Petrology and geochemistry of the Central Mindano Volanic Arc, Southern Philippines

330 Pages·2011·21.29 MB·English

PETROLOGY AND GEOCHEMISTRY
Of THE CENTRAL MINDANAO VOLCANIC ARC,
SOUTHERN PHILIPPINES
A thesis
submitted in fulfillment
of the requirements for the Degree
of
Doctor of Philosophy in Geology
in the
University of Canterbury
by
ERNESTO SOLIMAN G. CORPUZ
'"
University of Canterbury
1992
;2\
In memory of my brother, Benjamin
CONTENTS
ABSTRACT .......................................................................................................... 1
CHAPTER
1.0. GENERAL INTRODUCTION .......................... , ......................................... 2
1.1. INTRODUCTION ............................................................................ 2
1.2. REGIONAL SETTING OF THE PHILIPPiNES ................................ 2
1.3. PRESENT DAY TECTONICS ........................................................ 4
1.3.1. EASTERN CONVERGENT MARGIN ........................................... 4
1.3.2. WeSTERN CONVERGENT MARGIN .......................................... 7
1.3.3. CONVERGENT MARGINS OF MINDANAO ................................... 9
1.3.4. SHEAR BETWEEN EASTERN AND WESTERN CONVERGENT
MARGINS ............................................................................. 13
1.4. DEVELOPMENT OF ARC SYSTEMS IN THE PHIUPPINES ......... 14
1 .4.1 . EAST luZON ARC ................................................................. 18
1.4.2. WEST LUZON .................. 19
1.4.3. TECTONIC HISTORY Of MiNOANAO ......................................... 20
1.5. VOLCANISM IN MINDANAO ......................................................... 23
2.0. GEOLOGY ............................................................................................... 27
2.1. GENERAL GEOLOGY OF MINOANAO ......................................... 27
2.1.1 PACIF!C CORDILLERA ............................................................ 29
2.1.2. AGUSAN-DAVAO BASIN ......................................................... 29
2.1.3. MINDANAO CENTRAL CORDILLERA .......................................... 35
2.1.4. COTAMTO BASiN .............................................................. , .. 36
2.1.5. TIRURAy·DAGUMA ..................... 37
2.1.6. ZAMSOANGA PENINSULA ....................................................... 37
2.1.7. SULU ISLANDS ...................................................................... 38
2.2. GEOLOGY OF CENTRAL MINDANAO VOLCANIC ARC
(CMVA) ...." . ..................................................................................... 38
2.2.1. MISAMIS VOLCANIC GROUP ............................................... " .. 39
BUKIONON VOLCANiC GROUP ............................................... .42
2.2.3. CAVAO VOLCANIC GROUP ..................................................... 46
2.3. VOLCANIC OF CAMIGUIN ISLAND ............................ 47
2.3.1, INTRODUCTION ....... " .•..• , .• ""• .••. , ............................................ 47
2.3.2. PREVlOUS STUDIES .............." . ............................................... 49
2.3.3. STRATIGRAPHIC CLASSIFICATION ........................................... 50
2.3.4. GEOLOGY OF PRE-HISTORIC DEPOSITS .................................. 50
2.3.5. GEOLOGY OF RECENT DEPOSITS ........................................... 61
2.3.6. EVOLUTION OF CAMIGUIN ISLAND ........................................... 67
Contents
3.0. PETROGRAPHY AND MINERALOGy ..................................................... 73
3.1. INTRODUCTION ............................................................................ 73
3.2. SAMPLE LOCATION AND ANALYTICAL METHODS .................... 73
3.3. CLASSiFiCATION .......................................................................... 74
3.4. GENERAL TEXTURES AND MODAL ANALYSES ......................... 75
3.4.1. BASALTS ............................................................................. 75
3.4.2. ANDESITES .......................................................................... 81
3.4.3 ................................ 85
3.5. PETROGRAPHY OF CRYSTAL CLOTS AND LITHIC
INCLUSIONS ................................................................................. 87
3.6. CHEMISTRY OF PHENOCRYST ASSEMBLAGES ....................... 91
3.6.1. FELDSPAR ........................................................................... 91
3.6.2. OUVlNE ............................................................................... 97
3.6.3. pyROXENfS ......................................................................... 107
3.6.4. SPiNEL ................................................................................ 122
3.B.5. AMPHIBOLE .......... ""., ........................................... " ............. 1"27
4.0. GEOCHEMiSTRy ........................... " .. " ................................................... 135
4.1. INTRODUCTION ........................................................................., .. 135
4.2. SAMPLE PREPARATION AND ANALYTICAL METHODS ............. 135
4.3. CLASSiFiCATION .......................................................................... 131
4.4. GEOCHEMISTRY OF CMVA LAVAS ............................................. 143
4.4.1 . MAJOR ELEMENTS ................................................................ 143
4.4.2. TRACE ELEMENTS ................................................................ 156
4.5. CHEMICAL VARIATIONS OF CAMIGUIN ISLAND
VOLCANOES ................................... _. ............................................ 164
4.5.1. MAJOR ELEMENTS .............................................. " ................ 164
4.5.2. TRACE ELEMENTS ................................................................ 167
4.8. COMPARISON OF MAJOR AND TRACE ELEMENT
CHARACTERISTICS BETWEEN THE CMVA AND LAVAS
FROM OTHER TECTONIC SETTINGS ......................................... 172
4.6.1. MAJOR ELEMENTS ................................................................ 172
4.6.2. TRACE ELEMENTS ......................................... , ......... , ............ 172
5.0. PETROGENESiS ..................................................................................... 181
5.1. INTRODUCTION ............................................................................ 181
5 .. 2. GEODYNAMIC CONSTRAINTS .................................................... 182
5.3. SOURCE REGION CHARA.CTERISTICS ....................................... 186
5.3.1. PRESSURE ( P). TEMPERATURE (T) AND AS102 ............. " ....... 186
5.3.2. PRIMITIVE COMPOSiTIONS ........................................................ 189
5.3.3. LlL-ELEMENT ENRiCHMENT .... , ................................................ 194
5.4. PARTIAL MELTING CONDITIONS ................................................ 197
Contents iii
5.5. DIFFERENTIATION PROCESSES ................................................ 202
5.5.1. FRACTIONAL CRYSTALLISATION ................................................ 202
5.5.2. MAGMA MlXING ....................................................................... 205
5.B. REGIONAL DISCUSSION OF 'BESFFlr PROCESSES ............... 206
5.6.1. HIBOK-HIBOK ......................................................................... 207
5.6.2. BUTAY, BENONI AND MT GINSIUBAN ......................................... 213
5.6.3. BUKlDNON .............................................................................. 219
5.6.4. MT Apo ................................................................................. 222
5.7. MODEL OF GEOCHEMICAL EVOLUTION .................................... 228
6.0. SUMMARY AND CONCLUSiONS ............................................................ 236
6.1. TECTONIC ASSOCiATION ........................................................... 236
6.2. VOLCANIC GEOLOGY .................................................................. 236
6.3. PETROLOGY AND GEOCHEMiSTRy ........................................... 237
6.4. PETROGENESiS ........................................................................... 238
6.4.1. SOURCE REGION CHARACTERISTICS AND PARTIAL
MnT ING CONDmONS ........................................................... 238
6.4.2. DIFFERENTIATION PROCESSES .............................................. 239
6.4.3. GEOCHEMICAL EVOLUTION .................................................... 240
ACKNOWLEDGEMENTS .................................................................................... 241
REFERENCES ..................................................................................................... 242
APPENDiCES ...................................................................................................... 259
tv
LIST OF FIGURES
Page
1-1 Regional setting map of the Philippines ................................................................. 3
1-2 Sketch map showing mal n islands of the Philippines ............................................. 5
1-3 Map of the Philippine region showing tectonic elements of the
South China and West Philippine Sea Plate boundary .......................................... 6
1-4 Interpretation of seismic profile across Davao Gulf ................ " ........................... 13
1-5 Reconstruction of tectonic history o11l1e South China Basin region ..................... 15
1-6 Schematic reconstruction of collision between
West and East Mindanao Arcs ............................................................................ 22
1-7 Quatemary volcanic centres in Mindanao ............................................................ 24
2-1 Outline map of Mindanao showing major physiographic-structural units .............. 28
2-2 General geologic map of Mindanao ..................................................................... 30
2-3 Stratigraphic columns for Mindanao .................................................................... 31
2-4 Geologic map of the CMVA ................................................................................. 40
2-5 Photographs of Bukidnon Volcanic Group centres ............................................... 44
2-6 Geologic map of Camiguin Island ., ..................................................................... 48
2-7 Proposed stratigraphic column of Camlguin Island .............................................. 52
2-8 West-east cross--sedion of Benoni volcanics ....................................................... 54
2-9 Photograph of Mt GlnsUiban and Benoni ............................................................. 57
2-10 Stereo-photograph of NW Camlguin Island ......................................................... 59
2-11 GeOlogy of historical deposits of Camiguin Island ............................................... 62
2-12 Panoramic view of northern Camiguin Island showing HiooK-HlboK,
Kanangkaan and !tum lava flows, and pyroclastic flow deposits of 19.51 ............. 64
2-13 Photograph of (a) view to NNE showing paths of 4 and 6 December
pyrodastic flows and (b) ridge-top deposit of 1951 pyroclastic flow ..................... 66
2-14 Proposed geological evolution of Camiguin Island .............................................. 69
n
3-1 Graph of modal occurrence at mafic phenoCl)'sts vs Si02 wt% ...........................
3-2 Maximum crystal size for most common phenocrysts vS Si02 content. ............... 78
3-3 Microphotographs of basaltic rocks ..................................................................... 80
3--4 Microphotographs of representative basaltic andesites ........................................ 83
3-5 Microphotographs of representative dacites ........................................................ 88
3-6 Microphotographs of crystal clots ........................................................................ 88
3-7 Microphotographs of inclusions ........................................................................... 90
3-88 Variation of NS20 and CaO with Si02 in CMVA plagioclases ............................. 92
3--8b Variation of FeO and MgO with An in CMVA plagioclases ................................... 93
List of Figures v
3-9 Ab-An-Or ternary diagram showing plagioclase compositions for
representative rocks ofthe CMVA ....................................................................... 94
3-10 Microphotographs of plagioclase ......................................................................... 96
3-11 Microphotographs of olivines in basatts ............................................................... 98
3-12 MgO-FeO relations in olivine for selected CMVA bulk compositions .................. 102
3-13a CaO variation with MgO in selected olivines ..................................................... 104
3--13b MnO distribution with changing MgO in selected olivines of CMVA lavas .......... 105
3-13c Plot of NiO concentrations with MgO in selected olivines .................................. 106
3-14 Variation of AI203 with Si02ln pyroxenes of the CMVA ................................... 109
3-15 Variation of Ti02 with Si02 in pyroxenes ofthe CMVA ..................................... 110
3.-16 Frequency distribution of tetrahedrally coordinated
aluminum in pyroxenes of Cent rat Mindanao .......................... " ......................... 111
3-17 Discriminant diagram for clinopyroxene phenoaysts from the CMVA ................ 112
3-18 Discriminant diagram for pyroxenes of Central Mindanao ................................. 113
3-19 Frequency distribution of tetrahedrally-coordinated AI with Fe.lFe+Mg ............... 115
3-20 Ca and Mn variations in pyroxenes from basalts to dacites ............................... 116
3-21 Negative correlation of Mg#(px) with Fe/Mg ratios ............................................ 117
3-22 Compositional fields of pyroxenes from the CMVA ............................................ 118
3-23 Distribution of quadrilateral components in pyroxenes among CMVA lavas ....... 119
3-24 Microphotographs of pyroxene in basalts .......................................................... 121
3-25 Microphotographs of pyroxene In S;02 ~r1ch compositions ................................ 123
3-26 Distribution graph of n~magnet!tes in CMVA lavas ........................................... 126
3-27a Effect of ferric iron on tetrahedral AI and A-site atoms ........................ " ............ 128
3-27b Effect of entry of ferric iron on AI and A~site atoms in amphibole ...................... 129
3-28 Plot of A. B(charge) and T sUe occupancies in amphibole composition
space for Mt Apo and Camlguin Island lavas ..................................................... 131
3-29 AI(IV)·n distribution in amphiboles of Si02-rich lavas ....................................... 132
3-30 Oxide variation diagrams for hornblende and co-existing clinopyroxene ............ 133
4~ 1 Outline map of the Philippines showing proposed zonation from tholeiitic to
calcalkalic and from calcalkalic to alkalic suites ................................................ 136
4-2 T ota I alkali-si Ii ca diagram (T AS) for CMVA lavas .............................................. 138
4-3 AFM plot of representative CMVA lavas ............................................................ 140
4-4 Projection of CMVA lavas onto basallriangle ne'·ol-Q of the cpx-ol-ne'-Q
tetrahedron ....................................................................................................... 141
4-5 Discrimination of high FeO"JMgO ratios for Mt Balatocan and
other lavas of the CWJA .................................................................................. 142
4-6 Distribution of CMVA lavas with respect to normative Ab, An and Or ................ 144-
4-7 Variation of K20 with 5102 showing predominantly
medium-K andesites in the CMVA. .................................................................... 145
4-8 Grouping of CMVA lavas defined by different K20-Si02 distributions ............... 146
4-9 Na20 concentration in CMVA lavas ........ " ........................................................ 147
4-10 Variation oHotal Fe (as FeO") in CMVA lavas .................................................. 149
4-11 Variation of FeO" vs 5;02 for Mt Balatocan samples ........................................ 149
List of Figures vi
4·12 Change in MgO concentrations wtth 8i02 ........ " ............................................... 150
4-13 Ti02 'VS Si02 for CMVA lava5 ........................................................................... 151
4-14 CaO vs Sj~ ..................................................................................................... 152
4-15 A1203 vs Sl02 ................................................................................................. 152
4-16 P205 \IS S;02 ................................................................................................... 154-
4-17 MnO vs 5i02 .................................................................................................... 155
4-18 Distribution of Ba and Rb in CMVA la\l/Ss .................................................. " ...... 157
4-19 Variable Sr distribution tn CMVA la\lBs .............................................................. 158
4-20 Zr concentration \IS Si02 in CMVA lavas .......................................................... 159
4-21 Y vs Zr diagram for northern CMVA lavas ......................................................... 161
4-22 Variation in Cr and Ni with MgO In CMVA lavas ................................................ 162
4-23 DIstribution of V \IS Si02 ....................................................... " .......................... 163
4-24 Major element distribution of Camiguin island 18\18S .......................................... 168
4-25 Variation of ea, Rb and Sr with Si02 for Camiguin island la\las ........................ 168
4-28 Variation of Nb and Y using Zr as a fractionation index ..................................... 110
4-27 Cr and Ni distribution in Camiguin Island lavas .................................................. 171
4-28 Selected K-group trace element ratios of CMVA basalts ................................... 174
4-29 Rb/Sr ratios of CMVA la\las compared with other island arc bBsatts
of the Pacific region .......................................................................................... 175
4-30 Nb vs Zr diagram of CMVA la\las ..................................................................... 176
4-31 Variation of ZrN ratios with Zr for CMVA basalts .............................................. 177
4-32a N-MORB normalised element abundance diagrams for CMVA .......................... 179
4-32b N-MORB normalised element abundance diagrams for
Camiguin island basalts .................................................................................... 180
5-1 West-east seismic section across Mindanao. along Latitude to30'N.
After Cardwell et al (1980) ................................................................................ 183
5-2 West-east seismic section across Mindanao, along
Latitude 6°, 7° and 90 using earthquakes located by the
Philippine Institute of Volcanology and Seismology ........................................... 184
5-3 Pressure estlmates of selected CMVA using T and silica activity ...................... 186
S-4 Plot of selected CMVA basalts in tenTIS of variation of silica activity with
temperature ...................................................................................................... 190
5-5 Plot of Sa \IS. Nb for CMVA basalts ................................................................... 196
5-8 Projection of selected CMVA basalt compositions onto the
(Jaderte + CaTs) . Q ~ 01 face of the CIPW molecular normative tetrahedron ... 199
5-7 Plot of Ce/Nb vs. BalNb for 2 representative basalts showing affinity with
E-type MORBJOIB and continental crust ........................................................... 203
5-8 N-MORB normalised element plot of Camiguln Island basaltic lavas ................. 208
5-9 Pearce element ratio plot of a comagmatic calcalkaUne suite
from Hibok-Hibok .............................................................................................. 214
5-10 (a & b) Valiation of V, Cr, and Ni for southern Camiguin Island volcanoes ....... 216
5-10 (c & d) Variation of V. Cr, and Ni for southem Camiguin Island \lolcanoes ....... 217
List of Figures vii
5-11 Photographs of Mt Apo outcrops showing (a) lava block and (b) Si02-rich
andesite enclave in basal1ic andesite host ......................................................... 223
5-12 Composition of Mt Ape volcanics projected on the
Olivine - Quartz· Plagioclase pseudotemary .................................................... 227
5-13 Schematic diagram of dehydration of amphibole from subducted
lithosphere and fluxing of overlying peridotite mantle ........................................ 230
5-14 Schematic diagram of subduction zone beneath CMVA .................................... 231
5-15 Cartoon showing inferred varying depths to
magma chambers beneath CMVA. .................................................................... 233
5-16 Schematic summary of inferred magma chamber
processes at shallow levels « Sk.m) .................................................................. 234
A5-1 Estimate of silica activity (melt) and ProTAl .................................................... 307
vii;
LIST OF TABLES
Page
3-1 Representative modal data for CMVA lavas ...................................................... 76
3-2 Selected whole rock analyses which contain modal olivine ................... " ......... 101
4-1 Representative and average whole-rock
chemical analyses of CMVA lavas .................................................................. 139
4-2 Representative analyses of Camig uin island lavas ......................... "' ............... 165
5-1 Crystallising conditions of CMVA lavas ........................................................... 187
5-2 Examples of primitive MORB compositions and selected CMVA basaHs ......... 191
5-3 Corrected major element abundances in CMVA basalts .................................. 193
5-4 Inferred source chemistry of CMVA basalts ..................................................... 201
5-5a Mass balance calculations to demonstrate fractional crystallisation of
Hibok-Hlbok (Camlguln Island) from basaltic
andesite to Si0Z-rich andesite ........................................................................ 210
5-5b Mass balance calculations to demonstrate fradional crystallisation
of Hibok-Hibok (Camlguln Island) from SI0Z-nch andesite
to more evolved Si0Z-nch andesite ............. " ................................................. 211
5-6 Least squares mass balance calculation for proposed magma mixing of
Benoni-Butay lavas to produce Mt Ginsiliban compositions ............................. 216
5-7a Mass balance calculation to model possible fradional
crystallisation between basaltic andesite to andesite from
Bukidnon volcanoes (sample BUTS to MUS15) ............................................... 220
5-7b Alternative mass balance calculation to model possible
fractional crystallisation between basaltic andesite to
andesite from Bukidnon volcanoes (sample QUE7 to MUS15) ........................ 221
5-8£1 Mass balance calculation to derive SI0Z-rich hornblende andesite from
basaHic andesite .............................................................................................2 25
5-8b Mass balance calculation 10 derive Type 2 dacite from Si0Z-rich
homnblende andesite at Mt Apo ...................................................................... 226
A3--1 a Microprobe analyses of plagioclase in basalts ................................................. 266
A3-1b Microprobe analyses of plagioclase in basaltic andesites ................................ 267
A3-1c Microprobe analyses of plagioclase in Si0Z-rich andesttes .............................. 268
A3-1d Microprobe analyses of plagioclase in dacites ................................................. 271
A3-2a Microprobe analyses of olivine from basalts .................................................... 273
A3-2b Microprobe analyses of olivine from basaltic andesites and
Si0Z-rich andesites ........................................................................................ 274
A3-3a Microprobe analyses of pyroxene from basalts (analyses 1~3) and basaltic
andesites ........................................................................................................2 75
A3-3b Microprobe analyses of pyroxene from basaltic andesites ............................... 276
A3-3c Microprobe analyses of pyroxene from SI0z-rich andesites and dacites ......... 277