Geochemical Characteristics of Cenozoic Basaltic High2K Volcanic ...

Vol . 23 No. 1 　　　　　　　CHIN ES E J OURNAL O F GEOCHEMIS TR Y 　　　　　　　2004

Geochemical Characteristics of Cenozoic Basaltic High2 K Volcanic Rocks from Maguan Area , Eastern Tibet 3 WEI Qirong ( 魏启荣) 1 ,2) and WAN G Jianghai ( 王江海) 2) 1) ( College of M aterials Science & Chemical Engi neeri ng , Chi na U niversity of Geosciences , W uhan 430074 , Chi na) 2) ( Guangz hou I nstit ute of Geochemist ry , Chi nese A cademy of Sciences , Guangz hou 510640 , Chi na)

Abstract : The major element , trace element and Nd2Sr isotopic composition of Cenozoic basaltic volcanic rocks from t he Maguan area , eastern Tibet , indicates t hat t he volcanic rocks are enriched in alkalis , especially K ( K2 O up to 3. 81 %) and depleted in Ti ( TiO2 = 1. 27 % 2. 00 %) . These rocks may be classified as two groups , based on t heir Mg # numbers : one may represent primary magma ( Mg # numbers from 68 to 69) , and t he ot her , t he evolved magma ( Mg # numbers from 49 to 57 ) . Their REE contents are very high ( ∑REE = 155. 06 239. 04μg/ g) . Their REE distribution patterns are of t he right2inclined type , characterized by L REE enrichment [ (La/ Yb) N = 12. 0 - 19. 2 ] , no Ce anomaly ( Ce/ Ce 3 = 1. 0 ) , and weak negative Eu anomaly ( Eu/ Eu 3 = 0. 9) . The rocks are highly enriched in Rb , Sr and Ba ( 59. 5 - 93. 8 μg/ g , 732 - 999 μg/ g , and 450 - 632μg/ g , respectively) , high in U and Th ( 1. 59 - 2. 31 μg/ g and 4. 73 - 8. 16μg/ g , respectively) , and high in Nb , Ta , Zr and Hf ( 70 - 118 μg/ g , 3. 72 - 5. 93 μg/ g , 215 - 381 μg/ g , and 5. 47 - 9. 03 μg/ g , respectively ) . In t he primitive mantle2normalized incompatible element spidergram , Nb , Ta , Zr , Hf and P show positive anomalies , whereas Ba , Ti and Y show negative anomalies. The 87 Sr/ 86 Sr ratios range from 0. 704029 to 0. 704761 ; 143 Nd/ 144 Nd from 0. 512769 to 0. 512949 ; andεNd from + 2. 6 to + 6. 1. These geochemical features might suggest t hat t he potential source of t he basaltic high2 K volcanic rocks in t he Maguan area is similar to t he O IB2source mantle of Hawaii and Kergeulen volcanic rocks. Key words : Cenozoic ; basaltic high2 K volcanic rocks; geochemistry; Nd2Sr isotope ; eastern Tibet ; Maguan area

1 Introduction The collision between t he India and Eurasia plates and int racontinental deformation since 55 Ma not only const rained t he formation and evolution of t he Tibet plateau ( Pan Guitang et al. , 1990 ; Yin An , 2000 ) , but also cont rolled t he Cenozoic tectonism and magma activities in eastern Tibet ( Yin An , 2000 ; Wang Jianghai et al. , 2001) . Cenozoic tectonism in eastern Tibet may have involved t hree stages : ( 1) continental subduction during 40 and 28 Ma ( Meyer et al. , 1998 ; Wang Jianghai et al. , 2001) ; ( 2) large2scale t ransten2 sion st retching f rom 24 to 16 Ma ( Harrison et al. , 1996) ; and ( 3) east2west extension f rom 16 Ma to t he present ( Masek et al. , 1994 ; Yin An , 2000 ; Wang Jianghai et al. , 2001) . Corresponding to ISSN 100029426 3 The study was supported jointly by t he State Key Projects for Basic Research (No . G1998040807) , t he National Natural Science Foundation of China ( No . 49972026) , t he Knowledge2innovation project of t he Chinese Academy of Sciences ( No . KZCX22SW2 117) , and t he China Postdoctoral Science Foundation.

© 1995-2004 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.

CHIN ES E J OURNAL O F GEOCHEMIS TR Y 　　　　　　　Vol . 23

58

t he tectonism , two pulses of Cenozoic high2 K magmatism developed in eastern Tibet ( Wang Jiang2 hai et al. , 2001) : ( 1) t he early2stage magmatic activities (f rom 40 to 28 Ma) along t he whole Jin2 shajiang River2Honghe River tectonic belt ; and ( 2 ) t he late2stage ( f rom 16 to 0 Ma ) along t he sout hern segment of t he Honghe River fault belt . The basaltic high2 K volcanic rocks in t he Maguan area are t he product of t he late2stage magmatism ( Wang Jianghai et al. , 2001) , and abundant pyro2 lite xenolit hs were found in t he Maguan basanite meat us ( Mei Houjun , 1966 ; Shu Xiaoxin , 1995 ; Sun Hongjuan , 2000) . Relative to pyrolite xenolit hs and Cenozoic basaltic volcanic rocks in eastern China ( Chi Jis2 hang , 1988 ; Qi Qu et al. , 1995 ; Xu Yigang et al. , 1997 , 1998 ; Zheng Jianping et al. , 1999 ) , t he equivalent rocks in western China have been poorly documented , which severely rest rict s our un2 derstanding of t he st ruct ure and nat ure of t he lit hosp heric mantle in western China , and also limit s t he develop ment in t he st udy of t he continental dynamics mechanism of formation and evolution of t he Tibet plateau. The Cenozoic basaltic volcanic rocks t hat consist of basanite and py2 rolite xenolit hs in t he basanite pipes in t he Maguan area , eastern Tibet , provide us wit h ideal samples for st udying t he signat ures and nat ure of upper mantle in t his area. In t his pa2 per , t he geochemical characteristics of t he basaltic high2 K volcanic rocks in t he Maguan area will be described in detail so as to explore t he potential mantle source in western China.

2 Geological setting The Cenozoic basaltic high2 K volcanic rocks bearing pyrolite xeno2 lit hs are exposed in t he Bazhai2 Muchangjie area , Maguan County , Yunnan Province ( Fig. 1) . They are composed mainly of basanite and sub2 ordinately of alkali basalt , t rachy2 Fig. 1. The geological sketch map of t he Bazhai2Muchangjie area , basalt and t rachyte. Their host rocks Maguan , eastern Tibet ( after t he No. 1 Geology Party of t he Yunnan are Cambrian to Ordovician meta2 Geology and Mineral Resources Bureau , 1976) . morp hic rocks. The basanite , ex2 posed as rock pipe groups , is dist ributed along t he fault belt , and it s 40 Ar/ 39 Ar isotopic ages range f rom 12. 4 - 11. 9 Ma ( Wang Jianghai et al. , 2001 , 2002 ) , i. e. , belonging to Late Tertiary. Xenolit hs in t he basanite pipes are round and elliptoid in shape , and are measured at 1 - 30 cm in di2 ameter. The types of xenolit hs include spinel2lherzolite , spinel2harzburgite , spinel2clinopyroxene peridotite , spinel2olivine websterite , pyroxenite , and megacryst s of p hlogopite , clinopyroxene , gar2 net , sanidine and so on.


No. 1 　　　　　　　　CHIN ES E J OURNAL O F GEOCHEMIS TR Y 　　　　　　　　

59

3 Analytical technology and results Samples were prepared by two steps. Firstly , t hey were washed wit h water and air2dried to remove surficial contaminant s , and t hen crushed to 200 mesh. The major element s and t race ele2 ment s were determined at t he Instit ute of Geochemist ry , Chinese Academy of Sciences. The major element s of t he whole rock were determined by wet chemical analytical met hod , while t he t race ele2 ment s were analyzed by ICP2MS techniques ( Liu Ying et al. , 1996 ) . Analytical result s of major and t race element s for nine Cenozoic basaltic high2 K volcanic rocks in t he Maguan area are listed in Tables 1 and 2. In addition , t his paper also present s t he Sr2Nd isotopic data of seven basaltic high2 K volcanic rocks f rom t he Maguan area ( Sun Hongjuan , 2000 ; Wang Jianghai et al. , 2001) for f ur2 t her discussion of t heir sources. Table 1. Major element compositions of the Cenozoic basaltic high2 K volcanic rocks from the Maguan area , eastern Tibet ( %) Sample No.

M G012121

M G012122

M G0122

M G01227

M G01212

M G0122121

M G0122122

M G0122421

M G0122422

Location Shiyamoshan Haoziba Laofangzi SiO2 50. 36 50. 57 49. 49 48. 81 45. 92 49. 89 45. 54 45. 41 46. 69 TiO2 1. 77 1. 75 2. 00 1. 90 2. 00 1. 27 1. 79 1. 80 1. 65 Al2O3 16. 18 15. 75 17. 06 15. 69 12. 25 16. 40 12. 90 13. 56 12. 68 Fe2 O3 3. 33 3. 75 3. 94 2. 92 2. 03 3. 34 3. 57 2. 43 2. 52 FeO 5. 90 5. 80 5. 10 7. 65 7. 50 6. 70 7. 10 7. 05 7. 20 MnO 0. 19 0. 16 0. 19 0. 15 0. 20 0. 19 0. 18 0. 20 0. 21 MgO 3. 90 3. 90 3. 90 4. 20 9. 60 3. 90 8. 60 8. 70 8. 70 CaO 4. 50 5. 40 4. 30 5. 60 9. 00 4. 90 5. 50 5. 90 6. 00 Na2O 4. 98 4. 77 4. 80 4. 00 1. 99 4. 50 1. 94 1. 96 2. 05 K2O 3. 81 3. 29 3. 50 2. 20 1. 85 3. 69 2. 41 2. 49 2. 43 P2 O5 0. 86 0. 45 1. 10 1. 06 0. 83 0. 86 0. 73 0. 80 8. 53 LO I 3. 98 3. 71 3. 95 5. 23 5. 70 3. 92 9. 33 9. 13 0. 73 CO2 0. 50 Total 99. 76 99. 30 99. 33 99. 41 99. 37 99. 56 99. 59 99. 43 99. 40 54 54 57 49 69 51 68 69 68 Mg # Note : Mg # = 100 ×Mg/ (Mg + Fe2 + ) ; basaltic trachyandensites include samples M G012121 , M G012122 , M G0122 , M G01227 , and M G012 2121 ; basalts include samples M G01212 , M G0122122 , M G0122421 , and M G0122422.

4 Discussion 4. 1 Major elements The types of Cenozoic volcanic rocks in t he Maguan area are shown in Figs. 2 and 3. These rocks are classified mainly as basanite ( U 1 ) , t rachybasalt ( S1 ) , basaltic t rachyandensite ( S2 ) , and basalt (B) ( Fig. 2) . However , t hey all fall wit hin t he high2 K volcanic rock area ( Fig. 3) . The content s of SiO2 in t hese Cenozoic basaltic high2 K volcanic rocks range f rom 45. 41 % to 50. 57 % ( Table 1 ) ; TiO2 content s f rom 1. 27 % to 2. 00 % , close to t hose of t he low2 Ti volcanic rocks defined by Gibson et al. ( 1996) ; Al2 O3 f rom 12. 25 % to 17. 06 % ; and FeO 3 f rom 8. 65 % to 10. 31 %. MgO is lower in most of t he rocks , ranging f rom 3. 90 % to 9. 60 % ; and CaO , Na2 O and K2 O content s vary f rom 4. 30 % to 9. 00 % , 1. 94 % to 4. 98 % and 1. 85 % to 3. 81 % , respectively. In summary , t hese rocks are characterized by low Mg and Ti , and high Fe and Alk ( Na2 O + K2 O) , especially K. Cenozoic basalt s in East China are high in Na and Ti ( Na2 O and TiO2 range f rom 2 % to 5 % , and 0. 5 % to 3. 8 % , respectively) , and low in K2 O ( Chi Jishang , 1988) . © 1995-2004 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.


60

Table 2. Trace element compositions of the Cenozoic basaltic high2 K volcanic rocks from the Maguan area , eastern Tibet (μg/ g) Sample No. La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y ∑REE L REE HREE (La/ Yb) N (La/ Sm) N ( Gd/ Yb) N Ce/ Ce 3 Eu/ Eu 3 Rb Sr Ba Th U Nb Ta Zr Hf Sc Ti V Cr Mn Co Ni Cu Pb Zn

M G012121 46. 88 90. 85 10. 55 45. 46 10. 03 3. 04 9. 24 1. 30 6. 82 1. 14 2. 59 0. 30 1. 80 0. 20 30. 10 230. 22 206. 81 23. 40 18. 6 3. 0 4. 2 1. 0 0. 9 93. 8 924 496 8. 13 2. 16 105 5. 85 342 8. 85 10. 87 7787 90. 0 89. 4 1115 27. 7 60. 6 45. 1 6. 61 173

M G012122 47. 31 92. 16 10. 56 47. 69 11. 00 2. 95 9. 24 1. 36 7. 04 1. 15 2. 70 0. 32 1. 79 0. 22 32. 47 235. 47 211. 66 23. 81 18. 9 2. 8 4. 3 1. 0 0. 9 59. 5 961 545 8. 09 2. 31 114 5. 88 368 8. 80 11. 06 10689 104. 9 73. 3 1263 31. 6 59. 5 46. 1 5. 63 195

M G0122 47. 29 94. 02 10. 97 48. 54 11. 13 3. 03 9. 25 1. 35 7. 21 1. 19 2. 75 0. 34 1. 77 0. 22 32. 10 239. 04 214. 98 24. 06 19. 2 2. 7 4. 3 1. 0 0. 9 84. 2 961 559 8. 03 2. 19 115 5. 84 370 8. 70 10. 84 11224 102. 7 89. 9 1301 31. 8 64. 3 51. 3 5. 10 198

M G01227 45. 78 91. 23 10. 77 48. 50 10. 87 3. 07 9. 04 1. 33 7. 06 1. 18 2. 84 0. 32 1. 79 0. 20 33. 29 233. 98 210. 22 23. 76 18. 3 2. 7 4. 2 1. 0 0. 9 75. 2 999 632 7. 51 2. 26 114 571 365 8. 27 11. 34 11893 115. 9 71. 1 1286 34. 8 70. 0 51. 1 4. 91 208

M G01212 36. 05 71. 46 8. 50 38. 11 8. 81 2. 34 7. 16 1. 04 5. 48 0. 95 2. 42 0. 27 1. 74 0. 22 26. 40 184. 55 165. 27 19. 28 14. 8 2. 6 3. 4 1. 0 0. 9 72. 6 789 450 6. 52 1. 59 80. 2 3. 95 242 5. 58 15. 48 12656 182. 7 335. 8 1294 54. 6 293. 0 57. 4 6. 52 144

M G0122121 46. 69 92. 19 10. 80 47. 76 10. 92 2. 98 9. 19 1. 36 7. 00 1. 16 298 0. 34 1. 91 0. 22 32. 72 235. 49 211. 34 24. 16 17. 5 2. 8 4. 0 1. 0 0. 9 89. 8 999 536 8. 16 2. 30 118 5. 93 381 9. 03 10. 61 11567 110. 2 67. 9 1363 32. 2 54. 5 53. 3 5. 51 197

M G0122122 31. 30 63. 64 7. 67 35. 90 8. 37 2. 35 7. 32 1. 11 5. 59 1. 01 2. 53 0. 35 1. 87 0. 21 27. 52 169. 22 149. 23 19. 99 12. 0 2. 4 3. 2 1. 0 0. 9 73. 4 747 465 4. 92 1. 69 71. 6 3. 94 221 5. 73 15. 65 11987 163. 8 265. 7 1255 49. 9 247. 9 68. 3 10. 32 166

M G0122421 28. 97 58. 54 6. 98 32. 36 7. 69 2. 15 6. 70 1. 00 5. 25 0. 96 2. 28 0. 30 1. 66 0. 22 25. 60 155. 06 136. 70 18. 36 12. 5 2. 4 3. 3 1. 0 0. 9 74. 6 753 464 4. 73 1. 70 70. 4 3. 72 215 5. 48 14. 71 11147 155. 8 249. 1 1146 46. 6 239. 5 60. 3 9. 79 146

M G0122422 29. 55 59. 59 7. 06 32. 85 7. 99 2. 25 6. 93 1. 07 5. 64 0. 99 2. 44 0. 31 1. 76 0. 22 26. 30 158. 62 139. 28 19. 34 12. 1 2. 4 3. 3 1. 0 09 70. 5 732 461 4. 86 1. 78 71. 0 3. 72 218 5. 47 15. 99 10731 158. 2 282. 2 1162 47. 5 239. 2 59. 1 9. 84 152

Based on t heir Mg # numbers , t hese rocks may be classified as two groups , one may represent t he primary magma ( Chi Jishang , 1988 ; Frey et al. , 1978) , t heir Mg # numbers range f rom 68 to 69 ; and t he ot her represent s t he evolved magma ( Chi Jishang , 1988 ; Frey et al. , 1978 ) , t heir Mg # numbers f rom 49 to 57. 4. 2 Rare2earth elements Rear2eart h element ( REE) abundances of t he basaltic high2 K volcanic rocks in t he Maguan area © 1995-2004 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.


61

Fig. 2. TAS diagram of t he Cenozoic basaltic high2 K Fig. 3. SiO22 K2 O diagram of t he Cenozoic basaltic volcanic rocks from t he Maguan area ( after Le Bas et high2 K volcanic rocks from t he Maguan area ( t he al. , 1986 ) . Pc. Picrite basalt ; B. basalt ; S1 . tra2 dashed lines after Le Maitre et al. , 1989 ; t he shaded chybasalt ; S2 . basaltic trachyandensite ; S3 . trachyan2 bands in t he parent heses after Rickwood , 1989) . desite ; U1 . basanite ( tenp hrite) ; U2 . p honolite ten2 p hrite ; U3 . tenp hrite p honolite ( rock series divided are high , and t he ∑REE ranges f rom 155. 06 to after Irvine and Baragar , 1971) ; A. alkali series ; S. 239. 04 μg/ g ( Table 2 ) . These rocks have sub2alkali series. obviously experienced L REE and HREE f ractiona2

tion , and t he values of ( La/ Yb) N , ( La/ Sm ) N and ( Gd/ Yb) N ( Table 2) range f rom 12. 0 to 19. 2 , 2. 4 to 3. 0 , and 3. 2 to 4. 3 , respectively. The REE patterns are oblique to t he HREE side wit h L REE enrichment ( Fig. 4) , and t hese rocks show no Ce anomaly ( Ce/ Ce 3 = 1. 0) , but have slight negative Eu anomaly ( Eu/ Eu 3 = 0. 9) . The REE patterns of t he basaltic high2 K volcanic rocks in t he Maguan area are very similar to t hose of t he al2 kali basalt of O IB ( Wilson , 1989) . 4. 3 Trace elements The abundances of t he large ion lit hop hi2 le element s ( L IL E) Rb , Sr , and Ba f rom t he basaltic high2 K volcanic rocks in t he Maguan area are high ( Table 2 ) , and t heir content s range f rom 59. 5 to 93. 8 μg/ g , 732 to 999μg/ g , and 450 to 632 μg/ g , respectively. The content s of radioactive heat2generating ele2 ment s such as U and Th are also very high , ranging f rom 1. 59 to 2. 31 μg/ g and 4. 73 to 8. 16 μg/ g , respectively. The high field st rengt h element s ( HFSE) Nb , Ta , Zr , and Hf are also very high , varying f rom 70 to 118 μg/ g , 3. 72 to 5. 93 μg/ g , 215 to 381 μg/ g , Fig. 4. The chondrite \ | normalized REE patterns of t he and 5. 47 to 9. 03 μg/ g , respectively. In t he Cenozoic basaltic high2 K volcanic rocks from t he Maguan primitive mantle2normalized spidergrams of area ( after Sun and McDonough , 1989) . © 1995-2004 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.


62

t race element s , t here are observed positive Nb , Ta , Zr , Hf , P anomalies , and negative Ba , Ti , Y anomalies ( Fig. 5) . The spidergrams are , as a whole , consistent wit h t hose of t he alkali basalt s ( Wilson , 1989) .

Fig. 5. Primitive mantle2normalized incompatible element spidergrams of t he Cenozoic basaltic high2 K volcanic rocks from t he Maguan area ( after Sun and McDonough , 1989) .

As for t he t ransition element s in t he basaltic high2 K volcanic rocks f rom t he Maguan area , t he content s of Cr and Ni are low , but have a wide range f rom 67. 9 to 335. 8 μg/ g and 54. 5 to 293. 0 μg/ g , respectively. The primitive mantle2normalized t ransition element dist ribution curves show ob2 vious positive Ti anomalies and remarkable negative Cr , Ni anomalies ( Fig. 6) . The t ransition ele2 ment dist ribution curves are of t he type2W ( Fig. 6 ) , indicating again t hat t he Cenozoic basaltic high2 K volcanic rocks in t he Maguan area are t he product s of crystallization of magma rat her t han t hose of direct crystallization of primary magma. 4. 4 Sr2 Nd isotopes The measured Sr/ Nd isotope ratio of basal tic high2 K volcanic rocks in t he Maguan area may be approximately regarded as t he initial value because t he rocks are very young in age ( 12. 4 - 11. 9 Ma ) ( Wang Jianghai et al. , 2001 , 2002 ) . The Sr2Nd isotope data ( Sun Hongjuan , 2000 ; Wang Jianghai et al. , 2002) showed t hat 87 Sr/ 86 Sr ratios vary f rom 0. 704029 to 0. 704761 , 143 Nd/ 144 Nd f rom 0. 512769 to 0. 512949 , and εNd values f rom + 2. 6 to + 6. 1. In t he Sr2Nd isotope correlo2 gram , t he data point s representing Sr2Nd iso2 Fig. 6. Primitive mantle \ | normalized transition element topic composition fall mainly in t he isotopic distribution curves of Cenozoic basaltic high2 K volcanic rocks in t he Maguan area ( after Jagoutz et al. , 1979) . composition range of t he Hawaii volcanic rocks © 1995-2004 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.


63

( Zindler and Hart , 1986 ) , while also a part of t he point s fall in t he Kergeulen volcanic rock area ( Zindler and Hart , 1986) . It is suggested t hat t he potential source of t he basaltic high2 K volcanic rocks in t he Maguan area is similar to t he O IB2type mantle for t he Hawaii and Kergeulen volcanic rocks.

5 Conclusions According to t he above discussion , some conclusions can be drawn as follows : ( 1) Cenozoic basaltic high2 K volcanic rocks in t he Maguan area , eastern Tibet , are character2 ized by enrichment in alkalis , especially K ( K2 O f rom 1. 85 % to 3. 81 %) , which is higher t han t hat of t he Cenozoic alkali basalt s in eastern China , which are high in Na ( Na2 O f rom 2 % to 5 %) . ( 2) These rocks may be classified as two groups based on t heir Mg # numbers : one may repre2 sent t he primary magma ( Mg # = 68 - 69) , and t he ot her , t he evolved magma ( Mg # = 49 - 57) . ( 3) The potential source of basaltic high2 K volcanic rocks in t he Maguan area is similar to t he O IB type mantle of t he Hawaii and Kergeulen volcanic rocks. References Chi Jishang , 1988 , The study of Cenozoic basalts and upper mantle beneat h eastern China (attachment kimberlites) [ M ] : Wuhan , China University of Geosciences Press , 277p . (in Chinese) Frey , F. A. and M. Prinz , 1978 , Ultramafic inclusions from San Clarlos Arizona : Petrologic and geochemical data bearing on t heir petrologenesis [J ] : Eart h and Planetary Science Letters , v. 38 , p . 129 - 176. Gibson , S. A. , R. N. Thompson , A. P. Dickin , and O. H. Leonardos , 1996 , High2Ti and low2Ti mafic potassic magmas : Key to plume2lit hosphere interactions and continental flood2basalt genesis [J ] : Eart h and Planetary Science Letters , v. 141 , p . 325 341. Harrison , T. M. , P. H. Leloup , F. J . Ryerson , P. Tapponnier , R. Lacassin , and W. J . Chen , 1996 , Diachronous initiation of transtension along t he Ailaoshan2Red River shear zone , Yunnan and Vietnam , in Yin An and T. M. Harrison , eds. , The tectonic evolution of Asia [ C] : New York , Cambridge University Press , p . 208 - 226. Irvine , T. N. and W. R. A. Baragar , 1971 , A guide to t he chemical classification of t he common volcanic rocks [J ] : Canadian Journal of Eart h Sciences , v. 8 , p . 523 - 548. Jagoutz , E. , H. Palme , H. Baddenhausen , K. Blum , M. Cendales , G. Dreibus , B. Spottel , V. Lorenz , and H. Wanke , 1979 , The abundances of major , minor and trace elements in t he eart h ’s mantle as derived from primitive ultramafic nodules [ J ] : Geochimica et Cosmochimica Acta , v. 11 , p . 2031 - 2050. Le Bas , M. J . , R. W. Le Maitre , A. Streckheisen , and B. Zanettin , 1986 , A chemical classification of volcanic rocks based on t he total alkali2silica diagram [J \ 〗: Journal of Petrology , v. 27 , p . 745 - 750. Liu Ying , Liu Haichen , and Li Xianhua , 1996 , Simultaneous and precise determination of 40 trace elements in rock samples using ICP2MS [J ] : Geochimica , v. 25 p . 552 - 558 (in Chinese wit h English abstract) . Masek , J . G. , B. L . Isacks , F. J . Fielding , and J . Browaeys , 1994 , Rift flank uplift in Tibet : Evidence for a viscous lower crust [J ] : Tectonics , v. 13 , p . 659 - 667. Mei Houjun , 1966 , Olivine basalt and camptonite wit h peridotite xenolit hs from Maguan , Yunnan [J ] : Scientia Geologica Sinica , v. 1 , p . 50 - 63 (in Chinese wit h English abstract) . Meyer , B. , P. Tapponnier , L . Bourjot , F. Metivier , Y. Gaudemer , G. Peltzer , S. M. Guo , and Z. T. Chen , 1998 , Crustal t hick2 ening in Gansu2Qinghai , lit hospheric mantle subduction , and oblique , strike2slip controlled growt h of t he Tibet Plateau [J ] : Geo2 physical Journal International , v. 135 , p . 1 - 47. Pan Guitang , Wang Peisheng , and Xu Yaorong , 1990 , Cenozoic tectonic evolution of Qinhai2Xizang Plateau [ M ] : Beijing , Geological Publishing House , 190p . (in Chinese) Qi Qu , L . A. Taylor , and X. M. Zhou , 1995 , Petrology and geochemistry of mantle peridotite xenolit hs from SE China [J ] : Journal of Petrology , v. 36 , p . 55 - 79. Rickwood , P. C. , 1989 , Boundary lines wit hin petrologic diagrams which use oxides of major and minor elements [J ] : Lit hos. , v. 22 , p . 247 - 263. Shu Xiaoxin , 1995 , The genesis of Cpx2peridotitic xenolit hs in basanite of Maguan , Yunnan Province [J ] : Acta Petrologica et Miner2 alogica , v. 14 , n. 1 , p . 47 - 51 (in Chinese wit h English abstract) .


64


Sun , S. S. and W. F. McDonough , 1989 , Chemical and isotopic systematics of oceanic basalts : implications for mantle composition and processes , in A. D. Saunders and M. J . Norry , eds. , Magmatism in t he ocean basins [ C] : London , Geological Society Spe2 cial Publication , 345p . Sun Hongjuan , 2000 , The Cenozoic potassic magmatism in eastern Tibet and sout heast Yunnan Province [ D ] : Beijing , Institute of Geology and Geophysics , Chinese Academy of Sciences , Ph. D. dissertation , 75p . (in Chinese) Wang Jianghai , Yin An , T. M. Harrison , M. Grove , Zhang Yuquan , and Xie Guanghong , 2001 , A tectonic model for Cenozoic ig2 neous activities in t he eastern Indo2Asian collision zone [J ] : Eart h and Planetary Science Letters , v. 188 , p . 123 - 133. \ = Wang Jianghai , Yin An , T. M. Harrison , M. Grove , Zhou Jiangyu , Zhang Yuquan , and Xie Guanghong , 2002 , Ther2 mochronological constraints on two pulses of Cenozoic high2 K magmatism in eastern Tibet [J ] : Science in China ( Series D) , v. 32 , p . 529 - 537 (in Chinese) . Wilson , M. , 1989 , Igneous petrogenesis [ M ] : London , Oxford University Press , 466p . Xu Yigang , M. A. Menzies , Lin Chuanyong , and R. W. Hinton , 1997 , Trace element compositions of mantle2derived xenolit hs from Yitong , Jilin Province and t heir petrogenetic implications [J ] : Acta Petrologica Sinica , v. 13 , p . 14 - 26 (in Chinese wit h English abstract) . Xu Yigang , M. A. Menzies , P. Vroon , J . C. Mercier , and Lin Chuanyong , 1998 , Texture2temperature2geochemistry relationship in t he upper mantle as revealed from spinel peridotite xenolit hs form Wangqing , N E China [J ] : Journal of Petrology , v. 39 , p . 1 25. Yin An , 2000 , Mode of Cenozoic east2west extension in Tibet suggesting a common origin of rifts in Asia during t he Indo2Asian colli2 sion [J ] : Journal of Geophysical Research , v. 105 , p . 21745 - 21759. Zheng Jianping , 1999 , Mesozoic2Cenozoic mantle replacement and lit hospheric t hinning beneat h eastern China [ M ] : Wuhan , China University of Geosciences Press , 126p . (in Chinese) Zindler , A. and S. Hart , 1986 , Chemical geodynamics [J ] : Annual Reviews of Eart h and Planetary Science , v. 14 , p . 493 - 571.
