TY - JOUR

T1 - Ankaramites of Gorny Altai

T2 - Mineralogical, petrographic, and petrochemical features of diopside porphyry basalts of the ust'-sema formation

AU - Khlif, N.

AU - Vishnevskiy, A. V.

AU - Izokh, A. E.

PY - 2020/3/1

Y1 - 2020/3/1

N2 - The mineral composition, petrography, and petrochemistry of middle Cambrian diopside porphyry basalts of the Ust'-Sema Formation in Gorny Altai are considered in comparison with ankaramites of different geodynamic settings. The basalts of the Ust'-Sema Formation are enriched in phenocrysts of high-Mg clinopyroxene (Mg# ≤ 94) (20 to 40-50 vol.%) with a high content of Cr2O3 (up to 1.11 wt.%), enclosed in the clinopyroxene-plagioclase microlitic groundmass. In addition, there are minor phenocrysts of saussuritized plagioclase (An49-71), olivine replaced by secondary minerals, amphibole with Mg# = 55.7-68.2, and Cr-spinel with Cr# = 36.2-41.7. Inclusions of Cr-spinel in high-Mg clinopyroxene are richer in Cr (Cr# ≤ 72.8). The basalts of the Ust'-Sema Formation are chemically heterogeneous and are subdivided into two main groups: high-Ca (MgO = 7.98-14.77 wt.% and CaO/Al2O3 = 1.0-1.8) and low-Ca (MgO = = 2.84-9.89 wt.% and CaO/Al2O3 = 0.2-0.9). The obtained data on the high-Ca basalts of the Ust'-Sema Formation show that the rocks are similar to the reviewed ankaramites and thus can be assigned to this type of rocks. The low-Ca basalts of the Ust'-Sema Formation might have resulted from the fractionation of ankaramitic melt in intermediate magma chambers. The Gorny Altai ankaramites formed through the melting of the wehrlitized suprasubductional lithospheric mantle during the closure of the Paleoasian Ocean.

AB - The mineral composition, petrography, and petrochemistry of middle Cambrian diopside porphyry basalts of the Ust'-Sema Formation in Gorny Altai are considered in comparison with ankaramites of different geodynamic settings. The basalts of the Ust'-Sema Formation are enriched in phenocrysts of high-Mg clinopyroxene (Mg# ≤ 94) (20 to 40-50 vol.%) with a high content of Cr2O3 (up to 1.11 wt.%), enclosed in the clinopyroxene-plagioclase microlitic groundmass. In addition, there are minor phenocrysts of saussuritized plagioclase (An49-71), olivine replaced by secondary minerals, amphibole with Mg# = 55.7-68.2, and Cr-spinel with Cr# = 36.2-41.7. Inclusions of Cr-spinel in high-Mg clinopyroxene are richer in Cr (Cr# ≤ 72.8). The basalts of the Ust'-Sema Formation are chemically heterogeneous and are subdivided into two main groups: high-Ca (MgO = 7.98-14.77 wt.% and CaO/Al2O3 = 1.0-1.8) and low-Ca (MgO = = 2.84-9.89 wt.% and CaO/Al2O3 = 0.2-0.9). The obtained data on the high-Ca basalts of the Ust'-Sema Formation show that the rocks are similar to the reviewed ankaramites and thus can be assigned to this type of rocks. The low-Ca basalts of the Ust'-Sema Formation might have resulted from the fractionation of ankaramitic melt in intermediate magma chambers. The Gorny Altai ankaramites formed through the melting of the wehrlitized suprasubductional lithospheric mantle during the closure of the Paleoasian Ocean.

KW - Accretionary magmatism

KW - Ankaramite

KW - Clinopyroxene

KW - Cr-diopside

KW - Gorny Altai

KW - High-Ca magma

KW - Island arc magmatism

KW - Middle Cambrian

KW - Ural-Alaskan type

KW - AVACHINSKY VOLCANO

KW - accretionary magmatism

KW - ORIGIN

KW - clinopyroxene

KW - PRIMITIVE MAGMAS

KW - GEOCHEMISTRY

KW - OLIVINE

KW - PETROGENESIS

KW - island arc magmatism

KW - middle Cam-brian

KW - MELT INCLUSIONS

KW - HIGH-MAGNESIAN BASALTS

KW - Anlcaramite

KW - high-Ca magma

KW - ISLAND-ARC ANKARAMITES

KW - LAVAS

UR - http://www.scopus.com/inward/record.url?scp=85089091655&partnerID=8YFLogxK

U2 - 10.15372/RGG2019143

DO - 10.15372/RGG2019143

M3 - Article

AN - SCOPUS:85089091655

VL - 61

SP - 250

EP - 267

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 3

ER -