HR: 1330h
AN: V13B-05    [Abstracts]
TI: Kimberlite-Clan-Rocks in India: Significance of new VGP, T, and GP Observations.
AU: * Haggerty, S E
EM: haggerty@fiu.edu
AF: Florida International University, Dept. of Earth Sciences, Miami, FL 33199
AB: Although India is acknowledged for the first description of diamond some 2000 BCE, it should also rightfully be credited for the 17th C recognition that diamond is a product of volcanism. With this extraordinary background, it is surprising that the host rocks remain controversial, being neither archetypical kimberlites, nor classic lamproites. Lacking affinities to micro-diamond-bearing UHPT metamorphic rocks and being unequivocally volcanic, the term Kimberlite-Clan-Rock (KCR) is applied. Over 200 KCR pipes and dikes, many of which are richly mineralized, have recently been discovered in the Diamond Corridor (1000 x 200 km) of the Eastern Dharwar Craton, and in adjoining cratons to the N and NE. From 32 absolute age determinations on KCRs, the remaining intrusions, in comparable stratigraphic settings, are assumed to be 1.1 Ga, equivalent to the Argyle lamproite (Australia, highest diamond grade), and the Premier kimberlite (RSA, largest known diamond). India has the largest number of known Proterozoic KCR intrusions that over the centuries have produced a wealth of famous diamonds. The primary source of these extraordinary stones, however, remains unknown, possibly because the unusual host rocks defy conventional exploration protocols. Six new observations make the setting even more unusual: (1) Coeval, large scale magmatism in the Kalahari (>2 m sq km) and Laurentian (>300 k cub km) Cratons at 1085-1112 Ma, during assembly of Rodinia, confirms the relation between and among KCR volcanism, LIPs, and supercontinents; Proterozoic Rodinia, into which the India KCRs, Argyle and Premier were intruded, was constructive, whereas the other, globally-wide, diamond-intrusive event, that occurred during the Mesozoic (80-120 Ma), was related to the breakup of Pangea and the dispersion of Gondwana; both events occurred during long period geomagnetic chrons implying a core relation, and superplume activity from the CMB. (2)The transcontinental Mumbai-Chennai gravity lineament that separates diamond (North) from barren (South) KCRs is interpreted as a sub-lithospheric, architectural discontinuity, with a shallow keel to the N and deeper penertration to the S. (3)An intrusive carbonatite stock into one KCR, and intensely carbonatized xenoliths in another, has rekindled the unsettled VGP debate of kimberlite-carbonatite relations; the new discoveries strongly support a kinship. (4) An eclogite xenolith from Kaliandurg has euhedral inclusions of re-equilibrated majorite in garnet; the assemblage has important implications for depths of origin (in or close to the TZ), and the controversial issue of Archean ocean crust recycling, recognizing that there are other ways to generate mantle eclogites. (5) Heterogeneities in the source regions of KCRs, and in the degrees of mantle melting, metasomatism and mixing, are well displayed in the Chigicherla KCR cluster; CC5 has unprecedented 2-10cm diameter autoliths (ol + cc + sp + perv), that are partially to totally assimilated in closely associated bodies, or are absent in others; (6)Groundmass olivine in KCRs from Naryanpet (non-diamond) and Wajrakur (diamond-bearing) have densely packed, crystal-oriented laths of rutile in association with blebs of metal + sulfide; these intergrowths bear on the unresolved solubility of Ti in olivine and its appeal to super high P-T conditions in diamond and coesite-bearing metamorphic terrains; the KCR settings, however, imply crystallization of olivine at low P, coupled with or followed by Ti metasomatism. With increased activities in diamond exploration many more VGP, T and GP mantle revelations are expected from this geologically classic and historically important part of the sub-continent.
DE: 1025 Composition of the mantle
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 3640 Igneous petrology
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 9619 Precambrian
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly