Overview of Results from the Greenstone ... - Geology Ontario
Overview of Results from the Greenstone ... - Geology Ontario
Overview of Results from the Greenstone ... - Geology Ontario
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Table 7. Diagnostic mineral assemblages (point data) are <strong>the</strong> basis for <strong>the</strong> definition <strong>of</strong> metamorphic grade in each metamorphic zone. Metamorphic zones (see also Thompson<br />
2005, Figure 2, back pocket) are derived <strong>from</strong> <strong>the</strong> grade in one or more rock associations. The first digit <strong>of</strong> <strong>the</strong> two-digit number in each cell indicates <strong>the</strong> rock association. The<br />
second digit indicates <strong>the</strong> relative metamorphic grade for <strong>the</strong> rock association (higher number, higher grade). The relative positions <strong>of</strong> <strong>the</strong> boundaries in rock associations 2 to 7<br />
that correspond approximately to <strong>the</strong> lower/upper greenschist zone boundary on <strong>the</strong> map are inferred. The precise positions <strong>of</strong> <strong>the</strong>se boundaries relative to each o<strong>the</strong>r have yet to<br />
be calibrated. Mineral name abbreviations: ab - albite, act - actinolite, am – amphibole undifferentiated, and - andalusite, bt - biotite, cb – carbonate (ankerite, calcite, dolomite,<br />
magnesite, siderite), cht - chlorite, crd - cordierite, ctd - chloritoid, cum - cummingtonite, diop - diopside, epg - epidote group, grt - garnet, gru - grünerite,<br />
hn - hornblende, kf - potassium-feldspar, mt - magnetite, plg - plagioclase, se - serpentine, sil - sillimanite, st - staurolite, tlc - talc, trm - tremolite, wm - white mica (muscovite,<br />
paragonite, talc).<br />
Metamorphic Grade<br />
Rock Association<br />
1) Metabasites: metabasalt/gabbro/diabase,<br />
greenstone, amphibolite, meta-andesite<br />
2) Metaquartz<strong>of</strong>eldspathic rocks:<br />
metarhyolite/dacite, qtz-fp metaporphyry,<br />
felsic metavolcaniclastite, metawacke<br />
3) Metamorphosed ultramafic rocks:<br />
metakomatiite, metaperidotite/dunite<br />
4) Metamorphosed aluminum-rich rocks:<br />
metashale/siltstone, metahydro<strong>the</strong>rmal<br />
alteration<br />
5) Chemical metasedimentary rocks,<br />
meta-iron formation<br />
6) Metamorphosed granitoids:<br />
metagranite to metatonalite<br />
7) Metamophosed carbonate-rich rocks:<br />
carbonate metasediments, meta-interpillow<br />
rock, metahydro<strong>the</strong>rmal alteration, cht-cb<br />
schist<br />
8) Unmetamorphosed granitoids:<br />
granite to tonalite<br />
Sub-greenschist<br />
Facies<br />
Subgreenschist<br />
Zone<br />
Lower Greenschist<br />
Zone<br />
Greenschist Facies Amphibolite Facies<br />
Metamorphic Zones on Map<br />
Upper Greenschist<br />
Zone<br />
Transition<br />
Zone<br />
Diagnostic Mineral Assemblages<br />
10 prn, prn-pu 11 act-cht-epg-ab 12 act-hn 13 hn-plg(calcic)<br />
20 prn, prn-pu<br />
cht-wm<br />
30<br />
21 cht-wm cht-kf<br />
cht-wm-cb<br />
31 cht-tlc-cb, se-cht<br />
cht-tlc-se-cb<br />
22 bt<br />
epg-act<br />
32 clinoamphibole (trm, cum)<br />
40 41 cht-wm 42 bt, bt-grt, ctd-cht<br />
50 minesotaite<br />
greenalite<br />
51 qtz-cht, cht-cb,<br />
mt-qtz<br />
23 bt-hn<br />
52 clinoamphibole (cum/gru), am-grt, two am<br />
60 prn, prn-pu 61 cht-kf, cht-wm 62 bt, bt-epg, bt-epg-am<br />
70<br />
71 cht-cb-qtz<br />
cht-cb-wm-qtz<br />
72 bt-cht-cb<br />
epg-cht-am-cb<br />
80 no metamorphic minerals<br />
Amphibolite Zone<br />
43 crd-and/sil-bt<br />
st-and/sil-bt, crd orthoamphibole<br />
73 diop-am-grt, hn-bt-qtz<br />
76