Mineralogy of the P-12 K-Ti-richterite diopside olivine lamproite from Wajrakarur, Andhra Pradesh, India: implications for subduction-related magmatism in eastern India

Abstract

The P-12 Bpara-kimberlite^from Wajrakarur consists of forsteritic olivine, Al-Na-poor diopside, Fe-Tirich, Al-poor phlogopite, K-Ti-richterite, spinel, perovskite, cymrite, apatite, barite, Ba-Sr-bearing calcite, gittinsite, witherite, strontianite, and hydrogrossular (hydrogarnet). The rock also contains small clasts consisting dominantly of calcite, with lesser Ba-Srbearing calcite, cymrite, barite, strontianite, witherite, apatite, and hydrogrossular. Two generations of forsteritic olivine (Fo 80-93 ) crystals are present: common phenocrystalto-microphenocrystal; and rare anhedral macrocrystic olivines. Phlogopite occurs as microphenocrysts and as groundmass poikilitic plates with inclusions of spinel, perovskite, apatite, and chlorite pseudomorphs (after pyroxene). Phlogopites also occur as reaction rims around olivine crystals. The phlogopites have extremely low Al 2 O 3 (2.2-3.8 wt.%) , moderate-to-high FeO (6.9-16 wt.%), TiO 2 (1.9-4.6 wt.%), and Na 2 O (0.4-2.7 wt.%) contents and are enriched in fluorine (up to 6.0 wt.%) and considered to be tetraferriphlogopite. The pyroxenes occur in five parageneses as: (1) phenocrysts and microphenocrysts; (2) small slender crystals(<30 μm) forming part of the groundmass; (3) the cores of richterite crystals; (4) reaction products replacing earlier-formed olivine; (5) acicular crystals mantling carbonate clasts. These pyroxenes do not differ significantly in composition and are all diopsides with minor variation in their TiO 2 , Al 2 O 3 , Na 2 O contents. Titanian-potassium richterite commonly occurs as: (1) groundmass poikilitic plates;(2) small prismatic crystals (<30 μm); (3) reaction rims on olivine and pyroxene crystals. Groundmass poikilitic richterites commonly enclose pyroxene and apatite. Perovskites have a bimodal size distribution. Small (<20 μm) euhedral perovskites are scattered throughout the groundmass, whereas larger (100-300 μm) subhedral-to-euhedral perovskites are patchily-zoned and commonly broken. Micro-clasts consisting of accumulations of perovskite with phlogopite and apatite are also present. Spinels occur as large atoll crystals and small (<20 μm), euhedral-to-subhedral crystals, scattered throughout the groundmass. Some small spinel crystals are also present in the rims of olivine and pyroxene crystals. Atoll spinels are up to 100 μm in size, commonly with single and double cores. Atoll spinels are typically associated with perovskites. The euhedral-tosubhedral small spinels are ulvospinels. The atoll spinels have cores of titanian aluminous magnesiochromite with rims of magnesian titaniferous magnetite. The spinels have compositions which evolve along the lamproite-spinel compositional trend. Zoned calcite crystals occur as residual phases. Late stage residual calcite and carbonate clasts host prismatic cymrite crystals which are interpreted as pseudomorphs after potassium feldspar and/or barite. Subhedral-to-euhedral gittinsite and its Sr-analog are reported for the first time from the groundmass carbonatechlorite mesostasis of a lamproit...

Geochemistry, Sr-Nd Isotope Compositions, and U-Pb Chronology of Apatite from Kimberlite in Wafangdian, North China Craton: Constraints on the Late Magmatic Processes

“…The #110 apatite has a slightly higher SO3 concentration (0.01 wt.%-0.17 wt.%) than the #50 apatite (0.01 wt.%-0.11 wt.%). The F content (#50 apatite: 1.54 wt.%-2.20 wt.%; #110 apatite: 1.75 wt.%-3.26 wt.%) reported in this study is slightly lower than that previously reported for apatite in lamproite (2.09 wt.%-4.83 wt.%) [46,47] and that measured for the apatite in the Mengyin kimberlite (1.95 wt.%-5.67 wt.%) [48]. However, the F content of the apatite is slightly higher than that in other kimberlites.…”

Igneous Rock Associations 26. Lamproites, Exotic Potassic Alkaline Rocks: A Review of their Nomenclature, Characterization and Origins

“…Apart from the complexities of their tectonic setting, studies of the petrogenesis of Indian lamproites have been hindered by problems in terminology resulting from resistance to using modern mineralogical-genetic classification schemes and undue reliance upon bulk rock geochemical studies. Many rocks previously described as "kimberlites" have now been reclassified as bona fide lamproites (Fareeduddin and Mitchell 2012;Gurmeet Kaur and Mitchell 2016). The numerous occurrences of "para-kimberlites" have not been investigated using detailed mineralogical studies and are probably varieties of olivine lamproite, e.g.…”

Petrogenesis of lamprophyres synchronous to kimberlites from the Wajrakarur kimberlite field: Implications for contrasting lithospheric mantle sources and geodynamic evolution of the eastern Dharwar Craton of southern India

“…Mesoproterozoic alkaline, potassic, and ultrapotassic intrusive rocks of the Wajrakarur kimberlite field (WKF) occur over an area of ~7,000 km 2 in southern India. Rock types present include kimberlites, orangeites/olivine lamproites, lamprophyres, and carbonatites (e.g., Dongre, Chalapathi Rao, Viljoen, & Lehmann, ; Kaur & Mitchell, ; Smith, Haggerty, Chatterjee, Beard, & Townend, ). Earlier studies focused primarily on the kimberlites and other related rock types basically focusing on their mineralogy, geochemistry, geochronology, and petrogenesis.…”