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1.
New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic Indr avati Basin are presented.The kimberlite has been subjected to extensive and pervasive low-temperature alteration.Spinel is the only primary phase identifiable,while olivine macrocrysts and juvenile lapilli are largely pseudomorphed(talc-serpentinecarbonate alteration).However,with the exception of the alkalies,major element oxides display systematic fractionation trends; likewise,HFSE patterns are well correlated and allow petrogenetic interpretation.Various crustal contamination indices such as(SiO2+Al2O3+Na2O)/(MgO+ K2O) and Si/Mg are close to those of uncontaminated kimberlites.Similar La/Yb(79-109) of the Tokapal samples with those from the kimberlites of Wajrakarur(73-145) and Narayanpet(72-156),Eastern Dharwar craton,southern India implies a similarity in their genesis.In the discriminant plots involving HFSE the Tokapal samples display strong affinities to Group II kimberlites from southern Africa and central India as well as to ‘transitional kimberlites' from the Eastern Dharwar craton,southern India,and those from the Prieska and Kuruman provinces of southern Africa.There is a striking similarity in the depleted-mantle(TDM) Nd model ages of the Tokapal kimberlite system,Bastar craton,the kimberlites from NKF and WKF,Eastern Dharwar craton,and the Majhgawan diatreme,Bundelkhand craton,with the emplacement age of some of the lamproites from within and around the Palaeo-Mesoproterozoic Cuddapah basin,southern India.These similar ages imply a major tectonomagmatic event,possibly related to the breakup of the supercontinent of Columbia,at 1.3-1.5 Ga across the three cratons.The ‘transitional'geochemical features displayed by many of the Mesoproterozoic potassic-ultrapotassic rocks,across these Indian cratons are inferred to be memories of the metasomatising fluids/melts imprinted on their source regions during this widespread event.  相似文献   

2.
New mineralogical and bulk-rock geochemical data for the recently recognised Mesoproterozoic(ca.1100 Ma) and late Cretaceous(ca.90 Ma) kimberlites in the Timmasamudram cluster(TKC) of the Wajrakarur kimberlite field(WKF),Eastern Dharwar Craton,southern India,are presented.On the basis of groundmass mineral chemistry(phlogopite,spinel,perovskite and clinopyroxene),bulk-rock chemistry(SiO_2.K_2O,low TiO_2.Ba/Nb and La/Sm),and perovskite Nd isotopic compositions,the TK-1(macrocrystic variety) and TK-4(Macrocrystic variety) kimberlites in this cluster are here classified as orangeites(i.e.Group Ⅱ kimberlites),with geochemical characteristics that are very similar to orangeites previously described from the Bastar Craton in central India,as well as the Kaapvaal Craton in South Africa.The remaining kimberlites(e.g.,TK-2,TK-3 and the TK-1 microcrystic variant),are more similar to other 1100 Ma,Group Ⅰ-type kimberlites of the Eastern Dharwar Craton,as well as the typical Group Ⅰkimberlites of the Kaapvaal Craton.Through the application of geochemical modelling,based on published carbonated peridotite/melt trace element partition coefficients,we show that the generation of the TKC kimberlites and the orangeites results from low degrees of partial melting of a metasomatised,carbonated peridotite.Depleted mantle(T_(DM)) Nd perovskite model ages of the 1100 Ma Timmasamudram kimberlites show that the metasornatic enrichment of their source regions are broadly similar to that of the Mesoproterozoic kimberlites of the EDC.The younger,late Cretaceous(ca.90 Ma) TK-1(macrocrystic variant)and TK-4 kimberlites,as well as the orangeites from the Bastar Craton,share similar Nd model ages of1100 Ma,consistent with a similarity in the timing of source enrichment during the amalgamation of Rodinia supercontinent.The presence of late Cretaceous diamoncliferous orangeite activity,presumably related to the location of the Marion hotspot in southern India at the time,suggests that thick Iithosphere was preserved,at least locally,up to the late Cretaceous,and was not entirely destroyed during the breakup of Gondwana,as inferred by some recent geophysical models.  相似文献   

3.
Tourmaline occurs as a minor but important mineral in the alteration zc,ne of the Archean orogenic gold deposit of Guddadarangavanahalli (G.R.Halli) in the Chitradurga greenst~ne belt of the western Dharwar craton, southern India. It occurs in the distal alteration halo of the G.R.Halli golcl deposit as (a) clusters of very fine grained aggregates which form a minor constituent in the natrix of the altered metabasalt (AMB tourmaline) and (b) in quartz-carbonate veins (vein tourmaline). ~['he vein tourmaline, based upon the association of specific carbonate minerals, is further grouped as (i) albite-tourmaline-ankerite-quartz veins (vein-1 tourmaline) and (ii) albite-tourmaline-calcite-quartz veins (vein-2 tourmaline). Both the AMB tourmaline and the vein tourmalines (vein-I and vein-2) belong to the alkali group and are clas- sified under schorl-dravite series. Tourmalines occurring in the veins are zoned while the AMB tour- malines are unzoned. Mineral chemistry and discrimination diagrams 1eveal that cores and rims of the vein tourmalines are distinctly different. Core composition of the ve:n tourmalines is similar to the composition of the AMB tourmaline. The formation of the AMB tourmaline and cores of the vein tour- malines are proposed to be related to the regional D1 deformational event associated with the emplacement of the adjoining ca. 2.61 Ga Chitradurga granite whilst rims of the vein tourmalines vis-a- vis gold mineralization is spatially linked to the juvenile magmatic accretion (2.56-2.50 Ga) east of the studied area in the western part of the eastern Dharwar craton.  相似文献   

4.
《地学前缘(英文版)》2020,11(3):793-805
Detailed mineralogy,bulk rock major,trace and Sr-Nd isotope compositions,and ~(40)Ar/~(39)Ar dating of the Pipe-8 diamondiferous ultramafic intrusion in the Wajrakarur cluster of southern India,is reported.Based on the presence of Ti-rich phlogopite,high Na/K content in amphibole,Al-and Ti-rich diopside,a titanomagnetite trend in spinel and the presence of Ti-rich schorlomite garnet and carbonates in the groundmass,the Pipe-8 intrusion is here more precisely classified as an ultramafic lamprophyre(i.e.,aillikite).An aillikite affinity of the Pipe-8 intrusion is further supported by the bulk rock major and trace element and Sr-Nd isotope geochemistry.Sr-Nd isotope data are consistent with a common,moderately depleted upper mantle source region for both the Pipe-8 aillikite as well as the Wajrakarur kimberlites of southern India.A phlogopite-rich groundmass ~(40)Ar/~(39)Ar plateau age of 1115.8±7.9 Ma(2σ) for the Pipe-8 intrusion falls within a restricted 100 Ma time bracket as defined by the 1053-1155 Ma emplacement ages of kimberlites and related rocks in India.The presence of ultramafic lamprophyres,carbonatites,kimberlites,and olivine lamproites in the Wajrakarur kimberlite field requires low degrees of partial melting of contrasting metasomatic assemblages in a heterogeneous sub-continental lithospheric mantle.The widespread association of kimberlite and other mantle-derived magmatism during the Mesoproterozoic(ca.1.1 Ga) have been interpreted as being part of a single large igneous province comprising of the Kalahari,Australian,West Laurentian and Indian blocks of the Rodinia supercontinent that were in existence during its assembly.In India only kimberlite/lamproite/ultramafic lamprophyre magmatism occurred at this time without the associated large igneous provinces as seen in other parts of Rodinia.This may be because of the separated paleo-latitudinal position of India from Australia during the assembly of Rodinia.It is speculated that the presence of a large plume at or close to 1.1 Ga within the Rodinian supercontinent,with the Indian block located on its periphery,could be the reason for incipient melting of lithospheric mantle and the consequent emplacement of only kimberlites and other ultramafic,volatile rich rocks in India due to comparatively low thermal effects from the distant plume.  相似文献   

5.
The AravallieDelhi and Satpura Mobile Belts(ADMB and SMB)and the Eastern Ghat Mobile Belt(EGMB)in India form major Proterozoic mobile belts with adjoining cratons and contemporary basins.The most convincing features of the ADMB and the SMB have been the crustal layers dipping from both sides in opposite directions,crustal thickening(w45 km)and high density and high conductivity rocks in upper/lower crust associated with faults/thrusts.These observations indicate convergence while domal type refectors in the lower crust suggest an extensional rifting phase.In case of the SMB,even the remnant of the subducting slab characterized by high conductive and low density slab in lithospheric mantle up to w120 km across the PurnaeGodavari river faults has been traced which may be caused by fuids due to metamorphism.Subduction related intrusives of the SMB south of it and the ADMB west of it suggest NeS and EeW directed convergence and subduction during MesoeNeoproterozoic convergence.The simultaneous EeW convergence between the Bundelkhand craton and Marwar craton(Western Rajasthan)across the ADMB and the NeS convergence between the Bundelkhand craton and the Bhandara and Dharwar cratons across the SMB suggest that the forces of convergence might have been in a NEeSW direction with EeW and NeS components in the two cases,respectively.This explains the arcuate shaped collision zone of the ADMB and the SMB which are connected in their western part.The Eastern Ghat Mobile Belt(EGMB)also shows signatures of E eW directed MesoeNeoproterozoic convergence with East Antarctica similar to ADMB in north India.Foreland basins such as Vindhyan(ADMBeSMB),and Kurnool(EGMB)Supergroups of rocks were formed during this convergence.Older rocks such as Aravalli(ADMB),MahakoshaleBijawar(SMB),and Cuddapah(EGMB)Supergroups of rocks with several basic/ultrabasic intrusives along these mobile belts,plausibly formed during an earlier episode of rifting during PaleoeMesoproterozoic period.They are highly disturbed and deformed due to subsequent MesoeNeoproterozoic convergence.As these Paleoproterozoic basins are characterized by large scale basic/ultrabasic intrusives that are considerably wide spread,it is suggested that a plume/superplume might have existed under the Indian cratons at that time which was responsible for the breakup of these cratons.Further,the presence of older intrusives in these mobile belts suggests that there might have been some form of convergence also during Paleoproterozoic period.  相似文献   

6.
Based on the measurements of refractive index,specific gravity,unit cell parameter,and mineral chemistry and infrared absorption spectrum analyses of pyropes in kimberlites from China,systematic studies of the Physical properties and compositional variations of pyropes of different colors and diverse paragenetic types,within and between kimberlite provinces have been undertaken,The origin of pyropes in the Kimberlites and the depth of their formation have been discussed.Pyropes of the purple series are different from those of the orange series in physical and chemical properties,for exaple,pyropes of the puple series are higher in α0,RI,SG,Cr2O3,MgO,Cr/(Cr Al),Mg/(Mg Fe),and Mg/(Mg Ca),and lower in Al2O3,Fe2O3 FeO than those of the orange series.The classification of garnets in kimberlites from china by the Dawson and Stephens‘ method(1975) has been undertaken and clearly demonstrates that pyropes of diamond-rich kimberlites contain much more groups than those of diamond-poor,especially diamond-free kimberlites.The higher in α0,RI,SG,Cr2O(3.Cr/(Cr Al),knorringite and Cr-component the pyropes are ,the richer in diamond the kimberlites will be.The infrared absorption spectrum patterns of pyropes change with their chemical composition regularly,as reflected in the shape and position of infrared absorption peaks.Two absortpion bands at 862-901 cm^-1 will grade into degeneration from splitting and the absorption band positions of pyropes shift toward lower frequency with increasing Cr2O3 content and Cr/(Cr Al) ratio of pyropes,LREE contents of orange pyrope megacrysts are similar to those of porple pyrope macrocrysts,but the former is higher in HREE than the latter,showing their different chondrite-normalized patterns.The formation pressures of pyropes calculated by Cr-component,Ca-component,knorringite molecules of pyropes show that some pyropes of the purple series in diamondiferous kimberlites fall into the diamond stability field.but all pyropes of diamond-free kimberlites lie outside the diamond stability field.The megacrysts were formed through early crystallization of kimberlites magma at high pressure condition,the majority of the purple pyrope macrocrysts have been derived from disaggregated xenoliths but the minoirty of them appear to be fragments of the discrete megacryst pyropes,or phenocrysts.  相似文献   

7.
The Pranhita-Godavari Basin in central eastern India is one of the Proterozoic "Purana" basins of cratonic India.New geochronology demonstrates that it has a vast depositional history of repeated basin reactivation from the Palaeoproterozoic to the Mesozoic.U-Pb laser ablation inductively coupled plasma mass spectrometry dating of detrital zircons from two samples of the Somanpalli Group—a member of the oldest sedimentary cycle in the valley-constrains its depositional age to ~1620 Ma and demonstrates a tripartite age provenance with peaks at ~3500 Ma,~2480 Ma and ~1620 Ma,with minor age peaks in the Eoarchaean(~3.8 Ga) and at ~2750 Ma.These ages are consistent with palaeocurrent data suggesting a southerly source from the Krishna Province and Enderby Land in East Antarctica.The similarity in the maximum depositional age with previously published authigenic glauconite ages suggest that the origin of the Pranhita-Godvari Graben originated as a rift that formed at a high angle to the coeval evolving late Meosproterozoic Krishna Province as Enderby Land collided with the Dharwar craton of India.In contrast,detrital zircons from the Cycle III Sullavai Group red sandstones yielded a maximum depositional age of 970±20 Ma and had age peaks of ~2550 Ma,~1600 Ma and then a number of Mesoproterozoic detrital zircons terminating in three analyses at ~970 Ma.The provenance of these is again consistent with a southerly source from the Eastern Ghats Orogen and Antarctica.Later cycles of deposition include the overlying Albaka/Usur Formations and finally the late Palaeozoic to Mesozoic Gondwana Supergroup.  相似文献   

8.
Oldest rocks are sparsely distributed within the Dharwar Craton and little is known about their involvement in the sedimentary sequences which are present in the Archean greenstone successions and the Proterozoic Cuddapah basin.Stromatolitic carbonates are well preserved in the Neoarchean greenstone belts of Dharwar Craton and Cuddapah Basin of Peninsular India displaying varied morphological and geochemical characteristics.In this study,we report results from U-Pb geochronology and trace element composition of the detrital zircons from stromatolitic carbonates present within the Dharwar Craton and Cuddapah basin to understand the provenance and time of accretion and deposition.The UPb ages of the detrital zircons from the Bhimasamudra and Marikanve stromatolites of the Chitradurga greenstone belt of Dharwar Craton display ages of 3426±26 Ma to 2650±38 Ma whereas the Sandur stromatolites gave an age of 3508±29 Ma to 2926±36 Ma suggesting Paleo-to Neoarchean provenance.The U-Pb detrital zircons of the Tadpatri stromatolites gave an age of 2761±31 Ma to1672±38 Ma suggesting Neoarchean to Mesoproterozoic provenance.The Rare Earth Element(REE)patterns of the studied detrital zircons from Archean Dharwar Craton and Proterozoic Cuddapah basin display depletion in light rare earth elements(LREE)and enrichment in heavy rare earth elements(HREE)with pronounced positive Ce and negative Eu anomalies,typical of magmatic zircons.The trace element composition and their relationship collectively indicate a mixed granitoid and mafic source for both the Dharwar and Cuddapah stromatolites.The 3508±29 Ma age of the detrital zircons support the existence of 3.5 Ga crust in the Western Dharwar Craton.The overall detrital zircon ages(3.5-2.7 Ga)obtained from the stromatolitic carbonates of Archean greenstone belts and Proterozoic Cuddapah basin(2.7-1.6 Ga)collectively reflect on^800-900 Ma duration for the Precambrian stromatolite deposition in the Dharwar Craton.  相似文献   

9.
The occurrence of rhythmic layering of chromite and host serpentinites in the deformed layered igneous complexes has been noticed in the Nuggihalli schist belt (NSB) in the western Dharwar craton, Karnataka, South India. For this study, the chromitite rock samples were collected from Jambur, Tagadur, Bhakatarhalli, Ranganbetta and Byrapur in the NSB. Petrography and ore microscopic studies on chromite show intense cataclasis and alteration to ferritchromite. The ferritchromite compositions are characterized by higher Cr number (Cr/[Cr+Al]) (0.68–0.98) and lower Mg number (Mg/[Mg+Fe]) (0.33–0.82) ratios in ferritchromite compared to that of parent chromite. The formation process for the ferritchromite is thought to be related to the exchange of Mg, Al, Cr, and Fe between the chromite, surrounding silicates (serpentines, chlorites), and fluid during serpentinization.  相似文献   

10.
<正>Precambrian ophiolites are abundant in the ArabianNubian Shield of NE Africa and Arabia and range in age from 690 to 890 Ma.In Egypt,they are widely distributed in the central and southern Eastern Desert and occur as nape complexes along sature zone or dismembered masses in metavolcano-sedimenatry assemblages.The ophiolite  相似文献   

11.
Detailed mineralogical, bulk-rock geochemical and Sr-Nd isotopic data for the recently discovered Ahobil kimberlite (Pipe-16) from the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton (EDC), southern India, are presented. Two generations of compositionally distinct olivine, Ti-poor phlogopite showing orangeitic evolutionary trends, spinel displaying magmatic trend-1, abundant perovskite, Ti-rich hydrogarnet, calcite and serpentine are the various mineral constituents. On the basis of (i) liquidus mineral composition, (ii) bulk-rock chemistry, and (iii) Sr-Nd isotopic composition, we show that Ahobil kimberlite shares several characteristic features of archetypal kimberlites than orangeites and lamproites. Geochemical modelling indicate Ahobil kimberlite magma derivation from small-degree melting of a carbonated peridotite source having higher Gd/Yb and lower La/Sm in contrast to those of orangeites from the Eastern Dharwar and Bastar cratons of Indian shield. The TDM Nd model age (~2.0 Ga) of the Ahobil kimberlite is (i) significantly older than those (1.5–1.3 Ga) reported for Wajrakarur and Narayanpet kimberlites of EDC, (ii) indistinguishable from those of the Mesoproterozoic EDC lamproites, and (iii) strikingly coincides with the timing of the amalgamation of the Columbia supercontinent. High bulk-rock Fe-Ti contents and wide variation in oxygen fugacity fO2, as inferred from perovskite oxybarometry, suggest non-prospective nature of the Ahobil kimberlite for diamond.  相似文献   

12.
The petrology and geochemistry of some new occurrences of Mesoproterozoic diamondiferous hypabyssal-facies kimberlites from the Chigicherla, Wajrakarur-Lattavaram and Kalyandurg clusters of the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton (EDC), southern India, are reported. The kimberlites contain two generations of olivine, and multiple groundmass phases including phlogopite, spinel, calcite, dolomite, apatite, perovskite, apatite and rare titanite, and xenocrysts of eclogitic garnet and picro-ilmenite. Since many of the silicate minerals in these kimberlites have been subjected to carbonisation and alteration, the compositions of the groundmass oxide minerals play a crucial role in their characterisation and in understanding melt compositions. While there is no evidence for significant crustal contamination in these kimberlites, some limited effects of ilmenite entrainment are evident in samples from the Kalyandurg cluster. Geochemical studies reveal that the WKF kimberlites are less differentiated and more primitive than those from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton. Highly fractionated (La/Yb = 108–145) chondrite-normalised distribution patterns with La abundances of 500–1,000 × chondrite and low heavy rare earth elements (HREE) abundances of 5–10 × chondrite are characteristic of these rocks. Metasomatism by percolating melts from the convecting mantle, rather than by subduction-related processes, is inferred to have occurred in their source regions based on incompatible element signatures. While the majority of the Eastern Dharwar craton kimberlites are similar to the Group I kimberlites of southern Africa in terms of petrology, geochemistry and Sr–Nd isotope systematics, others show the geochemical traits of Group II kimberlites or an overlap between Group I and II kimberlites. Rare earth element (REE)-based semi-quantitative forward modelling of batch melting of southern African Group I and II kimberlite source compositions involving a metasomatised garnet lherzolite and very low degrees of partial melting demonstrate that (1) WKF and NKF kimberlites display a relatively far greater range in the degree of melting than those from the on-craton occurrences from southern Africa and are similar to that of world-wide melilitites, (2) different degrees of partial melting of a common source cannot account for the genesis of all the EDC kimberlites, (3) multiple and highly heterogeneous kimberlite sources involve in the sub-continental lithospheric mantle (SCLM) in the Eastern Dharwar craton and (4) WKF and NKF kimberlites generation is a resultant of complex interplay between the heterogeneous sources and their different degrees of partial melting. These observations are consistent with the recent results obtained from inversion modelling of REE concentrations from EDC kimberlites in that both the forward as wells as inverse melting models necessitate a dominantly lithospheric, and not asthenospheric, mantle source regions. The invading metasomatic (enriching) melts percolating from the convecting (asthenosphere) mantle impart an OIB-like isotopic signature to the final melt products.  相似文献   

13.
Tokapal kimberlite is the only well preserved crater facies kimberlite intruded within sedimentary sequence of Indravati basin in Bastar craton of central India. We present detailed petrographical and whole rock geochemical studies, carried out on ten samples collected from different locations from Tokapal kimberlite to constrain its genesis and also the mantle processes involved in the origin of this earlier characterized Group I kimberlite. Geochemical studies show that only SiO2 content and the mobile trace elements Ba, Sr, and K vary in the crater facies while rest others show restricted range and can be successfully used in evaluating the petrogenetic processes. Very low abundances of Rb (<2 ppm), Sr (<28 ppm), Ba (<52 ppm) and Cs (0.02–3 ppm) are observed which show possible effects of late-stage alteration rather than significant crustal contamination. The LREE enriched REE pattern, absence of positive Eu anomalies and HREE depletion also provide further additional evidence against crustal contamination considerably modifying magma composition. We infer the presence of less enriched (metasomatised) mantle source regions and comparatively greater degrees of partial melting responsible for the genesis of Tokapal kimberlite. Present study also suggests that crater facies Tokapal kimberlite intruding the Indravati basin, Bastar craton has a Group II kimberlite (orangeite) affinity. This finding is important in light of recent identification of Mainpur kimberlites of Bastar craton as orangeites.  相似文献   

14.
The Late Cretaceous (ca. 100 Ma) diamondiferous Fort à la Corne (FALC) kimberlite field in the Saskatchewan (Sask) craton, Canada, is one of the largest known kimberlite fields on Earth comprising essentially pyroclastic kimberlites. Despite its discovery more than two decades ago, petrological, geochemical and petrogenetic aspects of the kimberlites in this field are largely unknown. We present here the first detailed petrological and geochemical data combined with reconnaissance Nd isotope data on drill-hole samples of five major kimberlite bodies. Petrography of the studied samples reveals that they are loosely packed, clast-supported and variably sorted, and characterised by the presence of juvenile lapilli, crystals of olivine, xenocrystal garnet (peridotitic as well as eclogitic paragenesis) and Mg-ilmenite. Interclast material is made of serpentine, phlogopite, spinel, carbonate, perovskite and rutile. The mineral compositions, whole-rock geochemistry and Nd isotopic composition (Nd: + 0.62 to − 0.37) are indistinguishable from those known from archetypal hypabyssal kimberlites. Appreciably lower bulk-rock CaO (mostly < 5 wt%) and higher La/Sm ratios (12–15; resembling those of orangeites) are a characteristic feature of these rocks. Their geochemical composition excludes any effects of significant crustal and mantle contamination/assimilation. The fractionation trends displayed suggest a primary kimberlite melt composition indistinguishable from global estimates of primary kimberlite melt, and highlight the dominance of a kimberlite magma component in the pyroclastic variants. The lack of Nb-Ta-Ti anomalies precludes any significant role of subduction-related melts/fluids in the metasomatism of the FALC kimberlite mantle source region. Their incompatible trace elements (e.g., Nb/U) have OIB-type affinities whereas the Nd isotope composition indicates a near-chondritic to slightly depleted Nd isotope composition. The Neoproterozoic (~ 0.6–0.7 Ga) depleted mantle (TDM) Nd model ages coincide with the emplacement age (ca. 673 Ma) of the Amon kimberlite sills (Baffin Island, Rae craton, Canada) and have been related to upwelling protokimberlite melts during the break-up of the Rodinia supercontinent and its separation from Laurentia (North American cratonic shield). REE inversion modelling for the FALC kimberlites as well as for the Jericho (ca. 173 Ma) and Snap Lake (ca. 537 Ma) kimberlites from the neighbouring Slave craton, Canada, indicate all of their source regions to have been extensively depleted (~ 24%) before being subjected to metasomatic enrichment (1.3–2.2%) and subsequent small-degree partial melting. These findings are similar to those previously obtained on Mesozoic kimberlites (Kaapvaal craton, southern Africa) and Mesoproterozoic kimberlites (Dharwar craton, southern India). The striking similarity in the genesis of kimberlites emplaced over broad geological time and across different supercontinents of Laurentia, Gondwanaland and Rodinia, highlights the dominant petrogenetic role of the sub-continental lithosphere. The emplacement of the FALC kimberlites can be explained both by the extensive subduction system in western North America that was established at ca. 150 Ma as well as by far-field effects of the opening of the North Atlantic ocean during the Late Cretaceous.  相似文献   

15.
The northern part of the Nellore–Khammam schist belt and the Karimnagar granulite belt, which are juxtaposed at high angle to each other have unique U–Pb zircon age records suggesting distinctive tectonothermal histories. Plate accretion and rifting in the eastern part of the Dharwar craton and between the Dharwar and Bastar craton indicate multiple and complex events from 2600 to 500 Ma. The Khammam schist belt, the Dharwar and the Bastar craton were joined together by the end of the Archaean. The Khammam schist belt had experienced additional tectonic events at \(\sim \)1900 and \(\sim \)1600 Ma. The Dharwar and Bastar cratons separated during development of the Pranhita–Godavari (P–G) valley basin at \(\sim \)1600 Ma, potentially linked to the breakup of the Columbia supercontinent and were reassembled during the Mesoproterozoic at about 1000 Ma. This amalgamation process in southern India could be associated with the formation of the Rodinia supercontinent. The Khammam schist belt and the Eastern Ghats mobile belt also show evidence for accretionary processes at around 500 Ma, which is interpreted as a record of Pan-African collisions during the Gondwana assembly. From then on, southern India, as is known today, formed an integral part of the Indian continent.  相似文献   

16.
We report groundmass perovskite U–Pb (SIMS) ages, perovskite Nd isotopic (LA-ICPMS) composition and bulk-rock geochemical data of the Timmasamudram diamondiferous kimberlite cluster, Wajrakarur kimberlite field, in the Eastern Dharwar craton of southern India. The kimberlite pipes gave similar Mesoproterozoic ages of 1086 ± 19 Ma (TK-1, microcrystic variant) and 1119 ± 12 Ma (TK-3). However, a perovskite population sampled from the macrocrystic variant of TK-1 gave a much younger Late Cretaceous age of ca. 90 Ma. This macrocrystic kimberlite phase intrudes the Mesoproterozoic microcrystic phase and has a distinct bulk-rock geochemistry. The Nd-isotope composition of the ~ 1100 Ma perovskites in the cluster show depleted εNd(T) values of 2.1 ± 0.6 to 6.7 ± 0.3 whereas the ~ 90 Ma perovskites have enriched εNd(T) values of − 6.3 ± 1.3. The depleted-mantle (DM) model age of the Cretaceous perovskites is 1.2 Ga, whereas the DM model age of the Proterozoic perovskites is 1.2 to 1.5 Ga. Bulk-rock incompatible trace element ratios (La/Sm, Gd/Lu, La/Nb and Th/Nb) of all Timmasamudram kimberlites show strong affinity with those from the Cretaceous Group II kimberlites from the Bastar craton (India) and Kaapvaal craton (southern Africa). As the Late Cretaceous age of the younger perovskites from the TK-1 kimberlite is indistinguishable from that of the Marion hotspot-linked extrusive and intrusive igneous rocks from Madagascar and India, we infer that all may be part of a single Madagascar Large Igneous Province. Our finding constitutes the first report of Cretaceous kimberlite activity from southern India and has significant implications for its sub-continental lithospheric mantle evolution and diamond exploration programs.  相似文献   

17.
A number of limestone and metasomatised carbonate xenoliths occur in the 1,090 Ma Siddanpalli kimberlite cluster, Raichur kimberlite Field, Eastern Dharwar craton, southern India. These xenoliths are inferred to have been derived from the carbonate horizons of the Kurnool (Palnad) and Bhima Proterozoic basins and provide evidence for a connection between these basins in the geological past. A revised Mesoproterozoic age is proposed for the Bhima and Kurnool (Palnad) basins based on this kimberlite association and is in agreement with similar proposals made recently for the Chattisgarh and Upper Vindhyan sediments in Central India. The observed Bhima–Kurnool interbasinal uplift may have been caused by: (1) extension- or plume-related mafic alkaline magmatism that included the emplacement of the southern Indian kimberlites at ~1.1 Ga, (2) mantle plume-related doming of the peninsular India during the Cretaceous, or (3) Quaternary differential uplift in this region. It is not possible, with the currently available geological information to constrain the exact timing of this uplift. The deep erosion of primary diamond sources in the Raichur kimberlite Field in the upper reaches of the Krishna River caused by this uplift could be the elusive source of the alluvial diamonds of the Krishna valley. Mesoproterozoic sedimentary basins can host world class unconformity-type uranium deposits. In light of its inferred Mesoproterozoic age, a more detailed stratigraphic and metallogenic analysis of the Kurnool basin is suggested for uranium exploration.  相似文献   

18.
The Siddanpalli kimberlites constitute a newly discovered cluster (SKC) of Mesoproterozoic (1090 Ma) dykes occurring in the granite-greenstone terrain of the Gadwal area in the Eastern Dharwar Craton (EDC), Southern India. They belong to coherent facies and contain serpentinized olivines (two generations), phlogopite, spinel, perovskite, ilmenite, apatite, carbonate and garnet xenocrysts. A peculiar feature of these kimberlites is the abundance of carbonate and limestone xenoliths of the eroded platformal Proterozoic (Purana) sedimentary cover of Kurnool/Bhima age. Chemically, the Siddanpalli dykes are the most magnesium-rich (up to 35 wt.% MgO) and silica-undersaturated (SiO2?<?35 wt.%) of all kimberlites described so far from the Eastern Dharwar Craton. The La/Yb ratio in the Siddanpalli kimberlites (64–105) is considerably lower than that in the other EDC kimberlites (108–145), primarily owing to their much higher HREE abundances. Since there is no evidence of any crustal contamination by granitic rocks we infer this to be a specific character of the magmatic source. A comparison of the REE geochemistry of the Siddanpalli kimberlites with petrogenetic models for southern African kimberlites suggests that they display involvement of a wide range in the degree of melting in their genesis. The different geochemical signatures of the SKC compared to the other known kimberlites in the EDC can be explained by a combination of factors involving: (i) higher degrees of partial melting; (ii) relatively shallower depths of derivation; (iii) possible involvement of subducted component in their mantle source region; and (iv) previous extraction of boninitic magmas from their geological domain.  相似文献   

19.
The Archaean-Proterozoic Dharwar craton has many recorded occurrences of diamondiferous kimberlites. Reports of kimberlite emplacement in parts of the tectonically complex eastern Dharwar craton and a significant density contrast between kimberlites and the host peninsular gneisses motivated us to conduct gravity studies in the Narayanpet-Irladinne area of the eastern Dharwar craton. This region is contiguous with the Maddur-Narayanpet kimberlite that lies to its north, while the river Krishna lies to its south. From observed association of reported kimberlites in the Maddur-Narayanpet field with subsurface topography of the assumed three-layer earth section obtained by Bouguer gravity modelling, we developed a subsurface criterion for occurrence of kimberlites in the present study area. Using this criterion, five potential zones for kimberlite localization were identified in the Narayanpet-Irladinne region, eastern Dharwar craton.  相似文献   

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