# Genesis and Magmatic Evolution of the Gejiu Complex in Southeastern Yunnan, China
## 4 Results
### Geochemistry
#### 4.2.2 Trace Element Geochemistry  
The trace element geochemistry of the samples is presented in Table 2. The trace element geochemical characteristics of granites, gabbros, syenites, diorites, and monzonites collectively showed depletion in specific high-field-strength elements (HFSEs: P, Ti) and K from the large-ion lithophile element (LILE) group, while exhibiting selective enrichment in U (LILE) and Th (HFSE). In contrast, compared to other rocks, granites exhibited negative anomalies in Ba (LILE) and Nb (HFSE) but positive anomalies in Ta (HFSE) (Figure 5a). Gabbros and diorites/monzonites showed enrichments (LILEs, e.g., Ba), indicating geochemical signatures typical of arc-related igneous rocks (Figure 5b,c). The significant depletions in Ba, Nb, P, and Ti (Figure 5a) indicate magmatic differentiation during granite formation [14].  
The Geju granites are characterized by high concentrations of Rb (average = 385.79 ppm), Y (average = 30.89 ppm), and Nb (average = 29.51 ppm), indicating a highly differentiated magmatic environment. As an incompatible element, Rb preferentially concentrates in late-stage melts during prolonged magmatic evolution. The high Rb content suggests extensive fractional crystallization and significant late-stage fluid activity, facilitating Rb enrichment in the residual melt. The elevated Y abundances may be attributed to either a Y-rich source mineralogy (e.g., amphib) or the incorporation of Y-enriched materials during magma generation and evolution. Additionally, interactions with garnet and zircon, which selectively sequester HREEs, could further enhance Y retention in the melt. The pronounced Nb enrichment likely reflects a high degree of partial melting in the magma source. As a high-field-strength element (HFSE), Nb exhibits relatively high partition coefficients during partial melting, favoring its concentration in the melt phase. This geochemical signature aligns with magmatic systems derived from metasomatized mantle or crustal sources undergoing advanced differentiation. Collectively, the Rb-Y-Nb systematics underscore the roles of prolonged fractional crystallization, fluid-melt interactions, and source characteristics in shaping the geochemical evolution of the Geju granites.  
The ratios of mobile versus immobile elements indicate magma source characteristics [3]. The Geju complex exhibits significant variations in trace element ratios among its lithologies. Granites displayed elevated Rb/Sr ratios (0.26-19.90, average 4.68) significantly higher than or comparable to the primitive mantle value (0.88) [32], indicating that these rocks experienced significant magmatic differentiation. In contrast, gabbros, diorites, monzonites, and syenites exhibited lower Rb/Sr ratios (0.04-0.57, 0.11-0.84, and 0.34-2.05, with averages of 0.23, 0.29, and 0.91, respectively). Granites displayed the lowest Nb/Taratios (3.31-24.15, average 11.07), comparable to highly evolved mineralized granites [33]. The Nb/Ta ratios of gabbros, diorites, monzonites, and syenites were comparable (19.13-27.18, 20.38-21.35, 19.51-33.49, and 9.85-25.79, with averages of 22.81, 20.87, 28.67, and 18.24, respectively), being significantly higher than the mantle Nb/Ta ratio (17.5 \(\pm\) 2) [34; 35]. Granites exhibited Zr/Hf ratios ranging from 10.89 to 47.52, with an average of 33.80, which are lower than the primitive mantle and chondritic values (34-36) [36]. In contrast, gabbros and diorites/monzonites exhibited Zr/Hf ratios higher than the primitive mantle and chondritic values (40.19-50.39 and 35.27-78.21, with averages of 45.26 and 46.36, respectively). Syenites displayed Zr/Hf ratios ranging from 47.74 to 85.66, with an average of 66.16, which are significantly higher than the primitive mantle and chondritic values. Therefore, the gabbros, diorites, monzonites, and syenites in the Geju complex likely originated from a similar magma source, while the source of granites is distinct from that of these rocks.