1. Petrochemical characteristics of granite in Nanling series (series I) (Table 2-6)
There are 36 petrochemical analysis samples in this series, which come from Zhuguangshan, Dadongshan, Guidong, Xiaokeng, Fogang, Shintautou, Dajianshan, Dawangshan, near Wubeiling (Sapporo Gangxian), Xinpeng and Shenpeng. The content of Al2O3 is also relatively high, most of AKCN is greater than 1.1, with an average of 1.15; Corundum (c) appears in standard minerals; The content of TiO _ 2 is low, and the average w (TiO _ 2) × 1/w (SiO _ 2) is only .27; Low MgO content, w(MgO)/w(FeO) only .18; The average value of alk and ar is 3.48, w (K2O) > w (Na2O), and w (K2O)/w (Na2O) is 1.3. The biggest feature is that the differentiation index is high, most of the DI swings between 85 and 9, with an average of 89, and the FO is low, and most of them are less than .2, etc. These indicate that the series I granite is rich in SiO2 _ 2, Al _ 2O _ 3, ALK and W (K2O) >: W(Na2O), well-differentiated granite with low fo2.
Table 2-4 Content of Secondary Minerals in Deep-melting Granite Formation in Wuchuan Sihui Fault Zone (WB/1-6)
"+"indicates that there are individual granular secondary minerals in heavy sand; "++"contains a small amount of accessory minerals (less than 1× 1-6); Source: ① Guangdong Bureau of Geology and Mineral Resources (1988). ② Geological Brigade 719 of Guangdong Bureau of Geology and Mineral Resources, internal data of regional survey, 1989. ③ Regional survey report of 1 ∶ 5, Yangchun amplitude of 74 Geological Brigade of Guangdong Bureau of Geology and Mineral Resources. (4) Guangdong Provincial Bureau of Geology and Mineral Resources regional survey brigade, 1 ∶ 2, Yangchun amplitude regional survey report. ⑤ Report of 1 ∶ 2, high-profile regional survey conducted by Guangdong Bureau of Geology and Mineral Resources.
Table 2-5 Content of accessory minerals in migmatite formation of Wuchuan-Sihui fault zone (WB/1-6)
"+"indicates that the heavy sand contains individual granular accessory minerals; "++"contains a small amount of accessory minerals (less than 1× 1-6); The data source is the same as Table 2-4.
Table 2-6 Petrochemical Composition of Nanling Series (Series Ⅰ) of Magmatic Granite Formation in Wuchuan-Sihui Fault Zone
Continued Table
Continued Table
Note: ①-w (TiO _ 2) × 1/w (SiO _ 2), AKCN-n (Al _ 2O _ 3)/n (.
ii. petrochemical characteristics of the Yangtze series (series Ⅱ) granite (Table 2-7)
There are 32 petrochemical analysis samples in the series, which come from Shanglong, Fuxi (Zhuguangshan), Dabaoshan, Xiaokeng (Guidong), Fogang, Lianhe, Sihui, Huangtian, Wucun, Lunshui, Gangmei and Shicun. The content of TiO _ 2 is high, and the average value of W (TiO _ 2) × 1/W (SiO _ 2) is .85, which is several times higher than that of Series I; The content of MgO is high, and the average w(MgO)/w(FeO) is .42. W (K2O) > w (Na2O), w (K2O)/w (Na2O) is 1.46 on average; The degree of DIfferentiation is slightly poor, and the average di is 7; The oxidation index is slightly higher, and the average fo2 is .35. Therefore, the series Ⅱ granite is a kind of granite which is relatively poor in SiO2 _ 2, rich in TiO2 _ 2, MgO and high in oxidation coefficient.
Comparison and distinguishing marks of main chemical compositions of the three and two series of granites
Figure 2-1 shows that both series of granites have the trend of CA (calc-alkali) change, and the composition points of series I granites are mostly concentrated near the A end (i.e. alkali-rich), while series II granites are scattered in the CA area, which has a good CA evolution trend; According to the σ index in Table 2-6 and Table 2-7, both are less than 3.3, it is judged that the two series of granites belong to calc-alkaline granites.
figure 2-2 shows that there are obvious differences in chemical composition between the two series of granites. Most of the composition points of series I granites are in S-type granite area (Chappell et al., 1974), while most of series II granites are in I-type granite area. The former has the characteristics of metamorphic sedimentary source rocks (equivalent to recycled crustal materials) and the latter has the characteristics of igneous source rocks (equivalent to primary crustal materials).
figure 2-3 shows that the contents of stAndard minerals Ab, Or, an in the two series of granites are obviously different, and the point formation of series I granites is mostly concentrated in the low-temperature trough area, indicating that magmatic * * * knot granites are in the majority, while series II granites, on the other hand, are only put into this area individually, and most of them are outside the trough and in the high-temperature and high-pressure magmatic granite area closer to the An end.
as can be seen from fig. 2-4, the series Ⅱ granite is in the areas with high TiO2 _ 2 and low SiO2 _ 2, while the series Ⅰ granite is the opposite, so the two series granites are in two areas respectively, with only a few overlapping.
as can also be seen in figure 2-5, the series Ⅱ granite is in the area with high TiO2 _ 2 and low AKCN, while the series Ⅰ granite is the opposite. Although the two areas are partially overlapped, it can be generally seen that there are two areas.
in fig. 2-6, the two series of granites are clearly divided into two areas, that is, the series ⅱ component points are invested in the high w(MgO)/w(FeO) area, and the series workers are invested in the low w(MgO)/w(FeO) area, with little overlap between the two areas.
the above analysis indicates that there are obvious differences in chemical composition between the two series of granites. Series I granites are rich in Si, Al, poor in Ti, Mg, Ca and have relatively low oxidation coefficient, which is reflected in the high values of many parameters such as SiO _ 2, AKCN, DI, C, Q, Ab and Or, while W (TiO _ 2) × 1/W (SiO _ 2) and W (MgO). Series Ⅱ granite is the opposite (Table 2-7). Figure 2-5 and Figure 2-6 show that the granite source area of series I may be dominated by recycled crustal materials, rich in Si and Al, poor in Ti, Mg and Ca and relatively reducing environment. However, the source area of series ⅱ granite may be dominated by primary crustal material or upper mantle material, so series ⅱ granite is relatively poor in Si and Al, rich in Mg, Ti and Ca and relatively oxidized environment.
Table 2-7 Petrochemical Composition of Yangtze River Series (Series Ⅱ) Constructed by Magmatic Granite in Wuchuan-Sihui Fault Zone
Continued Table
Continued Table
Notes are the same as those in Table 2-6.
Figure 2-1 Granite Series, Construction AFM Diagram (CA Ca-Alkali Change Trend)
Figure 2-2 Granite Series, Construction ACF Diagram (I-type and S-type Granite Area)
In addition, the two series of granites in Wuchuan-Sihui Fault Zone are mainly calcium-alkaline granites and W (K2O) > W (Na2O), etc., which may also imply that.
it should be pointed out that many of the above chemical parameters and diagrams can also be used as indicators to distinguish two series of granites.
Figure 2-3 Diagram of Granite Series and Ab-Or-An Construction
Figure 2-4 Diagram of Two Series Granite W (TiO _ 2) × 1/W (SiO _ 2)-W (SiO _ 2)
●-Series Ⅱ Granite and O-Series I Granite
Figure 2-5 Diagram of Two Series Granite W. ○— Series I Granite
IV. Chemical composition characteristics of plutonic granite and migmatite formation
1. Plutonic granite formation
There are few chemical analysis samples in this formation (Table 2-8). From the five chemical analysis samples from Guangning, Yunlong Mountain, Bajia (Tanshui) and Yangchun West (Miaolong), it can be seen that the chemical composition of plutonic granite formation is uniform. Al2O3: 13.5% ~ 15.88%, DI: 73.34 ~ 83.68. There are many standard minerals corundum (C), all of which are aluminum supersaturated rocks with little change in composition, belonging to rock formations with high homogenization.
2. There are 1 samples (Table 2-9) for chemical analysis of migmatite formation, which come from rock fields or rock bodies such as Shijian-Wuhe, Tiedong, Bajia (Tanshui) and Yunlong Mountain, and their chemical compositions vary greatly, such as SiO2 58.81% ~ 72.54% and Al2O3 13.47% ~ 17. Corundum (C) also appears in the standard mineral, which is also an aluminum supersaturated rock. Compared with anatexic granite, the chemical composition changes greatly, reflecting the low homogenization degree of the building.
3. Comparison between anatexic granite construction and migmatite construction
From the above, it can be seen that both of them have many features in common, both of which are aluminum supersaturated rocks and calc-alkaline rocks, so corundum (C) appears in standard minerals, and σ values (average values are 1.71 and 1.56 respectively) are all less than 3.3, which are all put into CA area in AFM diagram (Figure 2-1). * * * Similarity is also manifested in many average indices, such as w(MgO)/w(FeO), AKCN, fo2, w(K2O)/w(Na2O), and AR, which are all similar.
The above characteristics reflect that there are similarities in genesis between the plutonic granite formation and the migmatite formation, which may both come from the source areas dominated by recycled crustal materials (metamorphic rocks) and both are plutonic formations. Deep-melting granite has a high degree of deep melting, so its homogenization degree is also high. At the same time, it is relatively rich in SiO _ 2 (7.11%, the same below), σ _ (1.71) and DI value (average 78.74) are also high, while the contents of TiO2 _ 2 and MgO are low. The migmatite formation has a low degree of deep melting and homogenization, and its chemical composition changes greatly. At the same time, the values of SiO _ 2 (68.73%), σ(1.56) and DI(75.26) are low, while the contents of TiO2 _ 2 and MgO are high, reflecting the characteristics of more residues (high temperature resistance).
The genetic characteristics of the above two formations are also reflected in Figure 2-2 and Figure 2-3. In the ACF diagram, most components of migmatite are cast in the S-type granite area, and the anatexic granite is cast in the transition area between I and S, indicating that the material sources are close, and most of them are mainly sedimentary metamorphic rocks, but there are differences. The migmatite formation tends to the sedimentary metamorphic rock area, while the anatexic granite formation tends to the transition area. In Ab-Or-An diagram, some of the composition points of migmatite are in low-temperature trough, that is, they have low * * * melting components, and the other part is in high-temperature and high-pressure area, that is, they are quite residual material components (residues), while the deep-melting granite formation is different, and most of them are put into high-temperature and high-pressure magmatic area, indicating that their deep melting degree is high, not completely low * * * melt, but also "crystal porridge" formed by residual crystals.
V. Differences between the construction of migmatite, anatexic granite and magmatic granite
The chemical composition of the three constructions is obviously different, which is shown in Figure 2-1 ~ Figure 2-3, with different changing trends or concentration areas, but the composition points of migmatite and anatexic granite are closer, indicating that both of them have the possibility of anatexic products, while magmatic formation granite is different, and the construction can be further divided into two series (.
Figure 2-6 Two Series of Granites Fo2-W (MgO)/W (FeO) Figure
● A Series of II Granites, A Series of I Granites
VI. Summary
(1) The chemical composition of magmatic granite, anatexic granite and migmatite in this area reflects the characteristics of their different genesis, and magmatic granite is constructed as heavy lava slurry (melt). However, migmatite formation and anatexic granite formation are anatexic products, and the chemical composition of anatexic granite is closer to that of migmatite formation, reflecting the characteristics that their formation methods are dominated by anatexis and recycled crustal material sources.
table 2-8 petrochemical composition (WB/%) of deep-seated granite in wuchuan-sihui fault zone
the notes are the same as those in table 2-6.
table 2-9 petrochemical composition (WB/%) of migmatite formation in wuchuan-sihui fault zone
the table notes are the same as table 2-6.
(2) Magmatic granites are obviously divided into two series of granites: Series Ⅰ granites are magmatic products rich in SiO2 _ 2, Al _ 2O _ 3, ALK, W (K2O) > W (Na2O), well differentiated, low in fo2 and mainly composed of shallow recycled crustal materials; Series Ⅱ granites are relatively poor in SiO2 _ 2, high in TiO2 _ 2, MgO and Fo _ 2, and magmatic products mainly derived from deep primary crust or upper mantle materials.
(3) In Wuchuan-Sihui fault zone, there are * * * similarities among the three formations, such as the characteristics of calc-alkaline (CA), most W (K2O) > W (Na2O) and aluminum-rich with standard mineral corundum (C), which indicates that they may be the same reflection of the crustal and geochemical background, that is, they are controlled or influenced by the geochemical background of the upper crust in this area.