1 Introduction

The Qilian Orogenic Belt (QOB), one of the orogenic belt in the west of China, connects with the Inkling Orogenic Belt in the east and the Algin–West Kunlun Orogenic Belt in the west, forming the main part of the northern margin of the Qinghai–Tibet Plateau (Xiao et al. 2005; Yuan et al. 2005; Song et al. 2006; Zhang et al. 2006; Dong et al. 2007). The QOB records a long history of continental break up, seafloor spreading, and final continental collision from the Neoproterozoic to the Paleozoic (Li et al. 2017a, b; Liu et al. 2019; Song et al. 2009, 2014, Song and Niu 2013; Yang et al. 2015; Tung et al. 2016; Wang et al. 2016). Based on tectonics (Song et al. 2006, 2013, 2014), the QOB is divided into three sub-geotectonic units as following: (i) North Qilian Orogenic Belt (NQ–OB), (ii) Central Qilian Block (CQB), and (iii) South Qilian Miogeosyncline Belt (SQ–MB) (Feng 1997; IGMGM 1965). The previous studies of QOB mainly focused on the Northern Qilian Orogenic Belt in the north and the Northern Qaidam Basin in the south. However, the study on the intermediate-acid intrusive rocks in the eastern section of Central Qilian Block (E-CQB) is relatively weak (Gao et al. 2017). Yong et al. (2008) proposed that there were two magmatic periods in the E-CQB and determined the ages of Dongjiazhuang rock mass with 446 ± 1 Ma and Xindian rock mass with 454 ± 5 Ma, respectively. Li et al. (2014) concluded that the Caledonian granite in the E-CQB was probably the result of mixed fusion of residual subducted oceanic crust and continental sediments, and determined the weighted average ages of two samples of Qingchengshan rock mass with 430.0 ± 4.1 and 420.2 ± 2.4 Ma, as well as the emplacement ages at 440.5 ± 2.5 Ma in Tongwei area. Then it was found that the weighted mean value of the surface age of 206Pb/238U of rock mass in Juslang; Mengundao and Xiaogaoling was 444.1 ± 3.2, 445.1 ± 4.6 and 445.0 ± 4.1 Ma, respectively (IGSQP 2015).

This study focused on the detailed geochronology and whole-rock geochemistry of granites from the Huangyuan area in the E–CQB, and discussed the petrogenesis and geological significance of these granites.

2 Geological setting and samples

The study area is located in the Sanlian area of Haiyan county, belonging to CQB of Caledonian fold system, adjacent to the NQ–OB in the north and the SQ–MB with the fault of the southern margin of the Central Qilian and the Qinghai–Gulei fault in the south (IGSQP 2015; figure 1).

Figure 1
figure 1

Simplified geological map of the Huangyuan area and the eastern QB, showing the sample locations. Modified after IGSQP.

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The outcrop in the study area is relatively complete, including Dongchagou formation of Huangyuan Group (Pt1d), Liujiatai formation of Huangyuan Group (Pt1l), and Qingshipo formation of Changchengian (Chq). Lithologic assemblages of Dongchagou are mainly composed of mica quartz schist, quartz mica schist, and phyllite with laminated marble, and Liujiatai is mainly composed of biotite plagioclase gneiss, biotite monzonitic gneiss, and plagioclase hornblende schist, with Caledonian rocks (such as diorite and granodiorite) intruding into it. However, lithologic assemblages of Moshigou are mainly composed of ash black to off-white and fresh red block stratified quartzite, with phyllite at the top of some sections, quartz-conglomerate near the bottom, and mica quartz schist at the bottom. Similar to Moshigou, lithologic assemblages of Qingshipo are mainly composed of ash black to black phyllite, platy phyllite, phyllite slate, silty slate and silty metasandstone, with a small amount of mica schist at the bottom. The overlying strata are Xining formation (Ex) of Paleogene system (IGSQP 2015).

There is Syncline with NW–SE axis direction is developed in Liujiatai formation of Huangyuan Group (Pt1l), and the core lithology is quartz mica schist, the two limbs are biotite plagioclase gneiss. Due to the influence of late magmatic activity, the synclinal landform is not complete.

Under the influence of frequent magmatic activities, intrusive rocks are widely developed and distributed, but the exposed area is not large. The intrusive body is generally elliptic, which can be divided into granodiorite (γδO3) and monzonitic granite (ηγO3). The fault structure is well developed in the region, which is mainly NW or NWW trending longitudinal fault and NE or NEE trending transverse fault (IGSQP 2015).

Monzonite granites, located in the E-CQB and distributed in NW–SE direction, are distributed on both sides of deep and large faults and along the axis of the fold. And fluorite outcrops were found in it. Samples (SL; figure 2a) of monzonite granite are taken from the Sanlian area in Huangyuan, located in the E-CQB (36°49′16″N, 101°00′02″E), The samples are characterized by fractured granitic structure and blocky structure, which are mainly composed of biotite, plagioclase, potassium feldspar, quartz and opaque metallic minerals occasionally. Under the influence of brittle tectonics, the rock is broken and cemented by late siliceous hydrothermal solution, and about 20% of the debris is visible. They are characterized by the strong clayzation of plagioclase and chloritization of biotite. The biotite was produced by brown scaly structure aggregation with a particle size of 0.05–1.51 mm, and mainly distributed in the interstice of large particles of quartz, feldspar or wrapped inside the particles. Most of the particles developed clayzation with a content of about 8%. The plagioclase is idiomorphic to semi-idiomorphic plate columnar with a particle size of 0.11–3.25 mm. It has a strong clayzation, and its fine and dense agglomerated twin crystals can be vaguely seen. Some of the particles are contained in the potassium feldspar particles, or are produced as inlaid particles, with a content of about 26%. The potassium feldspar is semi-idiomorphic to heteromorphic plate columnar, mainly striated feldspar and orthoclase, with the largest particle size up to cm. Most of the particles are relatively complete, often containing a large number of idiomorphic plate columnar plagioclase, the content is about 30%. The quartz accounts for 35% of the sample content, is heteromorphic with particle size between the plagioclase and potassium feldspar, and exhibits slight brittle structural fracture and slight wavy extinction (figure 2b).

Figure 2
figure 2

Hand specimen photographs and optical photomicrographs in cross-polarized light of the monzonitic granites from the Huangyuan area, E-CQB. (a) Hand specimen of monzonitic granite; (b) photomicrographs of monzonitic granite. Pl: plagioclase; Bt: biotite; Q: quartz; (c) field of monzonitic granites; (d) outcrop of monzonitic granites.

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The original rock is biotite monzogranite, which has a slight brittle tectonic fragmentation and forms about 20% detrital granite. Irregular metallic minerals can be seen occassionally, the content is about 1%.

3 Whole-rock geochemistry

Major element contents of the sample were determined by X-ray fluorescence (XRF) at the Beijing Kuangyan Geoanalysis Laboratory Co. Ltd. The analytical uncertainty is typically less than 5%. Trace element and rare earth element (REE) contents were determined using an Agilent 7500a inductively coupled plasma mass spectrometer (ICP-MS) at the Beijing Kuangyan Geoanalysis Laboratory Co. Ltd. (Liu et al. 2010). The detailed analytical procedures and precisions are the same as those described by Liu et al. (2008b). The major and trace element analytical results are listed in tables 1 and 2, respectively.

Table 1 Major element compositions for the Sanlian monzonitic granitic.
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Table 2 Trace element compositions for the Sanlian monzonitic granitic.
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The sample chemistry was changed into a ‘dry’ system (excluding volatile water after converted to 100%), the main elements in the intrusive rock classification in the diagram (Middlemost 1985; figure 3), can be seen from the figure, granite rock sample points, nine points in the granite interval distribution, one point distribution within the range of granodiorite. The content of chemical composition of each intrusive rock is slightly different.

Figure 3
figure 3

Classification diagram of principal elements of monzonitic granites from Huangyuan area.

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It can be seen from table 1 that the monzonitic granites have high contents of SiO2 (70.34–5.92 wt.%), K2O (3.14–5.28 wt.%), Na2O (2.41–3.64 wt.%), and Al2O3 (12.76–14.94 wt.%). The samples showed calc-alkaline and high-K, calc-alkaline affinities on the SiO2 vs. K2O discrimination diagram (Peccerillo et al. 1976; figure 4a), calc-alkaline on AR vs. SiO2 (Wrighe and Doherty 1970; figure 4b) and AFM plots (TFeO vs. Na2O+K2O vs. MgO, figure 4c) (Irvine and Baragar 1971) and strongly peraluminous compositions (0.886 < A/CNK < 1.477, 1.319 < A/NK < 1.699) on the A/CNK vs. A/NK discrimination diagram (Rickwood 1989; figure 4d). In addition, there are relatively low contents of MnO (0.02–0.06 wt.%), MgO (0.26–0.83 wt.%) and P2O5 (0.08~0.14 wt.%) in samples. Therefore, the monzogranite in the Huangyuan area is a peraluminous calc-alkaline rock.

Figure 4
figure 4

Discrimination diagrams of (a) SiO2 vs. K2O, (b) AR vs. SiO2, (c) TFeO vs. (Na2O+K2O) vs. MgO and (d) A/CNK vs. A/NK showing compositions of the monzonitic granites from Huangyuan area. AR: alkalinity ratio, A: Al2O3, N: Na2O, K: K2O, C: CaO.

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Furthermore, the samples had ∑REE = 130.58–220.66 ppm with a slightly higher slope [(La/Yb)N = 14.41–28.68], which means that light rare earth elements (LREE) are enriched relative to heavy rare earth elements (HREE). Weak negative Eu anomalies with Eu/Eu* values of 0.38–0.63 (Rollinson 1983; figure 5a), which is shown that some plagioclase remained in the magma source area (unfinished plagioclase) or separated from the magma due to crystallization, resulting in granitic magma plagioclase loss (Sun and McDonough 1989).

Figure 5
figure 5

(a) Chondrite-normalized REE patterns and (b) primitive mantle-normalized spider diagrams of the monzonitic granites from Huangyuan area.

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In the spider diagrams, the nine samples show that they were clearly enriched in large-ion lithophile elements (LILEs; e.g., K, Th, and Rb), and strongly depleted in high field-strength element (HFSEs; e.g., Ti and P), weakly depleted in Nb, Ba and Sr (Sun and McDonough 1989, figure 5b). It is generally believed that the loss of Ti is caused by the crystallization of Ti-containing minerals, and the loss of P is caused by the crystalline differentiation of apatite, which indicates that they are derived from crust-derived magma or the magma was once crust-derived during the formation process.

4 Zircon U–Pb age analyses

Cathodoluminescence images (SL; figure 6) were acquired prior to U–Pb dating. Subsequently, zircon U–Pb dating was conducted using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the Beijing Kuangyan Geoanalysis Laboratory Co. Ltd. The detailed analytical procedures and precisions are the same as those described by Liu et al. (2008b). The off-line processing of the analysis data (including the selection of samples and blank signals, instrument sensitivity drift correction, element content and U–Th–Pb isotope ratio and age calculation) was completed by using the software ICPMSDataCal (Liu et al. 2008a, 2010).

Figure 6
figure 6

Representative CL images of zircons from samples SLCN.

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Apart from a few dark browns, most Zircons from sample SLCN (Sanlian monzonitic granites) were predominantly colourless. And they had prismatic lengths ranging from 90 to 220 μm, aspect ratios of 2:1 to 3.5:1 (figure 6). Most of the zircons displayed a typical rhythmic oscillating zoning (often narrow zoning) in CL images, which could indicate a low-temperature magmatic origin (Pagel et al. 2000; Wu and Zheng 2004). Some zircons show signs of rounded edges, cones, and pits, suggesting that the zircons were subjected to later hydrothermal alteration or metamorphic processes.

The study focused on the above zircons with oscillating zonings. U–Pb isotope dating was carried out by LA-ICP-MS method and its isotope parameters were listed in table 3. The analysis revealed that the zircon Th/U ratio ranged from 1.07 to 2.18. On the U–Pb Concordia diagrams for zircons (figure 7a), the six analysis points give the older 206Pb/238U age (956–1356 Ma), which may be the inherited zircon age. In addition, there are two younger 206Pb/238U ages and two points deviating from the Concordia lines. Excluding the above analysis points, the 206Pb/238U ages of the remaining nine analysis points are all concentrated, with a weighted average of 466 ± 4.5 Ma (MSWD = 0.27; figure 7b). This age is the magmatic crystallization age of Huangyuan monzonitic granites.

Table 3 LA-ICP-MS U–Pb data from zircons for the Sanlian monzonitic granites.
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Figure 7
figure 7

(a) U–Pb Concordia diagrams for zircons from the Huangyuan monzonitic granites and (b) their weighted average ages.

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5 Discussion

5.1 Timing of granite emplacement

Zircon grains from the gneissic granite sample SL had length/width ratios ranging from 2:1 to 3.5:1 and showed oscillatory zoning in CL images (figure 6). They also showed high Th/U ratios ranging from 1.07 to 2.18, indicating a magmatic origin. In addition, the 206Pb/238U ages of the remaining nine analysis points are similar, with a weighted average of 466 ± 4.5 Ma (figure 7b), which represents the crystallization age of Huangyuan monzonitic granites.

The main emplacement age of the rock samples is the Ordovician. In addition, it can also be found that a small number of samples may contain records of late magmatic activity (396 Ma). At the same time, there are 956–1356 Ma residual cores of inherited zircons in the rock mass, it can be found that there was magma activity during this period (IGSQP 2015). The rock emplacement age is Ordovician, but may also contain records of late magmatic events (396 Ma). At the same time, there are 956–1356 Ma residual cores of inherited zircons in the rock mass, we can also see from other literature that there was magma activity during this period.

5.2 Petrogenesis and source nature

The monzonitic granites in the study area have high contents of SiO2 (70.34–75.92%), and the A/NK ratio (1.32–1.70) is greater than the average value of A-type granite (1.05). The TFeO/MgO value (1.41–2.52) is far less than the typical A-type granite (13.4), and it does not have the characteristics of A-type granite. Moreover, the Zr content (108.08×10−6 – 200.00 × 10−6) and (Zr + Nb + Ce + Y) of Muscovite granite (192.80 × 10−6 – 363.43×10−6) were significantly lower than that A-type granite (Zr > 250×10−6 and (Zr + Nb + Ce + Y)>350×10−6). In the (Zr + Nb + Ce + Y) – (Na2O + K2O)/CaO classification diagram (Whalen et al. 1996; figure 8), Most of the samples fall into FG (fractionated granite) area and belong to the I-type, S-type and M-type granite with high fractionation. It is also clear that mica granite does not belong to A-type granite.

Figure 8
figure 8

(Zr + Nb + Ce + Y) – (Na2O+K2O)/CaO classification diagram of monzonitic granites from the Huangyuan. FG: fractionated granite, OGT: other granite type.

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It is difficult or even impossible to identify I-type granite, S-type granite or A-type granite, since the mineral composition and chemical composition tend to be low co-coalescence granite when the above granites undergo highly fractionated crystallization (Chappell and White 1992; Chappell et al. 2000; Wu et al. 2007). Therefore, the identification of monzonitic granite needs to be discussed synthetically with petrographic and geochemical characteristics. In the Harker diagrams (figure 9), Al2O3, CaO, TFe2O3, MgO, TiO2, and P2O5 contents in these granites decrease with increasing SiO2. This geochemical signature of the monzonitic granites of Huangyan is characteristic of high-K, calc-alkaline, strongly peraluminous, and S-type granites.

Figure 9
figure 9

Harker diagrams illustrating major element variations in the monzonitic granites from the Huangyuan area.

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The petrogenesis of peraluminous granites is usually attributed to be the result of Al-poor magma (Petford and Atherton 1996; Springer and Seck 1997; Sylvester 1998; Clemens 2003). The fractionation of Al-poor magma usually produces rocks containing metals, rich in Na, and low in K2O/Na2O acids in closed systems (Zen 1986; Gaudemer et al. 1988; Springer and Seck 1997; Sylvester 1998; Clemens 2003). However, the samples analyzed in the study are strongly peraluminous, K-rich rocks. Thus, the diagenesis of these granites cannot be explained simply by fractionation in a closed system (Liu et al. 2019). The finding is also supported by discrimination plots of Sm vs. La/Sm and La vs. (La/Yb)N (figure 10).

Figure 10
figure 10

Compositional variation diagrams of (a) Sm vs. La/Sm and (b) La vs. (La/Yb)N for monzonitic granites from the Huangyuan area.

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Previous researchers have proposed three origins of silica-rich, strong peraluminous granites: (1) partial melting of Al-rich metapelite and metagreywacke (Miller 1985; Sylvester 1998; Patiňo Douce 1999); (2) tonalite and granodiorite at pressures ≥8 kbar with clinopyroxene in the restite (Patiňo Douce 1999); (3) partial melting of basaltic rocks and/or amphibolites under H2O-saturated conditions (Ellis and Thompson 1986). The composition of most samples indicates that at low pressure (5 kbar ≤ P ≤ 12 kbar, figure 11a, b), and the high K2O/Na2O ratios and negative Eu anomalies indicate a dominantly granitic melt generated under inconsistent H2O-saturated conditions. Thus, most of the strongly peraluminous granites in our study may have been generated by partial melting of metapelite and metagreywacke, the others have been generated by tonalite and granodiorite.

Figure 11
figure 11

Diagrams of (a) CaO + Al2O3 vs. CaO/Al2O3; (b) Al2O3 + Fe2O3T + MgO + TiO2 vs. Al2O3/(Fe2O3T + MgO + TiO2), for monzonitic granites from the Huangyuan area.

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The ratio of CaO/Na2O (wt.%) can be used as an indicator of an S-type granite source, where melts produced from plagioclase-rich and clay-poor sources will tend to have higher ratios than melts derived from pelitic sources (Sylvester 1998). The gneissic granite samples show relatively lower CaO/Na2O ratios (figure 12), suggesting that clay is the main source, and lower Al2O3/TiO2 indicates that it was formed at high temperatures.

Figure 12
figure 12

Diagrams of Al2O3/TiO2 vs. CaO/Na2O for monzonitic granites from the Huangyuan area.

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In A–B analysis (figure 13), the degree of aluminization decreases with the increase of the degree of differentiation of granite. In addition, it is considered that the mica minerals in granite are mainly biotite. The samples can be divided into cordierite-bearing peraluminous granitoids (CPGs) in the granitoid classification of Barbarin (1990) because of their strongly high aluminum content, and it must be the partial melting of sedimentary rock (Barbarin 1990, 1999). There is no cordierite in the granite, which may be due to the high water activity in the magma source area. In the A/MF–C/FM classification diagram (Altherr et al. 2000; figure 14), almost all samples fall into the partial melts from metapelitic sources.

Figure 13
figure 13

Diagrams of A vs. B for monzonitic granites from the Huangyuan area. A=Al–(K+Na+2Ca), reflecting the characteristics of Al. B=Fe+Mg+Ti decreased from most primitive granite magma to most evolved granitic magma.

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Figure 14
figure 14

A/MF–C/FM classification diagram of monzonitic granites from the Huangyuan.

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5.3 Tectonic setting and implications

Regarding the tectonic setting of the CQB in the Middle-Late Ordovician, many studies found that the granites were arc-type or collision-type granitoids (Wan et al. 2000, 2003; Gehrels et al. 2003; Liu et al. 2006; Chen et al. 2008; Tung et al. 2016). Previous studies suggested that CQB was formed at the active continental margin (Guo et al. 1999; Wan et al. 2000). Also, some basement rocks suggest an intraplate environment (Wan et al. 2000).

According to the geotectonic background of the study area and previous research data, the early Paleozoic evolution of the E-CQB can be roughly divided into four stages (Feng 1997; Xia et al. 1996): (1) Subduction of oceanic crust on both sides of Central Qilian in Late Cambrian to early Middle Ordovician; (2) the ancient ocean basin closed, and land (arc)–land collision occurred in middle–late of Middle Ordovician, the crust thickened during this period; (3) the subducting plate breaks off in Late Ordovician to late Early Silurian; (4) the crust melts under the influence of plate fragmentation in late Early Silurian to early Middle Silurian.

On the Y–Nb diagram of the granite (Pearce et al. 1984; figure 15a), the samples fall on the volcanic arc granite (VAG) area and the syn-collisional (Syn-COLG) area. Then, on the (Nb + Y)–Rb diagram of the granite (Pearce et al. 1984; figure 15b), the sample projection points are all located in the volcanic arc granite (VAG) region. Most of the samples on the R1–R2 diagram of the granite (Batchelor and Bowden 1985; figure 16a) fall on the area of pre-plate collisional granite, and several of the samples fall on mantle-differentiated granite.

Figure 15
figure 15

(a) Y–Nb classification diagram and (b) (Nb + Y)–Rb classification diagram of monzonitic granites from the Huangyuan area. WPG: Within-Plate Granite, ORG: Oceanic Ridge Granite, VAG: Volcanic Arc Granite, Syn-COLG: Syn-Collisional Granite.

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Figure 16
figure 16

(a) R1–R2 classification diagram and (b) Rb/10–Hf–3Ta classification diagram of monzonitic granites from the Huangyuan area. ①: mantle-differentiated granite, ②: pre-plate collisional granite, ③: post-plate collisional granite, ④: late orogenic granite, ⑤: anorogenic granite, ⑥: syn-collisional granite, ⑦: post-orogenic granite, WPG: Within-Plate Granite, ORG: Oceanic Ridge Granite, VAG: Volcanic Arc Granite.

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In Rb/10-Hf-3Ta diagram of the granite (figure 16b), the samples are all located in the junction of WPG and collision of granite on the geotectonic background. In summary, the Middle Ordovician Huangyuan monzonitic granites (466 ± 4.5 Ma) are volcanic arc granite formed before the plate collision, and orogeny is about to happen.

The study area is adjacent to NQ–OB. According to the previous research, NQ–OB is a subduction zone, where subduction direction has some theories, such as northward subduction (Xu et al. 1994; Xia et al. 1995; Zhang and Xu 1997; Hou et al. 2005; Song et al. 2009), southward subduction (Wang and Liu 1976; Zuo and Wu 1997) and double subduction (Zuo and Wu 1987; Zuo and Liu 1997; Wu et al. 2006, 2011; Wang et al. 2008; Hou et al. 2015). Its subduction age is generally believed to have occurred at 469–445 Ma (Xia et al. 1996; Su et al. 2004).

According to the previous research, muscovite occurs in Dongjiazhuang rock mass (less than 5%), and R1–R2 discriminant maps of tectonic environment are concentrated in the collision zone (Yong et al. 2008). Therefore, the Middle Qilian was probably a Japanese-type island arc terrane in the early Paleozoic.

The late Ordovician Beigou rocks outcropped from the Lajishan belt in the south of the study area are similar to the standard Adakite and belong to the island arc (subduction) rock structural association (IAG). The discovery of Adakite further indicates that oceanic crust subduction occurred at that time. Adakites are closer to the trench than normal island-arc magmatic rocks (Defant and Drummond 1990). Therefore, the direction from Adakite to normal island-arc magmatic rocks represents the subduction direction of the oceanic crust.

The late Ordovician rocks, early diorites and granodiorites, continental arc (subduction) rock structural assemblages (CAG) occur in the Qilian belt. The occurrence of rocks in this period is the result of the closure of Lajishan small ocean basin and the subduction of ocean and continent, and the subduction of Lajishan small ocean basin can be further determined from the spatial position of the out-crowd intrusive rocks. The collisional granites exposed in late Ordovician and early Silurian belong to continental collisional rock tectonic assemblage (CCG). In the early late Ordovician, the lateral compression caused by subduction led to the shrinking of the residual basin, and in the late Ordovician, the basin closed and the collision of the middle and south Qilian continental blocks led to the formation of a new collisional orogenic belt. Therefore, the magmatic activity in the Qilian Mountains led to orogeny.

In the southeast direction of the study area, Dongjiazhuang rock (446 ± 1 Ma), Xindian rock (454 ± 5 Ma), Mengundao rock (445.1 ± 4.6 Ma) and Xiaogaoling rock (445.0 ± 4.1 Ma) (figure 1) belong to the contemporaneous rock mass. In other words, all are the Syn-COLG, Juslang rock (444.1 ± 3.2 Ma) belongs to anorogenic granite. But the samples from the study area were 466 ± 4.5 Ma which are pre-plate collisional granite. The comparison shows that the subduction age started at about 466 Ma, and ended at 444 Ma, which is early than previous research results.

6 Conclusions

By comparing the research results of this paper with those of previous studies, the following conclusions can be concluded:

  1. (1)

    Monzonitic granites sampled in the Huangyuan area, E-CQB, formed at 466 ± 4.5 Ma. The geochemical and geochronological analyses of the samples show high-K, calc-alkaline, strongly peraluminous and S-type characteristics.

  2. (2)

    The geochemical features of the samples indicate that the samples can be classified as cordierite-bearing peraluminous granitoids, and the provenance is mainly partial melting of metapelite and metagreywacke.

  3. (3)

    The Middle Ordovician Huangyuan monzonitic granites are volcanic arc granite formed before the plate collision. The subduction age of E-CQB started at about 466 Ma and ended at 444 Ma.