Publication details

Petrography, Mineralogy, and Origin of the Syenite Pegmatitic Segregation Veins from La PeNa Alkaline Complex, Mendoza, Argentina

Authors

PAGANO Diego Sebastian GALLISKI Miguel Angel MÁRQUEZ-ZAVALÍA Maria Florencia NOVÁK Milan ŠKODA Radek

Year of publication 2016
Type Article in Periodical
Magazine / Source Canadian Mineralogist
MU Faculty or unit

Faculty of Science

Citation
web https://doi.org/10.3749/canmin.1600015
Doi http://dx.doi.org/10.3749/canmin.1600015
Keywords pegmatitic segregation; malignite; potassic alkaline rocks; interstitial melt; La Pena complex; Mendoza; Argentina
Description The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Pena alkaline complex (LPC), Mendoza, Argentina, are emplaced in a malignite body. They occur as veins, parallel layers, and small elliptical bodies 1 to 6 cm wide and 0.2 to 1 m in length. The veins with a pegmatitic to micropegmatitic texture have a thin dark border composed of andradite, potassic-hastingsite, and dark micas and a thicker internal zone of poikilitic Ba-Sr-poor K-feldspar (Or(90.3)Ab(8.9)An(0.8)), nepheline (Ne(74.9)Ks(19.4)Qz(5.7) to Ne(78.7)Ks(20.0)Qz(1.3)), potassic-hastingsite, dark mica, andradite, scarce clinopyroxene (diopside-hedenbergite), and locally zoned microphenocrysts of Ba-Sr-rich K-feldspar (Or(75.6)Ab(21.7)An(2.7)). Accessory fluorapatite, titanite, interstitial sodalite, and magnetite and secondary abundant Na- and K-rich zeolites, calcite, chlorite-group minerals, and possibly cancrinite have been identified. The textural and mineralogical characteristics of the SPSV show genetic links with the host malignite that belongs to the potassic alkaline series. The SPSV were formed from a residual syenitic melt (malignite) extracted from a parental tephritic magma. In the residual malignite, the concentration of primary crystals (apatite, clinopyroxene, Ba-Sr-rich K-feldspar, and nepheline) formed a crystal network (mush) with the open spaces occupied by small amounts of residual melt enriched in Al, Na, K, and volatiles and depleted in Ba and Sr. Deformation (by shear movements plus magmatic pressures) produced microfractures and fractures which were occupied by residual interstitial melt. In situ crystallization within these fractures resulted in the formation of the SPSV.

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