Origin of Granitoid Rocks Amines and Secretory Pathways

=NA=TU=R=E-'-VO-=-=L'-'--'.3:..:..:05'--'1C...::S=EPT-=-=E=M=BE=R--=.:19:...:..:83'------MATIERS ARISING------~73

Origin of granitoid rocks I have no argument with the overall We fully concur with Dr Moorbath in isotopic conclusions of Clayburn et al. 1 his criticisms of indiscriminate grouping CLAYBURN ET AL. 1 have recently stated that the granitoid rocks of the Etive of petrogenetically different granitoids by 2 4 that "Moorbath has presented Pb-Sr Igneous Complex, ranging from calc Allegre and Othman , but, again, we were isotopic evidence that a mantle com alkaline to granitic types, were produced only concerned to draw attention to ponent is present in granitic rocks of all as a result of melting of both contem diverse views, however securely (or other ages, a feature which can be considered porary mantle and lower continental wise) founded. It remains of significance indicative of continuous primary con crust, or with their interpretation that the that our conclusions for the Etive Igneous tinental accretion". This is an uninten process represents combined primary Complex, which is of undoubtedly calc tional partial misrepresentation of my crustal growth coupled with assimilation alkaline parentage, recognize an appreci views on this subject, which have also of older stabilized continental crust. able (though difficult to quantify) com been misquoted in other recent papers. This type of situation is currently being ponent derived from much older lower This confusion arises because Clayburn et modelled from many other igneous prov crust and subjacent basic lithosphere as al., as well as many other workers, tend inces. However, I ask these and other distinct from contemporary (Caledonian) to use and interpret the broad, all-encom workers on crustal evolution to be specific mantle. passing term 'granitoid' interchangeably and unambiguous in their use and inter R. J. PANKHURST with the specific term 'granitic', thereby pretation of accepted terminology. Only British Antarctic Survey, frequently lumping together rock units of by specifying precisely the investigated Natural Environment totally different petrogenetic lineages, for rock types can confusion and misunder Research Council, which there is no justification in most of standing in the study of the great, poly c/o Institute of the published data from isotope geology genetic family of crust-forming granitoid Geological Sciences, 3 or experimental petrology -6. rocks be avoided. 64 Gray's Inn Road, Published isotopic evidence demon London WClX BNG, UK strates that true granites of any geological S. MOORBATH age in continental tectonic environments Department of Geology frequently have a significant or major and Mineralogy, 1. Clayburn, J. A. P., Harmon, R. S .• Pankhurst, R. J. & component derived from older sialic crust. University of Oxford, Brown, J. F. Nature 303,492-497 (1983). 2. O'Nions, R. K. & Pankhurst, R. J. Earth planet. Sci. Lett. Indeed, many granites (s.s.) may be the Parks Road, 38, 211-236 (1978). products of pure crustal anatexis (see ref. Oxford OXl 3PR, UK 3. Pankhurst, R. J. in Origin of Granite Batholiths: Geochemical Evidence (eds Atherton, M. P. & Tarney, 7). In contrast, calc-alkaline granitoids J.) 18-33 (Shiva, Orpington, 1979). (such as diorite, tonalite, granodiorite) 4. Allegre, C. J. & Othman, D. B. Nature 286, 335-342 of any geological age-and especially 11980). 1. Clayburn, J. A. P., Harmon, R. S., Pankhurst, R. J. & voluminous orthogneisses of the major Brown, J. F. Nature 303,492-497 (1983). Precambrian shield areas-appear to be 2. Moorbath, S. Chern. Geol. 23, 151-187 (1977); Phil. Trans. R. Soc. A288, 401-413 (1978). predominantly derived from basic litho 3. Stern, C. R., Huang, W. L. & Wyllie, P. J. Earth planet. sphere with mantle-like geochemical and Sci. Lett. 28, 189-196 (1975). isotopic characteristics, although in some 4. Wyllie, P. J., Huang, W. L., Stern, C. R. & Maaloe, S. Can. I. Earth Sci. 13, 1007-1019 (1976). tectonic environments there may be 5. Wyllie, P. J. Tectonophysics 43,41-71 (1977). Amines and isotopic and other evidence for significant 6. Wyllie, P. J. Geol. Rdsch. 70, 128-153 (1981). 7. Moorbath, S., Taylor, P. N. & Goodwin, R. Geochim. secretory pathways crustal contamination of mantle-derived cosmochim. Acta 45, 1051-1060 (1981). magmas (see ref. 8). 8. Taylor, P. N., Moorbath, S., Goodwin, R. & Petrykowski, THE output of ACTH precursors from A. C. Geochim. cosmochim. Acta 44, 1437-1453 In this connection, the view of Allegre (1980). AtT -20 cells (a mouse pituitary line) has 9 1 1 and Othman (quoted by Clayburn et al. ) 9. Allegre, C. J. & Othman, D. B. Nature 286, 335-342 been shown by Moore et a/. to be that granitoids younger than -2,000 Myr (1980). enhanced by chloroquine (200 11M). The contain predominantly recycled crustal cells normally synthesize a 30,000 component but that older ones are molecular weight (30 K) precursor, from juvenile mantle extracts makes no PANKHURST REPLIES-We thank which they proteolytically cleave two petrogenetic, tectonic or other distinction Moorbath for his comments on the forms of ACTH, 13 K and 4.5 K, which between true granites and calc-alkaline, introduction to our article 1 on the isotope differ in their glycosylation. The precur intermediate rocks, whilst the limited geochemistry of the Etive Igneous Com sor is externalized constitutively, as are sampling of these authors for Nd-Sr plex and apologize for any unintended other molecules such as a viral membrane isotopic analysis of granitoids from a great misrepresentation of his view caused by glycoprotein, gp70. The cleaved products variety of Precambrian and Phanerozoic a poor choice of words. are mainly stored in secretory granules environments cannot be regarded as Our purpose was simply to set the scene and discharged in the presence of a adequate, in my view, to justify general by referring to two extreme schools of secretagogue, such as 8-bromo-cyclic ized global modelling of crust-mantle thought on the origin of granitoid rocks AMP. Since chloroquine reduces storage evolution. Every geological province, of (s.l.) which have polarized around the of products, Moore et a/. conclude that whatever age, must be investigated in older and necessarily restricted isotope molecules of precursor are diverted from detail and treated as an individual case data. Many workers have taken the primi the secretory to the constitutive pathway. study, whilst isotopic data should not be tive isotope characteristics of calc-alka They suggest that ACTH packaging "may discussed in isolation from geological, line granitoids (and sometimes true be another example in which a low petrological and structural evidence in granites as well) to indicate primary crus intraorganelle pH is required for correct complex terrains. Initial Sr, Nd and Pb tal accretion solely through the processes sorting of protein molecules". isotopic ratios of granitoid rocks are not of mantle melting and magma differenti Chloroquine possibly "prevents the directly dependent on their age but on ation, despite warnings that a basic rather delivery of precursor ACTH to the secre their petrogenesis which, in turn, is closely than ultrabasic immediate source for the tory granule, which contains the specific related to the presence or absence of older magmas could be inferred from trace ele protease", perhaps by elevation of the sialic crust. ment data (see refs 2, 3). granule pH, as in packaging of lysosomal