Abstract Aluminous metapelitic granulites from the central Namaqua Sector of the Namaqua–Natal Metamorphic Province, South Africa, host partly retrogressed hercynite–quartz assemblages. These assemblages record peak P–T conditions of 860–890 °C and 5–5.5 kbar, estimated via thermodynamic modelling and ternary feldspar thermometry. In-situ U–Pb geochronology and geochemistry of anatectic zircon and monazite constrains this event as part of the main Namaqua Orogeny affecting the terrane at c. 1040–1035 Ma. Detrital zircon age spectra span from about 1860 to 1100 Ma, peaking at c. 1800–1700 and 1400–1300 Ma, suggesting detritus was sourced from nearby Paleoproterozoic- and Mesoproterozoic terranes. Thin sections reveal narrow monomineralic coronae of garnet, cordierite or sillimanite separating formerly coexisting hercynite and quartz. Calculated chemical potential relationships show that coronae have developed in response to very minor, near-isobaric cooling shortly after the thermal peak, involving limited diffusion down gradients of μFeO–μMgO. Corona formation occurred in distinct compositional domains, controlled by neighbouring porphyroblasts such as garnet and/or sillimanite. Isolated hercynite–quartz pairs distal from porphyroblasts developed thin rinds of sillimanite, requiring no additional compositional gradients. Cordierite inclusions in garnet, limited melt production and extraction and corona-textures are consistent with an anticlockwise evolution, involving burial and concomitant heating to near-ultrahigh temperature conditions followed by near-isobaric cooling at mid-crustal depths. The hercynite–quartz equilibria record the highest metamorphic temperature affecting the Namaqua Sector, requiring a crucial component of advective heating via voluminous pre- to syn-metamorphic felsic-charnockitic magmatism of the Spektakel Suite. Namaqua-aged granulite facies metamorphism at the terrane scale was driven by a combination of mafic underplating and radiogenic heating. Calculated temperature–enthalpy profiles suggest that advective heating locally increased the suprasolidus enthalpy budget by a third which allowed peak temperatures to be some 50 °C higher than would otherwise have been achieved.

中文翻译：

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在南非纳马夸-纳塔尔变质省，炭黑岩浆作用对达到近超高温的贡献

摘要 南非纳马夸-纳塔尔变质区纳马夸中部的铝质变泥质麻粒岩含有部分退化的辉长岩-石英组合。这些组合记录了 860-890 °C 和 5-5.5 kbar 的峰值 P-T 条件，通过热力学模型和三元长石测温法估计。深熔锆石和独居石的原位 U-Pb 年代学和地球化学将此事件限制为影响 c. 地层的主要 Namaqua 造山运动的一部分。1040–1035 马。碎屑锆石年龄光谱范围从大约 1860 到 1100 Ma，在 c 处达到峰值。1800-1700 和 1400-1300 Ma，表明碎屑来自附近的古元古代和中元古代地体。薄切片显示石榴石、堇青石或硅线石的狭窄单矿物冠层，将以前共存的辉长岩和石英分开。计算出的化学势关系表明，在热峰值后不久，日冕已经形成，以响应非常微弱的、接近等压的冷却，涉及沿 μFeO-μMgO 梯度的有限扩散。日冕形成发生在不同的组成域中，由相邻的卟啉母细胞（如石榴石和/或硅线石）控制。远离斑纹母细胞的孤立的辉长岩-石英对形成了薄的硅线石外皮，不需要额外的成分梯度。石榴石中的堇青石内含物、有限的熔体产生和提取以及日冕结构与逆时针演化一致，包括埋藏和伴随加热至接近超高温条件，然后在中地壳深度接近等压冷却。辉长岩-石英平衡记录了影响 Namaqua Sector 的最高变质温度，需要通过 Spektakel Suite 的大量前变质到同变质长英质-charnockitic 岩浆作用进行平流加热的关键组成部分。Namaqua 时代麻粒岩相变质作用是由基性底镀层和放射成因加热共同驱动的。计算出的温度-焓曲线表明，对流加热局部增加了 suprasolidus 焓预算的三分之一，这使得峰值温度比否则会高出约 50 °C。Namaqua 时代麻粒岩相变质作用是由基性底镀层和放射成因加热共同驱动的。计算出的温度-焓曲线表明，对流加热局部增加了 suprasolidus 焓预算的三分之一，这使得峰值温度比否则会高出约 50 °C。Namaqua 时代麻粒岩相变质作用是由基性底镀层和放射成因加热共同驱动的。计算出的温度-焓曲线表明，对流加热局部增加了 suprasolidus 焓预算的三分之一，这使得峰值温度比否则会高出约 50 °C。