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Mineralogy and magmatic affinity of the Jasra intrusive complex, Shillong Plateau, India

  • L. Melluso (a1), R. K. Srivastava (a2), C. M. Petrone (a3), V. Guarino (a1) and A. K. Sinha (a2)...


The rocks of the Jasra intrusive complex (Shillong Plateau, northeastern India) include phlogopite clinopyroxenites (with olivine or perovskite relics), alkali gabbros/monzodiorites, syenites and nepheline syenites. They have a potassic affinity (Na2O/K2O ∼1), and their mineralogy is dominated by clinopyroxene with which phlogopite, olivine, amphibole, feldspars, feldspathoids, oxides, orthopyroxenes, perovskite, titanite and other accessory phases are variably associated. The Jasra intrusive rocks are cumulates derived from at least two distinct magmatic liquids. The potassic affinity of the Jasra rocks differs from the nearby Sung Valley ijolitic-carbonatitic complex and from the ultrapotassic lamproitic rocks of the Damodar Valley, which are of approximately the same age. This suggests major variability in the mantle sources of small-volume alkaline volcanism in the Early Cretaceous of northeastern India.


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Present address: Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK

Present address: Dr K.S. Krishnan Geomagnetic Research Laboratory, Jhusi, Allahabad 211505, India



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Type Description Title
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 1: bulk-rock, CIPW norms and isotopic data

 Excel (36 KB)
36 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary figures: thin section photomicrographs of the Jasra samples 2

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Supplementary materials

Melluso et al. supplementary material
Supplementary Table 2: oxide compositions

 Excel (33 KB)
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Supplementary materials

Melluso et al. supplementary material
Supplementary Table 3: olivine compositions

 Excel (27 KB)
27 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 4: clinopyroxene compositions

 Excel (36 KB)
36 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 5: amphibole and phlogopite compositions

 Excel (35 KB)
35 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 6: feldspar and nepheline compositions

 Excel (33 KB)
33 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 7: composition of apatite, titanite and garnet

 Excel (30 KB)
30 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary Table 8: composition of perovskite and zirconolite

 Excel (28 KB)
28 KB
Supplementary materials

Melluso et al. supplementary material
Supplementary figures: thin section photomicrographs of the Jasra samples 1

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1.3 MB


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