Magmatic lobes as “snapshots” of magma chamber growth and evolution in large, composite batholiths: An example from the Tuolumne intrusion, Sierra Nevada, California
Magmatic lobes as “snapshots” of magma chamber growth and evolution in large, composite batholiths: An example from the Tuolumne intrusion, Sierra Nevada, California
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岩浆叶作为大型复合基岩中岩浆室生长和演化的“快照”：加利福尼亚州内华达山脉图奥勒米侵入体的一个例子
DOI：
10.1130/b30004.1
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发表时间：
2010
影响因子：
4.9
通讯作者：
D. Okaya
中科院分区：
文献类型：
--
作者：
V. Memeti;S. Paterson;J. Matzel;R. Mundil;D. Okaya
精确的化学磨蚀-热电离质谱（CA-TIMS）U-Pb锆石年龄结合详细的现场测绘，40 Ar/ 39 Ar热年代学，和有限差分热模拟的Tuolumne岩基的岩浆裂片的特点，这些10-60平方公里的机构作为较短的寿命，简单的岩浆系统，代表增量的岩基生长。叶状体提供了内部和外部过程的短期记录，这些过程可能在长寿命复合岩基的主体中被抹去。热模拟补充的锆石年龄表明，叶状岩浆房存在于200.2到1百万年之间，仅代表熔体在主体中存在的总持续时间的一小部分。在这些较短的时间间隔内，正常的成分环带的同心模式，形成在向内结晶和广泛的锆石循环在瓣。叶状体在很大程度上是作为单独的岩浆体演化的，它们与更复杂的主岩浆房没有显著的相互作用。晶前锆石和自晶的范围，用于跟踪相互关联的熔体的程度，只记录了有限的年龄范围，并有对比的锆石人口中发现的相同单位的主要岩基。我们认为，要么是单一批次的连续岩浆流动过程中形成的，或多个，快速合并脉冲，在任何一种情况下，形成单独的岩浆房，未能合并与其他成分不同的脉冲，如发生在中央岩基。所有四个裂片和主体之间的锆石年龄比较意味着Tuolumne侵入体的增长不是静止的，但岩浆活动的轨迹向内和西北方向移动。
Precise chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon ages in combination with detailed field mapping, 40 Ar/ 39 Ar thermochronology, and finite difference thermal modeling in the magmatic lobes of the Tuolumne batholith characterize these 10–60 km 2 bodies as shorter-lived, simpler magmatic systems that represent increments of batholith growth. Lobes provide shorter-term records of internal and external processes that are potentially obliterated in the main body of long-lived, composite batholiths. Zircon ages complemented by thermal modeling indicate that lobe-sized magma chambers were present between ∼0.2 and 1 m.y., representing only a small fraction of the total duration of melt presence in the main body. During these shorter intervals, a concentric pattern of normal compositional zoning formed during inward crystallization and widespread zircon recycling in the lobes. Lobes largely evolved as individual magma bodies that did not interact significantly with the main, more complex magma chamber(s). Antecrystic zircons and the range of autocrysts, used to track the extent of interconnected melt, record only a limited range of ages and have contrasting zircon populations to those found in the same units in the main batholith. We consider lobes to either be single batches formed during continuous magma flow or multiple, quickly coalescing pulses that in either case formed separate magma chambers that failed to amalgamate with other compositionally distinct pulses such as those occurring in the central batholith. Zircon age comparisons between all four lobes and the main body imply that growth of the Tuolumne intrusion was not stationary, but that the locus of magmatism shifted both inward and northwestward.