Textural and mineralogical evidences of magma mixing in the trachyandesitic lava flows in the Ab-e-Torsh district, Western Qazvin, Iran

Abstract

Trachyandesitic rocks in the Ab-e-Torsh region, western Qazvin, have considerable thickness and extensive outcrops (>200 Km2) that form parts of the Alborz Paleogene volcanic belt. These rocks that can be correlated with the upper member of the Karaj formation, are subaerial eruptions with lava flows and some lava domes. Geochemically, these are classified as shoshonitic series. Occurrence of some textural evidences (e.g., reaction rims, sieve textures and oscillatory zoning in feldspars and augites phenocrysts) and coexistence of inequilibrium plagioclase phonocrysts
(An5-20, An36-61, An77-93), as well as compositional differences between phenocrysts and their surrounded mesostasis, all suggest that the magmatic evolutionary processes could have been occurred in an open system. On the other hand, existence of some alterations such as opacitization in phlogopitic biotites and paragasitic hornblends might be related to the late stages of the magmatic evolution with high ƒO2 and P < sub>H2O. Considering textural and mineralogical observations, as well as dispersion of the whole rock geochemical data, one may conclude that the magmatic evolution have been occurred by periodic refreshment of alkaline and basic magma by a more acidic intrusion.

Keywords


[1] De-Dual E., "Zur geologie des mittleren und unteren Karaj-Tales, Zentral Elburz (Iran)", Mitt.Geol.Inst.E.T.H.U., Thesis.Univ.Zurich, no.76 (1967) 125p.

[2] Annells R.N., Arthurton R.S., Bazely R.A., Davies R.G., "Explanatory text of the Qazvin and Rasht quadrangle map (1:250000)", G.S.I. Rep., noE3,E4 (1975) 94p.

[3] Stocklin J., Eftekhar-nezhad J., "Explanatory text of the Zanjan quadrangle map (1:250000)", G.S.I. Rep., noD4 (1969) 61p.

[4] آسیابانها ع.،" زمین شناسی و پتروژنز رخساره‌های آتشفشانی منطقه یوزباشی چای (غرب قزوین)". رساله دکتری دانشگاه تربیت مدرس (1380) 321ص.

[5] درویش زاده ع.، آسیابانها ع.، "نقش آذرآواریها در گسترش ترجیحی دگرسانی گرمابی در منطقه آتشفشانی آبترش"، فصلنامه علوم زمین، شماره 37-38 (1380) ص 48-59.

[6] حسینی م.، "آلونیت زایی در منطقه طارم"، مجموعه مقالات دومین همایش انجمن زمین شناسی ایران (1377) ص 179-185

[7] Le Maitre R.W.(eds)., "A classification of igneous rocks and glossary of terms", (1989), Blackwell. 128p.

[8] Halsor S.P., "Large glass inclusions in plagioclase phenocrysts and their bearing on the origin of mixed andesitic lavas at Toliman Volcano, Guatemala", Bull Volcanol 51 (1989) 271-280

[9] Eichberger J.C.,"Andesites in island arcs and continental margins: relationships to crustal evolution", Bull. Volcanol 41 (1978) 480-500

[10] Nelson S.T., Montana A., "Sieve-textured plagioclase in volcanic rocks produced by rapid decompression", American Mineralogist 77 (1992) 1242-1249

[11] Best M.G., Christiansen E.H., "Igneous Petrology", Blackwell (2001) 458p.

[12] Bard J.P., "Microtextures of igneous and metamorphic rocks", Reidel (1986) 264p.

[13] Tsuchiyama A., "Dissolution kinetics of plagioclase in the melt of the system diopside-albite-anorthite and origin of dusty plagioclase in andesites", Contrib.Mineral.Petrol. 89 (1985) 1-16

[14] Stamatelopoulou-Seymor K., Vlassopoulos D., Pearce H.T., Rice C., "The record of magma chamber processes in plagioclase phenocryst at Thera Volcano, Aegean Volcanic Arc, Greece", Cont. Min. Pet. 104 (1990) 73-84.

[15] Singer S.B., Pearce H.T., Kolisnik A.M., Myers D.J., "Plagioclase zoning in mid-Pleistocene lavas from the Seguam volcanic center, central Aleutian arc", Alaska. Am. Min. 78(1993) 143-157.

[16] Kawamoto T., "Dusty and honeycomb plagioclase: indicators of processes in the Uchino stratified magma chamber", Izu Peninsula, Japan. Journal of Volcanology and Geothermal Research. 49(1992) 191-208.

[17] Dungan M.A., Rhodes J.M., "Residual glasses and melt inclusions in basalts from DSDP Legs 45 and 46: evidence from magma mixing", Contrib.Mineral.Petrol. 67 (1978) 417-431

[18] Hess P.C., "Origins of Igneous Rocks", Harvard University. Cambridge. (1989) 336p.

[19] Sigurdsson H., Houghton B., Rymer H., Stix J., McNutt S., "Encyclopedia of Volcanoes", Academic Press. (2000) 1000p.

[20] Merzbacher C., Eggler DH., "A magmatic geohygrometer: Application to Mount St. Helens and other dacitic magmas", Geology 14 (1984) 804-806

[21] درویش زاده ع.،" پترولوژی"، انتشارات دانشگاه پیام نور (1382). 310ص

[22] کریم‌پور م.ح. ،"پترولوژی سنگهای آذرین و کانسارهای ماگمایی"، نشر مشهد (1377). 343ص.