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In the central Klamath Mountains, the Eastern Hayfork terrane (EHF) accreted directly seaward of the North Fork ophiolitic arc. The EHF trench mélange consists of very fine-grained, quartzose meta-argillite + boudinaged metachert layers as well as scattered blocks derived from both oceanic and inboard arc-margin sources. Among the exotic blocks are coarse-grained feldspathic metasandstones. Detrital zircon SHRIMP U-Pb ages ranging from the latest Archean to the early Proterozoic were reported by Scherer and colleagues in 2010 for five metasandstone blocks from the central and southern Klamaths; Phanerozoic zircons were totally lacking. It was concluded that the blocks were olistostromal and that erosion of a nearby thrust sheet outlier of the Proterozoic Antelope Mountain Quartzite of the Eastern Klamath belt, Yreka subterrane, was a likely source. To determine the provenance and time of deposition of the EHF muddy matrix host of the metasandstone blocks, we separated zircons from three very fine-grained, intimately interstratified, feldspar-poor meta-argillites from the Sawyers Bar map area. New laser ablation multicollector inductively coupled plasma mass spectrometry zircon U-Pb data indicate maximum sedimentary ages for the meta-argillites as ∼272, ∼211, and ∼201 Ma. Thus, the muddy strata were deposited near the end of Triassic time. The meta-argillites contain scattered Proterozoic and Paleozoic–early Mesozoic detrital zircons, indicating local inboard Klamath sources, including the Antelope Mountain Quartzite thrust sheet. St. Clair Creek distal turbidites in the landward North Fork terrane contain Paleozoic and Triassic–Early Jurassic (∼188 Ma) zircons as well as scattered Precambrian grains similar to those in the EHF. The EHF surficially docked against the North Fork terrane by ∼174–173 Ma because the amalgamated but unmetamorphosed terrane contact was invaded by the English Peak plutonic complex beginning at ∼172 Ma. Regional metamorphism and deformation took place throughout the central Klamath Mountains during the Siskiyou transpressive accretionary event at ∼170–168 Ma.

Zircon SHRIMP dating of granites from Dulan, east segment of North Qaidam UHP belt shows that they are 406.6±3.5 Ma for Yematan-E, 407.3±4.3 and 397±6 Ma for Balijiehatan-W, 404.5±4.0 and 397.0±3.7 Ma for Shuiwenzhan-N, 380.5±5.0 Ma for Shuiwenzhan-S, 382.5±3.6 and 372.5±2.8 Ma for Chachagongma. These granites from Dulan represent the products of the third and fourth periods of Paleozoic magmatism in North Qaidam. Geochemically, the granitoids with metalumious to weak peratuminous are quartz diorite, granodiorite, and granite in composition and mainly belong to calc-alkaline series, a few samples to calc or alkali-calc series. The third period of granites is a rock association of granodiorite + granite, with initial 87 Sr/ 86 Sr ratios from 0.7082 to 0.7110 and T 2DM model ages from 1.41–1.90 Ga; and the fourth period of granites is a rock association of quartz diorite+granodiorite+granite, with initial 87 Sr/ 86 Sr ratios from 0.7072 to 0.7091 and T 2DM model ages from 1.07–1.38 Ga. Therefore, the third period of granites has higher initial 87 Sr/ 86 Sr ratios and T 2DM model ages. On the contrary, the fourth period of granites has ɛ Nd ( t ) values from 0.6 to −3.0, higher than that of the third granite with ɛ Nd ( t ) values −3.2 to −9.3. Thus, the data comparison indicates that the third granites may derive from Paleo-proterzoic continental crust with mantle material whereas the fourth granites may derive from the Meso-proterzoic basalt crust with continental material. Combined with regional geology, we thought that the third granites were formed relative to plate exhumation and the fourth granites to delamination of the lithospheric mantle.

Granitoid intrusives such as Saishitenshan, Tuanyushan, Aolaohe and Sanchagou occur widely in the western segment of North Qaidam. All these bodies trend NW, roughly parallel to the regional structure. Zircon SHRIMP dating for these granites show that they range in age from Ordovician to Permian; 465.4±3.5 Ma for Saishitenshan, 469.7±4.6 Ma and 443.5±3.6 Ma for Tuanyushan, 372.1±2.6 Ma for Aolaohe, and 271.2±1.5 Ma and 259.9±1.2 Ma for Sanchagou. Both the Tuanyshan and Aolaohe plutons record two distinct intrusive events. Geochemically, the early Paleozoic granites have an island arc or active continental margin affinity, and their protolith may have been Mesoproterozoic oceanic crust derived from depleted mantle. The protolith of the late Paleozoic granites may have been Mesoproterozoic lower crust from the root of an island arc with the magmas reflecting a mixture of mantle and crustal material. [PUBLICATION ABSTRACT]

The A’nyemaqen (阿尼玛卿) ophiolite belt along the southern margin of the East Kunlun (昆仑) Mountains marks the suture formed by the closure of paleo-Tethys. The Dur’ngoi ophiolite in the eastern part of this belt consists of meta-peridotite, mafic-ultramafic cumulates, sheeted dikes and basaltic lavas. The meta-peridotites consist of dunite, harzburgite, lherzolite, feldspar-bearing lherzolite and garnet-bearing lherzolite and contain residual spinel with Cr # [100×Cr/(Cr+Al)] ranging from 30 to 57 and Mg # [100×Mg/(Mg+Fe 2+ )] ranging from 50 to 75, indicating an Al- and Mg-rich series. The meta-peridotites have a relatively narrow range of composition with Mg# of 89.2–92.6, Al 2 O 3 contents of (1–4) wt.% and slightly depleted chondrite normalized REE patterns, indicating that they represent relict mantle material that has undergone intermediate to low degrees of partial melting. Garnets in the lherzolite are andradite, enriched in Ca and Fe and depleted in Mg and Al (And=95–97, Pyr=0.3–5, Gro=0–3), indicating a metamorphic origin. The cumulate rocks mainly consist of dunite, wehrlite, pyroxenite and gabbro. A well-layered gabbro-pyroxenite complex is defined by modal variations in plagioclase and pyroxene. Blocks of garnet-pyroxenite or rodingite are locally present in the meta-peridotites. Garnets in the cumulate rocks are grossular (Gro=69–90, And=9–19, Br=1–12), also metamorphic origin. The diabase dikes are moderately depleted in LREE [(La/Sm)N=0.5–0.8] and HREE resulting in slightly convex chondrite-normalized patterns with slightly positive Eu anomalies ( δ Eu=1.1–1.3). The basaltic lavas have REE patterns similar to those of MORB with (La/Sm) N ratios of 0.5–1 and small negative Eu anomalies. They appear to have been derived from a depleted mantle source and to have undergone little or no differentiation during crystallization. SHRIMP U-Pb dating of zircons from the basalts yields 206 Pb/ 238 U ages of 276–319 Ma (average 308.0±4.9 Ma). The Dur’ngoi ophiolite is interpreted as a dismembered fragment of paleo-oceanic crust emplaced during closure of the paleo-Tethyan Ocean basin. Three other suites of oceanic lavas are recognized in the area: island arc volcanic (IAV) rocks, possible back arc basin (BAB) basalts and possible post-collisional volcanic (PCV) and plutonic rocks. The distribution of these rocks suggests north-directed subduction. Opening of the A’nyemaqen oceanic basin started at least as early as Late Carboniferous (308 Ma) and the basin probably closed during the Early Triassic. The IAV formed in Late Permian (260 Ma), the BAB in Early-Middle Triassic, and the PCV in Late Triassic. Several large scale, ductile, sinistral strike-slip fault zones, extending hundreds to thousands kilometers, formed along or north of the suture during the Early-Late Triassic, e.g., they are the south margin fault zone of East Kunlun (200–220 Ma), the Altyn Tagh fault (220–230 Ma), and the North Qaidam fault zone (240–250 Ma). These strike-slip faults were probably generated by oblique subduction and closure of the paleo-Tethyan Ocean basin, possibly during exhumation of the subducted plate or uplift of the overriding plate, coincident with post-collisional magmatism.

The Bashikaogong-Shimierbulake granitoid complex is about 30 km long and 2-6 km wide,with an area of 140 km2,located at the north margin of the Bashikaogong Basin in the north Altun terrain.It intruded into schist,metapelite and metatuff of Precambrian ages.This granitoid complex consists of darkish quartz diorite,grey granite,pink granite and pegmatite.Geochemically,the quartz diorite has I-type granite affinity and belongs to Calc-alkaline sereies,and the other granites have S-type affinity and to high-K calc-alkaline series.Zircon SHRIMP U-Pb dating shows that the quartz diorite has a bigger age than those of other granites,which is 481.6±5.6 Ma for quartz diorite,437.0±3.0 Ma-433.1±3.4 Ma for grey granite and 443±11 Ma-434.6±1.6 Ma for pink granite,respectively.Combined with regional geology,we think that the quartz diorite formed in tectonic environment related to oceanic crust subduction and the granites in post-collision.

The pyroxenite xenoliths in the volcanic rocks of Hoh Xil consist of clinopyroxenes and orthopyroxenes. The mineral composition of these pyroxenes is similar to that of mantle xenoliths including peridotite and pyroxenite from China and abroad, and different from that of granulites. The pyroxenes formed at 1101–1400°C (averaging 1250°C) and under 30–60 kb (averaging 46 kb). We deduced that the magma was derived from the mantle at a depth of more than 150 km, which fits in with the geophysical conclusion that the low-velocity layer existed in the mantle under 150 km.