The ca. 280 Ma, postorogenic, S-type Dartmoor pluton was assembled from numerous sheets of granitic magma, emplaced into the shallow crust. The main magma source lies in the middle crust and is most probably Proterozoic metagreywackes, with minor metapelites and metavolcanic or plutonic rocks, possibly formed in a syncollisional environment. Partial melting of this source may have occurred under fluid-deficient conditions, and the magmas most likely had relatively high initial H₂O contents. The pluton contains substantial, whole-rock-Sr and quartz-O isotope heterogeneities on scales down to a meter or less, and such small-scale heterogeneities are probably common in granitic intrusions derived from heterogeneous protoliths. Thus, variations in source terranes may not be fully captured with the sample numbers and scales commonly applied in studies of granitic plutons. The preservation of both large- and small-scale isotopic heterogeneities suggests that the Dartmoor magmas were never efficiently homogenized by flow-driven mechanical mixing. This implies a source terrane with lithological variations on scales of tens of meters or less. The granitic rocks form five texturally, chemically, and isotopically distinct groups, each of which had somewhat different sources or mixtures of sources. The main chemical variations cannot have been formed through fractionation of any combination of the major minerals in the rocks. Instead, entrainment of variable proportions of peritectic plagioclase, orthopyroxene, and ilmenite was responsible, together with local crystal fractionation. Low-density, late-magmatic melts and aqueous fluids produced patchy enrichment in light elements and extreme enrichment in some of the highly silicic, two-mica microgranites. However, although they are also enriched in light elements, the “aplites” were not produced through fractionation and seem to have had independent magmatic origins.

中文翻译：

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地壳衍生花岗岩中成分变化的起源和尺度：以英国西南部 Cornubian 基岩中的 Dartmoor 岩体为例

约。280 Ma，造山后的 S 型 Dartmoor 岩体由无数片花岗岩岩浆组合而成，进入浅地壳。主要岩浆源位于中地壳，最有可能是元古代变灰岩，少量变泥质岩和变质火山岩或深成岩，可能形成于同碰撞环境中。该源的部分熔融可能发生在流体不足的条件下，而且岩浆很可能具有相对较高的初始 H ₂哦内容。岩体包含大量的全岩 Sr 和石英 O 同位素异质性，其尺度低至一米或更小，这种小尺度的异质性可能在源自异质原岩的花岗岩侵入体中很常见。因此，用花岗岩岩体研究中常用的样本数量和尺度可能无法完全捕捉到源地体的变化。大尺度和小尺度同位素异质性的保存表明，达特穆尔岩浆从未被流动驱动的机械混合有效地均质化。这意味着源地层在数十米或更小的尺度上具有岩性变化。花岗岩形成五个在结构上、化学上和同位素上不同的组，每个组都有一些不同的来源或来源的混合物。主要的化学变化不可能是通过对岩石中主要矿物的任何组合进行分馏而形成的。相反，夹带了不同比例的包晶斜长石、斜方辉石和钛铁矿，以及局部晶体分馏。低密度、晚期岩浆熔体和含水流体产生了轻元素的斑片状富集和一些高硅质、二云母微花岗岩的极端富集。然而，虽然它们也富含轻元素，但“aplites”并不是通过分馏产生的，似乎具有独立的岩浆成因。与局部晶体分馏一起。低密度、晚期岩浆熔体和含水流体产生了轻元素的斑片状富集和一些高硅质、二云母微花岗岩的极端富集。然而，虽然它们也富含轻元素，但“aplites”并不是通过分馏产生的，似乎具有独立的岩浆成因。与局部晶体分馏一起。低密度、晚期岩浆熔体和含水流体产生了轻元素的斑片状富集和一些高硅质、二云母微花岗岩的极端富集。然而，虽然它们也富含轻元素，但“aplites”并不是通过分馏产生的，似乎具有独立的岩浆成因。