granite suite of Lesser Himalaya, Pithoragarh District, Uttar P r a d e s h , by Shabbir Hussain et al., in the Jour. Geol. Soc. India, v. 44(1), pp. 17-25, 1994).
Comment
-
1
I appreciate the efforts by the authors to elucidate the stratigraphic status and geochemical characteristics of the Champawat granite. It renders support to my idea of continental collision environment for the emplacement of such granites in the ]Lesser Himalaya during its Late Proterozoic to Early Phanerozoic history as deduced from almost similar studies carried out for the Ranga Valley granitoids of Arunachal Himalaya where extensive studies were carried out by me over a decade. However, a serious error has been noted in this paper and which needs to be clarified and corrected. The authors have used a term 'Great Boundary Fault' (GBF) which instantaneously conveys the meaning of the tectonic plane between the Vindhyan Supergroup and the Hindoli Group in the western Rajasthan. In fact it should have been 'Main Boundary Fault' (MBF).
A -51, Triveni Nagar, Jaipur-302 01 8. SURENDRA SINGH
Our paper is about Himalayan granite and therefore the Great Boundary Fault mentioned inadvertently in the text of our paper refers to the Main Boundary Fault only
(please see inset figure of Figure-1 (p. 18) of our paper where it has been shown as Main Boundary Fault).
Comment
-
2
In an article in the Jour. Geol. Soc. India vol. 42(3), 1993, pp. 289-302, B.N. Singh
et al., have characterised the Champawat granite of Pithoragarh district in Uttar Pradesh, as
"A "- type. In the paper by Shabbir Hussain eta/., (1994)' the lateral continuity of the same Champawat granite in the same district is characterised as "S"- type. Such sharp shift in characterisation of one single formation with the aid of identical parameter, namely geochemistry, poses veritable challenge for researches in geoscience, especially to the forthcoming generations. The authors of both the above-mentioned papers should interact and strike a consensus on this fundamental issue, since strategies for exploratory work relating to the search for Nb-Ta, Sn, W and other vital minerals would hinge on this characterisation.
Geological Survey of India, Bandlaguda, Hyderabad 500 068
T.M. BABU
360 DISCUSSION
corundum, absence of normative alkali-metasilicates and acmite, low total Zr+Ce+ Y + Nb) it would belie their interpretation of Champawat granite as A-type and these chemical parameters favour it to be a S-type granite. We could not refer Singh et al., (1993) in our paper because of the time overlap during the publication process of these two papers. Our paper has a stronger field, petrographic and geochemical data base (it is not the geochemistry alone as commented by Babu) to show that the Champawat granite is not only as-type granite but is related to a collisional accretionary history
or
the region. Such tectonic environment for the evolution of the Lesser Himalayan granite is rather common (Pitcher, 1982; S.Singh, in the comment - 1 of our paper, see above).In most scientific enquiries conclusions are made on the basis of interpretation of a set of data and seldom such conclusions are dependent on consensus. It is to the researchers and exploration geologists who opt to pursue this problem further to study all the published work, verify the facts, if necessary, and arrive at their own conclusions.
References
PITCHER, W.S. (1982). Granite types and tectonic environment, In: KJ. Hsu (ed.) Mountain Building Processes.
London, Academic Press, pp. 19-40. .
SINGH, B.N., GOEL, O.P., JOSHl, M. and SHERATON, J.W. (1993). Geochemistry and petrogenesis of the Champawat granitoids occurring around Dhunaghat, District Pithoragarh, 'Uttar Pmdesh, India. Jour. Geol. Soc. India, v.
42, pp. 289-302.
SINGH, B.N., GaEL, O.P., JOSHI, M. and SHERATON, J.W. (1994). Reply on the paper "Geochemistry and petrogenesis· of the Champawat granitoids occurring around Dhunaghat, District Pithoragarh, Uttar Pradesh, India. Jour.
Geot. Soc. India, v. 43, pp. 211-212. .
Comment-3
We appreciate the new data on the Cambrian Champawat Granitoids (CCG) by Hussain et aI., (1994). The conclusions of Hussain et al., are at variance with those of Singh
et al .• (1991. 1993). We suggest that a clear picture for the genesis of the CCG merits the consideration of the following points.
1. The lithotectonic succession of the Almora Group of rocks stands rationally and . preCisely classified by Valdiya (1980) intolhe medium to high grade metasediments (Singh
et al., 1993) of the Saryu Formatiqn and the low-grade metapelites of the Gumalikhet Formation with the CCG intruded in between (Valdiya, 1980, Singh et at., op. cit.).
2. The augen gneisses shown at the southern contact of the CCG (Fig. 1; Hussain et
al., 1994) are actually mylonites (Singh et al., 1993) which are less conspicuous along the
. northern contact with the Gumalikhet Formation. This observation is consistent with the intrusive nature of the CCG.
3. Firstly, we do not agree with their geological map which shows their augen gneisses grading into the CCG and secondly this information, if correct, contradicts the Rb-Sr date of 560±20 Ma (Trivedi et al., 1984) for the Champawat Granodiorite ,(biotite-rich granitoids of Singh et al.~ 1991, 1993) and of 1820±130 Ma for the Almora gneisses (Tri vedi
et al., 1984). How do rocks with such temporal diversity show gradational contact (Hussain
-et al., 1994, p. 17). . .
4. Under what circumstances does a concordantly emplaced intrusive body (Val di ya, 1980; Singh et al., 1991, 1993; Hussain et al., 1994) show a gradational contact at the southern margin (Hussain et al., 1994, p. 17)?
5. Many studies (eg. Vernon et al., 1988; Didier and Barbarin, 1991) suggest that unless mechanism (s) suitably explaining the distribution of country rock xenoliths (other than restitic material) are defined, the xenoliths must be confined to the peripheral parts of the batholith. However; the mechanism by which the so-called xenoliths of country rocks
are found distributed throughout the entire CCG plutonic body has not been described by Hussain et al .. , (1994).
. 6. According to Singh et al., (1993) the CCG shows geochemical affinities to 'A'-type (anorogenic) granites. Further, it has also been noted that reported mafic magmatic enclaves (MME) are relatively more alkaline than the host CCG (Singh et al., op cit.). We .
feel that the major element chemistry should not be the sole criteria to describe and designate granite types and their 'tectonic environment.
Geology Laboratory, Dept. o/Civil Engineering,
Institute o/Technology, Banaras Hindu University, Varanasi-22/005.
Department o/Geology, Science Faculty, Banaras Hindu University, Varanasi-22/005.
References
B.N. SINGH MALLICKARJUN 10SI;II
SANTOSH KUMAR
DIDIER, l. and BARBARlN, B. (1991). Enclaves and granite petrology. Elsevier (Amsterdam), 600 p.
HUSSAIN SHABBIR, RAJU, S., DAYAL, B. and FAREEDUDDIN (1994). Petrochemistry and tectonic setting of the Champawat Granite Suite of Lesser Himalaya, Pithoragarh District, Uttar Pradesh. lour. Geol. Soc. India, v. 44, pp. 17-25.
SINGH, B.N., Goa, O.P. and lOSHI MALLICKARJUN (1991). Chemical- mineralogical classification of granitoid rocks: A case study from Dhunaghat area of Kumaun Lesser Himalaya. Bull. Ind., Geologists Assoc., Chandigarh, v. 24(2), pp.
SINGH B.N., GOEL, O.P.:IOSHI MALLICKARJUN and SHERATON, l.W. (1993). Geochemistry and petrogenesis of the Champawat granitoids occurring around Dhunaghat, District Pithoragarh, Uttar Pradesh, India. Jour. Geol. Soc. Ind., v. 42, pp. 289-302.
TRIVEDI, 1.R., GOPALAN, K. and VALDIYA, K.S. (1984). Rb-Sr ages of granitic rocks within the Lesser Himalayan Nappes, Kumaun, India. Jour. Geol. Soc. Ind., v. 25, pp. 641-654.
VALDIYA, K.S. (1980). Geology of Kumaun Lesser Himalaya. Wadia Institute of Himalayan Geology, Dehradun,
p.291. .
VERNON, R.H., ETIlERIDGE, M.A. and WALL, VJ. (1988). Shape and microstructure of microgranitoid enclaves: indicators of magma mingling and flow. Lithos, v. 22, pp. 1-11.
Reply
1. The phyllites and quartzites occurring on the southern and the northern side of the Champawat Granite Suite (CGS) have been classified as Gumalikhet and Saryu Formations by Valdiya (1980) while as Gorakhnath and Gumalikhet Formations by Sharma and A wasthi (1980). Our mapping has indicated that these metasediments which occur at upper level of the Almora Synform represent same stratigraphic horizons. The radiometric ages of the region suggest that all the sequences' in this region of Lesser Himalaya are parts of an undivided succession of once continuous sheet of metasediments (Trivedi et ai., 1984, p. 651, para 3, lines 1-5). Since there is neither a structural nor geochronological backing for the reported precise classification, we have presented in our paper the lithotectonic succession of the study area without adopting the formal nomenclatures of the earlier workers.
2. Thin strips of augen gneisses occur between CGS and metasediments. They have been identified after careful field and petrological studies. Although at several places augen gneisses are sheared,but the ductile deformation is not as intense as to classify this unit as mylonites. Trivedi et ai., (1984) have reported this unit as augen gneisses and all other earlier workers as gneissose granites (for references see Singh et al., 1993).
3. Sharma and Awasthi (1980), Rajan and Saxena (1974) and Saxena (1975, 1976) have reported that the CGS contact with augen gneisses is gradational. Our studies indicated that it is gradational and migmatized. It is not correct to state that these two units show a great temporal diversity. The 1820 ± 130 Ma old augen gneiss, as reported by Trivedi et ai.,
362 DISCUSSION
(1 984), occur towards north of Almora Group new North Almora thrust. Another strip of 1765 2 60 Ma old granite gneiss occurs near Rarngarh thrust. Both these units occur far away ,
from the study area (PI. see maps in our paper and Trivedi et al., paper). We have reported gradational and rnigrnatized contact of the porphyritic biotite granite phase of the CGS with augen gneiss that occur immediately to the south of the former. Trivedi et al., (p. 647, lines 1 1 - 16) have given model ages of 550 to 700 Ma for similar augen gneisses which occur near
southern border zone of Almora Nappe near Dhaun.
4. The reason for this type of contact relationship may be the one suggested by . Sharrna and Awasthi (1980) i.e. anataxis of metasedimentary protoliths (found as xenoliths
and feldspathic schists) along the southern contact zone by the quartzofeldspathic mobilizates. Further our studies (I-iussain et al., p. 24) have suggested that temperature of crystallizing melt was not constant at all places which usually happens in the process sf anataxis. The contact therefore is gradational in terms of intensity of anatexis and rnigmatized in terms of
abundance of palaeosomatic material along this zone.
5. In our paper nowhere have we mentioned that the xenoliths occur throughout the CGS. It is rather difficult to isolate core and margins in the CGS because in the narrow, linear composite intrusion (average width 3-4 km) with at least four mappable granite phases, a margin of one intrusive phase could be a core to another phase.
6. For "A" versus " S' ' type granite controversy please see reply to Babu's comment. The xenoliths (including MME of Singh et al., 1993) are extensively granitized (also see Sharrna and Awasthi, 1980, p. 27), and therefore tend to be richer in alkalies. They should
not be mistaken
for
true alkaline rocks. We subscribe to this idea of Singh et al., that more data is necessary to narrow down the differences onCGS.
Geological Survey of India, Jhlam Dungri,
Jaipur.
Geological Survey of lndia, A liganj,
Luck~zow.
References
RAIAN, T.N. and S ~ AA. (1974). Geology of parts of Champawat-Lohaghat , area, district Pithoragarh, U.P., Unpublished Progress Report of GSI, F.S. 1973-74.
SAXENA, A. (1975). The geology of parts of Champawat Tehsil area, dismct Pithoragarh, U.P. Unpublished Progr-e s report of GSI for F.S., 1974-75.
(1976). Geology of parts of Champawat Tehsil, district Pithoragarh, U.P. Unpublished progress report of GSI for F.S. 1975-76.
SINGH, B.N., GOEL, O.P., JOSH MUICKARSUN and SHERAMN, J.W. (1993). Geochemistry, and petrogenesis of the Champawat granjtoids occurring around Dhunaghat, district Pithoragarh, Uttar Pradesh India. Jour. Geol. Soc.
Ind., v. 42, pp. 289-302.
SHARMA, R.P. and A W A ~ I , S.D. (1980). Petrography of Champawat granite granodiorite rocks of Almora Group, I ~ s s e r Kumaun Himalaya, Indian Mineralogist, v. 21, (1) pp. 21-37.
TRIVEDI, J.R., GOPMAN, K. and VALDIYA, K.S. (1984). Rb-Sr ages of granitic rocks within the Lesser Himalayan Nappes, Kumaun, India. Jour. Geol. Soc. Iird., v. 25, pp. 641-654.
COLOMBIA
Our readers will be interested to know that gold is being degassed and deposited at Galeras Volcar)~, Columbia. According to a report in GSA Today (vo1.4, No. 10, October 1994) analysis of hydrothemally altered rocks, vein ore, 1992-93 andesite, 200-300°C fumerole sublimates show that Galeras Volcano has deposited Au in past hydrothermal events and that solidified andesite and magmatic volatiles contain Au at levels of about 0.015 mgkg and 0.04 m&g respectively. The high sulfidation hydrothermal environment around the magma conduit appears to have provided favourable condition to depositing of Au, Cu and other metals. It is estimated that the Galeras Volcano is releasing 0.5 kg/d Au to the atmosphere and is probably depositing 0.06 kg/d (>20 kg/yr) Au inside the volcanic edifice.
If such flux rates remained continuous it is pointed out a moderate sized precious-metal deposit (>200 t contained Au) would form in only 10 ka.
The report should be of interest to all those engaged in gold exploration. Volcanogenic sulphide facies iron formation should be special target of exploration for Au.
-
B.P.R.CONTROLS
OF
METAMORPHISM 1994The international conference on 'Controls of Metamorphism' 1994 was held at the Department of Earth Sciences, University of Liverpool, from 12- 14th September 1994, marking the thirtieth anniversary of the first conference held at the same place with the same title.
Keynote addresses were delivered on the following aspects.
Controls on porphyroblast nucleation and growth
(W.D.
Carlson,,C. Denison and R. Ketcharn)Mechanistic interactions between deformation and metamorphism (E.H. Rutter and
K. Bordie).
The characterisation of ultra-high temperature metamorphism (S.L. Harley) Metamorphic CO, emission from active metamorphism
(D.M.
Kerrick) Rate and time controls on metamorphic processes (D. Vance)Integrated petrologic and kinematic constraints on orogenic-scale interplay between collison, extension, and metamorphism (J. Selverstone).
These instructive and marvellous keynote lectures are not just state-of-the-art reports, but provided superb guidelines to future directions
of
research, giving a glimpse of the emerging challenges.Due to constraints on space, brief abstracts of only a limited number of the presentations are given below:
