Gabbro (/ˈɡæb.roʊ/) - magniy va temirga boy magmaning sekin sovishi natijasida hosil bo'lgan fanerit (qo'pol donali), mafik intruziv magmatik jins bo'lib, yer yuzasining chuqur ostidagi golokristal massaga aylanadi. Sekin soviydigan, qoʻpol donali gabbro kimyoviy jihatdan tez soviydigan, mayda donali bazaltga teng. Yerning okean qobig'ining katta qismi okeanning o'rta tizmalarida hosil bo'lgan gabbrodan iborat. Gabbro shuningdek, kontinental vulqonizm bilan bog'liq plutonlar sifatida ham topilgan. O'zining xilma-xilligi tufayli, gabbro atamasi keng ko'lamli intruziv jinslarga nisbatan qo'llanilishi mumkin, ularning aksariyati shunchaki "gabbroik". Qo'pol o'xshashlik bo'yicha, gabbro bazaltga, granit riolitga o'xshaydi.

Gabbro namunasi
Gabbroning yupqa qismining fotomikrografi

EtimologiyaTahrirlash

"Gabbro" atamasi 1760-yillarda Italiyadagi Apennin tog'lari ofiyolitlarida topilgan jinslar to'plamini nomlash uchun ishlatilgan[1]. U Toskanadagi Rosignano Marittimo yaqinidagi Gabbro qishlog'i sharafiga nomlangan. Keyin, 1809-yilda nemis geologi Kristian Leopold fon Bux ushbu italyan ofiyolitik jinslarini tavsiflashda ushbu atamani yanada cheklanganroq ishlatgan[2]. U bugungi kunda geologlar qattiqroq "metagabbro" (metamorflangan gabbro) deb ataydigan jinslarga "gabbro" nomini berdi[3].

PetrologiyaTahrirlash

 
Magmatik jinslarning mineral birikmasi

Gabbro - qo'pol donali (faneritik) magmatik jins bo'lib, u nisbatan kam kremniyga ega va temir, magniy va kaltsiyga boy. Bunday tosh mafik deb ta'riflanadi. Gabbro piroksen va kaltsiyga boy plagioklazdan iborat bo'lib, oz miqdorda shoxli, olivin va yordamchi minerallar mavjud[4]. Mavjud bo'lganda, shoxlar odatda augit kristallari atrofida yoki boshqa minerallarning kichikroq donalarini (poykilitik donalar) o'rab turgan yirik donalar shaklida topiladi[5][6].

 
Sariq rangda ta'kidlangan gabroid/dioritoid maydonlari bilan QAPF diagrammasi. Gabbroidlar dioritoidlardan plagioklazlarning 50% dan ortiq anortozit miqdori bilan ajralib turadi.
 
Sariq rang bilan ta'kidlangan gabbro maydoniga ega QAPF diagrammasi. Gabbro dioritdan anortozit tarkibidagi plagioklazning 50% dan ortiqligi va anortitdan mafik mineralning 10% dan ortiqligi bilan ajralib turadi.

Geologlar qo'pol taneli magmatik jinslarni jinsning mineral tarkibiga qarab tasniflash uchun qat'iy miqdoriy ta'riflardan foydalanadilar. Asosan silikat minerallaridan tashkil topgan va mineral tarkibining kamida 10% kvarts, dala shpati yoki dala shpati minerallaridan tashkil topgan magmatik jinslar uchun tasnif QAPF diagrammasidan boshlanadi. Kvars (Q), ishqorli dala shpati (A), plagioklaz (P) va dala shpati (F) ning nisbiy ko'pligi tog 'jinslarining diagrammadagi holatini chizish uchun ishlatiladi[7][8][9]. Agar kvarts QAPF tarkibining 20% dan kamini, feldspatoid QAPF tarkibining 10% dan kamini va plagioklaz umumiy dala shpati tarkibining 65% dan ko'prog'ini tashkil etsa, jins gabbroid yoki dioritoid deb tasniflanadi. Gabbroidlar dioritoidlardan ularning umumiy plagioklazasining 50% dan ortiq anortit (kaltsiy plagioklaza) qismi bilan ajralib turadi.

Plagioklazning tarkibini dala sharoitida osongina aniqlash mumkin emas, keyin mafik minerallar tarkibiga qarab dioritoid va gabroid o'rtasida dastlabki farq qilinadi. Gabbroid odatda 35% dan ortiq mafik minerallarga ega, asosan piroksenlar yoki olivin, dioritoid esa odatda 35% dan kam mafik minerallarga ega bo'lib, odatda shoxli minerallarni o'z ichiga oladi[10].

Gabbroidlar monzogabbro, kvarts gabbro yoki nefelinli gabbro kabi gabroga o'xshash jinslar oilasini tashkil qiladi. Gabbroning o'zi yanada torroq bo'lib, gabbroid sifatida kvarts QAPF tarkibining 5% dan kamrog'ini tashkil qiladi, dala shpatilari mavjud emas, plagioklaz esa dala shpati tarkibining 90% dan ko'prog'ini tashkil qiladi. Gabbro 10% dan kam mafik minerallarni o'z ichiga olgan anortozitdan farq qiladi[11][7][8].

Dag'al donali gabroidlar lava bilan bir xil tarkibga ega bo'lgan magmaning sekin kristallanishi natijasida hosil bo'ladi, ular tez qotib, nozik taneli (afanitik) bazaltni hosil qiladi[7][8].

SubtiplarTahrirlash

Geologlar tomonidan tan olingan gabbroning bir qator kichik turlari mavjud. Gabrosni keng ma'noda leykogabrolarga bo'lish mumkin, mafik mineral tarkibi 35% dan kam; 35% dan 65% gacha mafik mineral tarkibiga ega mezogabro; va 65% dan ortiq mafik mineral tarkibiga ega melagabrolar. 90% dan ortiq mafik mineral tarkibiga ega bo'lgan tog 'jins o'rniga ultramafik jins sifatida tasniflanadi. Mafik mineral tarkibi 10% dan kam bo'lgan gabbroik jinslar anortozit sifatida tasniflanadi[8][12].

FoydalanishTahrirlash

Gabbro ko'pincha qimmatli miqdorda xrom, nikel, kobalt, oltin, kumush, platina va mis sulfidlarini o'z ichiga oladi[13][14][15].

ManbalarTahrirlash

  1. Bortolotti, V. et al. Chapter 11: Ophiolites, Ligurides and the tectonic evolution from spreading to convergence of a Mesozoic Western Tethys segment in F. Vai, G.P. and Martini, I.P. (editors) (2001) Anatomy of an Orogen: The Apennines and Adjacent Mediterranean Basins, Dordrecht, Springer Science and Business Media, p. 151. ISBN 978-90-481-4020-6
  2. Bortolotti, V. et al. Chapter 11: Ophiolites, Ligurides and the tectonic evolution from spreading to convergence of a Mesozoic Western Tethys segment in F. Vai, G.P. and Martini, I.P. (editors) (2001) Anatomy of an Orogen: The Apennines and Adjacent Mediterranean Basins, Dordrecht, Springer Science and Business Media, p. 152. ISBN 978-90-481-4020-6
  3. Gabbro at SandAtlas geology blog. Retrieved on 2015-07-09.
  4. Allaby, Michael „gabbro“,. A dictionary of geology and earth sciences, Fourth, Oxford: Oxford University Press, 2013. ISBN 9780199653065. 
  5. „gabbro“,Glossary of geology., Fourth, Alexandria, Viriginia: American Geological Institute, 1997. ISBN 0922152349. 
  6. Blatt, Harvey; Tracy, Robert J.. Petrology : igneous, sedimentary, and metamorphic., 2nd, New York: W.H. Freeman, 1996 — 53 bet. ISBN 0716724383. 
  7. 7,0 7,1 7,2 Le Bas, M. J.; Streckeisen, A. L. (1991). "The IUGS systematics of igneous rocks". Journal of the Geological Society 148 (5): 825–833. doi:10.1144/gsjgs.148.5.0825. 
  8. 8,0 8,1 8,2 8,3 "Rock Classification Scheme - Vol 1 - Igneous". British Geological Survey: Rock Classification Scheme 1: 1–52. 1999. http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf. 
  9. Philpotts, Anthony R.; Ague, Jay J.. Principles of igneous and metamorphic petrology, 2nd, Cambridge, UK: Cambridge University Press, 2009 — 139–143 bet. ISBN 978-0-521-88006-0. 
  10. Blatt & Tracy 1996, p. 71.
  11. Jackson 1997, "gabbro".
  12. Philpotts & Ague 2009, p. 142.
  13. Iwasaki, I.; Malicsi, A.S.; Lipp, R.J.; Walker, J.S. (August 1982). "By-product recovery from copper-nickel bearing duluth gabbro". Resources and Conservation 9: 105–117. doi:10.1016/0166-3097(82)90066-9. 
  14. Lachize, M.; Lorand, J. P.; Juteau, T. (1991). "Cu-Ni-PGE Magmatic Sulfide Ores and their Host Layered Gabbros in the Haymiliyah Fossil Magma Chamber (Haylayn Block, Semail Ophiolite Nappe, Oman)". Ophiolite Genesis and Evolution of the Oceanic Lithosphere. Petrology and Structural Geology 5: 209–229. doi:10.1007/978-94-011-3358-6_12. ISBN 978-94-010-5484-3. 
  15. Arnason, John G.; Bird, Dennis K. (August 2000). "A Gold- and Platinum-Mineralized Layer in Gabbros of The Kap Edvard Holm Complex: Field, Petrologic, and Geochemical Relations". Economic Geology 95 (5): 945–970. doi:10.2113/gsecongeo.95.5.945. 

Tashqi havolalarTahrirlash