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克拉玛依市西盆山交界处发育体罗纪杏仁玄武岩-橄榄玄武岩-含菱铁矿橄榄玄武岩组合,主要由橄榄石、单斜辉石、斜长石(中长石—拉长石为主)、钛铁矿、玄武玻璃及少量磷灰石组成,含菱铁矿橄榄玄武岩中存在原生菱铁矿(≈10%)和少量碱性长石。橄榄石及单斜辉石的Mg~#为≈70,单斜辉石属于富Ti普通辉石。含菱铁矿橄榄玄武岩中的菱铁矿常常包裹浑圆状斜长石,且与斜长石呈锯齿状接触。本文提供的岩相学观察表明,菱铁矿与玄武玻璃、斜长石、单斜辉石和钛铁矿呈明显的共生关系。在有些情况下观察到玄武玻璃与菱铁矿充填在斜长石格架的现象。含菱铁矿橄榄玄武岩玻璃中FeO含量最高至29.2%,CaO含量<1.5%,即熔体具有富Fe贫Ca的特点。早结晶的碳酸盐矿物是以菱铁矿为主的菱铁矿-白云石固溶体(另含少量菱锰矿)。斜长石大量结晶促使熔体不断亏损CaO,并导致较晚结晶的碳酸盐矿物向菱铁矿端元演化。菱铁矿发育有明显的成分梯变带(FeO和CaO含量表现出突变)。玄武玻璃的Mg~#普遍较低且变化范围大,橄榄玄武岩中玻璃的Mg~#值最高为64,含菱铁矿橄榄玄武岩中玻璃的Mg~#值最低至≈23。依据地质温压计,克拉玛依侏罗纪玄武岩浆的形成温度为1300℃～1340℃,压力为3.0～4.0GPa。基于本文的研究,我们认为克拉玛依侏罗纪含菱铁矿橄榄玄武岩岩浆由含CO_2,橄榄岩在软流圈中经极低程度部分熔融形成,该岩浆在快速上升过程中通过结晶分异作用形成了菱铁矿。
Karamay City, the junction of the western basin to develop body Luoji almond basalt - olive basalts - siderite olivine basalt combination, mainly by olivine, clinopyroxene, plagioclase (in the feldspar - labradorceous), titanium Iron ore, basaltic glass and a small amount of apatite. There are primary siderite (≈10%) and a small amount of alkaline feldspar in olivine basalts containing siderite. The Mg ~ # of olivine and clinopyroxene is ≈70, and clinopyroxene belongs to Ti-rich pyroxene. Siderite in olivine basalts, often containing round plagioclase, is serrated in contact with plagioclase. The petrographic observations provided in this paper show that siderite and basaltic glass, plagioclase, clinopyroxene and ilmenite show a clear symbiotic relationship. In some cases, it was observed that basaltic glass and siderite filled the plagioclase framework. Siderite olivine basalt glass contains up to 29.2% FeO and CaO <1.5%, ie, the melt has the characteristics of rich Fe-poor Ca. The early crystallized carbonate minerals are siderite - dolomite solid solution (with a small amount of rhodochrosite) based on siderite. The massive crystallization of plagioclase prompted the melt to continuously lose CaO and lead to the evolution of later crystallized carbonate minerals to the siderite of siderite. Siderite development obvious composition ladder (FeO and CaO content showed mutation). The Mg ~ # of basaltic glass is generally low and has a wide variation range. The Mg ~ # value of the glass in olivine basalts is up to 64, and the Mg ~ # value of the glass in siderite olivine basalts is as low as ~ 23. Based on the geothermometer, the formation temperature of the Karamay basaltic magma was 1300 ℃ ~ 1340 ℃ and the pressure was 3.0 ~ 4.0GPa. Based on the study in this paper, we consider that the Jurassic siderite olivine basalts from Karamay are formed by the partial melting of CO 2 -containing peridotites in the asthenosphere, and the magma forms a rhombohedron by crystal differentiation during the rapid ascent iron ore.