The 147Sm/144Nd ratio of granite samples from the Indosinian to early Yanshanian and Yanshanian periods in the Shaluli Mountain granite belt is between 0.0739 and 0.3305, with an average value of 0.1536; 143Nd/144Nd is between 0.5118 and 0.5124. , the average value is 0.5122; εNd (t) is between -9.4609~-3.9721, and the average value is -6.2376. The εNd(t) values ??of the Shaluli Mountain magmatic belt are all negative, which indicates that the magma originated from the crust or enriched mantle source.
The granite depleted mantle model ages (tDM) of the Shaluli Mountain granite belt from the Indosinian to the early Yanshanian and Yanshanian periods vary widely, ranging from 0.94 to 2.45G a, with an average age of 1.64G a. The average age is older than the Yajiang-Jiulong granite belt. The depleted mantle model ages (tDM) of rock bodies of different ages in the two magmatic belts are much larger than their diagenetic ages.
In the εNd(t)-εSr(t) diagram (Figure 7-5), except for 2 samples from the Shaluli Mountain magmatic belt, all fall into the young crustal material area in the upper part of the IV quadrant. This shows that the magmatic material in this area mainly comes from the upper crust.
In general, the relatively small εNd(t) characteristic values ??and very old Nd model ages of different magmatic belts in western Sichuan indicate that their sources may be ancient lower crustal materials, which may be related to the Proterozoic crust. It is related to the material and may be formed by partial melting and crystallization fractionation of the neutral lower crust of the Yangtze continental block. However, there are certain differences in the εNd(t) characteristic value and depleted mantle model age (tDM) between the Yajiang-Jiulong granite to the east of the Garze-Litang suture zone and the Shalulishan granite to the west, which may indicate that the two The magma formation mechanism and the involvement of the lower crust and mantle in the source area have different characteristics. The εSr(t) of the granite in western Sichuan is basically positive. In Figures 7-6 and 7-7, the projection points of the granite in this area obviously deviate from the "main trend line of the mantle", and most of them deviate to the upper right of the main trend line. , fell into the crust source area, French Variscan and Australian I S-type granite distribution areas, indicating that the origin of its magma is mainly continental crust, and the source of some rock masses may be a mixture of continental crust and enriched mantle.
Figure 7-6 Strontium-neodymium isotope composition diagram of granite in the Yajiang-Jiulong granite belt
(According to M.T.M c. Culoch et al., 1982)
(Legend Same as Figure 7-1)
Figure 7-7 Strontium-neodymium isotope composition diagram of granite in the Shaluli Mountains granite belt
(According to M.T.M c. Culloch et al., 1982)
(The legend is the same as Figure 7-2)