2% and Li 2 O reserves of 100,000 tons, while the Li 2 O reserves of the Zhawulong deposit are approximately 160,000 tons, approaching the scale of large lithium deposits [28].
Minerals 2019, 9, x FOR PEER REVIEW 7 of 26 sandstone (Figure 1) along the Zhawulong anticline, occurring as an irregular fusiform intrusion with an outcrop area of 58 km 2 .The residual roof of wall rock still remains at the top of the granitic intrusion, indicating a low degree of regional denudation.
In the ore field, 111 pegmatites are mainly distributed around the contact zone of the Zhawulong granitic intrusion and the Triassic sediments; 36% of them show mineralization of rare metals (Figure 5).More than 20 pegmatites demonstrate significant mineralization with Li2O content ranging from 1.2% to 1.5%.Among them, pegmatite No. 14 has the largest Li mineralization scale, with a surface outcropping extension of approximately 2000 m and a thickness of approximately 5 m.The entire vein is mineralized with an average Li2O grade of 1.2% and Li2O reserves of 100,000 tons, while the Li2O reserves of the Zhawulong deposit are approximately 160,000 tons, approaching the scale of large lithium deposits [28].

Ke'eryin Li-Be-Ta-Nb Deposit
The Ke'eryin pegmatite deposit is located in the central area of the Songpan-Ganzê orogenic belt (location E; Figure 1).In the ore field, a complex granitic intrusion, composed of a series of mediumacidity magmatic rocks, intruded into the Triassic sandstone during the late Indosinian period.Twomica granite, with an outcrop area of 188 km 2 , dominates this intrusion that was controlled by the axial lobe of the Ke'eryin anticline (Figure 6).On the basis of the intrusion and incision relationships, the granitic intrusion formed in a full fractional crystallization process that produced quartz diorite, biotite granite, biotite adamellite, biotite K-feldspar granite, two-mica granite, and muscovite-albite granite in turn [27].Similarly to the metamorphic belt in the Jiajika deposit, the pyroxene-hornfels facies, amphibolite-hornfels facies, albite-epidote-hornfels facies, andalusite belt, staurolite-

Ke'eryin Li-Be-Ta-Nb Deposit
The Ke'eryin pegmatite deposit is located in the central area of the Songpan-Ganzê orogenic belt (location E; Figure 1).In the ore field, a complex granitic intrusion, composed of a series of medium-acidity magmatic rocks, intruded into the Triassic sandstone during the late Indosinian period.Two-mica granite, with an outcrop area of 188 km 2 , dominates this intrusion that was controlled by the axial lobe of the Ke'eryin anticline (Figure 6).On the basis of the intrusion and incision relationships, the granitic intrusion formed in a full fractional crystallization process that produced quartz diorite, biotite granite, biotite adamellite, biotite K-feldspar granite, two-mica granite, and muscovite-albite granite in turn [27].Similarly to the metamorphic belt in the Jiajika deposit, the pyroxene-hornfels facies, amphibolite-hornfels facies, albite-epidote-hornfels facies, andalusite belt, staurolite-grossularite belt, and biotite belt surround the complex granitic intrusions.In the Ke'eryin ore field, approximately 548 mineralized pegmatite dikes, including 263 spodumene pegmatite dikes, have been discovered [30].These pegmatite dikes are 50-300 m in length and 2-10 m in thickness.They occur in groups around the complex granitic intrusion.The Ke'eryin ore field contains six main types of dikes: two-mica microcline, muscovite-microcline, muscovitemicrocline-albite, muscovite-albite, muscovite-albite-spodumene, and muscovite-albite-lepidolite.The first four types are mineralization-barren pegmatite dikes that mainly occur within granite, and the second two types are rare metal pegmatites that mainly occur in Triassic sandstones.The Ke'eryin ore field produced two super-large lithium deposits (Li2O reserves ≥500,000 tons)-the Dangba and Lijiagou deposits and several medium-large lithium deposits.The Dangba large-scale pegmatite dikes of muscovite-albite-spodumene with massive reserves are located primarily in the southeastern area of the ore field.The main rare metal minerals found in the Ke'eryin pegmatite are spodumene, beryl, columbite-tantalite minerals, and cassiterite [30].The potential reserves of Li2O in this region may be greater than 7,000,000 tons [25].

Sampling and Dating Methods
In this study, the muscovite samples used for Ar-Ar dating were extracted from the spodumene pegmatites of the Dahongliutan, Zhawulong, and Ke'eryin ore fields, and the zircon and columbitetantalite samples used for U-Pb dating were extracted from the Zhawulong ore field.Muscovite samples Dm90 and Dm102 were sampled from spodumene pegmatite dikes No. 90 and No. 102 in In the Ke'eryin ore field, approximately 548 mineralized pegmatite dikes, including 263 spodumene pegmatite dikes, have been discovered [30].These pegmatite dikes are 50-300 m in length and 2-10 m in thickness.They occur in groups around the complex granitic intrusion.The Ke'eryin ore field contains six main types of dikes: two-mica microcline, muscovite-microcline, muscovite-microcline-albite, muscovite-albite, muscovite-albite-spodumene, and muscovite-albite-lepidolite.The first four types are mineralization-barren pegmatite dikes that mainly occur within granite, and the second two types are rare metal pegmatites that mainly occur in Triassic sandstones.The Ke'eryin ore field produced two super-large lithium deposits (Li 2 O reserves ≥500,000 tons)-the Dangba and Lijiagou deposits and several medium-large lithium deposits.The Dangba large-scale pegmatite dikes of muscovite-albite-spodumene with massive reserves are located primarily in the southeastern area of the ore field.The main rare metal minerals found in the Ke'eryin pegmatite are spodumene, beryl, columbite-tantalite minerals, and cassiterite [30].The potential reserves of Li 2 O in this region may be greater than 7,000,000 tons [25].

Sampling and Dating Methods
In this study, the muscovite samples used for Ar-Ar dating were extracted from the spodumene pegmatites of the Dahongliutan, Zhawulong, and Ke'eryin ore fields, and the zircon and columbite-tantalite samples used for U-Pb dating were extracted from the Zhawulong ore field.Muscovite samples Dm90 and Dm102 were sampled from spodumene pegmatite dikes No. 90 and No. 102 in the Dahongliutan deposit, respectively (Figure 3).Dm90 and Dm102 were white in color, shaped as large sheets, and coexisted with quartz, albite, and spodumene (Figure 7a,b).In the Ke'eryin ore field, muscovite sample Km1 was sampled from the Dangba spodumene pegmatites (Figure 6).Km1 was white in color and shaped as fine sheets with straight quartz and feldspar boundaries (Figures 7c,d).In the Zhawulong ore field, muscovite samples Zm-1 and Zm-2 were sampled from the spodumene pegmatite dikes No. 14 and No. 97, respectively (Figure 5).Zm-1 and Zm-2 were white in color, shaped as large sheets, and coexisted with quartz, albite, and spodumene (Figure 7e,f).Zircon samples ZG-1 were sampled from fresh muscovite granite in the southeast part of the Zhawulong granite (Figure 7g,h).The columbite-tantalite samples of Zct-1 were sampled from the No. 14 spodumene pegmatite dikes.Most were shaped as hypidiomorphic long or short columns and coexisted with quartz, albite, and spodumene (Figure 7e).
Due to the large sheets, the fresh muscovite samples of Dm90 and Dm102 from the Dahongliutan ore field were removed by hand.These individual muscovite crystals were then cut into chips ≤0.15In the Ke'eryin ore field, muscovite sample Km1 was sampled from the Dangba spodumene pegmatites (Figure 6).Km1 was white in color and shaped as fine sheets with straight quartz and feldspar boundaries (Figure 7c,d).In the Zhawulong ore field, muscovite samples Zm-1 and Zm-2 were sampled from the spodumene pegmatite dikes No. 14 and No. 97, respectively (Figure 5).Zm-1 and Zm-2 were white in color, shaped as large sheets, and coexisted with quartz, albite, and spodumene (Figure 7e,f).Zircon samples ZG-1 were sampled from fresh muscovite granite in the southeast part of the Zhawulong granite (Figure 7g,h).The columbite-tantalite samples of Zct-1 were sampled from the No. 14 spodumene pegmatite dikes.Most were shaped as hypidiomorphic long or short columns and coexisted with quartz, albite, and spodumene (Figure 7e).
Due to the large sheets, the fresh muscovite samples of Dm90 and Dm102 from the Dahongliutan ore field were removed by hand.These individual muscovite crystals were then cut into chips ≤0.15 mm in size prior to cleaning in an ultrasonic bath.The Km1 muscovite samples were separated from spodumene pegmatite samples weighing approximately 6 kg.The samples were crushed, and grains <0.5 mm were separated by sieving, with >99% pure fresh muscovite removed by hand using a binocular microscope.Zm-1 and Zm-2 were separated from two spodumene pegmatite samples.They were then crushed, and grains <0.5 mm were separated by sieving, with >99% pure fresh muscovite removed by hand using a binocular microscope.
During Ar-Ar dating, muscovite samples were sealed in a quartz ampoule that was irradiated for 1440 minutes in the nuclear reactor (The Swimming Pool Reactor, Chinese Institute of Atomic Energy, Beijing).The reactor delivers a neutron flux of ~2.60×10 13 n•cm −2 s −1 ; The integrated neutron flux is about 2.25×10 18 n•cm −2 .The monitor irradiated together with the samples is an internal standard: Fangshan biotite (ZBH-25) whose age is 132.7 Ma and its potassium content is 7.6% [31].Following irradiation, the samples were incrementally heated to release argon in the extremely high-vacuum argon extraction system at the Laboratory of Ar-Ar Isotopic Dating, Institute of Geology, Chinese Academy of Geological Sciences in Beijing, China.The purified argon extracted during heating was analyzed by Mass Spectrometer GV Helix MC (GV Instruments, Ltd; Manchester, UK).
Apparent ages for each heating stage were corrected for mass discrimination, atmospheric Ar concentration, blank values, and interfering isotopes, and 37 Ar values were corrected for radioactive decay.The correction factors for interfering isotopes produced during irradiation used in this study were as follows: ( 36 Ar/ 37 Ar) Ca = 2.40 × 10 −4 , ( 40 Ar/ 39 Ar) K = 47.82 × 10 −4 , and ( 39 Ar/ 37 Ar) Ca = 8.06 × 10 −4 .The 40 K decay constant used for analysis was λ = 5.543 × 10 −10 a −1 , with an age error of 1 σ.The entire analytical procedure used for the Ar-Ar analysis was identical to the one outlined in Chen and Zhang (2002) [32].
Zircon separation and cathodoluminescence (CL) imaging were performed at the Beijing SHRIMP Center at the Chinese Academy of Geological Sciences.Zircon grains were extracted from rock samples using conventional procedures of rock crushing, sieving, elutriating, drying, dressing by magnetic separation, electromagnetic selection, heavy liquid separation, and handpicking under a binocular microscope.Zircon grains were then mounted onto double-sided adhesive tape and enclosed in a 2.5-cm-diameter epoxy resin disk.The morphology of the zircon crystals was examined in both transmitted and reflected light, and images were captured using an optical microscope and a CL imaging system.The procedures were identical to those described in Liu et al. (2015) [33].
Zircon U-Pb dating analysis was performed via LA-ICP-MS at the National Research Center of Geoanalysis in Beijing, China.Laser sampling was performed using an ESI New Wave 193 laser ablation system (Electro-Sensors, Inc.; Hopkins, MN, USA).Ion signal intensities were detected with a Thermo ELMENT XR instrument (Thermo fisher scientific; Waltham, MA USA).Helium was used as a carrier gas and argon as the make-up gas; the two gases were mixed via a T-connector prior to entering the ICP.Each analysis incorporated background acquisition for approximately 20 s (gas blank) followed by 40 s of data acquisition from the sample.The ICPMSDataCal(11.4) software was used to perform off-line raw data selection, integration of background and analytical signals, and time-drift correction and quantitative calibration for U-Pb dating [34].Common Pb was corrected according to the method proposed in [35].
For the analysis, we used a spot size of 23 µm, and time-dependent elemental fractionation was minimized by using a laser frequency of 8 Hz.Zircon GJ-1 (601.0 ± 1.7 Ma, 2σ, [36]) was used as an external standard for U-Pb dating and was analyzed twice every 10 analyses.Time-dependent drifts of U-Th-Pb isotopic ratios were corrected using linear interpolation (with time) for every 10 analyses according to variations detected in GJ-1.The uncertainty in the preferred values (0.5%) for the external standard GJ-1 was propagated to the final results of the samples.Common Pb correction was found to be unnecessary for the analyzed zircons due to a low signal from common 204 Pb and a high 206 Pb/ 204 Pb ratio.The U, Th, and Pb concentrations were calibrated on the basis of glass standard NIST SRM 612 which was produced by National Institute of Standards and Technology (NIST, USA) to ensure that the 232 Th and 238 U signals were greater than 20 MeV.The oxide yield was controlled to less than 0.2%, and the isotope signal ratio of 238 U/ 232 Th was controlled to approximately 1 by monitoring the ThO + /Th + ratio.The Isoplot/Ex_ver3 tool was used to construct concordia diagrams and calculate weighted means.Plešovice zircons were dated as unknown samples and yielded a weighted mean 206 Pb/ 238 U age of 337 ± 2 Ma (2SD, n = 12), which is in good agreement with the standard 206 Pb/ 238 U age of 337.13 ± 0.37 Ma (2SD) [37].Determining the ages of zircons (>1000 Ma) must be based primarily on their 207 Pb/ 206 Pb ages.The zircon 206 Pb/ 238 U ages were reported at a 1σ uncertainty level.
The analytical procedures used for columbite-tantalite U-Pb dating are described in detail in Che et al. (2015) [38]; a brief overview is provided below.U-Pb dating was performed using a Resolution S-155 193-nm excimer ArF laser ablation system coupled to a Thermo Fisher Scientific iCAP-Q quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) at the State Key Laboratory for Mineral Deposits Research at Nanjing University, China.During analysis, the laser was set to a fluence of approximately 7.5 J/cm 3 , a spot size of 67 µm, and a repetition rate of 4 Hz.Each group of five unknowns was bracketed by the analysis of two zircon standards (91500 and GJ-1) and one columbite-tantalite reference material (Coltan 139).Each analysis consisted of approximately 30 s of background acquisition, 60 s of data acquisition with the laser running, and up to 60 s to flush the system.The external columbite-tantalite reference standard and data processing method were identical to those described in [38].The 206 Pb/ 238 U ages were reported at a 1σ uncertainty level.
These results indicate that the 40 Ar/ 39 Ar isotope system in muscovite samples, extracted from the pegmatite dikes in the Dahongliutan, Zhawulong, and Ke'eryin deposits, remained closed and was not affected by the presence of excess argon or argon loss after crystallization.

Zircon U-Pb Dating
The CL images of zircons captured from the Zhawulong granite are presented in Figure 9.The zircons are either hypidiomorphic or idiomorphic, and most are composed of a magmatic core with relatively obvious oscillatory zoning and a narrow metamorphic overgrowth rim with obscure zoning.These metamorphic overgrowth rims may have been recrystallized during late metamorphism and causes the decrease of the Th/U ratio of zircon [40,41].All 28 spots have Th/U ratios of 0.01-3.18,and 25 of them are between 0.04 and 1.85.The zircon U-Pb dating results are provided in Table A2.The majority of the analyses are concordant, and the discordant spots reveal the characteristics of 207   . 40Ar/ 39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the pegmatite dikes of the Dahongliutan, Zhawulong, and Ke'eryin deposits in the Songpan-Ganzê orogenic belt.(a-d) 40 Ar/ 39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Dahongliutan pegmatites; (e-h) 40 Ar/ 39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Zhawulong pegmatites; (i,j) 40 Ar/ 39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Ke'eryin pegmatite.

Zircon U-Pb Dating
The CL images of zircons captured from the Zhawulong granite are presented in Figure 9.The zircons are either hypidiomorphic or idiomorphic, and most are composed of a magmatic core with relatively obvious oscillatory zoning and a narrow metamorphic overgrowth rim with obscure zoning.These metamorphic overgrowth rims may have been recrystallized during late metamorphism and causes the decrease of the Th/U ratio of zircon [40,41].All 28 spots have Th/U ratios of 0.01-3.18,and 25 of them are between 0.04 and 1.85.The zircon U-Pb dating results are provided in Table A2.The majority of the analyses are concordant, and the discordant spots reveal the characteristics of 207 Pb/ 206 Pb > 207 Pb/ 235 U > 206 Pb/ 238 U (e.g., spots 7, 8, 13, 16, 18), which indicate various degrees of radiogenic lead loss.
Because the overgrowth rims were too narrow for measurement (<10 μm), 28 spot analyses were performed on the magmatic core of 28 zircon grains from ZG-1.A total of 14 spots deviated significantly from the concordia, and the remaining 14 spots yielded a weighted mean 206 Pb/ 238 U age of 211.6 ± 5.2 Ma (1σ, MSWD = 0.15, n = 14) (Figure 10).Because the overgrowth rims were too narrow for measurement (<10 µm), 28 spot analyses were performed on the magmatic core of 28 zircon grains from ZG-1.A total of 14 spots deviated significantly from the concordia, and the remaining 14 spots yielded a weighted mean 206 Pb/ 238 U age of 211.6 ± 5.2 Ma (1σ, MSWD = 0.15, n = 14) (Figure 10).

Columbite-Tantalite U-Pb Dating
The CL images of the columbite-tantalites captured from the Zhawulong No. 14 spodumene pegmatite dike are presented in Figure 9.Most of the columbite-tantalite grains were shaped as subhedral long or short columns, and several grains displayed weak oscillation zones.The U-Pb isotopic compositions of the columbite-tantalite grains were measured using spot analysis.All data obtained are provided in Table A2, and the calculated ages are plotted in Figure 10.
Forty spot analyses were performed on 40 columbite-tantalite grains from Zct-1.A total of 25 spots deviated significantly from the concordia due to the influence of inclusions (e.g., spot 7, 12, 13, and 17) or high concentrations of common Pb associated with cracks.A total of 15 spots yielded a weighted mean 206 Pb/ 238 U age of 204.5 ± 1.8 Ma (1σ, MSWD = 1.2, n = 15).

Ages of Pegmatite Deposits in the Songpan-Ganzê Orogenic Belt
The dating data presented in this paper provide reliable temporal constraints for the magmatic activities related to rare metal mineralization in the Songpan-Ganzê orogenic belt.The spodumene pegmatites of the Ke'eryin ore field produced muscovite Ar-Ar age of 159.0 ± 1.4 Ma, while the spodumene pegmatites in the Dahongliutan ore field produced muscovite Ar-Ar ages of 189.4 ± 1.1 Ma and 187.0 ± 1.1 Ma.In addition, the muscovite Ar-Ar ages of spodumene pegmatites in Zhawulong ore field were 179.6 ± 1.0 Ma and 174.3 ± 0.9 Ma.The zircon concordant age of 211.6 ± 5.2 Ma for the Zhawulong muscovite granite is interpreted to be its emplacement age, which is close to the columbite-tantalite U-Pb age of 204.5 ± 1.8 Ma of the spodumene pegmatites in the Zhawulong ore field.
In addition to the dating results obtained in this study, many other muscovite Ar-Ar ages, zircon U-Pb ages, and columbite-tantalite U-Pb ages of pegmatites in western Sichuan have been reported.The sampling locations and dating results are listed in Table 1.The dating results for the main granitic intrusions related to regional pegmatite deposits, including those in the Yanggonhai, Jiajika, Ke'eryin, and Dahongliutan granitic intrusions, are also summarized in Table 1.
The geochronological analyses summarized in Table 1 indicate that different isotope systems provide different ages, mainly due to the different closure temperatures for these isotopic systems in different minerals [42] rather than the crystallization order of the minerals.In granitic magma, the closure temperatures for the U-Pb system in zircon is 800-900 • C [43][44][45][46].This is consistent with the granitic magma temperature, and therefore the U-Pb age of zircon can be regarded as the granite emplacement age.Because the closure temperature of the Ar-Ar isotope system in muscovite (300 • C-400 • C; [43- 45,52,53]) is close to the lowest crystallization temperature of pegmatite (350 • C-450 • C; [54,55]), the Ar-Ar plateau ages of muscovite can represent the final crystallization age of the pegmatites.Although the closure temperature of the columbite-tantalite U-Pb system has never been reported, it should be similar to the closure temperature of the zircon U-Pb system based on the similarity between the U-Pb zircon age (216 ± 2 Ma) and the columbite-tantalite age (214 ± 2 Ma) in the Jiajika pegmatite [16].As a result, the ages that are similar to zircon U-Pb ages can represent the initial crystallization age of pegmatite.In addition, the closure temperature of the columbite-tantalite U-Pb system can be preliminarily inferred to be approximately 700 • C-500 • C, as pegmatite crystallization began in this temperature range in the Jiajika pegmatite [56].Therefore, it can be concluded that the crystallization of pegmatites in the Jiajika, Xuebaoding, Dahongliutan, Zhawulong, and Ke'eryin deposits finally began at approximately 223, 221, 220-217, 212, and 207-205 Ma, respectively.Furthermore, it can be supposed that crystallization of the corresponding pegmatite ceased at approximately 199-196, 195-190, 189-187, 180-174, and 159 Ma, respectively.
We then plotted the cooling paths of the main granitic pegmatite deposits in different sections of the Songpan-Ganzê orogenic belt (Figure 11).We discovered that from the outer areas (Jiajika, Xuebaoding, and Dahongliutan ore fields) to the middle area (Zhawulong ore field) and then to the inner area (Ke'eryin ore field), there was a lag from the peak in magmatic activity to the final crystallization ages of the pegmatite deposits.

Formation Mechanism of Granite-Pegmatite Systems in the Songpan-Ganzê Orogenic Belt
It is generally believed that the LCT pegmatite and the peraluminous S-type granite system have a genetic relationship with the melting of sedimentary and/or metamorphosed sedimentary or supracrustal rocks [1,3,54,[57][58][59][60].In addition, it is generally agreed upon that the emplacement of pegmatite occurred during a period of continental collision and crustal thickening, or at the end of

Formation Mechanism of Granite-Pegmatite Systems in the Songpan-Ganzê Orogenic Belt
It is generally believed that the LCT pegmatite and the peraluminous S-type granite system have a genetic relationship with the melting of sedimentary and/or metamorphosed sedimentary or supracrustal rocks [1,3,54,[57][58][59][60].In addition, it is generally agreed upon that the emplacement of pegmatite occurred during a period of continental collision and crustal thickening, or at the end of this period [61][62][63].Crustal thickening and subsequent decompression led to melting of the mica-rich (meta)sedimentary strata, which is a potentially important source of H 2 O, F, and rare metal elements.Finally, rare metal pegmatite was formed [41,[64][65][66][67][68][69][70][71][72][73].Many important rare metal deposits across the globe, such as the Ghost Lake deposit in North America, the Greenbushes deposit in Australia, and the pegmatite province in eastern Brazil, occurred in orogenic belts and formed through multistage magmatic superimposition in an orogenic tectonic setting [12,41,[74][75][76].
The Songpan-Ganzê orogenic belt formed during the convergence of the Yangtze, Qiangchang-Changdu, and North China blocks in the Indosinian period, accompanied by the closure of the Paleo-Tethys oceanic basin [15,[77][78][79][80].During the collisions, the northward and southward tectonic stresses caused decollement to occur between the basement and the cap rock (Triassic sediments) [13,15,81], accompanied by extensive folding and thrusting that led to large-scale crustal shortening and thickening.During deformation, the temperature increase may have been promoted by shear heating along the decollement [82,83].Finally, the accumulated heating led to the melting of Triassic metaturbidites and the widely distributed rare metal deposit formations [16][17][18][19]27,[47][48][49][50][51] from the outer areas (Jiajika, Xuebaoding, and Dahongliutan ore fields) to the middle area (the Zhawulong ore field) and then to the central area (Ke'eryin ore field), as illustrated in Figure 11 and Table 1.

Implications of Pegmatite Deposits for Orogeny in the Songpan-Ganzê Orogenic Belt
The granite-pegmatite systems in the Songpan-Ganzê orogenic belt resulted from tectonic-thermal movements caused by collisions of the Yangtze, Qingtang-Changdu, and North China blocks.As illustrated in Figure 11, from the outer to the middle to the inner areas of the Songpan-Ganzê orogeny belts, the granite emplacement ages as well as the initial and final crystallization ages of pegmatites become younger synchronously, indicating the tectonic-thermal stress transfer process.Furthermore, the lag from the peak in magmatic activities to the final crystallization of large spodumene pegmatite dikes increased in the same order.The lags observed in the Jiajika, Xuebaoding, and Dahongliutan ore fields in the outer areas of the orogeny belt were approximately 26-28, 21-29, and 27-36 million years, respectively, and the lags observed in the Zhawulong and Ke'eryin ore fields located in the middle and central areas of the orogeny belt were approximately 32-44 and 43-49 million years, respectively.The features discussed above indicate that the magma cooling rates of the Jiajika, Dahongliutan, and Xuebaoding deposits in the outer area of the orogenic belt are highest, while those of the Ke'eryin deposit in the central area are lowest, as shown in Figure 11.
These cooling rates are in good agreement with the stages and scales of granitic magma emplacements in these pegmatite deposits.Single-stage magma emplacement with a relatively small outcrop area occurred in the Jiajika, Dahongliutan, and Xuebaoding deposits, while multi-stage magma emplacement with a large outcrop area occurred in the Ke'eryin ore field.The residual Triassic laccolith at the top of the complex granitic intrusions in these ore fields indicates that these granitic intrusions underwent similar degrees of uplift erosions (Figures 2-5), eliminating the effect of erosion on the emergence of these magma intrusive stages and scales.The large-scale outcropping and multistage of granite with a low cooling rate may be due to the fact that Ke'eryin is located in the center of the Songpan-Ganzê orogenic belt, in which there was a convergence of northward and southward thermal stresses resulting from collisions between the Yangtze and Qiangtang-Chagndu blocks, and the Yangtze and North China blocks, respectively [81].As a result, the convergence of thermal stress in two directions led to greater heat flow and a slower cooling rate, resulting in extensive continuous magmatic activity and a high melting point.Adequate heat and a slow cooling rate will lead to crystallization and differentiation of magma over a long period of time, forming greater rare metal deposits with potential Li 2 O reserves of 7,000,000 tons, including the Lijiagou, Dangba, and Yelonggou deposits in the Ke'eryin ore field [25].
The above-mentioned temporal and spatial regularities indicate that the tectonic-thermal stress transfer process occurred in the northward and southward directions from the outer areas to the inner areas of the Songpan-Ganzê orogenic belt.On the basis of the dating results in this study, we propose a model for the orogenic processes of the Songpan-Ganzê orogenic belt (Figure 12).When bidirectional contracting stress was transferred from the collision boundaries in the Yangtze, Qiangtang-Changdu, and North China blocks, magmatism occurred in the Jiajika, Xuebaoding, and Dahongliutan ore fields approximately 223-217 Ma.The cooling rates in these regions were relatively high, resulting in the rare metal element pegmatite being formed in the relatively short range of 199-187 Ma.When the tectonic stress was transferred into the Zhawulong ore field, massive magma intruded approximately 212 Ma, and the formation of spodumene pegmatite dikes occurred during a relatively late stage lasting until approximately 180-174 Ma.Finally, the northward and southward tectonic stress converged in the Ke'eryin area, leading to magmatic activity approximately 207-205 Ma with a subsequent long pegmatite crystallization period that lasted until approximately 159 Ma.

Conclusions
In the Songpan-Ganzê orogenic belt in China, the Jiajika, Dahongliutan, Xuebaoding, Zhawulong, and Ke'eryin granitic pegmatite deposits, which have different ore-formation ages, are located in the southern, northern, western, and central areas, and the center of the eastern area in the Songpan-Ganzê orogenic belt, respectively.The No. Combining the previous dating results for pegmatite and pegmatite-related granite and regional granitic intrusions with different isotopic dating systems, we were able to derive the cooling paths in the different pegmatite deposits.We discovered that from the outer areas of the orogenic belt to the inner areas, the peak in magmatic activity and the final crystallization ages of the pegmatite deposits tended to lag, implying the migration process of tectonic stress.More heat flow is gathered in the

Conclusions
In the Songpan-Ganzê orogenic belt in China, the Jiajika, Dahongliutan, Xuebaoding, Zhawulong, and Ke'eryin granitic pegmatite deposits, which have different ore-formation ages, are located in the southern, northern, western, and central areas, and the center of the eastern area in the Songpan-Ganzê orogenic belt, respectively.The No. Combining the previous dating results for pegmatite and pegmatite-related granite and regional granitic intrusions with different isotopic dating systems, we were able to derive the cooling paths in the different pegmatite deposits.We discovered that from the outer areas of the orogenic belt to the inner areas, the peak in magmatic activity and the final crystallization ages of the pegmatite deposits tended to lag, implying the migration process of tectonic stress.More heat flow is gathered in the inner area at the convergent center of thermal stress in two directions, which leads to extensive continuous magmatic activity and a slow cooling rate.Adequate heat and a slow cooling rate lead to secondary crystallization and differentiation of magma, further forming greater rare metal deposits.
On the basis of the above regularity, we conclude that during the late Indosinian period, the bidirectional tectonic stresses in the Songpan-Ganzê orogenic belt resulting from the collision between the North China block, Qiangtang-Changdu block, and Yangtze block, were transferred from the outer area to the inner area of the orogenic belt.These processes may have resulted in magmatic activity and the mineralization of pegmatite dikes in the Jiajika, Xuebaoding, Dahongliutan, Zhawulong, and Ke'eryin ore fields during orogeny.

Figure 3 .
Figure 3. Geological map of the Dahongliutan Li-Be-Nb-Ta deposit in Xinjiang, China.1: Quaternary sediment; 2: Upper Triassic biotite schist and sillimanite-andalusite-biotite-quartz schist; 3: Pegmatite dikes with numbers; 4: Two-mica granite; 5: Stratigraphic boundary; 6: Muscovite sampling location with sample number in Table 1.The legend for the diagram in the upper right-hand corner is provided in Figure 1.

Figure 3 .
Figure 3. Geological map of the Dahongliutan Li-Be-Nb-Ta deposit in Xinjiang, China.1: Quaternary sediment; 2: Upper Triassic biotite schist and sillimanite-andalusite-biotite-quartz schist; 3: Pegmatite dikes with numbers; 4: Two-mica granite; 5: Stratigraphic boundary; 6: Muscovite sampling location with sample number in Table 1.The legend for the diagram in the upper right-hand corner is provided in Figure 1.

Figure 4 .
Figure 4. Geological map of the Xuebaoding granitic pegmatite W-Sn deposit, Sichuan Province, China.1: Marginal zone of granite; 2: Middle zone of granite; 3: Core zone of granite; 4: Quartz schist, marble, and biotite quartz schist of the Triassic Zhuwo Formation; 5: Marble-bearing mineralization pegmatite dikes of the Triassic Zhuwo Formation; 6: Calcium quartz schist and sericite-quartz schist of the Triassic Zhuwo Formation; 7: Area of mineralization pegmatite dikes; 8: Inferred fault; 9: Attitude of strata; 10: Muscovite sampling location with sample number in Table 1.The legend for the diagram in the upper right-hand corner is provided in Figure 1.

Figure 4 .
Figure 4. Geological map of the Xuebaoding granitic pegmatite W-Sn deposit, Sichuan Province, China.1: Marginal zone of granite; 2: Middle zone of granite; 3: Core zone of granite; 4: Quartz schist, marble, and biotite quartz schist of the Triassic Zhuwo Formation; 5: Marble-bearing mineralization pegmatite dikes of the Triassic Zhuwo Formation; 6: Calcium quartz schist and sericite-quartz schist of the Triassic Zhuwo Formation; 7: Area of mineralization pegmatite dikes; 8: Inferred fault; 9: Attitude of strata; 10: Muscovite sampling location with sample number in Table 1.The legend for the diagram in the upper right-hand corner is provided in Figure 1.

Figure 8 .
Figure 8.40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the pegmatite dikes of the Dahongliutan, Zhawulong, and Ke'eryin deposits in the Songpan-Ganzê orogenic belt.(a-d)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Dahongliutan pegmatites; (e-h)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Zhawulong pegmatites; (i,j)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Ke'eryin pegmatite.

Figure 8
Figure8.40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the pegmatite dikes of the Dahongliutan, Zhawulong, and Ke'eryin deposits in the Songpan-Ganzê orogenic belt.(a-d)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Dahongliutan pegmatites; (e-h)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Zhawulong pegmatites; (i,j)40 Ar/39 Ar plateau age spectra (left) and inverse isochron age spectra (right) for muscovite samples from the Ke'eryin pegmatite.

Figure 9 .
Figure 9. Cathodoluminescence images of representative zircons and columbite-tantalites from the Zhawulong deposit.White circles indicate the analytical spots that provide the measured ages below each image.

Figure 9 .
Figure 9. Cathodoluminescence images of representative zircons and columbite-tantalites from the Zhawulong deposit.White circles indicate the analytical spots that provide the measured ages below each image.

Figure 9 .
Figure 9. Cathodoluminescence images of representative zircons and columbite-tantalites from the Zhawulong deposit.White circles indicate the analytical spots that provide the measured ages below each image.

Figure 10 .
Figure 10.U-Pb concordia diagrams for samples from the Zhawulong deposit (acquired using LA-ICP-MS).(a) U-Pb concordia diagram for zircons from the Zhawulong granite; (b) U-Pb concordia diagram for columbite-tantalites from the Zhawulong pegmatite.

Figure 11 .
Figure 11.Cooling T-t paths in different areas of the Songpan-Ganzê orogenic belt, plotted from the closure temperatures of different isotope systems and the corresponding dating results.The widths and heights of rectangles represent the ranges in age and closure temperature, respectively.To calculate the average cooling rates, we assume that the closure temperatures of the U-Pb system in zircon and the Ar-Ar isotope system in muscovite are 850 °C and 350 °C, respectively, as described in the discussion.1: Zircon U-Pb age of granite; 2: Zircon/columbite-tantalite U-Pb age of pegmatite; 3: Muscovite Ar-Ar age of pegmatite; 4: Inferred cooling paths; 5-7: Age comparison of rare metal deposits, 5: Granite emplacement age, 6: Initial crystallization age of pegmatite, 7: Final crystallization age of pegmatite; Ms: Muscovite; C-T: Columbite-tantalite; Zr: Zircon.

Figure 11 .
Figure 11.Cooling T-t paths in different areas of the Songpan-Ganzê orogenic belt, plotted from the closure temperatures of different isotope systems and the corresponding dating results.The widths and heights of rectangles represent the ranges in age and closure temperature, respectively.To calculate the average cooling rates, we assume that the closure temperatures of the U-Pb system in zircon and the Ar-Ar isotope system in muscovite are 850 • C and 350 • C, respectively, as described in the discussion.1: Zircon U-Pb age of granite; 2: Zircon/columbite-tantalite U-Pb age of pegmatite; 3: Muscovite Ar-Ar age of pegmatite; 4: Inferred cooling paths; 5-7: Age comparison of rare metal deposits, 5: Granite emplacement age, 6: Initial crystallization age of pegmatite, 7: Final crystallization age of pegmatite; Ms: Muscovite; C-T: Columbite-tantalite; Zr: Zircon.

Minerals 2019, 9 ,
x FOR PEER REVIEW 18 of 26 bidirectional contracting stress was transferred from the collision boundaries in the Yangtze, Qiangtang-Changdu, and North China blocks, magmatism occurred in the Jiajika, Xuebaoding, and Dahongliutan ore fields approximately 223-217 Ma.The cooling rates in these regions were relatively high, resulting in the rare metal element pegmatite being formed in the relatively short range of 199-187 Ma.When the tectonic stress was transferred into the Zhawulong ore field, massive magma intruded approximately 212 Ma, and the formation of spodumene pegmatite dikes occurred during a relatively late stage lasting until approximately 180-174 Ma.Finally, the northward and southward tectonic stress converged in the Ke'eryin area, leading to magmatic activity approximately 207-205 Ma with a subsequent long pegmatite crystallization period that lasted until approximately 159 Ma.

Table 1 .
Dating results for pegmatite deposits and granitic intrusions in the Songpan-Ganzê orogenic belt.Numbered locations of samples are provided in Figures2-6.

Table A2 .
LA-ICP-MS U-Pb data for zircons and columbite-tantalites from the Zhawulong deposit.