Mafic Mineralogy of Ferroaugite Syenite from the Coldwell Alkaline Complex, Ontario, Canada
Mafic Mineralogy of Ferroaugite Syenite from the Coldwell Alkaline Complex, Ontario, Canada
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DOI：
10.1093/petrology/19.4.627
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发表时间：
1978-11
影响因子：
3.9
通讯作者：
R. Mitchell;R. G. Platt
中科院分区：
文献类型：
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作者：
R. Mitchell;R. G. Platt
一个1500米厚的片状铁辉石正长岩体在矿物学上可分为上部正长岩系列和下部正长岩系列。下部正长岩的特征是由镁铁质积云矿物定义的发育良好的火成分层。正长岩是饱和到过饱和的，并含有碱性长石、橄榄石（Fa 83 -93）、铁辉石（Di 50 Hd 45 Ac 5 − Di 5 Hd 90 Ac 5）和钛铁矿。从堆间液中结晶出来的角闪石，其成分范围从铁角闪岩到铁锌铁角闪岩再到铁铁阳起石锌铁角闪岩。上部系列为粗粒堆晶岩，分层不清楚，有丰富的斑晶伟晶岩。积云相是碱性长石、橄榄石（Fa 93）和酸性-铁铍石（Di 5 Hd50 Ac 5 − Ac 50 Hd50）。堆间液呈过碱性，结晶形成的霓霞岩和角闪石的成分范围从铁黄绿霞石到铁黄绿霞石。斑晶伟晶岩是由铁黄绿霞石、铁阳起石、碱性长石、霓霞岩、石英和锆石组成的过碱性岩石。铁辉石正长岩岩浆的极端分异作用产生富铁、过饱和、过碱性的残渣。根据矿物稳定性数据估计结晶的初始和最终温度分别为800-900 °C至500-550 °C。热力学数据和矿物成分表明，在结晶过程中，岩浆的氧逸度从大约10− 15巴下降到10−23-10− 24巴。铁辉石正长岩辉石成分的趋势是类似的不饱和过碱性正长岩（llimaussaq），并表明，尖晶石富集趋势是独立的二氧化硅活性和氧逸度下降的情况下发生。
A 1500 m thick sheet-like body of ferroaugite syenite is divisible mineralogically into an upper and lower series of syenites. The lower syenites are characterized by well developed igneous layering defined by mafic cumulus minerals. The syenites are saturated to oversaturated and contain as cumulus phases alkali feldspar, olivine (Fa83–93), ferroaugite (Di50Hd45Ac5−Di5Hd90Ac5) and ilmeno-magnetite. Amphiboles which crystallized from the intercumulus liquid range in composition from ferrohastingsitic hornblende to ferroedenitic hornblende to ferroactinolitic edenite. The upper series are coarse grained cumulates with poorly defined layering and abundant patch pegmatites. Cumulus phases are alkali feldspar, olivine (Fa93), and acmitic-hedenbergite (Di5Hd50Ac5−Ac50Hd50). Intercumulus liquids are peralkaline and crystallized to aenigmatite and amphiboles which range in composition from ferrorichteritic katophorite to ferrorichterite, Patch pegmatites are peralkaline rocks composed of ferrorichterite, ferroactinolite, alkali feldspar, aenigmatite, quartz and zircon. Extreme differentiation of ferroaugite syenite magma generates residua which are ironrich, oversaturated and peralkaline. Initial and final temperatures of crystallization are estimated from mineral stability data to be 800–900 °C to 500–550 °C respectively. Thermodynamic data and mineral compositions indicate that during crystallization the oxygen fugacity of the magma decreased from approximately 10−15to 10−23–10−24bars. Ferroaugite syenite pyroxene compositional trends are similar to those of undersaturated peralkaline syenites (llimaussaq) and demonstrate that acmite enrichment trends are independent of silica activity and take place under decreasing oxygen fugacities.