Geochemistry of Jawa and Panchor granite: the most northern granitic bodies of the Boundary Range Batholith

Transcription

1 Gelgical Sciety f Malaysia Bulletin 51 June 25 p.j Gechemistry f Jawa and Panchr granite: the mst nrthern granitic bdies f the Bundary Range Bathlith Azman A Ghani & Mhd Irfan Abadi Department f Gelgy University f Malaya 563 Kuala Lumpur Abstract: The Panchr and J awa granites are tw islated granitic bdies lcated at the nrth f the Bundary Range Bathlith. They cnsist f carse, K-feldspar megacrystic, bitite hrnblende granite with sme incipient tw-phase variatin in the Jawa granite. Mineralgy f bth Panchr and Jawa granites in decreasing abundance are K-feldspar, quartz, plagiclase, bitite, allanite, zircn, apatite and hrnblende. Bth granites shw many I type feature such as (i) mafic minerals are invariably hrnblende and bitite, (ii) muscvite, garnet and crdierite are absent, (iii) accessry minerals present include sphene, allanite and apatite (iv) mnazite is nt present, (v) sedimentary xenliths are very rare and (vi) Na2 is greater than 3.2% in rcks with apprximately 5% K2. Bth granites als shw many gechemical differences, which suggests that they are made up f individual batches f melt Bth Panchr and Jawa granite magma seems t be cntrlled by different mineral prprtin during magmatic fractinatin, thus, the Panchr granite is cntrlled by K-feldspar and bitite whereas in the Jawa Granite, plagiclase and K-feldspar are imprtant phases in magmatic evlutin. Hwever the cntinuus trend shwn by the Jawa and Panchr granites and the ther Bundary Range Granites in RblSr vs Si2, Sr vs CaO and and P2 S vs Si2 diagrams suggest that a cnnectin exists between all the rcks at sme stage f their magmatic evlutin. INTRODUCTION The Peninsula Malaysia granites are distributed in three parallel belts which have been gruped int 2 granite prvinces: the Main Range prvince with an age range f 2 t 23 Ma and the Eastern prvince with a range f 2 t 264 Ma. The eastern granitid prvince, which cnsists f the Central belt and the Eastern Belt, cmprises f an extended cmpsitinal spectrum frm gabbr t mnzgranite frm small bathliths and plutns, which are generally smaller than thse f the Main Range granites. Amng the largest granitic bathlith f the Eastern Belt Granite is the Bundary Range Bathlith lcated in the nrth part f the granite belt (Fig 1). The bathlith is the largest Eastern Belt granitic bdy f Terengganu-Kelantan sectr. Cbbing et al divided the bathlith int tw majr cmpnents that is Machang bathlith and which is 1 x 2 kin and the smaller Kerai bathlith situated n the western flank (Fig 1). The frmer generally cnsist f mre evlved rcks i.e. bitite granite and hrnblende granite whereas the Kerai bathliths is made up f mre wider spectrum f plutnic rcks ranging frm pyrxenite t gabbr t grandirite and granite. Cbbing et al (1992) have divided the Bundary Range Bathlith int mre than fifteen granitic units e.g. Bidang, Terekak, Lata Tunggil, Kerai, Jawa and Panchr. Amng these units, Jawa and Panch r are separated frm the prper Bundary Range Bathlith. These tw granitic bdies are tw islated hills lcated at the nrtheast f the bathlith. The aim f this paper is t reprt the majr and trace elements characteristic f the Jawa and Panchr granites. PETROLOGY Bth Jawa and Panchr granite cnsists f primary textured granite (Cbbing et al 1992). They cnsist f carse, K-feldspar magacrystic, bitite hrnblende granite with sme incipient tw-phase variatin in the Jawa granite. Mineralgy f bth Panchr and Jawa granites in decreasing abundance are K-feldspar, quartz, plagiclase, bitite, hrnblende, allanite, zircn and apatite. 1++'+'+1 Carse primary texture ~ bi1itegnmite I>H~-"'" nm =:"~IPc:=.e KAPAL BATHOUTH N A 3, Figure 1: Map f the Peninsular Malaysia shwing the lcatin f Panchr and Jawa plutn in the Bundary Range bathlith Annual Gelgical Cnference 25, June 5-7, Seremban, Negeri Sembilan

2 Azman A Ghani & Mhd Jrfan Abadi 3.5-r , ~ Z 3.8. a f----..,..--.,.---,-----,r----r----r ~ ~ 3.9 B t----r---..,r---.,..----r--.---r---/ r <a"> ~~v---, DO 3;---..,..--~---r--r_--_r_-~-~ SiCh Jawa Granite Panchr Granite Figure 2: Selected majr elements Harker diagram f the granitic rcks frm Panchr and Jawa Granites. 136 Gelgical Sciety f Malaysia, Bulletin 51

3 Gechemistry f Jawa and Panchr granite 25 2 Ba 35 Rb Th [jjo < [JI(] Si2 Si2 Si Y Zn ~O 24 [Jl2J Q:XJ Si2 Si2 Si2 Jawa Granite 15 Panchr Granite Cb Figure 3: Trace elements Harker diagram f the granitic rcks frm Panchr and Jawa Granites. CHEMICAL CHARACTERISTICS A data set f 16 samples f the Panchr and Jawa granites has been analysed. 4 additinal analyses were btained frm Cbbing et al. (1992). (Sample: COB51, COB 78 (Panchr) and COB 11, COB 124 (Jawa». Bth Jawa and Panchr granites have a similar Si2 cntent: 68.4 t % Si2 (Jawa) and 69.8 t 72.2 Si2 % (Panchr). Thus, bth Jawa and Panch r granites are amng the felsic rcks f the Bundary Range Bathliths (Si2 ranging frm t 76.5%). In general AI23, Ti2, Fe23, FeO, MgO, Na2 and CaO decrease with increasing Si2. The differences between bth Panchr and Jawa Granites are clearly shwn in Figure 2 and 3, thus Al23, CaO, Ba, ZI and Na2 are higher and K2, Rb, Th, Y and Zn are lwer in Jawa cmpared t the Panchr granites. All rcks frm bth units generally have high alkali cntent (Na2 + K2) ranging between 8.16 t 9.93 wt% fr Panchr granite, wt% fr Jawa Granite. Classificatin by alumina saturatin index (ASI) f Zen (1988) indicates that the Panchr granite has higher ACNK values ranging frm (mildly peraluminus), cmpared t the Jawa granites which ranges frm (metaluminus) (Fig 4). The samples frm bth plutns, hwever, plt in the I-type field f Chappell and White (1974). Furthermre, they shw a different ACNK behaviur with Si2, thus the ACNK trend f the Panchr rcks increase with increasing Si2 whereas thse frm Jawa frm a cluster with n clear trend with Si2. Bth granites share the same trend as the main Bundary Range Bathlith in the Rb/Sr vs Si2 plt (Fig 5). This plt emphasizes the imprtance f plagiclase crystallizatin in the magmatic evlutin f the magmas frm the Bundary Range Bathlith. The plt shw a 'J' shaped trend which suggest the imprtance f fractinal crystallisatin prcess with plagiclase as the majr precipitating felsic phase (Athertn 1993). The imprtant f K-feldspar, bitite and plagiclase in the differentiatin is cnsistent with large in lithphile (LIL) mdelling. Inter element LIL variatin diagram fr pair Ba-Sr is shwn in Figure 6. Als shwn in each f the diagram is the vectr diagram representing the net change in cmpsitin f the liquid after 3% Rayleigh fractinatin by remving K-feldspar, hrnblende, plagiclase r bitite. Tw trends have been identified in the early crystallizing phases, the first trend is dminated by K-fe1dspar and bitite and the secnd trend cntrlled by crystallizatin f plagiclase and k-feldspar. Bth trends cnverge int a single trend, which is dminated by plagiclase, K feldspar and bitite. Thus the Ba vs Sr lg-lg plts suggests that crystal fractinatin via crystallisatin f June

4 Azman A Ghani & Mhd Irfan Abadi , '5' type 1.1 'I'type 1 Peraluminus Metaluminus ACNK 8 '$ ~---r----r_--r_--r_-,r_- ; SiD2 Figure 4: AI2yCaO+Na2+K2 vs Si2 (ACNK) diagram fr the Panchr, Jawa and ther Bundary Range granite. Line at ACNK =1 divided between peraluminus and metaluminus and line at ACNK = 1.1 divided between 'I' and's' type granite. Symbls as in Figure 5. plagiclase + K-feldspar and bitite play an imprtant rle in the magmatic evlutin f the Bundary Range magmas. Interestingly, bth Panch r and Jawa granite shw a different mineralgical trend, thus the Panchr granite plts in the first trend, cntrlled by K-feldspar and bitite whereas in the Jawa Granite plts in the secnd trend which is dminated by plagiclase and K-feldspar. This suggests that bth Panchr and Jawa magmas may represent a different magmatic pulses. A Ba vs. Sr plt fr the rcks f bth Panchr and Jawa granites tgether with all Bundary Range analyses is shwn in Figure 7. Bth Panchr and Jawa granites have abut the same cncentratin f Sr (ppm) but the Ba (ppm) is higher in the later. Infact the Ba cncentratin in the Jawa plutn is amng the highest cmpared t the ther Bundary Range rcks (- 25 ppm). In general the Panchr analyses fall within the Bundary Range general trend. Majrity f the Panchr granite rcks plt belw the line BalSr =1 and can be cnsidered as lw Ba-Sr granite accrding t Tarney and Jnes (1994). 138 DISCUSSION In general, mineralgy f bth plutns especially the ccurrence f hrnblende and sphene suggest that they are 'I' type. This is supprted by ACNK values, all the samples analysed frm bth plutns plts well belw ACNK =1.1 (Fig 4) (Shand 1943; Zen 1988). The increase f ACNK values with Si2 is als similar t the I type feature (Chappell & White 1992; Chappell 1999). Hwever the trend shwn by bth plutns are different, thus the ACNK values f the Panchr granite increase with increasing Si2 whereas thse frm the Jawa granite cluster just belw the ACNK =1.1. The gechemistry als shws that bth Jawa and Panchr granites are made up f individual batches f melt. This is evident frm large in lithphile mdeling (Fig 7). Bth magmas are cntrlled by different grups f minerals during crystallizatin, K-feldspar and bitite fr the Jawa granite and plagiclase, K-feldspar and Gelgical Sciety f Malaysia, Bulletin 51

5 Gechemistry f Jawa and Panchr granite D Jawa Granite Panchr Granite Other Bundary Range Granite 12 1 Rb/Sr ~g Si2 Figure 5: Rb/Sr vs Si 2 plt fr the Panch r, Jawa and ther Bundary Range granite. bitite fr the Panchr granite. The Jawa granite has higher Ba cntent cmpared t the Panchr granite. The Ba cntent in the Jawa Granite is amng the highest f all Bundary Range Granite. The strng enrichment f these elements (Ba and Sr) is prbably related t transfer f enriched (hydrus?) fluids frm the mantle int the lwer crust (and pssibly initiated) melting t frm the granites (Stephens and Halliday 1984). It is als pssible fr this t be linked with mantle plumes (e.g. Hill et al.i992). Nt all deep mantle plumes are able t break thrugh thick lithsphere, and may just underplate it, but at the same time prvide energy fr melting f the June, 25 lwer crust. Mantle derived liquids are enriched in Ba and Sr as a result f partial melting f (prbably metasmatised) peridtite withut plagiclase as a stable phase pssibly fllwed by high pressure fractinatin (Halliday and Stephen 1984). If such magma interacted with the lwer crust, this nly serves t maintain Ba and Sr at high levels and lwer the Rb/Sr ratis (Rb/Sr : Jawa , Panchr ( ). Other pssibilities t create magma cmpsitin with high Ba and Sr with psitive anmalies fr Sr and P is simply by having garnet residual in the surce t sequester the heavy REE and depress the multi-elements variatin pattern (Tarney and 139

6 Azman A Ghani & Mhd Irfan Abadi D J awa Granite Panchr Granite Other Bundary Range Granite Sr O~~~----r---~--~----~--~--~~--~--~--~ Ba Figure 7: Ba vs Sr diagram f the granitic rcks frm bth Jawa and Panchr granite. Als plt in the diagram is the ther Bundary Range granites Jnes 1994). Halliday and Stephen (1984) als suggested that the high Sr magmas in the British Calednian granite are prduct f a particular prvince maintained by a particular prcess. Azman and Mustaffa (22) cnsidered that the high Ba and Sr values in the Raub area may result frm the penetratin f the lwer lithsphere by a small vlume f mantle material that is enriched in thse elements. The Panchr granite has yielded an initial 87Sr/86Sr rati f.7797 (Cbbing et al 1992), which pints t an rigin in highly enriched lithspheric mantle. Typlgy f bth Panchr and Jawa Granites are cnsistent with the 'r type rck (Chappell and White, , 1992). The I type characteristic f bth granites are cnsistent with the Eastern Belt Granite. Ntable T type features are: (a) mafic minerals are invariably hrnblende and bitite, (b) muscvite, garnet and crdierite are absent, (c) accessry minerals present include sphene, allanite and apatite. Mnazite is nt present, (d) sedimentary xenliths are very rare (e) Na2 is greater than 3.2% in rcks with apprximately 5% K2 Gelgical Sciety f Malaysia, Bulletin 51

7 Gechemistry f Jawa and Panchr granite Withut istpic data it is nt clear what the surce(s) f the bth granites were, but the limited istpic data available (Cbbing et al. 1992) suggest that the surces lie within the lwer crust and upper mantle. The granites tgether with ther Bundary Range granites prbably were generated during each f the main defrmatin episdes when, in respnse t a slight increase in heat flw and fllwed by a prgressive drp in pressure, a series f magma pulses f changing cmpsitin were frmed. Hwever the surce f heat necessary t generate the individual melts during the defrmatin episdes is nt clear. Sme f the features e.g. high Ba-Sr in the Panchr granite can nly be explained by melting in respnse t the heat supplies by underplated mafic magmas (Stephen and Halliday 1984; Yarr 1991; Tarney and Jnes 1994). These separate melts were cllected int discrete magmas which rse as a result f a buyancy natural t their lw density The cntinuus trend shwn by the Jawa and Panchr granites and the ther Bundary Range Granites in Rb/Sr vs Si2, Sr vs CaO and and P25 vs Si2 diagrams suggest that a cnnectin exists between all the rcks at sme stage f their magmatic evlutin. REFRENCES ATHERTON, M.P Granite Magmatism Jurnal f Gelgical Sciety f Lndn 25, AZMAN A GHANI AND MUSTAFA KAMAL SHUIB. 22. Twards a gedynamic mdel fr Peninsular Malaysia : evidence frm high Ba-Sr rcks frm the Central Belt f Peninsular Malaysia. Petrleum Gelgical Cnf, Oktber 22. Istana Htel Kuala Lumpur, pg. 13 CHAPPELL, B. W. AND WHITE, A. 1. R Tw cntrasting granite types. Pacific Gel.,8, CHAPPELL, B. W. AND WHITE, A. 1. R and S type granites in the Lachlan fld belt. Trans. Ry.Sc.Edinb:Earth Sciences,83, CHAPPELL, B.W Aluminium saturatin in 1- and S-type granites and characterizatin f fractinated haplgranite. Liths, 46, COBB lng, E. 1., PITFIELD, P. E. J., DARBYSHIRE, D. P. F., & MALUCK, D. 1 J The granites fthe Suth-East Asian tin belt. Overseas Memir 1, B.G.S. HALLIDAY, A. N. AND STEPHENS, W. E., Crustal cntrls n the genesis f the 4 Ma ld Calednian granites. Phys. Earth. Planet. Interirs, 35, HILL, R. I., CAMPBELL, 1 H., DAVIES, G. F. AND GRIFFITH, R. W Mantle plumes and cntinental tectnics. Science, SHAND, S. J Eruptive rcks. T Murby and C., Lndn, 2nd edn., 444 pp. STEPHENS, W. E. AND HALLIDAY, A. N., Gechemical cntrasts between late Calednian granitid plutns f nrthern, central and suthern Sctland. Trans. Ryal Sc. Edinburgh Earth Sciences 75, TARNEY, 1. AND JONES, C.E., Trace element gechemistry f rgenic igneus rcks and crustal grwth mdels. Jurnal f the Gelgical Sciety (Lndn), 151, Y ARR. T. R A petrlgical study f the appinite suite assciated with the Ardara plutn, C. Dnegal, Ireland. PhD thesis, Univ. St Andrews, Sctland. ZEN, E Phase relatins f peraluminus granitic rcks and their petrgenetic implicatins Ann.Rev.Earth and Planet. Sci., 16, Manuscript received 23 February 25 June.2S 141