Mineralogy of the P2-West ‘Kimberlite’, Wajrakarur kimberlite field, Andhra Pradesh, India: kimberlite or lamproite?

2013 ◽  
Vol 77 (8) ◽  
pp. 3175-3196 ◽  
Author(s):  
Gurmeet Kaur ◽  
R. H. Mitchell
Keyword(s):  
Andhra Pradesh ◽  
Evolutionary Trend ◽  
Evolutionary Trends ◽  
Similar Material ◽  
Alkaline Rocks ◽  
Fine Grained ◽  
Hypabyssal Kimberlite ◽  
Bona Fide ◽  
Kimberlite Field ◽  
Representative Material

AbstractA detailed mineralogical examination of representative material from the P2-West 'kimberlite' located in the Wajrakarur Kimberlite Field (India) demonstrates that significant differences exist between these rocks and archetypal hypabyssal kimberlite. The intrusion consists of an olivine-phyric facies which has been transected by, and includes clasts of, a consanguineous phlogopite-rich pegmatitic facies. The olivine-rich parts of P2-West are relatively fresh and consist of euhedral-to-subhedral microphenocrystal olivine set in a groundmass of fine-grained anhedral monticellite, amoeboid apatite, and subhedral-to-euhedral perovskite within a partially chloritized-to-fresh phlogopite-rich mesostasis. The rock lacks the abundant olivine macrocrysts characteristic of kimberlite. Monticellite crystals are commonly partially or completely replaced by pectolite and hydrogarnet. Similar material occurs as irregular aggregates randomly scattered throughout the groundmass. The groundmass, in contrast to that of hypabyssal kimberlites, is relatively poor in spinels. Atoll spinels are absent, with the majority of spinels occurring principally as mantles upon microphenocrystal olivine. Disaggregated cumulate-like assemblages of intergrown anhedral perovskite and spinel are common. Spinel compositions are unlike those of kimberlites and their evolutionary trend is similar to that of lamproite and lamprophyre spinels. The pegmatitic facies of the intrusion are highly and pervasively altered, and characterized by the presence of large clasts, veins, and irregular aggregates consisting of large (1–5 mm) crystals of pinkish-bronze Al-poor phlogopite intergrown with and/or including: apatite; pectolite-hydrogarnet pseudomorphs after an unidentified euhedral phase; chlorite laths; barytolamprophyllite; perovskite; tausonite; diverse Sr-Ba-carbonates; and baryte. The presence of barytolamprophyllite and tausonite are typical of potassic undersaturated alkaline rocks and have never been reported from kimberlite; however, neither feldspar nor feldspathoids are present in P2-West. Micas in fresh and altered rocks are Al2O3- and BaO-poor, and exhibit compositional evolutionary trends towards tetraferriphlogopite rather than kinoshitalite. On the basis of these mineralogical data it is suggested that P2-West represents an unusual lamproite-like intrusion which has undergone extensive hydrothermal deuteric alteration and should not be considered a bona fide kimberlite.

The Churchill kimberlite field, Nunavut, Canada: petrography, mineral chemistry, and geochronology

2008 ◽  
Vol 45 (9) ◽  
pp. 1039-1059 ◽  
Author(s):  
S. E. Zurevinski ◽  
L. M. Heaman ◽  
R. A. Creaser ◽  
P. Strand
Keyword(s):  
North America ◽  
Mantle Plume ◽  
Electron Microprobe ◽  
Mineral Chemistry ◽  
Eastern North America ◽  
Hudson Bay ◽  
Continental Extension ◽  
Group I ◽  
Hypabyssal Kimberlite ◽  
Kimberlite Field

Seventy-nine kimberlite intrusions have been identified in the Churchill Province, Nunavut, the result of an aggressive diamond exploration program by Shear Minerals Ltd. and their partners. This is one of Canada’s newest and largest kimberlite districts, situated immediately west of Hudson Bay between the communities of Rankin Inlet and Chesterfield Inlet. This study documents the occurrence of bonafide kimberlite rocks, classified as mainly sparsely macrocrystic, oxide-rich calcite evolved hypabyssal kimberlite and macrocrystic oxide-rich monticellite phlogopite hypabyssal kimberlite. Electron microprobe analyses of olivine, phlogopite, spinel, and perovskite support this petrographical classification. Low 87Sr/86Sr isotopic compositions determined from perovskite indicate a group I affinity. In addition, 27 precise U–Pb perovskite and Rb–Sr phlogopite emplacement ages have been determined for the Churchill kimberlites, indicating that magmatism spans ∼45 million years (225–170 Ma). The Churchill kimberlites belong to the NW–SE-trending corridor of Jurassic–Triassic kimberlite magmatism in eastern North America, which includes the Kirkland Lake, Timiskaming, and Attawapiskat kimberlite fields. Churchill kimberlites extend this corridor ∼800 km northwest, suggesting that the corridor may continue northwest with older kimberlites. This corridor is interpreted as the continental expression of magmatism linked to either a single or multiple mantle-plume hotspot track(s), a pattern geographically coincident with independent estimates for the timing and location of the continental extension of both the Great Meteor and Verde hotspot tracks.

Three compositional varieties of perovskite from kimberlites of the Lac de Gras field (Northwest Territories, Canada)

2001 ◽  
Vol 65 (1) ◽  
pp. 133-148 ◽  
Author(s):  
A. R. Chakhmouradian ◽  
R. H. Mitchell
Keyword(s):  
High Pressures ◽  
Compositional Variation ◽  
Type I ◽  
Evolutionary Trend ◽  
Type Ii ◽  
Type Iii ◽  
Composition I ◽  
End Members ◽  
Textural Evidence ◽  
Kimberlite Field

AbstractIn hypabyssal and crater-facies kimberlites of the Lac de Gras kimberlite field, perovskite occurs as reaction-induced rims on earlier-crystallized Ti-bearing minerals (magnesian ilmenite and priderite), inclusions in atoll spinels and discrete crystals in a serpentine-calcite mesostasis. The mineral is associated with spinels, apatite, monticellite, phlogopite, baryte, Fe-Ni sulphides, ilmenite, diopside and zircon. Uncommon accessory phases found in an assemblage with perovskite include titanite, monazite- (Ce), witherite, strontium-apatite, khibinskite, djerfisherite, wollastonite, pectolite, suolunite, hydroxyapophyllite and bultfonteinite. Three types of perovskite can be distinguished on the basis of composition: (I) REE-Nb-Al-poor perovskite with relatively high Sr and K contents (up to 2.2 and 0.6 wt.% oxides, respectively) occurring as mantles on priderite and inclusions in atoll spinels; (II) perovskite with elevated Al, Fe, Nb and LREE (up to 1.4, 8.3, 9.1 and 17.0 wt.% oxides, respectively) found as discrete crystals and rims on macrocrystic ilmenite; (III) perovskite significantly enriched in Na, Sr, Nb and LREE (up to 3.3, 3.4, 13.0 and 22.6 wt.% oxides, respectively) found as rims on perovskite I and II. The overwhelming majority of perovskite is represented by discrete crystals of type II. In some occurrences, this type of perovskite also has high Th contents (up to 5.5 wt.% ThO2) and Zr contents (up to 3.7 wt.% ZrO2). Textural evidence indicates that perovskite shows an overall evolutionary trend from the most primitive type I towards type III showing the highest Na, Nb and LREE contents. Perovskite of type I probably crystallized under relatively high pressures prior to the precipitation of MUM spinels. Perovskite II crystallized after magnesiochromite, pleonaste and MUM (magnesian ulvöspinel-magnetite) spinels, under increasing fO2. The most compositionally evolved type III formed during near-solidus re-equilibration of the earlier-crystallized perovskite. The compositional variation of the Lac de Gras perovskite can be adequately characterized in terms of five major end-members: CaTiO3 (perovskite), CeFeO3, NaNbO3 (lueshite), Na0.5LREE0.5TiO3 (loparite), and CaFe0.5Nb0.5O3 (latrappite).

Mineralogy and 40Ar/39Ar geochronology of orangeites (Group II kimberlites) from the Damodar Valley, eastern India

1998 ◽  
Vol 62 (3) ◽  
pp. 313-323 ◽  
Author(s):  
Ray W. Kent ◽  
Simon P. Kelley ◽  
Malcolm S. Pringle
Keyword(s):  
Western Australia ◽  
Southern Africa ◽  
Igneous Rocks ◽  
Stability Field ◽  
Eastern India ◽  
Alkaline Rocks ◽  
Damodar Valley ◽  
Bona Fide ◽  
Group Ii ◽  
The Stability

AbstractA suite of ultramafic-mafic alkaline igneous rocks in the Damodar Valley, eastern India, contains carbonate, phosphate and titanate minerals that are not characteristic or common in minettes or lamproites, but are typical of orangeites (Group II kimberlite) from southern Africa. Phlogopite grains from the Damodar alkaline rocks yield mean 40Ar/39Ar ages of 116.6±0.8 Ma, 113.5±0.5 Ma and 109.1±0.7 Ma (1σ errors) using laser dating techniques. These ages are similar to the Rb-Sr ages of African orangeites, which lie mostly in the range 121 to 114 Ma. Prior to this study, only one possible occurrence of orangeite (the ∼820 m.y.-old Aries pipe, Western Australia) was known outside the Kaapvaal craton and its environs. If the Damodar alkaline rocks are bona fide orangeites, it is likely that they were generated at depths of >150 km, within the stability field of diamond.

Petrology of Alkaline Rocks from Cuttingsville and the Shelburne Peninsula; Vermont

1973 ◽  
Vol 10 (8) ◽  
pp. 1244-1256 ◽  
Author(s):  
R. Laurent ◽  
T. C. Pierson
Keyword(s):  
Olivine Basalt ◽  
Coarse Grained ◽  
Basalt Magma ◽  
Uppermost Mantle ◽  
Alkaline Granite ◽  
Quartz Syenite ◽  
Thermal Plumes ◽  
Alkaline Rocks ◽  
Fine Grained ◽  
Sedimentary Sequences

The Cuttingsville composite stock has feldspathoid-bearing and quartz–bearing alkaline rocks emplaced in Precambrian schists of the Green Mountains. The main intrusions are, from oldest to youngest: (1) hastingsite foyaite and biotite foyaite, (2) diorite, (3) essexite, porphyritic essexite, plagifoyaite, and sodalite foyaite, (4) alkaline quartz syenite, (5) dikes of tephritic phonolite porphyry, phonolite porphyry, and microplagifoyaite. The K–Ar ages of 100 m.y. on the hastingsite foyaite and of 96.4 m.y. on the essexite indicate that this intrusion is perhaps the youngest manifestation of magmatic activity in New England.In the Shelburne peninsula, the alkaline rocks are intrusive into the Paleozoic sedimentary sequences of the Champlain Valley; they crop out on opposite sides of Lake Champlain. Intrusions consist of small stocks of alkaline syenite grading from a coarse-grained core to a fine-grained quartzose margin, which is cut by dikes of alkaline granite aplite, and of sills of trachyte porphyry. The alkaline rocks of the Shelburne peninsula are analogous to the alkaline syenites of unit 4 in Cuttingsville.We conclude that the rocks described did not originate through differentiation of an alkaline olivine basalt magma. Instead, partial and progressive melting of gabbroic phases in the uppermost mantle is proposed to account for the chemical relationships suggesting a source within the mantle. The absence of large amounts of mafic rocks, the order of emplacement which does not correlate with fractionation trends, and the presence of two syenitic melts of contrasted composition are evidences to support the proposal. Partial melting could have been caused by passage of the lithosphere over thermal "plumes" in the lower mantle.

The petrology and geochemistry of intrusive alkaline rocks of Elchuru, Prakasam District, Andhra Pradesh, India

2007 ◽  
Vol 19 (1) ◽  
pp. 57-76 ◽  
Author(s):  
S. Nag ◽  
P. S. Chakravorty ◽  
T. E. Smith ◽  
C. H. Huang
Keyword(s):  
Andhra Pradesh ◽  
Alkaline Rocks ◽  
Petrology And Geochemistry

scholarly journals Prismatine and ferrohögbomite-2N2S in granulite-facies Fe-oxide lenses in the Eastern Ghats Belt at Venugopalapuram, Vizianagaram district, Andhra Pradesh, India: do such lenses have a tourmaline-enriched lateritic precursor?

2003 ◽  
Vol 67 (5) ◽  
pp. 1081-1098 ◽  
Author(s):  
E. S. Grew ◽  
A. T. Rao ◽  
K. K. V. S. Raju ◽  
C. Hejny ◽  
J. M. Moore ◽  
...  
Keyword(s):  
South Africa ◽  
Andhra Pradesh ◽  
Granulite Facies ◽  
Eastern Ghats ◽  
Dehydration Melting ◽  
Fe Oxide ◽  
Eastern Ghats Belt ◽  
Fine Grained ◽  
Distinctive Type ◽  
Ultrahigh Temperature

AbstractFluorine-rich prismatine, (□,Fe,Mg)(Mg,Al,Fe)5Al4(Si,B,Al)5O21(OH,F), with F/(OH+F) = 0.36–0.40 and hercynite are major constituents of a Fe-Al-B-rich lens in ultrahigh-temperature granulite-facies quartz-sillimanite-hypersthene-cordierite gneisses of the Eastern Ghats belt, Andhra Pradesh, India. Hemo-ilmenite, sapphirine, magnetite, biotite and sillimanite are subordinate. Lithium, Be and B are concentrated in prismatine (140 ppm Li, 170 ppm Be, and 2.8 –3.0 wt.% B2O3). Another Fe-rich lens is dominantly magnetite, which encloses fine-grained zincian ferrohögbomite-2N2S, (Fe2+,Mg,Zn,Al)6 (Al,Fe3+,Ti)16O30(OH)2, containing minor Ga2O3 (0.30 –0.92 wt.%). Fe-Al-B-rich lenses with prismatine (or kornerupine) constitute a distinctive type of B-enrichment in granulite-facies rocks and have been reported from four other localities worldwide. A scenario involving a tourmalineenriched lateritic precursor affected by dehydration melting is our preferred explanation for the origin of the Fe-Al-B-rich lenses at the five localities. Whole-rock analyses and field relationships at another of these localities, Bok se Puts, Namaqualand, South Africa, are consistent with this scenario. Under granulite-facies conditions, tourmaline would have broken down to give kornerupine-prismatine (±other borosilicates) plus a sodic melt containing H2O and B. Removal of this melt depleted the rock in Na and B, but the formation of ferromagnesian borosilicate phases in the restite prevented total loss of B.

scholarly journals Assessing the Spatiotemporal Evolution of Anthropogenic Impacts on Remotely Sensed Vegetation Dynamics in Xinjiang, China

2021 ◽  
Vol 13 (22) ◽  
pp. 4651
Author(s):  
Jingyun Guan ◽  
Junqiang Yao ◽  
Moyan Li ◽  
Jianghua Zheng
Keyword(s):  
Human Activities ◽  
Vegetation Dynamics ◽  
Anthropogenic Impacts ◽  
Stepwise Multiple Regression ◽  
Anthropogenic Factors ◽  
Vegetation Changes ◽  
Evolutionary Trend ◽  
Evolutionary Trends ◽  
The World ◽  
The Impact

The dynamics of the ecosystem represented by vegetation under the influence of human activities have become an important issue in the study of the regional ecological environment. Xinjiang is one of the most ecologically fragile areas in the world, and vegetation changes have received extensive attention. Xinjiang is one of the most ecologically fragile areas in the world, and vegetation changes have received extensive attention. However, the spatiotemporal patterns and evolutionary trends of anthropogenic impacts on vegetation dynamics in Xinjiang are still unclear. In this study, the anthropogenic impacts on vegetation dynamics were quantitatively assessed by combining the improved normalized difference vegetation index (NDVI) prediction model and the residual analysis method in Xinjiang, China. The human driving factors were analyzed with the support of a stepwise multiple regression model for vegetation changes at the county scale. Based on trend analysis and the Hurst exponent, the spatiotemporal characteristics and evolutionary trends of the impact of human activities on vegetation change were discussed. The results show that (1) the NDVI values in Xinjiang showed a gradually increasing trend at a rate of 0.005/10 years from 1982 to 2018, and the vegetation dynamics mainly showed significant improvements (57.09% of the vegetated areas), especially for crops. (2) The anthropogenic effects of vegetation changes in Xinjiang mainly included positive impact increases (43.22% of the vegetated areas) from 2000 to 2018. Human activities promoted the increase in the NDVI of various vegetation types. Both the positive and negative impacts of human activities increased over the study period, and the growth rate of the positive influence (0.08%/10 years) was higher than that of the negative influence (0.04%/10 years). (3) The cultivated area, GDP of primary industry, and population are the main anthropogenic factors causing the increase in NDVI, which dominate the vegetation greening in 30.34%, 29.22%, and 28.09% of the counties in Xinjiang, respectively. The animal husbandry population, agricultural population, and livestock number are the main anthropogenic factors causing the decrease in NDVI, which dominate the vegetation degradation in 23.60%, 21.35%, and 17.98% of the counties in Xinjiang, respectively. (4) The evolutionary trend of the anthropogenic impact on vegetation dynamics in Xinjiang will be dominated by anti-persistence (53.84% of the vegetated areas), thereby mainly showing that the positive impacts continued to increase (22.56% of the vegetated areas), especially for crops, shrubs, grasslands, and alpine vegetation. Our results are helpful in understanding the characteristics and evolutionary trends of vegetation changes in arid areas caused by human activities and are of significance as a reference for policymakers to appropriately adjust policy guidance in a timely manner to promote the protection and sustainable development of fragile ecosystems.

scholarly journals Rapid Multi-Sensor Feature Fusion Based on Non-Stationary Kernel JADE for the Small-Amplitude Hunting Monitoring of High-Speed Trains

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3457 ◽  
Author(s):  
Jing Ning ◽  
Mingkuan Fang ◽  
Wei Ran ◽  
Chunjun Chen ◽  
Yanping Li
Keyword(s):  
Small Amplitude ◽  
High Speed ◽  
Feature Fusion ◽  
Evolutionary Trend ◽  
Fusion Method ◽  
Evolutionary Trends ◽  
Vibration Signals ◽  
Bearing Fault ◽  
High Speed Trains

Joint Approximate Diagonalization of Eigen-matrices (JADE) cannot deal with non-stationary data. Therefore, in this paper, a method called Non-stationary Kernel JADE (NKJADE) is proposed, which can extract non-stationary features and fuse multi-sensor features precisely and rapidly. In this method, the non-stationarity of the data is considered and the data from multi-sensor are used to fuse the features efficiently. The method is compared with EEMD-SVD-LTSA and EEMD-JADE using the bearing fault data of CWRU, and the validity of the method is verified. Considering that the vibration signals of high-speed trains are typically non-stationary, it is necessary to utilize a rapid feature fusion method to identify the evolutionary trends of hunting motions quickly before the phenomenon is fully manifested. In this paper, the proposed method is applied to identify the evolutionary trend of hunting motions quickly and accurately. Results verify that the accuracy of this method is much higher than that of the EEMD-JADE and EEMD-SVD-LTSA methods. This method can also be used to fuse multi-sensor features of non-stationary data rapidly.

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