Baimangshan (AJGS6), Shujiadian (SYSZK03), Jiguanshan (JGZ 1), Datuanshan (ADTS 1), Hucun (drilling core, HCZK683) and Hu Chengjian (drilling core, HCJZK/KLOC-) were collected respectively. YSZ3), Nanhongchong (07CL505), Tongguanshan (07CL507), Goose Egg Holdings (07CL5 12), Xinqiaotou (07CL5 16), Beach Foot (07CL5 19), Mi Zircon sorting was completed by Hebei Geological Survey Institute. Zircon and standard samples were glued to a glass plate, cast with epoxy resin, made into thin slices, polished, and photographed with reflected light and cathode ray luminescence. Finally, the isotopic contents of U, Th and Pb in zircon were determined by ion probe SHRIMP-RG and their ages were determined. Sample preparation, reflected light and cathodoluminescence photography and SHRIMP calibration were completed by the author in the ion probe laboratory of Stanford University. The selected standard sample is R33 [(419.01.1) Ma] (Black et al., 2004), and the error range of the data is 1 σ. The data processing adopts the calculation program compiled by Kenneth R.Ludwig of Berkeley Geochronology Center. 2003)。

5. 1.2 zircon SHRIMP dating results

Baimangshan and Shujiadian pyroxene diorites in the intrusive rocks of Ganlan 'an coarse rock series, Hucheng Jianhui gabbro, Jiguanshan, Datuanshan, Tongguan Mountain, Swan Yingyingshi gabbro, Miaojia Shiyinghui porphyrite, Hucun, Nanhongchong, Fenghuangshan, Tanjiao granodiorite, Yaoshan and Xinqiao granodiorite in the high-potassium calc-alkaline series.

Table 5.2 Zircon SHRIMP U-Pb Dating Results of Intermediate-acid Intrusive Rocks in Tongling Area

Note: MSWD-square of average weight deviation; N refers to the number of measuring points participating in the calculation.

Note: mswd-mean square weighted deviation; N— Calculate the number of measuring points.

Zircon characteristics and SHRIMP U-Pb dating results of each dating sample are described as follows:

(1) sample AJGS6 (Baimangshan pyroxene diorite)

Zircon is light yellow, short columnar and granular, with a particle size of 0.04~0.20 mm Most zircon cylinders (1 10) are more developed than (100), and cones (10/) are more developed than (2/kloc). The crystal forms of Pupin (1980) are mainly J4, J5, S24, S25, d and P5, and the basicity index (I.A) and temperature index (I.T) are 458 and 643, respectively (Wu Cailai et al., 1994). Zircon has obvious oscillation band (Figure 5. 1), and some zircon contains fine mineral inclusions. Obviously, this is a typical magmatic crystalline zircon (Pidgeon et al., 1998). The determination results of zircon 12 show that the contents of U and Th in zircon 10 are relatively high. Except for zircon 10-6 and zircon 53 × 10-6, the contents of U and Th in other zircons are relatively high, with a wide range [U: (600 ~)

Fig. 5. Zircon cathodoluminescence image of1peridotite intrusive rock.

(2) Sample SYSZK03 (Shujiadian pyroxene diorite)

This sample is taken from the borehole core (ZK03) of Shujiadian pyroxene diorite in Ganlannan coarse rock series. The rock mass is produced by irregular dikes in the northeast, and the exposed area in the middle of the rock mass is about 2500 m2 garnet skarn. The rock mass is rich in pyroxene and amphibole phenocrysts, the size of which is 1 ~3 cm. The surrounding rock is Silurian siltstone, with veinlet-disseminated copper mineralization. The rock is grayish black with authigenic-semi-authigenic granular structure. The main minerals are plagioclase (An = 45 ~ 55, 70% ~ 75%) and diopside (13% ~ 15%), followed by biotite (7% ~ 8%) and potash feldspar (3% ~). Zircon in this sample is columnar, and its length-width ratio is 1: 1 ~ 2: 1. CL images of most zircons are uniform gray, Some zircons have oscillatory zonal structure (such as No.6 zircon) or banded structure (such as No.7 zircon and No.65438 zircon +0 1 zircon) (Figure 5.65438+). The U and Th contents of zircons are (189 ~1086) ×1. The U-Pb age of kloc-0/ zircon changes from 145.8 1.2 Ma to 138. 1.5438+0.0 Ma, and the average age is 142 if zircon with high u is removed.

Fig. 5.2 Zircon 238U/206Pb-207Pb/206Pb Harmonic Curve and Average Age of Granite Series Intrusive Rock in Ganlan.

(3) sample HCJZK 1 (huchengjian gabbro)

This sample is taken from the drilled core of Huchengjian gabbro (ZK 1) and has high potassium, calcium and alkaline series. The rock is grayish black with porphyritic structure, and the porphyritic crystals are pyroxene and plagioclase with similar particle size. The matrix consists of elongated plagioclase, fine-grained interstitial pyroxene and magnetite. The aspect ratios of zircon in this sample are 1: 1 and 2: 1, and the cathodoluminescence image (CL image) is uniform gray (Figure 5.3). The range of zircon u content is (524 ~ 1545) × 10-6, and The range of zircon th is (66 1 ~ 2752) × 10-6. There is a good correlation between u and Th (the correlation coefficient is 0.8 1 Th/U ratio is generally > 1, and the range is 1.3 ~ 2.66 (attached table 1). The age range of all zircons is narrow, ranging from/kloc-0 146.4±0.6Ma to/kloc-0 139.5±0.7Ma, with an average age of142.7 0.6ma (mswd =1.8, n=8) (Figure 5.4).

(4) sample JGZ 1 (jiguanshan syenite diorite)

Zircon is short column type, with the general aspect ratio of 1.5: 1 and the individual ratio of 2: 1. The statistical results of zircon crystal form show that the development degree of conical surface (2 1 1) and (1kloc-0/) are similar, but the cylindrical surface (1 10) is more than (100). 12 zircon SHRIMP U-Pb determination results show that the contents of u and th in zircon are (136 ~ 676) × 10-6 and (10/kloc-0 ~ 777 )×/kloc-0, respectively. Th/U ratios range from 0.77 to 1.4 1, and most of them are >:1; The age range of 206Pb/238U is small, ranging from/kloc-0 143.0±0.9Ma to131.31.6ma.. Among them, zircon. 1, No.8 and No. 1 1 is relatively young. Combined with the characteristics of the cathodoluminescence image, it can be seen that these zircons may have been reformed by the later fluid, resulting in the loss of Pb, and the position of the measuring point has entered the part of Pb loss. Therefore, the average age of other zircons is139.91.1ma (mswd = 0.9, n =8), which is in harmony with the age of 238u/206pb-207pb/206pb (138).

(5) sample ADTS 1 (Datuanshan Yanshi diorite)

Zircon is columnar, and the length-width ratio is 2: 1 ~ 3: 1. Conical surface (10 1) is slightly more developed than (2 1 1), while cylindrical surface (100) is (65438). CL image shows that zircon has obvious banded structure with fine banded stripes (Figure 5.3). The results show that the contents of zircon U and Th in this sample are (119 ~ 462 )×10-6 and (48 ~ 435)× 10- respectively, and the ratio of Th/U is 0.36 ~/kloc-0.

Fig. 5.3 Zircon cathodoluminescence image of high potassium calcium alkaline intrusive rocks.

Fig. 5.4 Zircon 238U/206Pb-207Pb/206Pb Harmonic Curve and Average Age of Tongling High Potassium Calcium Alkaline Intrusive Rock.

(6) sample 07CL507 (Tongguanshan syenite diorite)

Zircon is columnar, and its length-width ratio is between 2: 1 ~ 4: 1. The CL images of most zircons show an oscillating zonal structure (Figure 5.3), which is a typical magmatic crystalline zircon (Pidgeon et al., 1998). Some zircons contain ancient inheritance nuclei, such as No.5 and No.7 zircon. The U and Th contents of zircons are (57 ~ 737) × 10-6 and (40 ~ 569) × 10-6, respectively, and the Th/U ratio is 0.35 ~ 1.32. 0.5。 The correlation coefficient between Th and u is 0.83. The U-Pb age range of zircon samples from 14 12 is 246115ma ~133.01.2ma. Except for the old inherited zircon survey point, the average age of other survey points is 14655. The ratio of zircon 238 U/206 Pb to zircon 207 Pb/206 Pb shows that the age of the intersection point on the harmonic line is 2467 120 Ma, and the age of the lower intersection point is143.13.9ma (Figure 5.4). The upper intersection age can be interpreted as inherited zircon age, and the lower intersection age can be interpreted as magmatic crystallization age, which is basically consistent with the average age (141.71.4ma) within the error range (Figure 5.4).

(7) Sample 07CL5 12 (timely diorite and swan egg)

Zircon has a good cylindrical surface and conical surface, the aspect ratio is 2: 1 ~ 3: 1, and there are obvious oscillation bands. Some zircons have ancient inheritance nuclei, such as zircon No.3, No.8 and 1 1 (Figure 5.5). The determination results of 12 zircon at 14 show That the u and th contents of zircon are (75 ~ 284) × 10-6 and (29 ~ 603) × 10-6, respectively, and the Th/U ratio of zircon is 0.4/u. The age of 206Pb/238U obtained at 14 is between 2606 7ma ~134.3 2.7ma, except zircon No.3, No.4, No.8,1and1. Zircon No.3, No.81,1.1are ancient inherited zircon cores, with ages of 837.6±6.3Ma, 2606±7Ma and 936.6 6 6.2 Ma, respectively. They are. The No.4 measuring point spans between the old core and the mantle, with an age of 778.7±4.7Ma. The ratio of zircon 238 U/206 Pb to zircon 207 Pb/206 Pb shows that the age of the intersection point on the harmonic line is 26 12 75 Ma, and the age of the lower intersection point is139.5 2.8 Ma (Figure 5.4). The age of the upper intersection can be interpreted as the age of inherited zircon, and the age of the lower intersection can be interpreted as the age of magmatic crystallization, which is basically consistent with the average age (141.31.3 ma) within the error range (Figure 5.4).

(8) Sample 07CL52 1 (Miaojiashiying diorite porphyrite)

Zircon is a short column with the aspect ratio of1:1~1.5:1,which has a good oscillation band (Figure 5.5). The dating results of 10 zircon show that the U and Th contents of zircon are (88 ~ 457) × 10-6 and (50 ~ 588) × 10-6, respectively, and the Th/U ratio of zircon is 0.56 ~1. The age of 206Pb/238U ranges from 164. 1. 1 Ma to 133.7 1.8 Ma, and the average age after excluding inconsistent measuring points is 142.8 6558. The ratio of zircon 238U/206Pb-207Pb/206Pb shows that the age of the harmonic line is146.0 3.0ma (mswd = 0.99) (Figure 5.4), which is within the error range with the average age (142.8 1.6 Ma).

(9) sample HCZK683 (hucun granodiorite)

Zircon is self-columnar, and its length-width ratio is 2: 1 ~ 3: 1. The crystal morphology is similar to that of Datuanshan rock mass, but the average temperature index (I.T) and average alkalinity index (I.A) are slightly higher than that of Datuanshan rock mass, which are 4 18 and 440 respectively, reflecting that the temperature and alkalinity of magma are slightly higher than that of Datuanshan rock mass. CL image shows that zircon has obvious zonal structure (Figure 5.5), and some zircons contain acicular mineral inclusions, such as zircon No.6.. The results show that the contents of U and Th in zircon are (161~ 614) ×16 and (86 ~ 813 )×16, respectively, and Th. 0.60 (attached table 1). Pb/U ages ranged from 142.8 1.3 Ma to 133.6 1.5 Ma, with an average age of140.91.2ma (mswd = 0.6, n

Fig. 5.5 Zircon cathodoluminescence image of high potassium calcium alkaline intrusive rocks.

(10) sample 07CL505 (Nanhongchong granodiorite)

The aspect ratio of zircon in this sample varies greatly, which is 1: 1 and 4: 1 respectively, and the cathodoluminescence image shows obvious ring structure (Figure 5.5). Zircon u content ranges from (79 ~ 52 1) × 10-6, and Th ranges from (50 ~ 397) × 10-6. There is a good correlation between u and Th (correlation coefficient is 0.97). Th/U ratio is generally greater than 0.5, ranging from 0.57 to 0.99 (table 1). Zircon ages range from 722.7 4.8 Ma to123.3 2.1Ma, in which zircon No.2 and No.6 are 577.9±5.8Ma and 722.7 4.8 Ma respectively. Zircon No.2 may be the captured old zircon, and its core seems to have been melted incompletely. The core of Zircon No.6 is different from the mantle. The content of radioactive 206Pb (20× 10-6) is much higher than that of other zircons [( 1.5 ~ 9.9 )× 10-6], which may reflect that zircon was reformed by later fluids and Pb was added or brought out (Cherniak et al., 2000). Excluding these two zircons, the average age of the remaining zircons is138.81.3ma (mswd =1.1,n = 12) (Figure 5.6). The ratio of zircon 238U/206Pb-207Pb/206Pb shows that the age of the intersection point on the harmonious line is 84 1 74ma, and the age of the lower intersection point is13713ma (MSWD =1.5) (Figure 5.6). The age of the upper intersection can be interpreted as the inherited zircon age of granodiorite, and the age of the lower intersection can be interpreted as the crystallization age of magma, but the error is large, which is basically consistent with the average age (138.8 1.3 Ma) (Figure 5.6).

(1 1) sample FHS2 (Fenghuangshan granodiorite)

Zircon is columnar, with the length-width ratio of 2: 1 ~ 3: 1, and it has a good oscillation zone, and some of it contains mineral inclusions (Figure 5.7). The u and Th contents of these zircons are (225 ~ 573) × 10-6 and (79 ~ 48 1) × 10-6, respectively, and the rest are >: 0.5 (the range is 0.59 ~ 1./kl The 206Pb/238U age of 1/zircon changed from 690.8 4.1ma to140.01.2ma,1,3 and1. Zirconia. 1 and 3 have ancient inheritance nuclei, and the measuring points span the core and mantle, resulting in mixed ages of 531.4 2.8 ma and 690.8 4.1ma, respectively. Unlike zirconium. 1 and No.3, and zirconium number 1 1. It shows that Pb was added or brought out of zircon through later fluid transformation (Cheriak et al., 2000), and the core age is 234.81.9ma.. The zircon 238U/206Pb-207Pb/206Pb ratio shows that the age of the intersection point on the harmony line is 837±53ma, and the age of the lower intersection point is/kloc-0 148.5±9.5Ma (Figure 5.6). The upper intersection age can be interpreted as the inherited zircon age of granodiorite, and the lower intersection age can be interpreted as the crystallization age of magma, which is basically consistent with the average age (142.0 0.8 Ma) within the error range (Figure 5.6).

(12) sample 07CL5 19 (beach foot granodiorite)

Zircon is columnar, with the length-width ratio of 2: 1 ~ 3: 1, and has a good oscillation band. Some zircons have ancient inheritance nuclei, such as zircon No.5, No.8, No.9 and 10 (Figure 5.7). The dating results of 14 zircon show that the U and Th contents of zircon are (85 ~ 408) × 10-6 and (42 ~ 203) × 10-6, respectively. The 232Th/238U ratio of zircon varies from 0.22 to 0.72 (except for zircon No.5, No.8, No.9 and 10 in Table 62, the average age of zircon is144.1.1.2ma (MSWD = 0 The zircon ratio of 238U/206Pb-207Pb/206Pb shows that the age of the intersection point on the harmonic line is1995 29 Ma, the age of the lower intersection point is144.3 2.3 Ma (MSWD = 0.9, n = 0.9), and the age of the upper intersection point can be interpreted as the inherited zircon of granodiorite.

Fig. 5.6 Zircon 238U/206Pb-207Pb/206Pb Harmonic Curve and Average Age of Tongling High Potassium Calcium Alkaline Intrusive Rock.

Fig. 5.7 Zircon cathodoluminescence image of high potassium calcium alkaline intrusive rocks.

(13) sample YSZ3 (Yaoshan granodiorite porphyry)

Zircon is a self-shaped long column with the length-width ratio of 2: 1 ~ 4: 1. CL images show that zircon has a very good oscillation zone and contains mineral inclusions (Figure 5.7), such as zircon 1, 5, 7. Zircon U and Th contents are low, which are (242 ~ 386) × 10-6 and (18 ~ 93) × 10-6, respectively, and the Th/U ratio is low, which is 0.06 ~ 0.53 (attached table 1 6 Zircon No.5 and No.7 contain ancient inheritance nuclei, and their ages are 233012ma and 210413ma respectively. The 206Pb/238U age of the rest zircon ranges from 155.6 1.3ma to143.6/.1.0ma, with an average age of146.0 0.9ma (. The ratio of n = 238 u/206 Pb-207 Pb/206 Pb shows that the age of the upper intersection reflects the inherited zircon age of granodiorite porphyry, and the age of the lower intersection represents the magmatic crystallization age, which is consistent with the average age (146.0 0.9 Ma) within the error range.

(14) Sample 07CL5 16 (Xinjiaotou granodiorite porphyry)

Zircon is a self-shaped long column with the length-width ratio of 2: 1 ~ 5: 1. CL images show that zircon has a very good oscillation band (Figure 5.7). Zircon U content is (137 ~ 497) × 10-6, and Th content is very low, which is (5 ~ 85) × 10-6, and Th/U ratio is low, except for zircon 12, which is 0.64. Zircon 12 is an old inheritance nucleus (age 2484 10 Ma), and the age of other zircons has not changed much (age of 206Pb/238U has changed from 152.3 1.0 Ma to 144.0 65438). The ratio of 238U/206Pb-207Pb/206Pb shows that the age of the intersection point on the harmony line is 2483±65ma, and the age of the lower intersection point is147.9 2.3ma (MSWD = 2.5) (Figure 5.6). The upper intersection age reflects the zircon age inherited by granodiorite porphyry, and the lower intersection age represents the magma crystallization age, which is consistent with the average age (147.2 1.5 Ma) within the error range.