Coupled and complex: Human-environment interaction in the Greater Yellowstone Ecosystem, USA

Complexity theory has received considerable attention over the past decade from a wide variety of disciplines. Some who write on this topic suggest that complexity theory will lead to a unifying understanding of complex phenomena; others dismiss it as a passing and disruptive fad. We suggest that for the analysis of coupled natural/human systems, the truth emerges from the middle ground. As an approach focused as much on the connections among system elements as the elements themselves, we argue that complexity theory provides a useful conceptual framework for the study of coupled natural/human systems. It is, if nothing else, a framework that leads us to ask interesting questions about, for example, sustainability, resilience, threshold events, and predictability.In this paper we attempt to demystify the ongoing discussions on complexity theory by linking its evocative and overloaded terminology to real-world processes. We illustrate how a shift in focus from system elements to connections among elements can lead to meaningful insight into human-environment interactions that might otherwise be overlooked. We ground our discussion in ongoing interdisciplinary research surrounding Yellowstone National Park’s northern elk winter range; a tightly coupled natural/human system that has been the center of debate, conflict, and compromise for more than 135 years.     

Oxygen Isotope Evidence for Chemical Interaction of Ki lauea Historical Magmas with Basement Rocks

Klauea historical summit lavas have a wide range in matrix ¹⁸O_VSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, ¹⁸O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine ¹⁸O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma ¹⁸O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine ¹⁸O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination     

Pervasive wetland flooding in the glacial drift prairie of North Dakota (USA)

This article describes a unique flood hazard, produced by the dramatic expansion of wetlands in Nelson County, located within the North American Prairie Pothole Region of North Dakota, USA. There has been an unprecedented increase in the number, average size, and permanence of prairie wetlands, and a significant increase in the size of a closed lake (Stump Lake) due to a decade-long wet spell that began in 1993 following a prolonged drying trend. Base-line land cover information from the 1992 USGS National Land Cover Characterization dataset, and a Landsat TM scene acquired 9 July 2001 are used to assess the growth of the closed lake and wetland pond surface areas, and to analyze the type and area of various land cover classes inundated between 1992 and 2001. The open water profile in Nelson County changed from one marked by relatively comparable coverage of closed lake and wetland pond areas in 1992, to one in which wetland open water accounted for the vast majority of total open water in 2001. The bulk of the wetland pond area expansion occurred by displacing existing wetland vegetation and agricultural cropland. Producers responded to the flood hazard by filing Federal Crop Insurance Corporation (FCIC) claims and enrolling cropland in the Conservation Reserve Program (CRP), a federal land retirement program. Land taken out of agricultural production has had an enormous impact upon the agricultural sector that forms the economic base of the rural economy. In 2001 the land taken out of production due to CRP enrollment and preventive planting claims represented nearly 42% of Nelson County’s 205.2 K ha base agricultural land. The patterns obtained from this detailed study of Nelson County are likely to be the representative of the more publicized flood disaster occurring within the Devils Lake Basin of North Dakota.     

华北克拉通北缘隆化地区S型花岗岩的独居石年龄图谱

位于华北克拉通北缘中段的隆化S型花岗岩由石榴石黑云母花岗岩、石榴石花岗岩以及片麻理化的黑云母花岗岩组成。其主体岩性石榴石黑云母花岗岩SiO_2和Al_2O_3含量分别为64.09%～69.6%以及14.6%～16.13%,K_2O/Na_2O>1.0,A/CNK>1,0,Mg~#在20.76～34.89之间变化,具有明显的Nb、Ta、P、Ti和Sr亏损以及Rb、K和Th富集。石榴石黑云母花岗岩(样品JB6031-1)采用独居石电子探针U-Th-Pb化学法进行测年,获得了2553±120Ma、2180±42Ma和1854±24Ma三个年龄峰值。一颗独居石内部成分分带上6个分析点定年结果构成2553±120Ma的峰值年龄,这一年龄与我们最新获得的2506±7Ma和2541±8Ma(继承锆石年龄)LA-ICP-MS锆石U-Pb同位素年龄相似,我们将这一独居石年龄解释为继承独居石的年龄,表明在赤城-隆化断裂以北存在太古宙陆块,并且在后期构造-热事件中发生部分熔融形成S型花岗岩。该独居石颗粒幔部成分分带上10个分析点的测年结果揭示的峰值年龄为2181±42Ma,该年龄也是出现频率最高的年龄值,我们建议2181±42Ma为S型花岗岩的结晶年龄,反映了S型花岗岩的侵位时代。独居石颗粒外部成分分带上8个分析点的测年结果构成1854±24Ma的峰值年龄,该年龄与华北克拉通中部带的变质年龄接近,我们将其解释为S型花岗岩的变质年龄,表明华北克拉通北缘的构造演化与中部带的构造演化密切相关。     

甘新交界红柳河蛇绿岩形成和侵位年龄的准确限定及大地构造意义

采用锆石SHRIMP U-Pb同位素定年方法,获得新甘交界红柳河蛇绿岩中的堆晶辉长岩年龄为516.2±7.1Ma,代表了红柳河蛇绿岩的形成年龄;侵入到红柳河蛇绿岩中未变形变质的黑云母花岗岩的年龄为404.8±5.2Ma,限定了红柳河蛇绿岩侵位的上限。作为南天山洋壳的残骸,红柳河蛇绿岩新的可靠年龄数据表明,南天山洋在早寒武世已经开始形成,并于早泥盆世埃姆斯阶之前在红柳河地区已经闭合。上述洋盆演化过程对进一步研究东天山的大地构造演化具有重要的意义。     

延边东部五道沟岩群的单颗粒锆石SHRIMP U-Pb 年代学及其地质意义

通过对延边地区东部五道沟岩群黑云阳起石片岩的单颗粒锆石SHRIMP U-Pb年龄测定.获得21个单点年龄,其中包括7组谐和年龄和1组不谐和年龄.谐和年龄分别为1347.8 Ma、844.8 Ma、340.2～313.7 Ma(平均值为323±23 Ma,N=4,MSWD=0.23,置信度=0.88)、292.9～288.3 Ma(平均值=291±25 Ma,N=3,MSWD=0.031.置信度=0.86)、279.2～266.2 Ma(平均值为279±28 Ma,N=4,MSWD=0.031,置信度=0.86)、127.4～124.2 Ma(206Pb/208U年龄平均值为126.5±3.7 Ma,N=5,MSWD=0.12;置信度=O.97)、116.1～106.3 Ma(平均值为115±39 Ma,N=2,MSWD=1.2置信度=0.27),不谐和年龄的下交点年龄为(451±120)Ma、上交点年龄为(1811±400)Ma(MSWD=7.2);这一结果表明:阳起石片岩的原岩主要是来自中元古代、新元古代和早古生代的碎屑物,指示五道沟群的沉积成岩作用发生在石炭世(323±23 Ma),变质作用发生在晚二叠世(291±25 Ma),之后在279.2～266.2 Ma、126.5～106.3 Ma先后受两次岩浆用和蚀变作用的改造.     

河南桐柏老湾花岗岩体锆石SHRIMP U-Pb年龄及其地质意义

通过对河南桐柏老湾花岗岩体开展锆石SHRIMP U-Pb测年,获得了一个高精度的U-Pb年龄(132.5±2.4)Ma,比较可靠地限定了老湾花岗岩体的形成时代属于燕山中期,而不是前人所认为的燕山晚期.结合区域构造-岩浆活动时间,认为在燕山中期,桐柏及其邻区存在次比较重要的构造-岩浆事件,老湾花岗岩体是这次构造-岩浆活动事件的产物.     

橄榄岩—熔体相互作用过程中Re-Os体系的变化趋势: 对华北新生代地幔橄榄岩Re-Os年龄含义的启示

橄榄岩的Re-Os同位素体系作为探讨岩石圈地幔形成年龄的重要手段已受到人们越来越多的重视。然而,Re-Os体系是否会受到橄榄岩的低温蚀变如蛇纹石化和地幔交代作用或橄榄岩—熔体相互作用的影响并不十分清楚。本文在总结国际上典型造山带橄榄岩剖面研究和地幔橄榄岩捕虏体研究的基础上,发现橄榄岩的Re-Os同位素体系基本不受蛇纹石化等低温蚀变作用的影响; 但橄榄岩—熔体相互作用会造成橄榄岩的Re-Os体系的变化即Re或Os的带入。当熔体/岩石比例较小时(≤1),橄榄岩—熔体相互作用会造成橄榄岩的Re含量显著增加,而放射成因的Os同位素即¹⁸⁷Os增量有限。但当熔体/岩石比例很大时(≥1),会造成¹⁸⁷Os同位素显著增加。同时,橄榄岩的Re含量与中等程度不相容主、微量元素如Al、Ti、Yb的正相关关系可以通过橄榄岩的两阶段演化模式来解释,即早期的部分熔融残留和后期的橄榄岩—熔体相互作用共同影响的结果。橄榄岩的Re含量与Cr含量的正相关关系进一步说明了这一问题。上述结果对华北东部岩石圈地幔的演化过程有重要的启示作用。因为华北东部古生代时期的确存在太古宙岩石圈地幔,然而新生代时期地幔橄榄岩捕虏体普遍具有元古宙而非太古宙的事实证明橄榄岩—熔体的相互作用的确广泛存在,从而造成岩石圈地幔橄榄岩变年轻。因此,新生代地幔捕虏体的Re-Os同位素年龄并不是岩石圈地幔的形成年龄,而是混合作用的结果。汉诺坝地幔橄榄岩的Re含量和Sr、Nd同位素组成符合橄榄岩—多元熔体相互作用的混合趋势,其橄榄岩的全岩Al₂O₃含量和橄榄石Fo的反相关性能够通过橄榄岩—熔体相互作用来解释。     

滇西南澜沧江结合带北段云县花岗岩的地质特征及形成环境

滇西南澜沧江结合带云县花岗岩体的岩石类型主要为黑云二长花岗岩,SiO2含量平均为68.57%,K2O/Na2O值平均为1.67,相对富钾,岩石属高钾钙碱性系列,岩石酸、碱度低于同类岩石平均值,而镁铁组分高于平均 值,显示岩石偏中性,与同碰撞构造环境形成的花岗岩特征类似.Al2O3含量较高,平均为13.66%,A/CNK平均为1.1,呈铝过饱和,CIPw计算结果均出现标准矿物刚玉分子(105).岩石总体上相对富集大离子亲石元素,亏损高场强元素.稀土元素总量较高,平均为240.75×10-6,轻稀土元素富集,重稀土元素亏损,(La/Yb)N为8.88～9.41,分异不是很大,Eu为中等负异常,銭u为0.52～0.57.经多种相关图解判别,岩石属S型花岗岩,其构造环境相当于大陆碰撞花岗岩类(CCG).锆石颗粒U-Pb测年结果显示,源岩的形成年龄最晚是晋宁期(778 Ma),岩体主体形成于华力西晚期一印支期.其中岩浆成因锆石样品的206Pb.238U和207Pb/235U年龄分别为49 Ma和61 Ma,反映在云县岩体中可能存在喜马拉雅期岩浆活动.