| Bawangling area is located in Hainan Changjiang County Johnsy recent field research process here we found shoshonitic intrusive rocks. Since shoshonitic intrusive rocks has a unique geochemical properties, it has a special significance(especially ancient tectonic reconstructions) study in crust-mantle interaction and regional tectonic evolution. Therefore, this study selected areas of Hainan Island Bawangling area Shoshonitic intrusive rocks as the main object, its petrological, geochemical characteristics were studied to investigate the causes and tectonic environment.Hainan Bawangling area Shoshonitic intrusive rocks located in Changjiang- Qionghai deep south of the fault, white sand dam south Gezhen fault rupture between Wang Ling, Jakarta Tai Ling area, exposed area of about 30km2, white sand along the fracture was NNE distribution. By monzonite- diorite- monzonite diorite- quartz diorite- quartz monzonite rocks shoshonitic intrusive rocks.Precision SHRIMP, LA-ICP-MS zircon U-Pb dating results show that the Bawangling area shoshonitic age intrusive rocks three samples were 252 ± 4 Ma(biotite(quartz) diorite), 247.5 ± 3.5 Ma(biotite-hornblende monzonite), 249 ± 2 Ma(biotite-hornblende diorite Eiji), closer to the age of three, about 250 Ma, show shoshonitic magma emplacement age for two stack- Triassic boundary, are Hercynian- Indosinian magmatism.Shoshonitic intrusive rocks Si O2 content medium- low(48.49% ~ 54.96%), alkali-rich(K2O + Na2 O = 6.43%~ 7.94%), potassium(K2O / Na2 O = 0.58 ~ 1.13), higher Al2O3 content and a wide range of variation(13.71% ~ 19.54%), showing shoshonitic rock characteristics.In Harker diagram, it can be seen on the most significant correlation with Si O2 oxide correlation diagram. Mg O, Ca O, TFe O, Ti O2, Mn O, P2O5 and Si O2 and Al2O3 have showed a good negative correlation, K2 O and Si O2 is a positive correlation between the display mixing crust and mantle magma or two(and) with the evolution of magma, hornblende, biotite, plagioclase, Ti-Fe oxide and apatite occur fractional crystallization. Samples REE ΣREE = 114.95 ~ 434.71 × 10-6, and the larger the higher the total range. LREE = 99.13 ~ 407.36 × 10-6,HREE = 13.35 ~ 30.08 × 10-6, w(LREE) / w(HREE) 6.27 ~ 21.32, showing a significant enrichment of light rare earth, rare earth obvious weight loss characteristics. δEu = 0.71 ~ 0.91, negative Eu anomaly is not obvious,suggesting that the initial magmatic differentiation is not obvious, the lower base of the degree of separation of plagioclase crystals. LILE elements(LILE) Ba, K, Sr, U is relatively enriched in high field strength elements(HFSE) Zr, Hf relative loss. Ta, Nb and Ti was a significant "TNT" negative anomaly, P obvious negative anomaly, suggesting there may be some degree of ilmenite, apatite and other fractional crystallization. ISr is 0.70729 ~ 0.70811; εNd(t) of-4.8 ~-5.5; T2 DM is 1416 ~ 1469 Ma, magma originated in similar EMⅡ mantle.Shoshonitic after intrusive rocks orogenic extensional tectonic environment, presumably in the Late Permian to Indochina and South China blocks to NE plate subduction process, due to the compression NE, NE-trending suture zone resulting in a fracture extensional extensional environment. When extensional lithosphere thickness thinned to 100 ~ 80 km, enriched lithospheric mantle peridotite garnet bottom gold mica occur low degree of vacuum dehydration melting, magma contamination occurred in the process of invasion and accompanied fractional crystallization(AFC), hornblende, biotite, plagioclase, Ti-Fe oxide and apatite and other minerals fractional crystallization and magma being subducted sediments containing component crust contamination, thereby formed shoshonitic Hainan Island Bawangling area intrusive rocks. |
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